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| </div> |
| <div class="section boost_localfunction_advanced_topics"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="boost_localfunction.advanced_topics"></a><a class="link" href="advanced_topics.html" title="Advanced Topics">Advanced Topics</a> |
| </h2></div></div></div> |
| <div class="toc"><dl> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.default_parameters">Default |
| Parameters</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.commas_and_symbols_in_macros">Commas |
| and Symbols in Macros</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.assignments_and_returns">Assignments |
| and Returns</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.nesting">Nesting</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.accessing_types__concepts__etc_">Accessing |
| Types (concepts, etc)</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.specifying_types__no_boost_typeof_">Specifying |
| Types (no Boost.Typeof)</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.inlining">Inlining</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.recursion">Recursion</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.overloading">Overloading</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.exception_specifications">Exception |
| Specifications</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.storage_classifiers">Storage |
| Classifiers</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.same_line_expansions">Same |
| Line Expansions</a></span></dt> |
| <dt><span class="section"><a href="advanced_topics.html#boost_localfunction.advanced_topics.limitations__operators__etc_">Limitations |
| (operators, etc)</a></span></dt> |
| </dl></div> |
| <p> |
| This section illustrates advanced usage of this library. At the bottom there |
| is also a list of known limitations of this library. |
| </p> |
| <div class="section boost_localfunction_advanced_topics_default_parameters"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.default_parameters"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.default_parameters" title="Default Parameters">Default |
| Parameters</a> |
| </h3></div></div></div> |
| <p> |
| This library allows to specify default values for the local function parameters. |
| However, the usual C++ syntax for default parameters that uses the assignment |
| symbol <code class="computeroutput"><span class="special">=</span></code> cannot be used. <sup>[<a name="boost_localfunction.advanced_topics.default_parameters.f0" href="#ftn.boost_localfunction.advanced_topics.default_parameters.f0" class="footnote">17</a>]</sup> The keyword <code class="computeroutput"><span class="keyword">default</span></code> |
| is used instead: |
| </p> |
| <pre class="programlisting"><code class="literal"><span class="emphasis"><em>parameter-type parameter-name</em></span></code><span class="special">,</span> <span class="keyword">default</span> <code class="literal"><span class="emphasis"><em>parameter-default-value</em></span></code><span class="special">,</span> <span class="special">...</span> |
| </pre> |
| <p> |
| For example, let's program a local function <code class="computeroutput"><span class="identifier">add</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> |
| <span class="identifier">y</span><span class="special">)</span></code> |
| where the second parameter <code class="computeroutput"><span class="identifier">y</span></code> |
| is optional and has a default value of <code class="computeroutput"><span class="number">2</span></code> |
| (see also <a href="../../../test/add_default.cpp" target="_top"><code class="literal">add_default.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">y</span><span class="special">,</span> <span class="keyword">default</span> <span class="number">2</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Default parameter.</span> |
| <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> |
| |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">==</span> <span class="number">3</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Programmers can define a <code class="computeroutput"><span class="identifier">WITH_DEFAULT</span></code> |
| macro similar to the following if they think it improves readability over |
| the above syntax (see also <a href="../../../test/add_with_default.cpp" target="_top"><code class="literal">add_with_default.cpp</code></a>): |
| <sup>[<a name="boost_localfunction.advanced_topics.default_parameters.f1" href="#ftn.boost_localfunction.advanced_topics.default_parameters.f1" class="footnote">18</a>]</sup> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">WITH_DEFAULT</span> <span class="special">,</span> <span class="keyword">default</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">y</span> <span class="identifier">WITH_DEFAULT</span> <span class="number">2</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Default.</span> |
| <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> |
| |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">==</span> <span class="number">3</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_commas_and_symbols_in_macros"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.commas_and_symbols_in_macros"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.commas_and_symbols_in_macros" title="Commas and Symbols in Macros">Commas |
