ceph/src/boost/libs/scope_exit/doc/html/scope_exit/tutorial.html

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  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="scope_exit.tutorial"></a><a class="link" href="tutorial.html" title="Tutorial">Tutorial</a>
  28 </h2></div></div></div>
  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="tutorial.html#scope_exit.tutorial.capturing_variables">Capturing Variables</a></span></dt>
  31 <dt><span class="section"><a href="tutorial.html#scope_exit.tutorial.capturing_the_object__this_">Capturing
  32       The Object <code class="computeroutput"><span class="keyword">this</span></code></a></span></dt>
  33 <dt><span class="section"><a href="tutorial.html#scope_exit.tutorial.capturing_no_variable">Capturing
  34       No Variable</a></span></dt>
  35 <dt><span class="section"><a href="tutorial.html#scope_exit.tutorial.capturing_all_variables__c__11_only_">Capturing
  36       All Variables (C++11 Only)</a></span></dt>
  37 <dt><span class="section"><a href="tutorial.html#scope_exit.tutorial.template_workaround__gcc_">Template
  38       Workaround (GCC)</a></span></dt>
  39 <dt><span class="section"><a href="tutorial.html#scope_exit.tutorial.same_line_expansions">Same Line Expansions</a></span></dt>
  40 </dl></div>
  41 <p>
  42       This section illustrates how to use this library.
  43     </p>
  44 <div class="section">
  45 <div class="titlepage"><div><div><h3 class="title">
  46 <a name="scope_exit.tutorial.capturing_variables"></a><a class="link" href="tutorial.html#scope_exit.tutorial.capturing_variables" title="Capturing Variables">Capturing Variables</a>
  47 </h3></div></div></div>
  48 <p>
  49         Imagine that we want to make many modifications to data members of some
  50         <code class="computeroutput"><span class="identifier">world</span></code> class in its <code class="computeroutput"><span class="identifier">world</span><span class="special">::</span><span class="identifier">add_person</span></code> member function. We start with
  51         adding a new <code class="computeroutput"><span class="identifier">person</span></code> object
  52         to a vector of persons:
  53       </p>
  54 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">world</span><span class="special">::</span><span class="identifier">add_person</span><span class="special">(</span><span class="identifier">person</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span>
  55     <span class="keyword">bool</span> <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span>
  56
  57     <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span>           <span class="comment">// (1) direct action</span>
  58     <span class="special">...</span>
  59 </pre>
  60 <p>
  61         Some operations down the road may throw an exception and all changes to involved
  62         objects should be rolled back. This all-or-nothing semantic is also known
  63         as <a href="http://www.research.att.com/~bs/glossary.html#Gstrong-guarantee" target="_top">strong
  64         guarantee</a>.
  65       </p>
  66 <p>
  67         In particular, the last added person must be deleted from <code class="computeroutput"><span class="identifier">persons_</span></code>
  68         if the function throws. All we need is to define a delayed action (release
  69         of a resource) right after the direct action (resource acquisition). For
  70         example (see also <a href="../../../test/world.cpp" target="_top"><code class="literal">world.cpp</code></a>):
  71       </p>
  72 <p>
  73 </p>
  74 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">world</span><span class="special">::</span><span class="identifier">add_person</span><span class="special">(</span><span class="identifier">person</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span>
  75     <span class="keyword">bool</span> <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span>
  76
  77     <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span>           <span class="comment">// (1) direct action</span>
  78     <span class="comment">// Following block is executed when the enclosing scope exits.</span>
  79     <span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(&amp;</span><span class="identifier">commit</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">persons_</span><span class="special">)</span> <span class="special">{</span>
  80         <span class="keyword">if</span><span class="special">(!</span><span class="identifier">commit</span><span class="special">)</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span>    <span class="comment">// (2) rollback action</span>
  81     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span>
  82
  83     <span class="comment">// ...                                  // (3) other operations</span>
  84
  85     <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span>                          <span class="comment">// (4) disable rollback actions</span>
  86 <span class="special">}</span>
  87 </pre>
  88 <p>
  89       </p>
  90 <p>
  91         The block below point <code class="literal">(1)</code> is a <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
  92         declaration. Unlike point <code class="literal">(1)</code>, an execution of the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a> body will be delayed until the
  93         end of the current scope. In this case it will be executed either after point
  94         <code class="literal">(4)</code> or on any exception. (On various versions of the GCC
  95         compiler, it is necessary to use <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_TPL.html" title="Macro BOOST_SCOPE_EXIT_TPL">BOOST_SCOPE_EXIT_TPL</a></code>
  96         instead of <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
  97         within templates, see later in this section for details.)
  98       </p>
  99 <p>
 100         The <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a> declaration starts
 101         with the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code> macro
 102         invocation which accepts a comma-separated list of captured variables (a
 103         <a href="http://www.boost.org/libs/preprocessor" target="_top">Boost.Preprocessor</a>
 104         sequence is also accepted for compilers that do not support variadic macros
 105         and for backward compatibility with older versions of this library, see the
 106         <a class="link" href="no_variadic_macros.html" title="Annex: No Variadic Macros">No Variadic Macros</a> section).
