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| 4 | <title>Detailed Semantics -- Optional Values</title> | |
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| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h4 class="title"> | |
| 27 | <a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics____optional_values"></a><a class="link" href="detailed_semantics____optional_values.html" title="Detailed Semantics -- Optional Values">Detailed | |
| 28 | Semantics -- Optional Values</a> | |
| 29 | </h4></div></div></div> | |
| 30 | <div class="note"><table border="0" summary="Note"> | |
| 31 | <tr> | |
| 32 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td> | |
| 33 | <th align="left">Note</th> | |
| 34 | </tr> | |
| 35 | <tr><td align="left" valign="top"><p> | |
| 36 | The following section contains various <code class="computeroutput"><span class="identifier">assert</span><span class="special">()</span></code> which are used only to show the postconditions | |
| 37 | as sample code. It is not implied that the type <code class="computeroutput"><span class="identifier">T</span></code> | |
| 38 | must support each particular expression but that if the expression is | |
| 39 | supported, the implied condition holds. | |
| 40 | </p></td></tr> | |
| 41 | </table></div> | |
| 42 | <p> | |
| 43 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 44 | </p> | |
| 45 | <a name="reference_optional_constructor"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 46 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span> | |
| 47 | <span class="keyword">noexcept</span><span class="special">;</span></code> | |
| 48 | </p></blockquote></div> | |
| 49 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 50 | <li class="listitem"> | |
| 51 | <span class="bold"><strong>Effect:</strong></span> Default-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 52 | </li> | |
| 53 | <li class="listitem"> | |
| 54 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>. | |
| 55 | </li> | |
| 56 | <li class="listitem"> | |
| 57 | <span class="bold"><strong>Notes:</strong></span> T's default constructor <span class="underline">is not</span> called. | |
| 58 | </li> | |
| 59 | <li class="listitem"> | |
| 60 | <span class="bold"><strong>Example:</strong></span> | |
| 61 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> | |
| 62 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span> | |
| 63 | </pre> | |
| 64 | </li> | |
| 65 | </ul></div> | |
| 66 | <p> | |
| 67 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 68 | </p> | |
| 69 | <a name="reference_optional_constructor_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 70 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 71 | <span class="identifier">none_t</span> <span class="special">)</span> | |
| 72 | <span class="keyword">noexcept</span><span class="special">;</span></code> | |
| 73 | </p></blockquote></div> | |
| 74 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 75 | <li class="listitem"> | |
| 76 | <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> uninitialized. | |
| 77 | </li> | |
| 78 | <li class="listitem"> | |
| 79 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>. | |
| 80 | </li> | |
| 81 | <li class="listitem"> | |
| 82 | <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 83 | default constructor <span class="underline">is not</span> called. | |
| 84 | The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code> | |
| 85 | denotes an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code> | |
| 86 | that can be used as the parameter. | |
| 87 | </li> | |
| 88 | <li class="listitem"> | |
| 89 | <span class="bold"><strong>Example:</strong></span> | |
| 90 | <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">none</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> | |
| 91 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">n</span><span class="special">(</span><span class="identifier">none</span><span class="special">)</span> <span class="special">;</span> | |
| 92 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">n</span> <span class="special">)</span> <span class="special">;</span> | |
| 93 | </pre> | |
| 94 | </li> | |
| 95 | </ul></div> | |
| 96 | <p> | |
| 97 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 98 | </p> | |
| 99 | <a name="reference_optional_constructor_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 100 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> | |
| 101 | </p></blockquote></div> | |
| 102 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 103 | <li class="listitem"> | |
| 104 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> | |
| 105 | is <code class="computeroutput"><span class="keyword">true</span></code>. | |
| 106 | </li> | |
| 107 | <li class="listitem"> | |
| 108 | <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 109 | </li> | |
| 110 | <li class="listitem"> | |
| 111 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> | |
| 112 | and its value is a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">v</span></code>. | |
| 113 | </li> | |
| 114 | <li class="listitem"> | |
| 115 | <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> | |
| 116 | <span class="special">)</span></code> throws. | |
| 117 | </li> | |
| 118 | <li class="listitem"> | |
| 119 | <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> | |
| 120 | <span class="special">)</span></code> is called. | |
| 121 | </li> | |
| 122 | <li class="listitem"> | |
| 123 | <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only | |
| 124 | be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> | |
| 125 | <span class="special">);</span></code> in that case, this constructor | |
| 126 | has no effect. | |
| 127 | </li> | |
| 128 | <li class="listitem"> | |
| 129 | <span class="bold"><strong>Example:</strong></span> | |
| 130 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> | |
| 131 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> | |
| 132 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 133 | </pre> | |
| 134 | </li> | |
| 135 | </ul></div> | |
| 136 | <p> | |
| 137 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 138 | </p> | |
| 139 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 140 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 141 | <span class="identifier">T</span><span class="special">&</span> | |
| 142 | <span class="identifier">ref</span> <span class="special">)</span></code> | |
| 143 | </p></blockquote></div> | |
| 144 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 145 | <li class="listitem"> | |
| 146 | <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 147 | </li> | |
| 148 | <li class="listitem"> | |
| 149 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> | |
| 150 | and its value is an instance of an internal type wrapping the reference | |
| 151 | <code class="computeroutput"><span class="identifier">ref</span></code>. | |
| 152 | </li> | |
| 153 | <li class="listitem"> | |
| 154 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 155 | </li> | |
| 156 | <li class="listitem"> | |
| 157 | <span class="bold"><strong>Example:</strong></span> | |
| 158 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> | |
| 159 | <span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span> | |
| 160 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">vref</span><span class="special">);</span> | |
| 161 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 162 | <span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> <span class="comment">// mutate referee</span> | |
| 163 | <span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">);</span> | |
| 164 | </pre> | |
| 165 | </li> | |
| 166 | </ul></div> | |
| 167 | <p> | |
| 168 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 169 | </p> | |
| 170 | <a name="reference_optional_constructor_move_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 171 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">v</span> | |
| 172 | <span class="special">)</span></code> | |
| 173 | </p></blockquote></div> | |
| 174 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 175 | <li class="listitem"> | |
| 176 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> | |
| 177 | is <code class="computeroutput"><span class="keyword">true</span></code>. | |
| 178 | </li> | |
| 179 | <li class="listitem"> | |
| 180 | <span class="bold"><strong>Effect:</strong></span> Directly-Move-Constructs an | |
| 181 | <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 182 | </li> | |
| 183 | <li class="listitem"> | |
| 184 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> | |
| 185 | and its value is move-constructed from <code class="computeroutput"><span class="identifier">v</span></code>. | |
| 186 | </li> | |
| 187 | <li class="listitem"> | |
| 188 | <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> | |
| 189 | throws. | |
| 190 | </li> | |
| 191 | <li class="listitem"> | |
| 192 | <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> | |
| 193 | is called. | |
| 194 | </li> | |
| 195 | <li class="listitem"> | |
| 196 | <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only | |
| 197 | be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code> | |
| 198 | in that case, the state of <code class="computeroutput"><span class="identifier">v</span></code> | |
| 199 | is determined by exception safety guarantees for <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>. | |
| 200 | </li> | |
| 201 | <li class="listitem"> | |
| 202 | <span class="bold"><strong>Example:</strong></span> | |
| 203 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v1</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">;</span> | |
| 204 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v1</span><span class="special">));</span> | |
| 205 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v2</span> <span class="special">)</span> <span class="special">;</span> | |
| 206 | </pre> | |
| 207 | </li> | |
| 208 | </ul></div> | |
| 209 | <p> | |
| 210 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 211 | </p> | |
| 212 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 213 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 214 | <span class="identifier">T</span><span class="special">&&</span> | |
| 215 | <span class="identifier">ref</span> <span class="special">)</span> | |
| 216 | <span class="special">=</span> <span class="keyword">delete</span></code> | |
| 217 | </p></blockquote></div> | |
| 218 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 219 | <span class="bold"><strong>Notes:</strong></span> This constructor is deleted | |
| 220 | </li></ul></div> | |
| 221 | <p> | |
| 222 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 223 | </p> | |
| 224 | <a name="reference_optional_constructor_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 225 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> | |
| 226 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code> | |
| 227 | </p></blockquote></div> | |
| 228 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 229 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> | |
| 230 | <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> | |
| 231 | <span class="identifier">T</span><span class="special">&</span> | |
| 232 | <span class="identifier">v</span> <span class="special">)</span> | |
| 233 | <span class="special">;</span></code> | |
| 234 | </p></blockquote></div> | |
| 235 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 236 | If condition is true, same as: | |
| 237 | </li></ul></div> | |
| 238 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 239 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> | |
| 240 | </p></blockquote></div> | |
| 241 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 242 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> | |
| 243 | <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> | |
| 244 | </p></blockquote></div> | |
| 245 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 246 | otherwise, same as: | |
| 247 | </li></ul></div> | |
| 248 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 249 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span></code> | |
| 250 | </p></blockquote></div> | |
| 251 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 252 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> | |
| 253 | <span class="special">::</span><span class="identifier">optional</span><span class="special">()</span></code> | |
| 254 | </p></blockquote></div> | |
| 255 | <p> | |
| 256 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 257 | </p> | |
| 258 | <a name="reference_optional_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 259 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span> | |
| 260 | <span class="keyword">const</span><span class="special">&</span> | |
| 261 | <span class="identifier">rhs</span> <span class="special">);</span></code> | |
