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| 4 | <title>Detailed Semantics -- Free Functions</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____free_functions"></a><a class="link" href="detailed_semantics____free_functions.html" title="Detailed Semantics -- Free Functions">Detailed | |
| 28 | Semantics -- Free Functions</a> | |
| 29 | </h4></div></div></div> | |
| 30 | <p> | |
| 31 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 32 | </p> | |
| 33 | <a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 34 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> | |
| 35 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> | |
| 36 | </p></blockquote></div> | |
| 37 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 38 | <li class="listitem"> | |
| 39 | <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><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> for the <span class="emphasis"><em>deduced</em></span> | |
| 40 | type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>. | |
| 41 | </li> | |
| 42 | <li class="listitem"> | |
| 43 | <span class="bold"><strong>Example:</strong></span> | |
| 44 | <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">foo</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">opt</span> <span class="special">)</span> <span class="special">;</span> | |
| 45 | ||
| 46 | <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional<int></span> | |
| 47 | </pre> | |
| 48 | </li> | |
| 49 | </ul></div> | |
| 50 | <p> | |
| 51 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 52 | </p> | |
| 53 | <a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 54 | <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">make_optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> | |
| 55 | <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> | |
| 56 | </p></blockquote></div> | |
| 57 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 58 | <li class="listitem"> | |
| 59 | <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">condition</span><span class="special">,</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span> | |
| 60 | type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>. | |
| 61 | </li> | |
| 62 | <li class="listitem"> | |
| 63 | <span class="bold"><strong>Example:</strong></span> | |
| 64 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">calculate_foo</span><span class="special">()</span> | |
| 65 | <span class="special">{</span> | |
| 66 | <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span> | |
| 67 | <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span> | |
| 68 | <span class="special">}</span> | |
| 69 | ||
| 70 | <span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span> | |
| 71 | <span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span> | |
| 72 | <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span> | |
| 73 | </pre> | |
| 74 | </li> | |
| 75 | </ul></div> | |
| 76 | <p> | |
| 77 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 78 | </p> | |
| 79 | <a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 80 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 81 | <span class="special">==</span> <span class="special">(</span> | |
| 82 | <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">x</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">y</span> <span class="special">);</span></code> | |
| 83 | </p></blockquote></div> | |
| 84 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 85 | <li class="listitem"> | |
| 86 | <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> | |
| 87 | shall meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>. | |
| 88 | </li> | |
| 89 | <li class="listitem"> | |
| 90 | <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code> | |
| 91 | and <code class="computeroutput"><span class="identifier">y</span></code> are initialized, | |
| 92 | <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span> | |
| 93 | <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>. | |
| 94 | If only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>. | |
| 95 | If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>. | |
| 96 | </li> | |
| 97 | <li class="listitem"> | |
| 98 | <span class="bold"><strong>Notes:</strong></span> This definition guarantees | |
| 99 | that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> | |
| 100 | not containing a value is compared unequal to any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equal | |
| 101 | to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers | |
| 102 | have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code> | |
| 103 | has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> directly in generic code which expect | |
| 104 | to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a> | |
| 105 | instead | |
| 106 | </li> | |
| 107 | <li class="listitem"> | |
| 108 | <span class="bold"><strong>Example:</strong></span> | |
| 109 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span> | |
| 110 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span> <span class="identifier">o1_</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span> | |
| 111 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o2</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">));</span> | |
| 112 | ||
| 113 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span> <span class="special">);</span> <span class="comment">// Identity implies equality</span> | |
| 114 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">//</span> | |
| 115 | ||
| 116 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN_</span> <span class="special">);</span> <span class="comment">// Both uninitialized compare equal</span> | |
| 117 | ||
| 118 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">// Initialized unequal to initialized.</span> | |
| 119 | ||
| 120 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1_</span> <span class="special">);</span> <span class="comment">// Both initialized compare as (*lhs == *rhs)</span> | |
| 121 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">o2</span> <span class="special">);</span> <span class="comment">//</span> | |
| 122 | </pre> | |
| 123 | </li> | |
| 124 | </ul></div> | |
| 125 | <p> | |
| 126 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 127 | </p> | |