 107         If a capture starts with the ampersand sign <code class="computeroutput"><span class="special">&amp;</span></code>,
 108         a reference to the captured variable will be available inside the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 109         body; otherwise, a copy of the variable will be made after the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 110         declaration at point <code class="literal">(1)</code> and only the copy will be available
 111         inside the body (in this case, the captured variable's type must be <a href="http://www.boost.org/doc/libs/release/doc/html/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a>).
 112       </p>
 113 <p>
 114         In the example above, the variables <code class="computeroutput"><span class="identifier">commit</span></code>
 115         and <code class="computeroutput"><span class="identifier">persons_</span></code> are captured
 116         by reference because the final value of the <code class="computeroutput"><span class="identifier">commit</span></code>
 117         variable should be used to determine whether to execute rollback actions
 118         or not, and the action should modify the <code class="computeroutput"><span class="identifier">persons_</span></code>
 119         object, not its copy. This is the most common case but passing a variable
 120         by value is sometimes useful as well.
 121       </p>
 122 <p>
 123         Finally, the end of the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 124         body must be marked by the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_END.html" title="Macro BOOST_SCOPE_EXIT_END">BOOST_SCOPE_EXIT_END</a></code>
 125         macro which must follow the closing curly bracket <code class="computeroutput"><span class="special">}</span></code>
 126         of the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a> body.
 127       </p>
 128 <div class="important"><table border="0" summary="Important">
 129 <tr>
 130 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td>
 131 <th align="left">Important</th>
 132 </tr>
 133 <tr><td align="left" valign="top"><p>
 134           In order to comply with the <a href="http://www.stlport.org/doc/exception_safety.html" target="_top">STL
 135           exception safety requirements</a>, the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 136           body must never throw (because the library implementation executes the
 137           body within a destructor call). This is true for all <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 138           macros (including <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_TPL.html" title="Macro BOOST_SCOPE_EXIT_TPL">BOOST_SCOPE_EXIT_TPL</a></code>
 139           and <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 140           seen below) on both C++03 and C++11.
 141         </p></td></tr>
 142 </table></div>
 143 <p>
 144         Consider a more complex example where <code class="computeroutput"><span class="identifier">world</span><span class="special">::</span><span class="identifier">add_person</span></code>
 145         can save intermediate states at some point and roll back to the last saved
 146         state. We use <code class="computeroutput"><span class="identifier">person</span><span class="special">::</span><span class="identifier">evolution_</span></code> to store a version of the changes
 147         and increment it to cancel all rollback actions associated with those changes.
 148         If we pass a current value of <code class="computeroutput"><span class="identifier">evolution_</span></code>
 149         stored in the <code class="computeroutput"><span class="identifier">checkpoint</span></code>
 150         variable by value, it remains unchanged within the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 151         body so we can compare it with the final value of <code class="computeroutput"><span class="identifier">evolution_</span></code>.
 152         If the latter was not incremented since we saved it, the rollback action
 153         inside the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a> body should
 154         be executed. For example (see also <a href="../../../test/world_checkpoint.cpp" target="_top"><code class="literal">world_checkpoint.cpp</code></a>):
 155       </p>
 156 <p>
 157 </p>
 158 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">world</span><span class="special">::</span><span class="identifier">add_person</span><span class="special">(</span><span class="identifier">person</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span>
 159     <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span>
 160
 161     <span class="comment">// This block must be no-throw.</span>
 162     <span class="identifier">person</span><span class="special">&amp;</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">back</span><span class="special">();</span>
 163     <span class="identifier">person</span><span class="special">::</span><span class="identifier">evolution_t</span> <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">;</span>
 164     <span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(</span><span class="identifier">checkpoint</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">p</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">persons_</span><span class="special">)</span> <span class="special">{</span>
 165         <span class="keyword">if</span><span class="special">(</span><span class="identifier">checkpoint</span> <span class="special">==</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">)</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span>
 166     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span>
 167
 168     <span class="comment">// ...</span>
 169
 170     <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="special">++</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">;</span>
 171
 172     <span class="comment">// Assign new identifier to the person.</span>
 173     <span class="identifier">person</span><span class="special">::</span><span class="identifier">id_t</span> <span class="keyword">const</span> <span class="identifier">prev_id</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">id</span><span class="special">;</span>
 174     <span class="identifier">p</span><span class="special">.</span><span class="identifier">id</span> <span class="special">=</span> <span class="identifier">next_id_</span><span class="special">++;</span>
 175     <span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(</span><span class="identifier">checkpoint</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">p</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">next_id_</span><span class="special">,</span> <span class="identifier">prev_id</span><span class="special">)</span> <span class="special">{</span>
 176         <span class="keyword">if</span><span class="special">(</span><span class="identifier">checkpoint</span> <span class="special">==</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">)</span> <span class="special">{</span>
 177             <span class="identifier">next_id_</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">id</span><span class="special">;</span>
 178             <span class="identifier">p</span><span class="special">.</span><span class="identifier">id</span> <span class="special">=</span> <span class="identifier">prev_id</span><span class="special">;</span>
 179         <span class="special">}</span>
 180     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span>
 181
 182     <span class="comment">// ...</span>
 183
 184     <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="special">++</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">;</span>
 185 <span class="special">}</span>
 186 </pre>
 187 <p>
 188       </p>
 189 <p>
 190         When multiple <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a> blocks are
 191         declared within the same enclosing scope, the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 192         bodies are executed in the reversed order of their declarations.