| 262 | </p></blockquote></div> | |
| 263 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 264 | <li class="listitem"> | |
| 265 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> | |
| 266 | is <code class="computeroutput"><span class="keyword">true</span></code>. | |
| 267 | </li> | |
| 268 | <li class="listitem"> | |
| 269 | <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 270 | </li> | |
| 271 | <li class="listitem"> | |
| 272 | <span class="bold"><strong>Postconditions:</strong></span> If rhs is initialized, | |
| 273 | <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 274 | is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the | |
| 275 | value of <code class="computeroutput"><span class="identifier">rhs</span></code>; else | |
| 276 | <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 277 | is uninitialized. | |
| 278 | </li> | |
| 279 | <li class="listitem"> | |
| 280 | <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> | |
| 281 | <span class="special">)</span></code> throws. | |
| 282 | </li> | |
| 283 | <li class="listitem"> | |
| 284 | <span class="bold"><strong>Notes:</strong></span> If rhs is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> | |
| 285 | is called. | |
| 286 | </li> | |
| 287 | <li class="listitem"> | |
| 288 | <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only | |
| 289 | be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> | |
| 290 | <span class="special">);</span></code> in that case, this constructor | |
| 291 | has no effect. | |
| 292 | </li> | |
| 293 | <li class="listitem"> | |
| 294 | <span class="bold"><strong>Example:</strong></span> | |
| 295 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uninit</span> <span class="special">;</span> | |
| 296 | <span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span> | |
| 297 | ||
| 298 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span> | |
| 299 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span> | |
| 300 | ||
| 301 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">);</span> | |
| 302 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 303 | ||
| 304 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span> | |
| 305 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span> | |
| 306 | </pre> | |
| 307 | </li> | |
| 308 | </ul></div> | |
| 309 | <p> | |
| 310 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 311 | </p> | |
| 312 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 313 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 314 | <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> | |
| 315 | <span class="special">);</span></code> | |
| 316 | </p></blockquote></div> | |
| 317 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 318 | <li class="listitem"> | |
| 319 | <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 320 | </li> | |
| 321 | <li class="listitem"> | |
| 322 | <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 323 | is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 324 | is initialized and its value is another reference to the same object | |
| 325 | referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; | |
| 326 | else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 327 | is uninitialized. | |
| 328 | </li> | |
| 329 | <li class="listitem"> | |
| 330 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 331 | </li> | |
| 332 | <li class="listitem"> | |
| 333 | <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 334 | is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> will refer to the same object | |
| 335 | (they alias). | |
| 336 | </li> | |
| 337 | <li class="listitem"> | |
| 338 | <span class="bold"><strong>Example:</strong></span> | |
| 339 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uninit</span> <span class="special">;</span> | |
| 340 | <span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span> | |
| 341 | ||
| 342 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span> | |
| 343 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span> | |
| 344 | ||
| 345 | <span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span> | |
| 346 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">ref</span><span class="special">);</span> | |
| 347 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 348 | ||
| 349 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span> | |
| 350 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 351 | ||
| 352 | <span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span> | |
| 353 | ||
| 354 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span> | |
| 355 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span> | |
| 356 | </pre> | |
| 357 | </li> | |
| 358 | </ul></div> | |
| 359 | <p> | |
| 360 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 361 | </p> | |
| 362 | <a name="reference_optional_move_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 363 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span> | |
| 364 | <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code> | |
| 365 | </p></blockquote></div> | |
| 366 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 367 | <li class="listitem"> | |
| 368 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> | |
| 369 | is <code class="computeroutput"><span class="keyword">true</span></code>. | |
| 370 | </li> | |
| 371 | <li class="listitem"> | |
| 372 | <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 373 | </li> | |
| 374 | <li class="listitem"> | |
| 375 | <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 376 | is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 377 | is initialized and its value is move constructed from <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized. | |
| 378 | </li> | |
| 379 | <li class="listitem"> | |
| 380 | <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> | |
| 381 | throws. | |
| 382 | </li> | |
| 383 | <li class="listitem"> | |
| 384 | <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>. | |
| 385 | </li> | |
| 386 | <li class="listitem"> | |
| 387 | <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 388 | is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="special">&&</span> | |
| 389 | <span class="special">)</span></code> is called. | |
| 390 | </li> | |
| 391 | <li class="listitem"> | |
| 392 | <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only | |
| 393 | be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code> | |
| 394 | in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains | |
| 395 | initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety | |
| 396 | of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>. | |
| 397 | </li> | |
| 398 | <li class="listitem"> | |
| 399 | <span class="bold"><strong>Example:</strong></span> | |
| 400 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uninit</span> <span class="special">;</span> | |
| 401 | <span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span> | |
| 402 | ||
| 403 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 404 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span> | |
| 405 | ||
| 406 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span> | |
| 407 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 408 | ||
| 409 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 410 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">);</span> | |
| 411 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="keyword">nullptr</span> <span class="special">);</span> | |
| 412 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">);</span> | |
| 413 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 414 | </pre> | |
| 415 | </li> | |
| 416 | </ul></div> | |
| 417 | <p> | |
| 418 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 419 | </p> | |
| 420 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 421 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 422 | <span class="identifier">optional</span> <span class="special">&&</span> | |
| 423 | <span class="identifier">rhs</span> <span class="special">);</span></code> | |
| 424 | </p></blockquote></div> | |
| 425 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 426 | <li class="listitem"> | |
| 427 | <span class="bold"><strong>Effect:</strong></span> Move-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 428 | </li> | |
| 429 | <li class="listitem"> | |
| 430 | <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 431 | is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 432 | is initialized and its value is another reference to the same object | |
| 433 | referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; | |
| 434 | else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 435 | is uninitialized. | |
| 436 | </li> | |
| 437 | <li class="listitem"> | |
| 438 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 439 | </li> | |
| 440 | <li class="listitem"> | |
| 441 | <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 442 | is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> will refer to the same object | |
| 443 | (they alias). | |
| 444 | </li> | |
| 445 | <li class="listitem"> | |
| 446 | <span class="bold"><strong>Example:</strong></span> | |
| 447 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uninit</span> <span class="special">;</span> | |
| 448 | <span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span> | |
| 449 | ||
| 450 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 451 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span> | |
| 452 | ||
| 453 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span> | |
| 454 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> | |
| 455 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 456 | ||
| 457 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 458 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 459 | ||
| 460 | <span class="special">*</span><span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span> | |
| 461 | ||
| 462 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span> | |
| 463 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span> | |
| 464 | </pre> | |
| 465 | </li> | |
| 466 | </ul></div> | |
| 467 | <p> | |
| 468 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 469 | </p> | |
| 470 | <a name="reference_optional_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 471 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 472 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 473 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code> | |
| 474 | </p></blockquote></div> | |
| 475 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 476 | <li class="listitem"> | |
| 477 | <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 478 | </li> | |
| 479 | <li class="listitem"> | |
| 480 | <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 481 | is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 482 | is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the | |
| 483 | value of rhs converted to type <code class="computeroutput"><span class="identifier">T</span></code>; | |
| 484 | else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 485 | is uninitialized. | |
| 486 | </li> | |
| 487 | <li class="listitem"> | |
| 488 | <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> | |
| 489 | <span class="special">)</span></code> throws. | |
| 490 | </li> | |
| 491 | <li class="listitem"> | |
| 492 | <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> | |
| 493 | <span class="special">)</span></code> is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, which requires | |
| 494 | a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code> | |
| 495 | to <code class="computeroutput"><span class="identifier">T</span></code>. | |
| 496 | </li> | |
| 497 | <li class="listitem"> | |
| 498 | <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only | |
| 499 | be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> | |
| 500 | <span class="special">);</span></code> in that case, this constructor | |
| 501 | has no effect. | |
| 502 | </li> | |
| 503 | <li class="listitem"> | |
| 504 | <span class="bold"><strong>Example:</strong></span> | |
| 505 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span> | |
| 506 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span> | |
| 507 | ||
| 508 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span> | |
| 509 | <span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span> | |
| 510 | </pre> | |
| 511 | </li> | |
| 512 | </ul></div> | |
| 513 | <p> | |
| 514 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 515 | </p> | |
| 516 | <a name="reference_optional_move_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 517 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 518 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 519 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> | |
| 520 | <span class="identifier">rhs</span> <span class="special">);</span></code> | |