| 128 | <a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 129 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 130 | <span class="special"><</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="keyword">const</span><span class="special">&</span> <span class="identifier">x</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">y</span> <span class="special">);</span></code> | |
| 132 | </p></blockquote></div> | |
| 133 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 134 | <li class="listitem"> | |
| 135 | <span class="bold"><strong>Requires:</strong></span> Expression <code class="computeroutput"><span class="special">*</span><span class="identifier">x</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">y</span></code> shall be well-formed and its result | |
| 136 | shall be convertible to <code class="computeroutput"><span class="keyword">bool</span></code>. | |
| 137 | </li> | |
| 138 | <li class="listitem"> | |
| 139 | <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">(!</span><span class="identifier">y</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">false</span> <span class="special">:</span> <span class="special">(!</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">true</span> <span class="special">:</span> <span class="special">*</span><span class="identifier">x</span> <span class="special"><</span> | |
| 140 | <span class="special">*</span><span class="identifier">y</span></code>. | |
| 141 | </li> | |
| 142 | <li class="listitem"> | |
| 143 | <span class="bold"><strong>Notes:</strong></span> This definition guarantees | |
| 144 | that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> | |
| 145 | not containing a value is ordered as less than any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equivalent | |
| 146 | to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers | |
| 147 | have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code> | |
| 148 | has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> directly in generic code which | |
| 149 | expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a> | |
| 150 | instead. <code class="computeroutput"><span class="identifier">T</span></code> need not | |
| 151 | be <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. Only | |
| 152 | single <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> | |
| 153 | is required. Other relational operations are defined in terms of this | |
| 154 | one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> | |
| 155 | satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity, | |
| 156 | antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optinal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. | |
| 157 | </li> | |
| 158 | <li class="listitem"> | |
| 159 | <span class="bold"><strong>Example:</strong></span> | |
| 160 | <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span> | |
| 161 | <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">T</span><span class="special">(</span><span class="number">0</span><span class="special">));</span> | |
| 162 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span> | |
| 163 | ||
| 164 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Identity implies equivalence</span> | |
| 165 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">);</span> | |
| 166 | ||
| 167 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN_</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Two uninitialized are equivalent</span> | |
| 168 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN_</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> | |
| 169 | ||
| 170 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">o0</span> <span class="special">);</span> <span class="comment">// Uninitialized is less than initialized</span> | |
| 171 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o0</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> | |
| 172 | ||
| 173 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o2</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Two initialized compare as (*lhs < *rhs)</span> | |
| 174 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 175 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> | |
| 176 | </pre> | |
| 177 | </li> | |
| 178 | </ul></div> | |
| 179 | <p> | |
| 180 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 181 | </p> | |
| 182 | <a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 183 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 184 | <span class="special">!=</span> <span class="special">(</span> | |
| 185 | <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">x</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">y</span> <span class="special">);</span></code> | |
| 186 | </p></blockquote></div> | |
| 187 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 188 | <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span> | |
| 189 | <span class="identifier">x</span> <span class="special">==</span> | |
| 190 | <span class="identifier">y</span> <span class="special">);</span></code> | |
| 191 | </li></ul></div> | |
| 192 | <p> | |
| 193 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 194 | </p> | |
| 195 | <a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 196 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 197 | <span class="special">></span> <span class="special">(</span> | |
| 198 | <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">x</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">y</span> <span class="special">);</span></code> | |
| 199 | </p></blockquote></div> | |
| 200 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 201 | <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span> | |
| 202 | <span class="identifier">y</span> <span class="special"><</span> | |
| 203 | <span class="identifier">x</span> <span class="special">);</span></code> | |
| 204 | </li></ul></div> | |
| 205 | <p> | |
| 206 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 207 | </p> | |
| 208 | <a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 209 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 210 | <span class="special"><=</span> <span class="special">(</span> | |
| 211 | <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">x</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">y</span> <span class="special">);</span></code> | |