 193       </p>
 194 </div>
 195 <div class="section">
 196 <div class="titlepage"><div><div><h3 class="title">
 197 <a name="scope_exit.tutorial.capturing_the_object__this_"></a><a class="link" href="tutorial.html#scope_exit.tutorial.capturing_the_object__this_" title="Capturing The Object this">Capturing
 198       The Object <code class="computeroutput"><span class="keyword">this</span></code></a>
 199 </h3></div></div></div>
 200 <p>
 201         Within a member function, it is also possible to capture the object <code class="computeroutput"><span class="keyword">this</span></code>. However, the special symbol <code class="computeroutput"><span class="identifier">this_</span></code> must be used instead of <code class="computeroutput"><span class="keyword">this</span></code> in the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 202         declaration and body to capture and access the object. For example (see also
 203         <a href="../../../test/world_this.cpp" target="_top"><code class="literal">world_this.cpp</code></a>):
 204       </p>
 205 <p>
 206 </p>
 207 <pre class="programlisting"><span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(&amp;</span><span class="identifier">commit</span><span class="special">,</span> <span class="identifier">this_</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Capture object `this_`.</span>
 208     <span class="keyword">if</span><span class="special">(!</span><span class="identifier">commit</span><span class="special">)</span> <span class="identifier">this_</span><span class="special">-&gt;</span><span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span>
 209 <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span>
 210 </pre>
 211 <p>
 212       </p>
 213 <p>
 214         It is not possible to capture the object <code class="computeroutput"><span class="identifier">this_</span></code>
 215         by reference because C++ does not allow to take a reference to <code class="computeroutput"><span class="keyword">this</span></code>. If the enclosing member function is
 216         constant then the captured object will also be constant, otherwise the captured
 217         object will be mutable.
 218       </p>
 219 </div>
 220 <div class="section">
 221 <div class="titlepage"><div><div><h3 class="title">
 222 <a name="scope_exit.tutorial.capturing_no_variable"></a><a class="link" href="tutorial.html#scope_exit.tutorial.capturing_no_variable" title="Capturing No Variable">Capturing
 223       No Variable</a>
 224 </h3></div></div></div>
 225 <p>
 226         A <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a> declaration can also
 227         capture no variable. In this case, the list of captured variables is replaced
 228         by the <code class="computeroutput"><span class="keyword">void</span></code> keyword (similarly
 229         to the C++ syntax that allows to declare a function with no parameter using
 230         <code class="literal"><span class="emphasis"><em>result-type function-name</em></span></code><code class="computeroutput"><span class="special">(</span><span class="keyword">void</span><span class="special">)</span></code>).
 231         <a href="#ftn.scope_exit.tutorial.capturing_no_variable.f0" class="footnote" name="scope_exit.tutorial.capturing_no_variable.f0"><sup class="footnote">[3]</sup></a> For example, this can be useful when the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 232         body only needs to access global variables (see also <a href="../../../test/world_void.cpp" target="_top"><code class="literal">world_void.cpp</code></a>):
 233       </p>
 234 <p>
 235 </p>
 236 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">world_t</span> <span class="special">{</span>
 237     <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">person</span><span class="special">&gt;</span> <span class="identifier">persons</span><span class="special">;</span>
 238     <span class="keyword">bool</span> <span class="identifier">commit</span><span class="special">;</span>
 239 <span class="special">}</span> <span class="identifier">world</span><span class="special">;</span> <span class="comment">// Global variable.</span>
 240
 241 <span class="keyword">void</span> <span class="identifier">add_person</span><span class="special">(</span><span class="identifier">person</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span>
 242     <span class="identifier">world</span><span class="special">.</span><span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span>
 243     <span class="identifier">world</span><span class="special">.</span><span class="identifier">persons</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span>
 244
 245     <span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// No captures.</span>
 246         <span class="keyword">if</span><span class="special">(!</span><span class="identifier">world</span><span class="special">.</span><span class="identifier">commit</span><span class="special">)</span> <span class="identifier">world</span><span class="special">.</span><span class="identifier">persons</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span>
 247     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span>
 248
 249     <span class="comment">// ...</span>
 250
 251     <span class="identifier">world</span><span class="special">.</span><span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span>
 252 <span class="special">}</span>
 253 </pre>
 254 <p>
 255       </p>
 256 <p>
 257         (Both compilers with and without variadic macros use this same syntax for
 258         capturing no variable, see the <a class="link" href="no_variadic_macros.html" title="Annex: No Variadic Macros">No
 259         Variadic Macros</a> section for more information.)
 260       </p>
 261 </div>
 262 <div class="section">
 263 <div class="titlepage"><div><div><h3 class="title">
 264 <a name="scope_exit.tutorial.capturing_all_variables__c__11_only_"></a><a class="link" href="tutorial.html#scope_exit.tutorial.capturing_all_variables__c__11_only_" title="Capturing All Variables (C++11 Only)">Capturing
 265       All Variables (C++11 Only)</a>
 266 </h3></div></div></div>
 267 <p>
 268         On C++11 compliers, it is also possible to capture all the variables in scope
 269         without naming them one-by-one using the special macro <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 270         instead of <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>.