| 521 | </p></blockquote></div> | |
| 522 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 523 | <li class="listitem"> | |
| 524 | <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 525 | </li> | |
| 526 | <li class="listitem"> | |
| 527 | <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 528 | is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 529 | is initialized and its value is move-constructed from <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; | |
| 530 | else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 531 | is uninitialized. | |
| 532 | </li> | |
| 533 | <li class="listitem"> | |
| 534 | <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code> | |
| 535 | throws. | |
| 536 | </li> | |
| 537 | <li class="listitem"> | |
| 538 | <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code> | |
| 539 | is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is | |
| 540 | initialized, which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code> | |
| 541 | to <code class="computeroutput"><span class="identifier">T</span></code>. | |
| 542 | </li> | |
| 543 | <li class="listitem"> | |
| 544 | <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only | |
| 545 | be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">);</span></code> | |
| 546 | in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains | |
| 547 | initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety | |
| 548 | guarantee of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> | |
| 549 | <span class="special">)</span></code>. | |
| 550 | </li> | |
| 551 | <li class="listitem"> | |
| 552 | <span class="bold"><strong>Example:</strong></span> | |
| 553 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span> | |
| 554 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span> | |
| 555 | ||
| 556 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">x</span><span class="special">))</span> <span class="special">;</span> | |
| 557 | <span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span> | |
| 558 | </pre> | |
| 559 | </li> | |
| 560 | </ul></div> | |
| 561 | <p> | |
| 562 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 563 | </p> | |
| 564 | <a name="reference_optional_constructor_factory"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 565 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span> | |
| 566 | <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 567 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 568 | <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code> | |
| 569 | </p></blockquote></div> | |
| 570 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 571 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span> | |
| 572 | <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 573 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> | |
| 574 | <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code> | |
| 575 | </p></blockquote></div> | |
| 576 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 577 | <li class="listitem"> | |
| 578 | <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained from the factory. | |
| 579 | </li> | |
| 580 | <li class="listitem"> | |
| 581 | <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> | |
| 582 | and its value is <span class="emphasis"><em>directly given</em></span> from the factory | |
| 583 | <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value | |
| 584 | <span class="underline">is not copied</span>). | |
| 585 | </li> | |
| 586 | <li class="listitem"> | |
| 587 | <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory | |
| 588 | throws. | |
| 589 | </li> | |
| 590 | <li class="listitem"> | |
| 591 | <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place | |
| 592 | Factories</a> | |
| 593 | </li> | |
| 594 | <li class="listitem"> | |
| 595 | <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only | |
| 596 | be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code> | |
| 597 | constructor used by the factory; in that case, this constructor has | |
| 598 | no effect. | |
| 599 | </li> | |
| 600 | <li class="listitem"> | |
| 601 | <span class="bold"><strong>Example:</strong></span> | |
| 602 | <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">C</span> <span class="special">{</span> <span class="identifier">C</span> <span class="special">(</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span> | |
| 603 | ||
| 604 | <span class="identifier">C</span> <span class="identifier">v</span><span class="special">(</span><span class="char">'A'</span><span class="special">,</span><span class="number">123.4</span><span class="special">,</span><span class="string">"hello"</span><span class="special">);</span> | |
| 605 | ||
| 606 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">in_place</span> <span class="special">(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// InPlaceFactory used</span> | |
| 607 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">in_place</span><span class="special"><</span><span class="identifier">C</span><span class="special">>(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// TypedInPlaceFactory used</span> | |
| 608 | ||
| 609 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 610 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 611 | </pre> | |
| 612 | </li> | |
| 613 | </ul></div> | |
| 614 | <p> | |
| 615 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 616 | </p> | |
| 617 | <a name="reference_optional_operator_equal_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 618 | <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> | |
| 619 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> | |
| 620 | <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> | |
| 621 | </p></blockquote></div> | |
| 622 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 623 | <li class="listitem"> | |
| 624 | <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized destroys its contained | |
| 625 | value. | |
| 626 | </li> | |
| 627 | <li class="listitem"> | |
| 628 | <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized. | |
| 629 | </li> | |
| 630 | </ul></div> | |
| 631 | <p> | |
| 632 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 633 | </p> | |
| 634 | <a name="reference_optional_operator_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 635 | <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> | |
| 636 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> | |
| 637 | <span class="keyword">const</span><span class="special">&</span> | |
| 638 | <span class="identifier">rhs</span> <span class="special">)</span> | |
| 639 | <span class="special">;</span></code> | |
| 640 | </p></blockquote></div> | |
| 641 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 642 | <li class="listitem"> | |
| 643 | <span class="bold"><strong>Effect:</strong></span> Assigns the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 644 | </li> | |
| 645 | <li class="listitem"> | |
| 646 | <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is | |
| 647 | a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">rhs</span></code>. | |
| 648 | </li> | |
| 649 | <li class="listitem"> | |
| 650 | <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> | |
| 651 | <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&)</span></code> | |
| 652 | throws. | |
| 653 | </li> | |
| 654 | <li class="listitem"> | |
| 655 | <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s assignment operator is used, | |
| 656 | otherwise, its copy-constructor is used. | |
| 657 | </li> | |
| 658 | <li class="listitem"> | |
| 659 | <span class="bold"><strong>Exception Safety:</strong></span> In the event of | |
| 660 | an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified | |
| 661 | as far as <code class="computeroutput"><span class="identifier">optional</span></code> | |
| 662 | is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 663 | <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>). | |
| 664 | If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 665 | is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 666 | <span class="emphasis"><em>copy constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized. | |
| 667 | </li> | |
| 668 | <li class="listitem"> | |
| 669 | <span class="bold"><strong>Example:</strong></span> | |
| 670 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span> | |
| 671 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> | |
| 672 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span> | |
| 673 | ||
| 674 | <span class="identifier">T</span> <span class="identifier">y</span><span class="special">;</span> | |
| 675 | <span class="identifier">def</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span> | |
| 676 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> | |
| 677 | <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span> | |
| 678 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> | |
| 679 | </pre> | |
| 680 | </li> | |
| 681 | </ul></div> | |
| 682 | <p> | |
| 683 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 684 | </p> | |
| 685 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 686 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> | |
| 687 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rhs</span> | |
| 688 | <span class="special">)</span> <span class="special">;</span></code> | |
| 689 | </p></blockquote></div> | |
| 690 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 691 | <li class="listitem"> | |
| 692 | <span class="bold"><strong>Effect:</strong></span> (Re)binds the wrapped reference. | |
| 693 | </li> | |
| 694 | <li class="listitem"> | |
| 695 | <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and it references | |
| 696 | the same object referenced by <code class="computeroutput"><span class="identifier">rhs</span></code>. | |
| 697 | </li> | |
| 698 | <li class="listitem"> | |
| 699 | <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, it is <span class="emphasis"><em>rebound</em></span> | |
| 700 | to the new object. See <a class="link" href="../../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a> | |
| 701 | for details on this behavior. | |
| 702 | </li> | |
| 703 | <li class="listitem"> | |
| 704 | <span class="bold"><strong>Example:</strong></span> | |
| 705 | <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span> | |
| 706 | <span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> | |
| 707 | <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> | |
| 708 | <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span> | |
| 709 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span> | |
| 710 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span> | |
| 711 | ||
| 712 | <span class="identifier">def</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb'</span> | |
| 713 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span> | |
| 714 | <span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span> | |
| 715 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span> | |
| 716 | <span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span> | |
| 717 | <span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span> | |
| 718 | <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">rc</span> <span class="special">;</span> <span class="comment">// REBINDS to 'c' through 'rc'</span> | |
| 719 | <span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span> | |
| 720 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span> | |
| 721 | </pre> | |
| 722 | </li> | |
| 723 | </ul></div> | |
| 724 | <p> | |
| 725 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 726 | </p> | |
| 727 | <a name="reference_optional_operator_move_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 728 | <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> | |
| 729 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span> | |
| 730 | <span class="special">)</span> <span class="special">;</span></code> | |
| 731 | </p></blockquote></div> | |
| 732 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 733 | <li class="listitem"> | |
| 734 | <span class="bold"><strong>Effect:</strong></span> Moves the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>. | |
| 735 | </li> | |
| 736 | <li class="listitem"> | |
| 737 | <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is | |
| 738 | moved from <code class="computeroutput"><span class="identifier">rhs</span></code>. | |
| 739 | </li> | |
| 740 | <li class="listitem"> | |
| 741 | <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> | |
| 742 | or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&&)</span></code> | |
| 743 | throws. | |
| 744 | </li> | |
| 745 | <li class="listitem"> | |
| 746 | <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s move-assignment operator is used, | |
| 747 | otherwise, its move-constructor is used. | |
| 748 | </li> | |