| 212 | </p></blockquote></div> | |
| 213 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 214 | <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span> | |
| 215 | <span class="identifier">y</span> <span class="special"><</span> | |
| 216 | <span class="identifier">x</span> <span class="special">);</span></code> | |
| 217 | </li></ul></div> | |
| 218 | <p> | |
| 219 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 220 | </p> | |
| 221 | <a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 222 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 223 | <span class="special">>=</span> <span class="special">(</span> | |
| 224 | <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">x</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">y</span> <span class="special">);</span></code> | |
| 225 | </p></blockquote></div> | |
| 226 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 227 | <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span> | |
| 228 | <span class="identifier">x</span> <span class="special"><</span> | |
| 229 | <span class="identifier">y</span> <span class="special">);</span></code> | |
| 230 | </li></ul></div> | |
| 231 | <p> | |
| 232 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 233 | </p> | |
| 234 | <a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 235 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 236 | <span class="special">==</span> <span class="special">(</span> | |
| 237 | <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">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span> | |
| 238 | <span class="keyword">noexcept</span><span class="special">;</span></code> | |
| 239 | </p></blockquote></div> | |
| 240 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 241 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 242 | <span class="special">==</span> <span class="special">(</span> | |
| 243 | <span class="identifier">none_t</span><span class="special">,</span> | |
| 244 | <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">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> | |
| 245 | </p></blockquote></div> | |
| 246 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 247 | <li class="listitem"> | |
| 248 | <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>. | |
| 249 | </li> | |
| 250 | <li class="listitem"> | |
| 251 | <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> | |
| 252 | need not meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>. | |
| 253 | </li> | |
| 254 | </ul></div> | |
| 255 | <p> | |
| 256 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 257 | </p> | |
| 258 | <a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 259 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 260 | <span class="special">!=</span> <span class="special">(</span> | |
| 261 | <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">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span> | |
| 262 | <span class="keyword">noexcept</span><span class="special">;</span></code> | |
| 263 | </p></blockquote></div> | |
| 264 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 265 | <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> | |
| 266 | <span class="special">!=</span> <span class="special">(</span> | |
| 267 | <span class="identifier">none_t</span><span class="special">,</span> | |
| 268 | <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">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> | |
| 269 | </p></blockquote></div> | |
| 270 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> | |
| 271 | <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span> | |
| 272 | <span class="identifier">x</span> <span class="special">==</span> | |
| 273 | <span class="identifier">y</span> <span class="special">);</span></code> | |
| 274 | </li></ul></div> | |
| 275 | <p> | |
| 276 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 277 | </p> | |
| 278 | <a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 279 | <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span> | |
| 280 | <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">x</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">y</span> | |
| 281 | <span class="special">)</span> <span class="special">;</span></code> | |
| 282 | </p></blockquote></div> | |
| 283 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 284 | <li class="listitem"> | |
| 285 | <span class="bold"><strong>Requires:</strong></span> Lvalues of type <code class="computeroutput"><span class="identifier">T</span></code> shall be swappable and <code class="computeroutput"><span class="identifier">T</span></code> shall be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>. | |
| 286 | </li> | |
| 287 | <li class="listitem"> | |
| 288 | <p class="simpara"> | |
| 289 | <span class="bold"><strong>Effects:</strong></span> | |
| 290 | </p> | |
| 291 | <div class="informaltable"><table class="table"> | |
| 292 | <colgroup> | |
| 293 | <col> | |
| 294 | <col> | |
| 295 | <col> | |
| 296 | </colgroup> | |
| 297 | <thead><tr></tr></thead> | |
| 298 | <tbody> | |
| 299 | <tr> | |
| 300 | <td> | |
| 301 | </td> | |
| 302 | <td> | |
| 303 | <p> | |
| 304 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span> | |
| 305 | </p> | |
| 306 | </td> | |
| 307 | <td> | |
| 308 | <p> | |
| 309 | <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span> | |
| 310 | </p> | |
| 311 | </td> | |
| 312 | </tr> | |
| 313 | <tr> | |
| 314 | <td> | |
| 315 | <p> | |
| 316 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 317 | contains a value</strong></span> | |
| 318 | </p> | |
| 319 | </td> | |
| 320 | <td> | |
| 321 | <p> | |
| 322 | calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">),</span> <span class="special">*</span><span class="identifier">rhs</span><span class="special">)</span></code> | |
| 323 | </p> | |
| 324 | </td> | |
| 325 | <td> | |
| 326 | <p> | |
| 327 | initializes the contained value of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> as if direct-initializing | |
| 328 | an object of type <code class="computeroutput"><span class="identifier">T</span></code> | |
| 329 | with the expression <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>, followed by <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><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>, | |