 271         <a href="#ftn.scope_exit.tutorial.capturing_all_variables__c__11_only_.f0" class="footnote" name="scope_exit.tutorial.capturing_all_variables__c__11_only_.f0"><sup class="footnote">[4]</sup></a>
 272       </p>
 273 <p>
 274         Following the same syntax adopted by C++11 lambda functions, the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code> macro accepts
 275         a comma-separated list of captures which must start with either <code class="computeroutput"><span class="special">&amp;</span></code> or <code class="computeroutput"><span class="special">=</span></code>
 276         to capture all variables in scope respectively by reference or by value (note
 277         that no variable name is specified by these leading captures). Additional
 278         captures of specific variables can follow the leading <code class="computeroutput"><span class="special">&amp;</span></code>
 279         or <code class="computeroutput"><span class="special">=</span></code> and they will override
 280         the default reference or value captures. For example (see also <a href="../../../test/world_checkpoint_all.cpp" target="_top"><code class="literal">world_checkpoint_all.cpp</code></a>):
 281       </p>
 282 <p>
 283 </p>
 284 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">world</span><span class="special">::</span><span class="identifier">add_person</span><span class="special">(</span><span class="identifier">person</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span>
 285     <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span>
 286
 287     <span class="comment">// This block must be no-throw.</span>
 288     <span class="identifier">person</span><span class="special">&amp;</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">back</span><span class="special">();</span>
 289     <span class="identifier">person</span><span class="special">::</span><span class="identifier">evolution_t</span> <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">;</span>
 290     <span class="comment">// Capture all by reference `&amp;`, but `checkpoint` and `this` (C++11 only).</span>
 291     <span class="identifier">BOOST_SCOPE_EXIT_ALL</span><span class="special">(&amp;,</span> <span class="identifier">checkpoint</span><span class="special">,</span> <span class="keyword">this</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Use `this` (not `this_`).</span>
 292         <span class="keyword">if</span><span class="special">(</span><span class="identifier">checkpoint</span> <span class="special">==</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">)</span> <span class="keyword">this</span><span class="special">-&gt;</span><span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span>
 293     <span class="special">};</span> <span class="comment">// Use `;` (not `SCOPE_EXIT_END`).</span>
 294
 295     <span class="comment">// ...</span>
 296
 297     <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="special">++</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">;</span>
 298
 299     <span class="comment">// Assign new identifier to the person.</span>
 300     <span class="identifier">person</span><span class="special">::</span><span class="identifier">id_t</span> <span class="keyword">const</span> <span class="identifier">prev_id</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">id</span><span class="special">;</span>
 301     <span class="identifier">p</span><span class="special">.</span><span class="identifier">id</span> <span class="special">=</span> <span class="identifier">next_id_</span><span class="special">++;</span>
 302     <span class="comment">// Capture all by value `=`, but `p` (C++11 only).</span>
 303     <span class="identifier">BOOST_SCOPE_EXIT_ALL</span><span class="special">(=,</span> <span class="special">&amp;</span><span class="identifier">p</span><span class="special">)</span> <span class="special">{</span>
 304         <span class="keyword">if</span><span class="special">(</span><span class="identifier">checkpoint</span> <span class="special">==</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">)</span> <span class="special">{</span>
 305             <span class="keyword">this</span><span class="special">-&gt;</span><span class="identifier">next_id_</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">id</span><span class="special">;</span>
 306             <span class="identifier">p</span><span class="special">.</span><span class="identifier">id</span> <span class="special">=</span> <span class="identifier">prev_id</span><span class="special">;</span>
 307         <span class="special">}</span>
 308     <span class="special">};</span>
 309
 310     <span class="comment">// ...</span>
 311
 312     <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="special">++</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution</span><span class="special">;</span>
 313 <span class="special">}</span>
 314 </pre>
 315 <p>
 316       </p>
 317 <p>
 318         The first <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a> declaration captures
 319         all variables in scope by reference but the variable <code class="computeroutput"><span class="identifier">checkpoint</span></code>
 320         and the object <code class="computeroutput"><span class="keyword">this</span></code> which are
 321         explicitly captured by value (in particular, <code class="computeroutput"><span class="identifier">p</span></code>
 322         and <code class="computeroutput"><span class="identifier">persons_</span></code> are implicitly
 323         captured by reference here). The second <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 324         declaration instead captures all variables in scope by value but <code class="computeroutput"><span class="identifier">p</span></code> which is explicitly captured by reference
 325         (in particular, <code class="computeroutput"><span class="identifier">checkpoint</span></code>,
 326         <code class="computeroutput"><span class="identifier">prev_id</span></code>, and <code class="computeroutput"><span class="keyword">this</span></code> are implicitly captured by value here).