| 749 | <li class="listitem"> | |
| 750 | <span class="bold"><strong>Exception Safety:</strong></span> In the event of | |
| 751 | an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified | |
| 752 | as far as <code class="computeroutput"><span class="identifier">optional</span></code> | |
| 753 | is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 754 | <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>). | |
| 755 | If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 756 | is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 757 | <span class="emphasis"><em>move constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized. | |
| 758 | </li> | |
| 759 | <li class="listitem"> | |
| 760 | <span class="bold"><strong>Example:</strong></span> | |
| 761 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span> | |
| 762 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> | |
| 763 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span> | |
| 764 | ||
| 765 | <span class="identifier">T</span> <span class="identifier">y1</span><span class="special">,</span> <span class="identifier">y2</span><span class="special">,</span> <span class="identifier">yR</span><span class="special">;</span> | |
| 766 | <span class="identifier">def</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y1</span><span class="special">)</span> <span class="special">;</span> | |
| 767 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span> | |
| 768 | <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y2</span><span class="special">)</span> <span class="special">;</span> | |
| 769 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span> | |
| 770 | </pre> | |
| 771 | </li> | |
| 772 | </ul></div> | |
| 773 | <p> | |
| 774 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 775 | </p> | |
| 776 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 777 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> | |
| 778 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span> | |
| 779 | <span class="special">)</span> <span class="special">=</span> | |
| 780 | <span class="keyword">delete</span><span class="special">;</span></code> | |
| 781 | </p></blockquote></div> | |
| 782 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 783 | <span class="bold"><strong>Notes:</strong></span> This assignment operator is | |
| 784 | deleted. | |
| 785 | </li></ul></div> | |
| 786 | <p> | |
| 787 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 788 | </p> | |
| 789 | <a name="reference_optional_operator_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 790 | <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> | |
| 791 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span> | |
| 792 | <span class="keyword">const</span><span class="special">&</span> | |
| 793 | <span class="identifier">rhs</span> <span class="special">)</span> | |
| 794 | <span class="special">;</span></code> | |
| 795 | </p></blockquote></div> | |
| 796 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 797 | <li class="listitem"> | |
| 798 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> | |
| 799 | is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">CopyAssignable</span></code>. | |
| 800 | </li> | |
| 801 | <li class="listitem"> | |
| 802 | <p class="simpara"> | |
| 803 | <span class="bold"><strong>Effects:</strong></span> | |
| 804 | </p> | |
| 805 | <div class="informaltable"><table class="table"> | |
| 806 | <colgroup> | |
| 807 | <col> | |
| 808 | <col> | |
| 809 | <col> | |
| 810 | </colgroup> | |
| 811 | <thead><tr></tr></thead> | |
| 812 | <tbody> | |
| 813 | <tr> | |
| 814 | <td> | |
| 815 | </td> | |
| 816 | <td> | |
| 817 | <p> | |
| 818 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span> | |
| 819 | </p> | |
| 820 | </td> | |
| 821 | <td> | |
| 822 | <p> | |
| 823 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span> | |
| 824 | </p> | |
| 825 | </td> | |
| 826 | </tr> | |
| 827 | <tr> | |
| 828 | <td> | |
| 829 | <p> | |
| 830 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 831 | contains a value</strong></span> | |
| 832 | </p> | |
| 833 | </td> | |
| 834 | <td> | |
| 835 | <p> | |
| 836 | assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> | |
| 837 | to the contained value | |
| 838 | </p> | |
| 839 | </td> | |
| 840 | <td> | |
| 841 | <p> | |
| 842 | initializes the contained value as if direct-initializing | |
| 843 | an object of type <code class="computeroutput"><span class="identifier">T</span></code> | |
| 844 | with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> | |
| 845 | </p> | |
| 846 | </td> | |
| 847 | </tr> | |
| 848 | <tr> | |
| 849 | <td> | |
| 850 | <p> | |
| 851 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 852 | does not contain a value</strong></span> | |
| 853 | </p> | |
| 854 | </td> | |
| 855 | <td> | |
| 856 | <p> | |
| 857 | destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code> | |
| 858 | </p> | |
| 859 | </td> | |
| 860 | <td> | |
| 861 | <p> | |
| 862 | no effect | |
| 863 | </p> | |
| 864 | </td> | |
| 865 | </tr> | |
| 866 | </tbody> | |
| 867 | </table></div> | |
| 868 | </li> | |
| 869 | <li class="listitem"> | |
| 870 | <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>; | |
| 871 | </li> | |
| 872 | <li class="listitem"> | |
| 873 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>. | |
| 874 | </li> | |
| 875 | <li class="listitem"> | |
| 876 | <span class="bold"><strong>Exception Safety:</strong></span> If any exception | |
| 877 | is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 878 | remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s copy constructor, no effect. | |
| 879 | If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 880 | copy assignment, the state of its contained value is as defined by | |
| 881 | the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 882 | copy assignment. | |
| 883 | </li> | |
| 884 | <li class="listitem"> | |
| 885 | <span class="bold"><strong>Example:</strong></span> | |
| 886 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> | |
| 887 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> | |
| 888 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> | |
| 889 | ||
| 890 | <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span> | |
| 891 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span> | |
| 892 | <span class="comment">// previous value (copy of 'v') destroyed from within 'opt'.</span> | |
| 893 | </pre> | |
| 894 | </li> | |
| 895 | </ul></div> | |
| 896 | <p> | |
| 897 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 898 | </p> | |
| 899 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 900 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> | |
| 901 | <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> | |
| 902 | <span class="special">)</span> <span class="special">;</span></code> | |
| 903 | </p></blockquote></div> | |
| 904 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 905 | <li class="listitem"> | |
| 906 | <span class="bold"><strong>Effect:</strong></span> (Re)binds thee wrapped reference. | |
| 907 | </li> | |
| 908 | <li class="listitem"> | |
| 909 | <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 910 | is initialized and it references the same object referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; | |
| 911 | otherwise, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 912 | is uninitialized (and references no object). | |
| 913 | </li> | |
| 914 | <li class="listitem"> | |
| 915 | <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized and so is <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>, | |
| 916 | <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 917 | is <span class="emphasis"><em>rebound</em></span> to the new object. See <a class="link" href="../../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a> | |
| 918 | for details on this behavior. | |
| 919 | </li> | |
| 920 | <li class="listitem"> | |
| 921 | <span class="bold"><strong>Example:</strong></span> | |
| 922 | <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span> | |
| 923 | <span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> | |
| 924 | <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> | |
| 925 | <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span> | |
| 926 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span> | |
| 927 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span> | |
| 928 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span> | |
| 929 | ||
| 930 | <span class="identifier">def</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb' wrapped within 'orb'</span> | |
| 931 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span> | |
| 932 | <span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">ora</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span> | |
| 933 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span> | |
| 934 | <span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span> | |
| 935 | <span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span> | |
| 936 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orc</span><span class="special">(</span><span class="identifier">rc</span><span class="special">)</span> <span class="special">;</span> | |
| 937 | <span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orc</span> <span class="special">;</span> <span class="comment">// REBINDS ora to 'c' through 'rc'</span> | |
| 938 | <span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span> | |
| 939 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">ora</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span> | |
| 940 | </pre> | |
| 941 | </li> | |
| 942 | </ul></div> | |
| 943 | <p> | |
| 944 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 945 | </p> | |
| 946 | <a name="reference_optional_operator_move_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 947 | <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> | |
| 948 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span> | |
| 949 | <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code> | |
| 950 | </p></blockquote></div> | |
| 951 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 952 | <li class="listitem"> | |
| 953 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> | |
| 954 | is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> | |
| 955 | and <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>. | |
| 956 | </li> | |
| 957 | <li class="listitem"> | |
| 958 | <p class="simpara"> | |
| 959 | <span class="bold"><strong>Effects:</strong></span> | |
| 960 | </p> | |
| 961 | <div class="informaltable"><table class="table"> | |
| 962 | <colgroup> | |
| 963 | <col> | |
| 964 | <col> | |
| 965 | <col> | |
| 966 | </colgroup> | |
| 967 | <thead><tr></tr></thead> | |
| 968 | <tbody> | |
| 969 | <tr> | |
| 970 | <td> | |
| 971 | </td> | |
| 972 | <td> | |
| 973 | <p> | |
| 974 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span> | |
| 975 | </p> | |
| 976 | </td> | |
| 977 | <td> | |
| 978 | <p> | |
| 979 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span> | |
| 980 | </p> | |
| 981 | </td> | |
| 982 | </tr> | |
| 983 | <tr> | |
| 984 | <td> | |
| 985 | <p> | |
| 986 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 987 | contains a value</strong></span> | |
| 988 | </p> | |
| 989 | </td> | |
| 990 | <td> | |
| 991 | <p> | |
| 992 | assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value | |
| 993 | </p> | |
| 994 | </td> | |
| 995 | <td> | |
| 996 | <p> | |
| 997 | initializes the contained value as if direct-initializing | |
| 998 | an object of type <code class="computeroutput"><span class="identifier">T</span></code> | |
| 999 | with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> | |
| 1000 | </p> | |
| 1001 | </td> | |
| 1002 | </tr> | |
| 1003 | <tr> | |
| 1004 | <td> | |
| 1005 | <p> | |
| 1006 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 1007 | does not contain a value</strong></span> | |
| 1008 | </p> | |
| 1009 | </td> | |
| 1010 | <td> | |
| 1011 | <p> | |
| 1012 | destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code> | |
| 1013 | </p> | |
| 1014 | </td> | |
| 1015 | <td> | |
| 1016 | <p> | |
| 1017 | no effect | |
| 1018 | </p> | |
| 1019 | </td> | |
| 1020 | </tr> | |
| 1021 | </tbody> | |
| 1022 | </table></div> | |
| 1023 | </li> | |
| 1024 | <li class="listitem"> | |
| 1025 | <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>; | |
| 1026 | </li> | |
| 1027 | <li class="listitem"> | |
| 1028 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>. | |
| 1029 | </li> | |
| 1030 | <li class="listitem"> | |
| 1031 | <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span> <span class="special">&&</span> | |
| 1032 | <span class="identifier">is_nothrow_move_assignable</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>. | |
| 1033 | </li> | |
| 1034 | <li class="listitem"> | |
| 1035 | <span class="bold"><strong>Exception Safety:</strong></span> If any exception | |