| and Symbols in Macros</a> |
| </h3></div></div></div> |
| <p> |
| The C++ preprocessor does not allow commas <code class="computeroutput"><span class="special">,</span></code> |
| within macro parameters unless they are wrapped by round parenthesis <code class="computeroutput"><span class="special">()</span></code> (see the <a href="http://www.boost.org/libs/utility/identity_type" target="_top">Boost.Utility/IdentityType</a> |
| documentation for details). Therefore, using commas within local function |
| parameters and bindings will generate (cryptic) preprocessor errors unless |
| they are wrapped with an extra set of round parenthesis <code class="computeroutput"><span class="special">()</span></code> |
| as explained here. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Also macro parameters with commas wrapped by angular parenthesis <code class="computeroutput"><span class="special"><></span></code> (templates, etc) or square parenthesis |
| <code class="computeroutput"><span class="special">[]</span></code> (multidimensional array |
| access, etc) need to be wrapped by the extra round parenthesis <code class="computeroutput"><span class="special">()</span></code> as explained here (this is because the |
| preprocessor only recognizes the round parenthesis and it does not recognize |
| angular, square, or any other type of parenthesis). However, macro parameters |
| with commas which are already wrapped by round parenthesis <code class="computeroutput"><span class="special">()</span></code> are fine (function calls, some value |
| expressions, etc). |
| </p></td></tr> |
| </table></div> |
| <p> |
| In addition, local function parameter types cannot start with non-alphanumeric |
| symbols (alphanumeric symbols are <code class="computeroutput"><span class="identifier">A</span><span class="special">-</span><span class="identifier">Z</span></code>, <code class="computeroutput"><span class="identifier">a</span><span class="special">-</span><span class="identifier">z</span></code>, |
| and <code class="computeroutput"><span class="number">0</span><span class="special">-</span><span class="number">9</span></code>). <sup>[<a name="boost_localfunction.advanced_topics.commas_and_symbols_in_macros.f0" href="#ftn.boost_localfunction.advanced_topics.commas_and_symbols_in_macros.f0" class="footnote">19</a>]</sup> The library will generate (cryptic) preprocessor errors if a |
| parameter type starts with a non-alphanumeric symbol. |
| </p> |
| <p> |
| Let's consider the following example: |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> |
| <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>&</span> <span class="identifier">m</span><span class="special">,</span> <span class="comment">// (1) Error.</span> |
| <span class="special">::</span><span class="identifier">sign_t</span> <span class="identifier">sign</span><span class="special">,</span> <span class="comment">// (2) Error.</span> |
| <span class="keyword">const</span> <span class="identifier">size_t</span><span class="special">&</span> <span class="identifier">factor</span><span class="special">,</span> |
| <span class="keyword">default</span> <span class="identifier">key_sizeof</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>::</span><span class="identifier">value</span><span class="special">,</span> <span class="comment">// (3) Error.</span> |
| <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">separator</span><span class="special">,</span> <span class="keyword">default</span> <span class="identifier">cat</span><span class="special">(</span><span class="string">":"</span><span class="special">,</span> <span class="string">" "</span><span class="special">)</span> <span class="comment">// (4) OK.</span> |
| <span class="special">)</span> <span class="special">{</span> |
| <span class="special">...</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> |
| </pre> |
| <p> |
| <span class="bold"><strong>(1)</strong></span> The parameter type <code class="computeroutput"><span class="keyword">const</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>&</span></code> contains a comma <code class="computeroutput"><span class="special">,</span></code> |
| after the first template parameter <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>. |
| This comma is not wrapped by any round parenthesis <code class="computeroutput"><span class="special">()</span></code> |
| thus it will cause a preprocessor error. <sup>[<a name="boost_localfunction.advanced_topics.commas_and_symbols_in_macros.f1" href="#ftn.boost_localfunction.advanced_topics.commas_and_symbols_in_macros.f1" class="footnote">20</a>]</sup> The <a href="http://www.boost.org/libs/utility/identity_type" target="_top">Boost.Utility/IdentityType</a> |
| macro <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span></code><code class="literal"><span class="emphasis"><em>type-with-commas</em></span></code><code class="computeroutput"><span class="special">))</span></code> defined in the <code class="literal">boost/utility/identity_type.hpp</code> |
| header can be used to wrap a type within extra parenthesis <code class="computeroutput"><span class="special">()</span></code> so to overcome this problem: |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">/</span><span class="identifier">identity_type</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> |