 327       </p>
 328 <p>
 329         Note that the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 330         macro follows the C++11 lambda function syntax which is unfortunately different
 331         from the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code> macro
 332         syntax. In particular:
 333       </p>
 334 <div class="orderedlist"><ol class="orderedlist" type="1">
 335 <li class="listitem">
 336             The <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 337             macro cannot capture data members without capturing the object <code class="computeroutput"><span class="keyword">this</span></code> while that is not the case for <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>. <a href="#ftn.scope_exit.tutorial.capturing_all_variables__c__11_only_.f1" class="footnote" name="scope_exit.tutorial.capturing_all_variables__c__11_only_.f1"><sup class="footnote">[5]</sup></a>
 338           </li>
 339 <li class="listitem">
 340             The <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 341             macro captures the object in scope using <code class="computeroutput"><span class="keyword">this</span></code>
 342             instead of <code class="computeroutput"><span class="identifier">this_</span></code>. <a href="#ftn.scope_exit.tutorial.capturing_all_variables__c__11_only_.f2" class="footnote" name="scope_exit.tutorial.capturing_all_variables__c__11_only_.f2"><sup class="footnote">[6]</sup></a>
 343           </li>
 344 <li class="listitem">
 345             The <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 346             body is terminated by a semicolon <code class="computeroutput"><span class="special">;</span></code>
 347             instead than by the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_END.html" title="Macro BOOST_SCOPE_EXIT_END">BOOST_SCOPE_EXIT_END</a></code>
 348             macro.
 349           </li>
 350 </ol></div>
 351 <p>
 352         If programmers define the configuration macro <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_CONFIG_USE_LAMBDAS.html" title="Macro BOOST_SCOPE_EXIT_CONFIG_USE_LAMBDAS">BOOST_SCOPE_EXIT_CONFIG_USE_LAMBDAS</a></code>
 353         then the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code> macro
 354         implementation will use C++11 lamda functions and the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
 355         macro will follow the same syntax of <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 356         macro, which is the C++11 lambda function syntax. However, <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
 357         will no longer be backward compatible and older code using <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
 358         might no longer compile (if data members were explicitly captured).
 359       </p>
 360 </div>
 361 <div class="section">
 362 <div class="titlepage"><div><div><h3 class="title">
 363 <a name="scope_exit.tutorial.template_workaround__gcc_"></a><a class="link" href="tutorial.html#scope_exit.tutorial.template_workaround__gcc_" title="Template Workaround (GCC)">Template
 364       Workaround (GCC)</a>
 365 </h3></div></div></div>
 366 <p>
 367         Various versions of the GCC compiler do not compile <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
 368         inside templates (see the <a href="../reference.html" target="_top">Reference</a> section
 369         for more information). As a workaround, <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_TPL.html" title="Macro BOOST_SCOPE_EXIT_TPL">BOOST_SCOPE_EXIT_TPL</a></code>
 370         should be used instead of <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
 371         in these cases. <a href="#ftn.scope_exit.tutorial.template_workaround__gcc_.f0" class="footnote" name="scope_exit.tutorial.template_workaround__gcc_.f0"><sup class="footnote">[7]</sup></a> The <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_TPL.html" title="Macro BOOST_SCOPE_EXIT_TPL">BOOST_SCOPE_EXIT_TPL</a></code>
 372         macro has the exact same syntax of <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>.
 373         For example (see also <a href="../../../test/world_tpl.cpp" target="_top"><code class="literal">world_tpl.cpp</code></a>):
 374       </p>
 375 <p>
 376 </p>
 377 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Person</span><span class="special">&gt;</span>
 378 <span class="keyword">void</span> <span class="identifier">world</span><span class="special">&lt;</span><span class="identifier">Person</span><span class="special">&gt;::</span><span class="identifier">add_person</span><span class="special">(</span><span class="identifier">Person</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span>
 379     <span class="keyword">bool</span> <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span>
 380     <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span>
 381
 382     <span class="identifier">BOOST_SCOPE_EXIT_TPL</span><span class="special">(&amp;</span><span class="identifier">commit</span><span class="special">,</span> <span class="identifier">this_</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Use `_TPL` postfix.</span>
 383         <span class="keyword">if</span><span class="special">(!</span><span class="identifier">commit</span><span class="special">)</span> <span class="identifier">this_</span><span class="special">-&gt;</span><span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span>
 384     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span>
 385
 386     <span class="comment">// ...</span>
 387
 388     <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span>
 389 <span class="special">}</span>
 390 </pre>
 391 <p>
 392       </p>
 393 <p>
 394         It is recommended to always use <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_TPL.html" title="Macro BOOST_SCOPE_EXIT_TPL">BOOST_SCOPE_EXIT_TPL</a></code>
 395         within templates so to maximize portability among different compilers.