| 1036 | is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 1037 | remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s move constructor, the state of | |
| 1038 | <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> | |
| 1039 | is determined by the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 1040 | move constructor. If an exception is thrown during the call to T's | |
| 1041 | move-assignment, the state of <code class="computeroutput"><span class="special">**</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by the exception | |
| 1042 | safety guarantee of T's move assignment. | |
| 1043 | </li> | |
| 1044 | <li class="listitem"> | |
| 1045 | <span class="bold"><strong>Example:</strong></span> | |
| 1046 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span> | |
| 1047 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> | |
| 1048 | ||
| 1049 | <span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span> | |
| 1050 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span> | |
| 1051 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> | |
| 1052 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 1053 | </pre> | |
| 1054 | </li> | |
| 1055 | </ul></div> | |
| 1056 | <p> | |
| 1057 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1058 | </p> | |
| 1059 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1060 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> | |
| 1061 | <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&&</span> <span class="identifier">rhs</span> | |
| 1062 | <span class="special">)</span> <span class="special">;</span></code> | |
| 1063 | </p></blockquote></div> | |
| 1064 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 1065 | <span class="bold"><strong>Effect:</strong></span> Same as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> | |
| 1066 | <span class="keyword">const</span><span class="special">&</span> | |
| 1067 | <span class="identifier">rhs</span> <span class="special">)</span></code>. | |
| 1068 | </li></ul></div> | |
| 1069 | <p> | |
| 1070 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1071 | </p> | |
| 1072 | <a name="reference_optional_operator_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1073 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> | |
| 1074 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> | |
| 1075 | <span class="special">)</span> <span class="special">;</span></code> | |
| 1076 | </p></blockquote></div> | |
| 1077 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1078 | <li class="listitem"> | |
| 1079 | <p class="simpara"> | |
| 1080 | <span class="bold"><strong>Effect:</strong></span> | |
| 1081 | </p> | |
| 1082 | <div class="informaltable"><table class="table"> | |
| 1083 | <colgroup> | |
| 1084 | <col> | |
| 1085 | <col> | |
| 1086 | <col> | |
| 1087 | </colgroup> | |
| 1088 | <thead><tr></tr></thead> | |
| 1089 | <tbody> | |
| 1090 | <tr> | |
| 1091 | <td> | |
| 1092 | </td> | |
| 1093 | <td> | |
| 1094 | <p> | |
| 1095 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span> | |
| 1096 | </p> | |
| 1097 | </td> | |
| 1098 | <td> | |
| 1099 | <p> | |
| 1100 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span> | |
| 1101 | </p> | |
| 1102 | </td> | |
| 1103 | </tr> | |
| 1104 | <tr> | |
| 1105 | <td> | |
| 1106 | <p> | |
| 1107 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 1108 | contains a value</strong></span> | |
| 1109 | </p> | |
| 1110 | </td> | |
| 1111 | <td> | |
| 1112 | <p> | |
| 1113 | assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> | |
| 1114 | to the contained value | |
| 1115 | </p> | |
| 1116 | </td> | |
| 1117 | <td> | |
| 1118 | <p> | |
| 1119 | initializes the contained value as if direct-initializing | |
| 1120 | an object of type <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1121 | with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> | |
| 1122 | </p> | |
| 1123 | </td> | |
| 1124 | </tr> | |
| 1125 | <tr> | |
| 1126 | <td> | |
| 1127 | <p> | |
| 1128 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 1129 | does not contain a value</strong></span> | |
| 1130 | </p> | |
| 1131 | </td> | |
| 1132 | <td> | |
| 1133 | <p> | |
| 1134 | destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code> | |
| 1135 | </p> | |
| 1136 | </td> | |
| 1137 | <td> | |
| 1138 | <p> | |
| 1139 | no effect | |
| 1140 | </p> | |
| 1141 | </td> | |
| 1142 | </tr> | |
| 1143 | </tbody> | |
| 1144 | </table></div> | |
| 1145 | </li> | |
| 1146 | <li class="listitem"> | |
| 1147 | <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>. | |
| 1148 | </li> | |
| 1149 | <li class="listitem"> | |
| 1150 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>. | |
| 1151 | </li> | |
| 1152 | <li class="listitem"> | |
| 1153 | <span class="bold"><strong>Exception Safety:</strong></span> If any exception | |
| 1154 | is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception | |
| 1155 | is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 1156 | constructor, no effect. If an exception is thrown during the call to | |
| 1157 | <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the | |
| 1158 | state of its contained value is as defined by the exception safety | |
| 1159 | guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy | |
| 1160 | assignment. | |
| 1161 | </li> | |
| 1162 | <li class="listitem"> | |
| 1163 | <span class="bold"><strong>Example:</strong></span> | |
| 1164 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> | |
| 1165 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> | |
| 1166 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span> | |
| 1167 | ||
| 1168 | <span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt0</span> <span class="special">;</span> | |
| 1169 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 1170 | </pre> | |
| 1171 | </li> | |
| 1172 | </ul></div> | |
| 1173 | <p> | |
| 1174 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1175 | </p> | |
| 1176 | <a name="reference_optional_operator_move_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1177 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> | |
| 1178 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span> | |
| 1179 | <span class="special">)</span> <span class="special">;</span></code> | |
| 1180 | </p></blockquote></div> | |
| 1181 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1182 | <li class="listitem"> | |
| 1183 | <p class="simpara"> | |
| 1184 | <span class="bold"><strong>Effect:</strong></span> | |
| 1185 | </p> | |
| 1186 | <div class="informaltable"><table class="table"> | |
| 1187 | <colgroup> | |
| 1188 | <col> | |
| 1189 | <col> | |
| 1190 | <col> | |
| 1191 | </colgroup> | |
| 1192 | <thead><tr></tr></thead> | |
| 1193 | <tbody> | |
| 1194 | <tr> | |
| 1195 | <td> | |
| 1196 | </td> | |
| 1197 | <td> | |
| 1198 | <p> | |
| 1199 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span> | |
| 1200 | </p> | |
| 1201 | </td> | |
| 1202 | <td> | |
| 1203 | <p> | |
| 1204 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span> | |
| 1205 | </p> | |
| 1206 | </td> | |
| 1207 | </tr> | |
| 1208 | <tr> | |
| 1209 | <td> | |
| 1210 | <p> | |
| 1211 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 1212 | contains a value</strong></span> | |
| 1213 | </p> | |
| 1214 | </td> | |
| 1215 | <td> | |
| 1216 | <p> | |
| 1217 | assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value | |
| 1218 | </p> | |
| 1219 | </td> | |
| 1220 | <td> | |
| 1221 | <p> | |
| 1222 | initializes the contained value as if direct-initializing | |
| 1223 | an object of type <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1224 | with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> | |
| 1225 | </p> | |
| 1226 | </td> | |
| 1227 | </tr> | |
| 1228 | <tr> | |
| 1229 | <td> | |
| 1230 | <p> | |
| 1231 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 1232 | does not contain a value</strong></span> | |
| 1233 | </p> | |
| 1234 | </td> | |
| 1235 | <td> | |
| 1236 | <p> | |
| 1237 | destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code> | |
| 1238 | </p> | |
| 1239 | </td> | |
| 1240 | <td> | |
| 1241 | <p> | |
| 1242 | no effect | |
| 1243 | </p> | |
| 1244 | </td> | |
| 1245 | </tr> | |
| 1246 | </tbody> | |
| 1247 | </table></div> | |
| 1248 | </li> | |
| 1249 | <li class="listitem"> | |
| 1250 | <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>. | |
| 1251 | </li> | |
| 1252 | <li class="listitem"> | |
| 1253 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>. | |
| 1254 | </li> | |
| 1255 | <li class="listitem"> | |
| 1256 | <span class="bold"><strong>Exception Safety:</strong></span> If any exception | |
| 1257 | is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception | |
| 1258 | is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s | |
| 1259 | constructor, no effect. If an exception is thrown during the call to | |
| 1260 | <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the | |
| 1261 | state of its contained value is as defined by the exception safety | |
| 1262 | guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy | |
| 1263 | assignment. | |
| 1264 | </li> | |
| 1265 | <li class="listitem"> | |
| 1266 | <span class="bold"><strong>Example:</strong></span> | |
| 1267 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> | |
| 1268 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> | |
| 1269 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span> | |
| 1270 | ||
| 1271 | <span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">;</span> | |
| 1272 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span> | |
| 1273 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt1</span> <span class="special">)</span> | |
| 1274 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 1275 | </pre> | |
| 1276 | </li> | |
| 1277 | </ul></div> | |
| 1278 | <p> | |
| 1279 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1280 | </p> | |
| 1281 | <a name="reference_optional_emplace"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1282 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> | |
| 1283 | <span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1284 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">emplace</span><span class="special">(</span> | |
| 1285 | <span class="identifier">Args</span><span class="special">...&&</span> | |
| 1286 | <span class="identifier">args</span> <span class="special">);</span></code> | |
| 1287 | </p></blockquote></div> | |
| 1288 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1289 | <li class="listitem"> | |
| 1290 | <span class="bold"><strong>Requires:</strong></span> The compiler supports rvalue | |
| 1291 | references and variadic templates. | |
| 1292 | </li> | |
| 1293 | <li class="listitem"> | |
| 1294 | <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized calls <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">none</span></code>. | |
| 1295 | Then initializes in-place the contained value as if direct-initializing | |
| 1296 | an object of type <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1297 | with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>. | |
| 1298 | </li> | |
| 1299 | <li class="listitem"> | |
| 1300 | <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>. | |
| 1301 | </li> | |
| 1302 | <li class="listitem"> | |
| 1303 | <span class="bold"><strong>Throws:</strong></span> Whatever the selected <code class="computeroutput"><span class="identifier">T</span></code>'s constructor throws. | |
| 1304 | </li> | |
| 1305 | <li class="listitem"> | |
| 1306 | <span class="bold"><strong>Exception Safety:</strong></span> If an exception | |
| 1307 | is thrown during the initialization of <code class="computeroutput"><span class="identifier">T</span></code>, | |
| 1308 | <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 1309 | is <span class="emphasis"><em>uninitialized</em></span>. | |
| 1310 | </li> | |
| 1311 | <li class="listitem"> | |
| 1312 | <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1313 | need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> | |
| 1314 | or <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>. | |
| 1315 | On compilers that do not support variadic templates, the signature | |
| 1316 | falls back to two overloads:<code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> | |
| 1317 | <span class="identifier">Arg</span><span class="special">></span> | |
| 1318 | <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">)</span></code> and <code class="computeroutput"><span class="keyword">void</span> | |
| 1319 | <span class="identifier">emplace</span><span class="special">()</span></code>. | |
| 1320 | On compilers that do not support rvalue references, the signature falls | |
| 1321 | back to three overloads: taking <code class="computeroutput"><span class="keyword">const</span></code> | |