| 330 | <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> | |
| 331 | contains a value and <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 332 | does not contain a value | |
| 333 | </p> | |
| 334 | </td> | |
| 335 | </tr> | |
| 336 | <tr> | |
| 337 | <td> | |
| 338 | <p> | |
| 339 | <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 340 | does not contain a value</strong></span> | |
| 341 | </p> | |
| 342 | </td> | |
| 343 | <td> | |
| 344 | <p> | |
| 345 | initializes the contained value of <code class="computeroutput"><span class="identifier">rhs</span></code> | |
| 346 | as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with the expression | |
| 347 | <code class="computeroutput"><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></code>, | |
| 348 | followed by <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>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value | |
| 349 | and <code class="computeroutput"><span class="identifier">rhs</span></code> contains | |
| 350 | a value | |
| 351 | </p> | |
| 352 | </td> | |
| 353 | <td> | |
| 354 | <p> | |
| 355 | no effect | |
| 356 | </p> | |
| 357 | </td> | |
| 358 | </tr> | |
| 359 | </tbody> | |
| 360 | </table></div> | |
| 361 | </li> | |
| 362 | <li class="listitem"> | |
| 363 | <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code> | |
| 364 | interchanged. | |
| 365 | </li> | |
| 366 | <li class="listitem"> | |
| 367 | <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever | |
| 368 | <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code> | |
| 369 | throws. If only one is initialized, 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> | |
| 370 | throws. | |
| 371 | </li> | |
| 372 | <li class="listitem"> | |
| 373 | <span class="bold"><strong>Example:</strong></span> | |
| 374 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span> | |
| 375 | <span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span> | |
| 376 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def0</span> <span class="special">;</span> | |
| 377 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def1</span> <span class="special">;</span> | |
| 378 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span> | |
| 379 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span> | |
| 380 | ||
| 381 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span> | |
| 382 | ||
| 383 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> | |
| 384 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span> | |
| 385 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span> | |
| 386 | ||
| 387 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span> | |
| 388 | ||
| 389 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span> | |
| 390 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span> | |
| 391 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span> | |
| 392 | </pre> | |
| 393 | </li> | |
| 394 | </ul></div> | |
| 395 | <p> | |
| 396 | <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> | |
| 397 | </p> | |
| 398 | <a name="reference_swap_optional_reference"></a><div class="blockquote"><blockquote class="blockquote"><p> | |
| 399 | <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span> | |
| 400 | <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">x</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">y</span> | |
| 401 | <span class="special">)</span> <span class="keyword">noexcept</span> | |
| 402 | <span class="special">;</span></code> | |
| 403 | </p></blockquote></div> | |
| 404 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 405 | <li class="listitem"> | |
| 406 | <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">x</span></code> | |
| 407 | refers to what <code class="computeroutput"><span class="identifier">y</span></code> refererred | |
| 408 | to before the swap (if anything). <code class="computeroutput"><span class="identifier">y</span></code> | |
| 409 | refers to whatever <code class="computeroutput"><span class="identifier">x</span></code> | |
| 410 | referred to before the swap. | |
| 411 | </li> | |
| 412 | <li class="listitem"> | |
| 413 | <span class="bold"><strong>Example:</strong></span> | |
| 414 | <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span> | |
| 415 | <span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span> | |
| 416 | ||
| 417 | <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> | |
| 418 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optX</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span> | |
| 419 | <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optY</span> <span class="special">(</span><span class="identifier">y</span><span class="special">);</span> | |
| 420 | ||
| 421 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span> <span class="identifier">optY</span><span class="special">);</span> | |
| 422 | <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optX</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span> | |
| 423 | <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optY</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">x</span><span class="special">));</span> | |
| 424 | ||
| 425 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">,</span> <span class="identifier">optX</span><span class="special">);</span> | |
| 426 | <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span> | |
| 427 | <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span> | |
| 428 | <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span> | |
| 429 | </pre> | |
| 430 | [endsect] | |
| 431 | </li> | |
| 432 | </ul></div> | |
| 433 | </div> | |
| 434 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 435 | <td align="left"></td> | |
| 436 | <td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p> | |
| 437 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 438 | 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>) | |
| 439 | </p> | |
| 440 | </div></td> | |
| 441 | </tr></table> | |
| 442 | <hr> | |
| 443 | <div class="spirit-nav"> | |
| 444 | <a accesskey="p" href="detailed_semantics____optional_references.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="header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> | |
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