 396       </p>
 397 </div>
 398 <div class="section">
 399 <div class="titlepage"><div><div><h3 class="title">
 400 <a name="scope_exit.tutorial.same_line_expansions"></a><a class="link" href="tutorial.html#scope_exit.tutorial.same_line_expansions" title="Same Line Expansions">Same Line Expansions</a>
 401 </h3></div></div></div>
 402 <p>
 403         In general, it is not possible to expand the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>,
 404         <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_TPL.html" title="Macro BOOST_SCOPE_EXIT_TPL">BOOST_SCOPE_EXIT_TPL</a></code>,
 405         <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_END.html" title="Macro BOOST_SCOPE_EXIT_END">BOOST_SCOPE_EXIT_END</a></code>, and
 406         <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code> macros
 407         multiple times on the same line. <a href="#ftn.scope_exit.tutorial.same_line_expansions.f0" class="footnote" name="scope_exit.tutorial.same_line_expansions.f0"><sup class="footnote">[8]</sup></a>
 408       </p>
 409 <p>
 410         Therefore, this library provides additional macros <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ID.html" title="Macro BOOST_SCOPE_EXIT_ID">BOOST_SCOPE_EXIT_ID</a></code>,
 411         <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ID_TPL.html" title="Macro BOOST_SCOPE_EXIT_ID_TPL">BOOST_SCOPE_EXIT_ID_TPL</a></code>,
 412         <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_END_ID.html" title="Macro BOOST_SCOPE_EXIT_END_ID">BOOST_SCOPE_EXIT_END_ID</a></code>,
 413         and <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL_ID.html" title="Macro BOOST_SCOPE_EXIT_ALL_ID">BOOST_SCOPE_EXIT_ALL_ID</a></code>
 414         which can be expanded multiple times on the same line as long as programmers
 415         specify a unique identifiers as the macros' first parameters. The unique
 416         identifier can be any token (not just numeric) that can be concatenated by
 417         the C++ preprocessor (e.g., <code class="computeroutput"><span class="identifier">scope_exit_number_1_at_line_123</span></code>).
 418         <a href="#ftn.scope_exit.tutorial.same_line_expansions.f1" class="footnote" name="scope_exit.tutorial.same_line_expansions.f1"><sup class="footnote">[9]</sup></a>
 419       </p>
 420 <p>
 421         The <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ID.html" title="Macro BOOST_SCOPE_EXIT_ID">BOOST_SCOPE_EXIT_ID</a></code>,
 422         <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ID_TPL.html" title="Macro BOOST_SCOPE_EXIT_ID_TPL">BOOST_SCOPE_EXIT_ID_TPL</a></code>,
 423         and <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL_ID.html" title="Macro BOOST_SCOPE_EXIT_ALL_ID">BOOST_SCOPE_EXIT_ALL_ID</a></code>
 424         macros accept a capture list using the exact same syntax as <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
 425         and <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 426         respectively. For example (see also <a href="../../../test/same_line.cpp" target="_top"><code class="literal">same_line.cpp</code></a>):
 427       </p>
 428 <p>
 429 </p>
 430 <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">SCOPE_EXIT_INC_DEC</span><span class="special">(</span><span class="identifier">variable</span><span class="special">,</span> <span class="identifier">offset</span><span class="special">)</span> <span class="special">\</span>
 431     <span class="identifier">BOOST_SCOPE_EXIT_ID</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">inc</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">),</span> <span class="comment">/* unique ID */</span> <span class="special">\</span>
 432             <span class="special">&amp;</span><span class="identifier">variable</span><span class="special">,</span> <span class="identifier">offset</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span>
 433         <span class="identifier">variable</span> <span class="special">+=</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span>
 434     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END_ID</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">inc</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">))</span> <span class="special">\</span>
 435     <span class="special">\</span>
 436     <span class="identifier">BOOST_SCOPE_EXIT_ID</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">dec</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">),</span> <span class="special">\</span>
 437             <span class="special">&amp;</span><span class="identifier">variable</span><span class="special">,</span> <span class="identifier">offset</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span>
 438         <span class="identifier">variable</span> <span class="special">-=</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span>
 439     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END_ID</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">dec</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">))</span>
 440
 441 <span class="preprocessor">#define</span> <span class="identifier">SCOPE_EXIT_INC_DEC_TPL</span><span class="special">(</span><span class="identifier">variable</span><span class="special">,</span> <span class="identifier">offset</span><span class="special">)</span> <span class="special">\</span>
 442     <span class="identifier">BOOST_SCOPE_EXIT_ID_TPL</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">inc</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">),</span> <span class="special">\</span>
 443             <span class="special">&amp;</span><span class="identifier">variable</span><span class="special">,</span> <span class="identifier">offset</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span>
 444         <span class="identifier">variable</span> <span class="special">+=</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span>
 445     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END_ID</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">inc</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">))</span> <span class="special">\</span>