| 1322 | and non-<code class="computeroutput"><span class="keyword">const</span></code> lvalue reference, | |
| 1323 | and third with empty function argument list. | |
| 1324 | </li> | |
| 1325 | <li class="listitem"> | |
| 1326 | <span class="bold"><strong>Example:</strong></span> | |
| 1327 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> | |
| 1328 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">;</span> | |
| 1329 | <span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> <span class="comment">// create in-place using ctor T(int)</span> | |
| 1330 | <span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">();</span> <span class="comment">// destroy previous and default-construct another T</span> | |
| 1331 | <span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// destroy and copy-construct in-place (no assignment called)</span> | |
| 1332 | </pre> | |
| 1333 | </li> | |
| 1334 | </ul></div> | |
| 1335 | <p> | |
| 1336 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1337 | </p> | |
| 1338 | <a name="reference_optional_operator_equal_factory"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1339 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span> | |
| 1340 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> | |
| 1341 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">InPlaceFactory</span> | |
| 1342 | <span class="keyword">const</span><span class="special">&</span> | |
| 1343 | <span class="identifier">f</span> <span class="special">);</span></code> | |
| 1344 | </p></blockquote></div> | |
| 1345 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1346 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span> | |
| 1347 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> | |
| 1348 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">TypedInPlaceFactory</span> | |
| 1349 | <span class="keyword">const</span><span class="special">&</span> | |
| 1350 | <span class="identifier">f</span> <span class="special">);</span></code> | |
| 1351 | </p></blockquote></div> | |
| 1352 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1353 | <li class="listitem"> | |
| 1354 | <span class="bold"><strong>Effect:</strong></span> Assigns an <code class="computeroutput"><span class="identifier">optional</span></code> | |
| 1355 | with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained | |
| 1356 | from the factory. | |
| 1357 | </li> | |
| 1358 | <li class="listitem"> | |
| 1359 | <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> | |
| 1360 | and its value is <span class="emphasis"><em>directly given</em></span> from the factory | |
| 1361 | <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value | |
| 1362 | <span class="underline">is not copied</span>). | |
| 1363 | </li> | |
| 1364 | <li class="listitem"> | |
| 1365 | <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory | |
| 1366 | throws. | |
| 1367 | </li> | |
| 1368 | <li class="listitem"> | |
| 1369 | <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place | |
| 1370 | Factories</a> | |
| 1371 | </li> | |
| 1372 | <li class="listitem"> | |
| 1373 | <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only | |
| 1374 | be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1375 | constructor used by the factory; in that case, the <code class="computeroutput"><span class="identifier">optional</span></code> | |
| 1376 | object will be reset to be <span class="emphasis"><em>uninitialized</em></span>. | |
| 1377 | </li> | |
| 1378 | </ul></div> | |
| 1379 | <p> | |
| 1380 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1381 | </p> | |
| 1382 | <a name="reference_optional_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1383 | <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1384 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code> | |
| 1385 | </p></blockquote></div> | |
| 1386 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 1387 | <span class="bold"><strong>Deprecated:</strong></span> same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span> | |
| 1388 | <span class="special">(</span> <span class="identifier">T</span> | |
| 1389 | <span class="keyword">const</span><span class="special">&</span> | |
| 1390 | <span class="identifier">v</span><span class="special">)</span> | |
| 1391 | <span class="special">;</span></code> | |
| 1392 | </li></ul></div> | |
| 1393 | <p> | |
| 1394 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1395 | </p> | |
| 1396 | <a name="reference_optional_reset"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1397 | <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> | |
| 1398 | <span class="special">;</span></code> | |
| 1399 | </p></blockquote></div> | |
| 1400 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 1401 | <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=(</span> | |
| 1402 | <span class="identifier">none_t</span> <span class="special">);</span></code> | |
| 1403 | </li></ul></div> | |
| 1404 | <p> | |
| 1405 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1406 | </p> | |
| 1407 | <a name="reference_optional_get"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1408 | <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1409 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code> | |
| 1410 | </p></blockquote></div> | |
| 1411 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1412 | <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> | |
| 1413 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code> | |
| 1414 | </p></blockquote></div> | |
| 1415 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1416 | <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span> | |
| 1417 | <span class="keyword">const</span><span class="special">&</span> | |
| 1418 | <span class="identifier">get</span> <span class="special">(</span> | |
| 1419 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code> | |
| 1420 | </p></blockquote></div> | |
| 1421 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1422 | <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span> | |
| 1423 | <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1424 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> | |
| 1425 | <span class="special">&)</span> <span class="special">;</span></code> | |
| 1426 | </p></blockquote></div> | |
| 1427 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1428 | <li class="listitem"> | |
| 1429 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized | |
| 1430 | </li> | |
| 1431 | <li class="listitem"> | |
| 1432 | <span class="bold"><strong>Returns:</strong></span> A reference to the contained | |
| 1433 | value | |
| 1434 | </li> | |
| 1435 | <li class="listitem"> | |
| 1436 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 1437 | </li> | |
| 1438 | <li class="listitem"> | |
| 1439 | <span class="bold"><strong>Notes:</strong></span> The requirement is asserted | |
| 1440 | via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. | |
| 1441 | </li> | |
| 1442 | </ul></div> | |
| 1443 | <p> | |
| 1444 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1445 | </p> | |
| 1446 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1447 | <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code> | |
| 1448 | </p></blockquote></div> | |
| 1449 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1450 | <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> | |
| 1451 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code> | |
| 1452 | </p></blockquote></div> | |
| 1453 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1454 | <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span> | |
| 1455 | <span class="keyword">const</span><span class="special">&</span> | |
| 1456 | <span class="identifier">get</span> <span class="special">(</span> | |
| 1457 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> | |
| 1458 | <span class="keyword">const</span><span class="special">&</span> | |
| 1459 | <span class="special">)</span> <span class="special">;</span></code> | |
| 1460 | </p></blockquote></div> | |
| 1461 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1462 | <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span> | |
| 1463 | <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">&)</span> | |
| 1464 | <span class="special">;</span></code> | |
| 1465 | </p></blockquote></div> | |
| 1466 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1467 | <li class="listitem"> | |
| 1468 | <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized | |
| 1469 | </li> | |
| 1470 | <li class="listitem"> | |
| 1471 | <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span> | |
| 1472 | reference contained. | |
| 1473 | </li> | |
| 1474 | <li class="listitem"> | |
| 1475 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 1476 | </li> | |
| 1477 | <li class="listitem"> | |
| 1478 | <span class="bold"><strong>Notes:</strong></span> The requirement is asserted | |
| 1479 | via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. | |
| 1480 | </li> | |
| 1481 | </ul></div> | |
| 1482 | <p> | |
| 1483 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1484 | </p> | |
| 1485 | <a name="reference_optional_operator_asterisk"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1486 | <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1487 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> | |
| 1488 | <span class="keyword">const</span><span class="special">&</span> | |
| 1489 | <span class="special">;</span></code> | |
| 1490 | </p></blockquote></div> | |
| 1491 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1492 | <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> | |
| 1493 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&;</span></code> | |
| 1494 | </p></blockquote></div> | |
| 1495 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1496 | <li class="listitem"> | |
| 1497 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized | |
| 1498 | </li> | |
| 1499 | <li class="listitem"> | |
| 1500 | <span class="bold"><strong>Returns:</strong></span> A reference to the contained | |
| 1501 | value | |
| 1502 | </li> | |
| 1503 | <li class="listitem"> | |
| 1504 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 1505 | </li> | |
| 1506 | <li class="listitem"> | |
| 1507 | <span class="bold"><strong>Notes:</strong></span> The requirement is asserted | |
| 1508 | via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. | |
| 1509 | On compilers that do not support ref-qualifiers on member functions | |
| 1510 | these two overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code> | |
| 1511 | member functions. | |
| 1512 | </li> | |
| 1513 | <li class="listitem"> | |
| 1514 | <span class="bold"><strong>Example:</strong></span> | |
| 1515 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span> | |
| 1516 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span> | |
| 1517 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span> | |
| 1518 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 1519 | <span class="identifier">T</span> <span class="identifier">w</span> <span class="special">;</span> | |
| 1520 | <span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">w</span> <span class="special">;</span> | |
| 1521 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">w</span> <span class="special">)</span> <span class="special">;</span> | |
| 1522 | </pre> | |
| 1523 | </li> | |
| 1524 | </ul></div> | |
| 1525 | <p> | |
| 1526 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1527 | </p> | |
| 1528 | <a name="reference_optional_operator_asterisk_move"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1529 | <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span> | |
| 1530 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&&;</span></code> | |
| 1531 | </p></blockquote></div> | |
| 1532 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1533 | <li class="listitem"> | |
| 1534 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value. | |
| 1535 | </li> | |
| 1536 | <li class="listitem"> | |
| 1537 | <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">);</span></code>. | |
| 1538 | </li> | |
| 1539 | <li class="listitem"> | |
| 1540 | <span class="bold"><strong>Notes:</strong></span> The requirement is asserted | |
| 1541 | via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. | |
| 1542 | On compilers that do not support ref-qualifiers on member functions | |
| 1543 | this overload is not present. | |
| 1544 | </li> | |
| 1545 | </ul></div> | |
| 1546 | <p> | |
| 1547 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1548 | </p> | |
| 1549 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1550 | <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span> | |
| 1551 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> | |
| 1552 | <span class="keyword">const</span><span class="special">&</span> | |
| 1553 | <span class="special">;</span></code> | |
| 1554 | </p></blockquote></div> | |