 446     <span class="special">\</span>
 447     <span class="identifier">BOOST_SCOPE_EXIT_ID_TPL</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">dec</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">),</span> <span class="special">\</span>
 448             <span class="special">&amp;</span><span class="identifier">variable</span><span class="special">,</span> <span class="identifier">offset</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span>
 449         <span class="identifier">variable</span> <span class="special">-=</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span>
 450     <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END_ID</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">dec</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">))</span>
 451
 452 <span class="preprocessor">#define</span> <span class="identifier">SCOPE_EXIT_ALL_INC_DEC</span><span class="special">(</span><span class="identifier">variable</span><span class="special">,</span> <span class="identifier">offset</span><span class="special">)</span> <span class="special">\</span>
 453     <span class="identifier">BOOST_SCOPE_EXIT_ALL_ID</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">inc</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">),</span> <span class="special">\</span>
 454             <span class="special">=,</span> <span class="special">&amp;</span><span class="identifier">variable</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span>
 455         <span class="identifier">variable</span> <span class="special">+=</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span>
 456     <span class="special">};</span> <span class="special">\</span>
 457     <span class="identifier">BOOST_SCOPE_EXIT_ALL_ID</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">dec</span><span class="special">,</span> <span class="identifier">__LINE__</span><span class="special">),</span> <span class="special">\</span>
 458             <span class="special">=,</span> <span class="special">&amp;</span><span class="identifier">variable</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span>
 459         <span class="identifier">variable</span> <span class="special">-=</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span>
 460     <span class="special">};</span>
 461
 462 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span>
 463 <span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">delta</span><span class="special">)</span> <span class="special">{</span>
 464     <span class="identifier">SCOPE_EXIT_INC_DEC_TPL</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">delta</span><span class="special">)</span> <span class="comment">// Multiple scope exits on same line.</span>
 465     <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
 466 <span class="special">}</span>
 467
 468 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span>
 469     <span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">delta</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span>
 470
 471     <span class="special">{</span>
 472         <span class="identifier">SCOPE_EXIT_INC_DEC</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">delta</span><span class="special">)</span> <span class="comment">// Multiple scope exits on same line.</span>
 473     <span class="special">}</span>
 474     <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
 475
 476     <span class="identifier">f</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">delta</span><span class="special">);</span>
 477
 478 <span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_NO_CXX11_LAMBDAS</span>
 479     <span class="special">{</span>
 480         <span class="identifier">SCOPE_EXIT_ALL_INC_DEC</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">delta</span><span class="special">)</span> <span class="comment">// Multiple scope exits on same line.</span>
 481     <span class="special">}</span>
 482     <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
 483 <span class="preprocessor">#endif</span> <span class="comment">// LAMBDAS</span>
 484
 485     <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span>
 486 <span class="special">}</span>
 487 </pre>
 488 <p>
 489       </p>
 490 <p>
 491         As shown by the example above, the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ID.html" title="Macro BOOST_SCOPE_EXIT_ID">BOOST_SCOPE_EXIT_ID</a></code>,
 492         <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ID_TPL.html" title="Macro BOOST_SCOPE_EXIT_ID_TPL">BOOST_SCOPE_EXIT_ID_TPL</a></code>,
 493         <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_END_ID.html" title="Macro BOOST_SCOPE_EXIT_END_ID">BOOST_SCOPE_EXIT_END_ID</a></code>,
 494         and <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL_ID.html" title="Macro BOOST_SCOPE_EXIT_ALL_ID">BOOST_SCOPE_EXIT_ALL_ID</a></code>
 495         macros are especially useful when it is necessary to invoke them multiple
 496         times within user-defined macros (because the C++ preprocessor expands all
 497         nested macros on the same line).
 498       </p>
 499 </div>
 500 <div class="footnotes">
 501 <br><hr style="width:100; text-align:left;margin-left: 0">
 502 <div id="ftn.scope_exit.tutorial.capturing_no_variable.f0" class="footnote"><p><a href="#scope_exit.tutorial.capturing_no_variable.f0" class="para"><sup class="para">[3] </sup></a>
 503           <span class="bold"><strong>Rationale.</strong></span> Unfortunately, it is not possible
 504           to simply invoke the <a class="link" href="../index.html" title="Chapter&#160;1.&#160;Boost.ScopeExit 1.1.0">Boost.ScopeExit</a>
 505           macro with no parameters as in <code class="computeroutput"><span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">()</span></code> because the C++ preprocessor cannot detect
 506           emptiness of a macro parameter when the parameter can start with a non-alphanumeric
 507           symbol (which is the case when capturing a variable by reference <code class="computeroutput"><span class="special">&amp;</span><span class="identifier">variable</span></code>).
 508         </p></div>
 509 <div id="ftn.scope_exit.tutorial.capturing_all_variables__c__11_only_.f0" class="footnote"><p><a href="#scope_exit.tutorial.capturing_all_variables__c__11_only_.f0" class="para"><sup class="para">[4] </sup></a>
 510           <span class="bold"><strong>Rationale.</strong></span> The <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 511           macro is only defined on C++11 compilers for which the <a href="http://www.boost.org/libs/config" target="_top">Boost.Config</a>
 512           macro <code class="computeroutput"><span class="identifier">BOOST_NO_CXX11_LAMBDAS</span></code>
 513           is not defined. Using <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 514           on C++03 compilers for which <code class="computeroutput"><span class="identifier">BOOST_NO_CXX11_LAMBDAS</span></code>
 515           is defined will generate (possibly cryptic) compiler errors. Note that
 516           a new macro <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 517           needed to be introduced instead of reusing <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
 518           because <code class="computeroutput"><span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(&amp;)</span></code> and <code class="computeroutput"><span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(=)</span></code> cannot be distinguished from <code class="computeroutput"><span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span></code> or
 519           <code class="computeroutput"><span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(</span><span class="identifier">this_</span><span class="special">)</span></code>
 520           using the C++ preprocessor given that the symbols <code class="computeroutput"><span class="special">&amp;</span></code>
 521           and <code class="computeroutput"><span class="special">=</span></code> are neither prefxied
 522           nor postfixed by alphanumeric tokens (this is not an issue for <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code> which always
 523           has the non-alphanumeric <code class="computeroutput"><span class="special">&amp;</span></code>
 524           or <code class="computeroutput"><span class="special">=</span></code> as the first capture
 525           so the first capture tokens are simply never compared with neither <code class="computeroutput"><span class="keyword">void</span></code> nor <code class="computeroutput"><span class="identifier">this_</span></code>
 526           for this macro).
 527         </p></div>
 528 <div id="ftn.scope_exit.tutorial.capturing_all_variables__c__11_only_.f1" class="footnote"><p><a href="#scope_exit.tutorial.capturing_all_variables__c__11_only_.f1" class="para"><sup class="para">[5] </sup></a>
 529               At present, there seems to be some discussion to allow C++11 lambda
 530               functions to capture data members without capturing the object <code class="computeroutput"><span class="keyword">this</span></code>. If the C++11 standard were changed
 531               to allow this, the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 532               macro syntax could be extended to be a superset of the <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT.html" title="Macro BOOST_SCOPE_EXIT">BOOST_SCOPE_EXIT</a></code>
 533               macro while keeping full backward compatibility.
 534             </p></div>
 535 <div id="ftn.scope_exit.tutorial.capturing_all_variables__c__11_only_.f2" class="footnote"><p><a href="#scope_exit.tutorial.capturing_all_variables__c__11_only_.f2" class="para"><sup class="para">[6] </sup></a>
 536               On compilers that support the use of the <code class="computeroutput"><span class="keyword">typename</span></code>
 537               outside templates as allowed by the C++11 standard, <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 538               can use both <code class="computeroutput"><span class="keyword">this</span></code> and
 539               <code class="computeroutput"><span class="identifier">this_</span></code> to capture the
 540               object in scope (notably, this is not the case for the MSVC 10.0 compiler).
 541             </p></div>
 542 <div id="ftn.scope_exit.tutorial.template_workaround__gcc_.f0" class="footnote"><p><a href="#scope_exit.tutorial.template_workaround__gcc_.f0" class="para"><sup class="para">[7] </sup></a>
 543           <span class="bold"><strong>Rationale.</strong></span> GCC versions compliant with
 544           C++11 do not present this issue and given that <code class="computeroutput"><a class="link" href="../BOOST_SCOPE_EXIT_ALL.html" title="Macro BOOST_SCOPE_EXIT_ALL">BOOST_SCOPE_EXIT_ALL</a></code>
 545           is only available on C++11 compilers, there is no need for a <code class="computeroutput"><span class="identifier">BOOST_SCOPE_EXIT_ALL_TPL</span></code> macro.
 546         </p></div>
 547 <div id="ftn.scope_exit.tutorial.same_line_expansions.f0" class="footnote"><p><a href="#scope_exit.tutorial.same_line_expansions.f0" class="para"><sup class="para">[8] </sup></a>
 548           <span class="bold"><strong>Rationale.</strong></span> The library macros internally
 549           use <code class="computeroutput"><span class="identifier">__LINE__</span></code> to generate
 550           unique identifiers. Therefore, if the same macro is expanded more than
 551           on time on the same line, the generated identifiers will no longer be unique
 552           and the code will not compile. (This restriction does not apply to MSVC
 553           and other compilers that provide the non-standard <code class="computeroutput"><span class="identifier">__COUNTER__</span></code>
 554           macro.)
 555         </p></div>
 556 <div id="ftn.scope_exit.tutorial.same_line_expansions.f1" class="footnote"><p><a href="#scope_exit.tutorial.same_line_expansions.f1" class="para"><sup class="para">[9] </sup></a>
 557           Because there are restrictions on the set of tokens that the C++ preprocessor
 558           can concatenate and because not all compilers correctly implement these
 559           restrictions, it is in general recommended to specify unique identifiers
 560           as a combination of alphanumeric tokens.
 561         </p></div>
 562 </div>
 563 </div>
 564 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 565 <td align="left"></td>
 566 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2012 Alexander Nasonov, Lorenzo Caminiti<p>
 567         Distributed under the Boost Software License, Version 1.0 (see accompanying
 568         file LICENSE_1_0.txt or a copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 569       </p>
 570 </div></td>
 571 </tr></table>
 572 <hr>
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