| 1555 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1556 | <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span> | |
| 1557 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> | |
| 1558 | <span class="special">&</span> <span class="special">;</span></code> | |
| 1559 | </p></blockquote></div> | |
| 1560 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1561 | <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span> | |
| 1562 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> | |
| 1563 | <span class="special">&&</span> <span class="special">;</span></code> | |
| 1564 | </p></blockquote></div> | |
| 1565 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1566 | <li class="listitem"> | |
| 1567 | <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized | |
| 1568 | </li> | |
| 1569 | <li class="listitem"> | |
| 1570 | <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span> | |
| 1571 | reference contained. | |
| 1572 | </li> | |
| 1573 | <li class="listitem"> | |
| 1574 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 1575 | </li> | |
| 1576 | <li class="listitem"> | |
| 1577 | <span class="bold"><strong>Notes:</strong></span> The requirement is asserted | |
| 1578 | via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. | |
| 1579 | On compilers that do not support ref-qualifiers on member functions | |
| 1580 | these three overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code> | |
| 1581 | member functions. | |
| 1582 | </li> | |
| 1583 | <li class="listitem"> | |
| 1584 | <span class="bold"><strong>Example:</strong></span> | |
| 1585 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span> | |
| 1586 | <span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span> | |
| 1587 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">vref</span> <span class="special">);</span> | |
| 1588 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">vref2</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span> | |
| 1589 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">vref2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 1590 | <span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> | |
| 1591 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 1592 | </pre> | |
| 1593 | </li> | |
| 1594 | </ul></div> | |
| 1595 | <p> | |
| 1596 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1597 | </p> | |
| 1598 | <a name="reference_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1599 | <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code> | |
| 1600 | </p></blockquote></div> | |
| 1601 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1602 | <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> | |
| 1603 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span></code> | |
| 1604 | </p></blockquote></div> | |
| 1605 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1606 | <li class="listitem"> | |
| 1607 | <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">*</span><span class="identifier">val</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>. | |
| 1608 | </li> | |
| 1609 | <li class="listitem"> | |
| 1610 | <span class="bold"><strong>Notes:</strong></span> On compilers that do not support | |
| 1611 | ref-qualifiers on member functions these two overloads are replaced | |
| 1612 | with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> | |
| 1613 | and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions. | |
| 1614 | </li> | |
| 1615 | <li class="listitem"> | |
| 1616 | <span class="bold"><strong>Example:</strong></span> | |
| 1617 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span> | |
| 1618 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">,</span> <span class="identifier">o1</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span> | |
| 1619 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">);</span> | |
| 1620 | ||
| 1621 | <span class="keyword">try</span> <span class="special">{</span> | |
| 1622 | <span class="identifier">o0</span><span class="special">.</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// throws</span> | |
| 1623 | <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">false</span> <span class="special">);</span> | |
| 1624 | <span class="special">}</span> | |
| 1625 | <span class="keyword">catch</span><span class="special">(</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span> | |
| 1626 | <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">true</span> <span class="special">);</span> | |
| 1627 | <span class="special">}</span> | |
| 1628 | </pre> | |
| 1629 | </li> | |
| 1630 | </ul></div> | |
| 1631 | <p> | |
| 1632 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1633 | </p> | |
| 1634 | <a name="reference_optional_value_move"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1635 | <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span> | |
| 1636 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span></code> | |
| 1637 | </p></blockquote></div> | |
| 1638 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1639 | <li class="listitem"> | |
| 1640 | <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">)</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>. | |
| 1641 | </li> | |
| 1642 | <li class="listitem"> | |
| 1643 | <span class="bold"><strong>Notes:</strong></span> On compilers that do not support | |
| 1644 | ref-qualifiers on member functions this overload is not present. | |
| 1645 | </li> | |
| 1646 | </ul></div> | |
| 1647 | <p> | |
| 1648 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1649 | </p> | |
| 1650 | <a name="reference_optional_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1651 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span> | |
| 1652 | <span class="identifier">v</span><span class="special">)</span> | |
| 1653 | <span class="keyword">const</span><span class="special">&</span> | |
| 1654 | <span class="special">;</span></code> | |
| 1655 | </p></blockquote></div> | |
| 1656 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1657 | <li class="listitem"> | |
| 1658 | <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span> | |
| 1659 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>. | |
| 1660 | </li> | |
| 1661 | <li class="listitem"> | |
| 1662 | <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1663 | is not <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code> | |
| 1664 | is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>, | |
| 1665 | the program is ill-formed. | |
| 1666 | </li> | |
| 1667 | <li class="listitem"> | |
| 1668 | <span class="bold"><strong>Notes:</strong></span> On compilers that do not support | |
| 1669 | ref-qualifiers on member functions this overload is replaced with the | |
| 1670 | <code class="computeroutput"><span class="keyword">const</span></code>-qualified member | |
| 1671 | function. On compilers without rvalue reference support the type of | |
| 1672 | <code class="computeroutput"><span class="identifier">v</span></code> becomes <code class="computeroutput"><span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span></code>. | |
| 1673 | </li> | |
| 1674 | </ul></div> | |
| 1675 | <p> | |
| 1676 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1677 | </p> | |
| 1678 | <a name="reference_optional_value_or_move"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1679 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span> | |
| 1680 | <span class="identifier">v</span><span class="special">)</span> | |
| 1681 | <span class="special">&&</span> <span class="special">;</span></code> | |
| 1682 | </p></blockquote></div> | |
| 1683 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1684 | <li class="listitem"> | |
| 1685 | <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>. | |
| 1686 | </li> | |
| 1687 | <li class="listitem"> | |
| 1688 | <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1689 | is not <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> | |
| 1690 | or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code> | |
| 1691 | is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>, | |
| 1692 | the program is ill-formed. | |
| 1693 | </li> | |
| 1694 | <li class="listitem"> | |
| 1695 | <span class="bold"><strong>Notes:</strong></span> On compilers that do not support | |
| 1696 | ref-qualifiers on member functions this overload is not present. | |
| 1697 | </li> | |
| 1698 | </ul></div> | |
| 1699 | <p> | |
| 1700 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1701 | </p> | |
| 1702 | <a name="reference_optional_value_or_call"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1703 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code> | |
| 1704 | </p></blockquote></div> | |
| 1705 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1706 | <li class="listitem"> | |
| 1707 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1708 | is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a> whose result type | |
| 1709 | is convertible to <code class="computeroutput"><span class="identifier">T</span></code>. | |
| 1710 | </li> | |
| 1711 | <li class="listitem"> | |
| 1712 | <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span> | |
| 1713 | <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">();</span></code>. | |
| 1714 | </li> | |
| 1715 | <li class="listitem"> | |
| 1716 | <span class="bold"><strong>Notes:</strong></span> On compilers that do not support | |
| 1717 | ref-qualifiers on member functions this overload is replaced with the | |
| 1718 | <code class="computeroutput"><span class="keyword">const</span></code>-qualified member | |
| 1719 | function. | |
| 1720 | </li> | |
| 1721 | <li class="listitem"> | |
| 1722 | <span class="bold"><strong>Example:</strong></span> | |
| 1723 | <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">complain_and_0</span><span class="special">()</span> | |
| 1724 | <span class="special">{</span> | |
| 1725 | <span class="identifier">clog</span> <span class="special"><<</span> <span class="string">"no value returned, using default"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> | |
| 1726 | <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> | |
| 1727 | <span class="special">}</span> | |
| 1728 | ||
| 1729 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> | |
| 1730 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">none</span><span class="special">;</span> | |
| 1731 | ||
| 1732 | <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun not called</span> | |
| 1733 | <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> | |
| 1734 | ||
| 1735 | <span class="keyword">int</span> <span class="identifier">j</span> <span class="special">=</span> <span class="identifier">oN</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun called</span> | |
| 1736 | <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> | |
| 1737 | </pre> | |
| 1738 | </li> | |
| 1739 | </ul></div> | |
| 1740 | <p> | |
| 1741 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1742 | </p> | |
| 1743 | <a name="reference_optional_value_or_call_move"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1744 | <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&&</span> | |
| 1745 | <span class="special">;</span></code> | |
| 1746 | </p></blockquote></div> | |
| 1747 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1748 | <li class="listitem"> | |
| 1749 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> | |
| 1750 | is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> | |
| 1751 | and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a> | |
| 1752 | whose result type is convertible to <code class="computeroutput"><span class="identifier">T</span></code>. | |
| 1753 | </li> | |
| 1754 | <li class="listitem"> | |
| 1755 | <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span> | |
| 1756 | <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> | |
| 1757 | <span class="identifier">f</span><span class="special">();</span></code>. | |
| 1758 | </li> | |
| 1759 | <li class="listitem"> | |
| 1760 | <span class="bold"><strong>Notes:</strong></span> On compilers that do not support | |
| 1761 | ref-qualifiers on member functions this overload is not present. | |
| 1762 | </li> | |
| 1763 | </ul></div> | |
| 1764 | <p> | |
| 1765 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1766 | </p> | |
| 1767 | <a name="reference_optional_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1768 | <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1769 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> | |
| 1770 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code> | |
| 1771 | </p></blockquote></div> | |
| 1772 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1773 | <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> | |
| 1774 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="keyword">default</span> | |
| 1775 | <span class="special">)</span> <span class="special">;</span></code> | |
| 1776 | </p></blockquote></div> | |
| 1777 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1778 | <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span> | |
| 1779 | <span class="keyword">const</span><span class="special">&</span> | |
| 1780 | <span class="identifier">get_optional_value_or</span> <span class="special">(</span> | |
| 1781 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">o</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span></code> | |
| 1782 | </p></blockquote></div> | |
| 1783 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1784 | <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get_optional_value_or</span> | |
| 1785 | <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1786 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>&</span> | |
| 1787 | <span class="identifier">o</span><span class="special">,</span> | |
| 1788 | <span class="identifier">T</span><span class="special">&</span> | |
| 1789 | <span class="keyword">default</span> <span class="special">)</span> | |
| 1790 | <span class="special">;</span></code> | |
| 1791 | </p></blockquote></div> | |
| 1792 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1793 | <li class="listitem"> | |
| 1794 | <span class="bold"><strong>Deprecated:</strong></span> Use <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code> instead. | |
| 1795 | </li> | |
| 1796 | <li class="listitem"> | |
| 1797 | <span class="bold"><strong>Returns:</strong></span> A reference to the contained | |
| 1798 | value, if any, or <code class="computeroutput"><span class="keyword">default</span></code>. | |
| 1799 | </li> | |
| 1800 | <li class="listitem"> | |
| 1801 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 1802 | </li> | |
| 1803 | <li class="listitem"> | |
| 1804 | <span class="bold"><strong>Example:</strong></span> | |
| 1805 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">,</span> <span class="identifier">z</span> <span class="special">;</span> | |
| 1806 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span><span class="special">;</span> | |
| 1807 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">def</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span> | |
| 1808 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">y</span> <span class="special">==</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span> | |
| 1809 | ||
| 1810 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span> | |
| 1811 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="identifier">get_optional_value_or</span><span class="special">(</span><span class="identifier">opt</span><span class="special">,</span><span class="identifier">z</span><span class="special">);</span> | |
| 1812 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 1813 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">!=</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span> | |
| 1814 | </pre> | |
| 1815 | </li> | |
| 1816 | </ul></div> | |
| 1817 | <p> | |
| 1818 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1819 | </p> | |
| 1820 | <a name="reference_optional_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1821 | <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1822 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> | |
| 1823 | <span class="keyword">const</span> <span class="special">;</span></code> | |
| 1824 | </p></blockquote></div> | |
| 1825 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1826 | <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span> | |
| 1827 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span></code> | |
| 1828 | </p></blockquote></div> | |
| 1829 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1830 | <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span> | |
| 1831 | <span class="keyword">const</span><span class="special">*</span> | |
| 1832 | <span class="identifier">get_pointer</span> <span class="special">(</span> | |
| 1833 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code> | |
| 1834 | </p></blockquote></div> | |
| 1835 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1836 | <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_pointer</span> | |
| 1837 | <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1838 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> | |
| 1839 | <span class="special">&)</span> <span class="special">;</span></code> | |
| 1840 | </p></blockquote></div> | |
| 1841 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1842 | <li class="listitem"> | |
| 1843 | <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized, a pointer to the | |
| 1844 | contained value; else <code class="computeroutput"><span class="number">0</span></code> | |
| 1845 | (<span class="emphasis"><em>null</em></span>). | |
| 1846 | </li> | |
| 1847 | <li class="listitem"> | |
| 1848 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 1849 | </li> | |
| 1850 | <li class="listitem"> | |
| 1851 | <span class="bold"><strong>Notes:</strong></span> The contained value is permanently | |
| 1852 | stored within <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, | |
| 1853 | so you should not hold nor delete this pointer | |
| 1854 | </li> | |
| 1855 | <li class="listitem"> | |
| 1856 | <span class="bold"><strong>Example:</strong></span> | |
| 1857 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> | |
| 1858 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> | |
| 1859 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">copt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> | |
| 1860 | <span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">opt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span> | |
| 1861 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">cp</span> <span class="special">=</span> <span class="identifier">copt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">();</span> | |
| 1862 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">p</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">opt</span><span class="special">)</span> <span class="special">);</span> | |
| 1863 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">cp</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">copt</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 1864 | </pre> | |
| 1865 | </li> | |
| 1866 | </ul></div> | |
| 1867 | <p> | |
| 1868 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1869 | </p> | |
| 1870 | <a name="reference_optional_operator_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1871 | <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> | |
| 1872 | <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> <span class="special">->()</span> | |
| 1873 | <span class="keyword">const</span> <span class="special">;</span></code> | |
| 1874 | </p></blockquote></div> | |
| 1875 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 1876 | <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span> | |
| 1877 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> | |
| 1878 | <span class="special">->()</span> <span class="special">;</span></code> | |
| 1879 | </p></blockquote></div> | |
| 1880 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1881 | <li class="listitem"> | |
| 1882 | <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized. | |
| 1883 | </li> | |
| 1884 | <li class="listitem"> | |
| 1885 | <span class="bold"><strong>Returns:</strong></span> A pointer to the contained | |
| 1886 | value. | |
| 1887 | </li> | |
| 1888 | <li class="listitem"> | |
| 1889 | <span class="bold"><strong>Throws:</strong></span> Nothing. | |
| 1890 | </li> | |
| 1891 | <li class="listitem"> | |
| 1892 | <span class="bold"><strong>Notes:</strong></span> The requirement is asserted | |
| 1893 | via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. | |
| 1894 | </li> | |
| 1895 | <li class="listitem"> | |
| 1896 | <span class="bold"><strong>Example:</strong></span> | |
| 1897 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="special">{</span> <span class="keyword">int</span> <span class="identifier">mdata</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span> | |
| 1898 | <span class="identifier">X</span> <span class="identifier">x</span> <span class="special">;</span> | |
| 1899 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span> | |
| 1900 | <span class="identifier">opt</span><span class="special">-></span><span class="identifier">mdata</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> | |
| 1901 | </pre> | |
| 1902 | </li> | |
| 1903 | </ul></div> | |
| 1904 | <p> | |
| 1905 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1906 | </p> | |
| 1907 | <a name="reference_optional_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1908 | <code class="computeroutput"><span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span> | |
| 1909 | <span class="keyword">bool</span><span class="special">()</span> | |
| 1910 | <span class="keyword">const</span> <span class="keyword">noexcept</span> | |
| 1911 | <span class="special">;</span></code> | |
| 1912 | </p></blockquote></div> | |
| 1913 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1914 | <li class="listitem"> | |
| 1915 | <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span></code>. | |
| 1916 | </li> | |
| 1917 | <li class="listitem"> | |
| 1918 | <span class="bold"><strong>Notes:</strong></span> On compilers that do not support | |
| 1919 | explicit conversion operators this falls back to safe-bool idiom. | |
| 1920 | </li> | |
| 1921 | <li class="listitem"> | |
| 1922 | <span class="bold"><strong>Example:</strong></span> | |
| 1923 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> | |
| 1924 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">==</span> <span class="number">0</span> <span class="special">);</span> | |
| 1925 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> | |
| 1926 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">);</span> | |
| 1927 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">);</span> | |
| 1928 | </pre> | |
| 1929 | </li> | |
| 1930 | </ul></div> | |
| 1931 | <p> | |
| 1932 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1933 | </p> | |
| 1934 | <a name="reference_optional_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1935 | <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">noexcept</span> | |
| 1936 | <span class="special">;</span></code> | |
| 1937 | </p></blockquote></div> | |
| 1938 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 1939 | <li class="listitem"> | |
| 1940 | <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>; else <code class="computeroutput"><span class="keyword">false</span></code>. | |
| 1941 | </li> | |
| 1942 | <li class="listitem"> | |
| 1943 | <span class="bold"><strong>Notes:</strong></span> This operator is provided for | |
| 1944 | those compilers which can't use the <span class="emphasis"><em>unspecified-bool-type | |
| 1945 | operator</em></span> in certain boolean contexts. | |
| 1946 | </li> | |
| 1947 | <li class="listitem"> | |
| 1948 | <span class="bold"><strong>Example:</strong></span> | |
| 1949 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">;</span> | |
| 1950 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">opt</span> <span class="special">);</span> | |
| 1951 | <span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">some_T</span> <span class="special">;</span> | |
| 1952 | ||
| 1953 | <span class="comment">// Notice the "double-bang" idiom here.</span> | |
| 1954 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!!</span><span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> | |
| 1955 | </pre> | |
| 1956 | </li> | |
| 1957 | </ul></div> | |
| 1958 | <p> | |
| 1959 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 1960 | </p> | |
| 1961 | <a name="reference_optional_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 1962 | <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code> | |
| 1963 | </p></blockquote></div> | |
| 1964 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 1965 | <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">explicit</span> <span class="keyword">operator</span> | |
| 1966 | <span class="keyword">bool</span> <span class="special">()</span> | |
| 1967 | <span class="special">;</span></code> | |
| 1968 | </li></ul></div> | |
| 1969 | </div> | |
| 1970 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 1971 | <td align="left"></td> | |
| 1972 | <td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p> | |
| 1973 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 1974 | file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) | |
| 1975 | </p> | |
| 1976 | </div></td> | |
| 1977 | </tr></table> | |
| 1978 | <hr> | |
| 1979 | <div class="spirit-nav"> | |
| 1980 | <a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics____optional_references.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> | |
| 1981 | </div> | |
| 1982 | </body> | |
| 1983 | </html> |