| <span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>&))</span> <span class="identifier">m</span><span class="special">,</span> <span class="comment">// OK.</span> |
| <span class="special">...</span> |
| <span class="special">)</span> <span class="special">{</span> |
| <span class="special">...</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> |
| </pre> |
| <p> |
| This macro expands to an expression that evaluates (at compile-time) exactly |
| to the specified type (furthermore, this macro does not use variadic macros |
| so it works on any <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| compiler). Note that a total of two set of parenthesis <code class="computeroutput"><span class="special">()</span></code> |
| are needed: The parenthesis to invoke the <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">(...)</span></code> macro plus the parenthesis to wrap the |
| type expression (and therefore any comma <code class="computeroutput"><span class="special">,</span></code> |
| that it contains) passed as parameter to the <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((...))</span></code> macro. Finally, the <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span></code> macro must be prefixed |
| by the <code class="computeroutput"><span class="keyword">typename</span></code> keyword <code class="computeroutput"><span class="keyword">typename</span> <span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">(</span></code><code class="literal"><span class="emphasis"><em>parenthesized-type</em></span></code><code class="computeroutput"><span class="special">)</span></code> when used together with the <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_TPL">BOOST_LOCAL_FUNCTION_TPL</a></code> |
| macro within templates. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Often, there might be better ways to overcome this limitation that lead |
| to code which is more readable than the one using the <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span></code> |
| macro. |
| </p></td></tr> |
| </table></div> |
| <p> |
| For example, in this case a <code class="computeroutput"><span class="keyword">typedef</span></code> |
| from the enclosing scope could have been used to obtain the following valid |
| and perhaps more readable code: |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">></span> <span class="identifier">map_type</span><span class="special">;</span> |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> |
| <span class="keyword">const</span> <span class="identifier">map_type</span><span class="special">&</span> <span class="identifier">m</span><span class="special">,</span> <span class="comment">// OK (and more readable).</span> |
| <span class="special">...</span> |
| <span class="special">)</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> |
| </pre> |
| <p> |
| <span class="bold"><strong>(2)</strong></span> The parameter type <code class="computeroutput"><span class="special">::</span><span class="identifier">sign_t</span></code> starts with the non-alphanumeric |
| symbols <code class="computeroutput"><span class="special">::</span></code> thus it will generate |
| preprocessor errors if used as a local function parameter type. The <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span></code> macro can also be used |
| to overcome this issue: |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> |
| <span class="special">...</span> |
| <span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((::</span><span class="identifier">sign_t</span><span class="special">))</span> <span class="identifier">sign</span><span class="special">,</span> <span class="comment">// OK.</span> |
| <span class="special">...</span> |
| <span class="special">)</span> <span class="special">{</span> |
| <span class="special">...</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> |
| </pre> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Often, there might be better ways to overcome this limitation that lead |
| to code which is more readable than the one using the <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span></code> |
| macro. |
| </p></td></tr> |
| </table></div> |
| <p> |
| For example, in this case the symbols <code class="computeroutput"><span class="special">::</span></code> |
| could have been simply dropped to obtain the following valid and perhaps |
| more readable code: |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> |
| <span class="special">...</span> |
| <span class="identifier">sign_t</span> <span class="identifier">sign</span><span class="special">,</span> <span class="comment">// OK (and more readable).</span> |
| <span class="special">...</span> |
| <span class="special">)</span> <span class="special">{</span> |
| <span class="special">...</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> |
| </pre> |
| <p> |
| <span class="bold"><strong>(3)</strong></span> The default parameter value <code class="computeroutput"><span class="identifier">key_sizeof</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>::</span><span class="identifier">value</span></code> |
| contains a comma <code class="computeroutput"><span class="special">,</span></code> after the |
| first template parameter <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>. |
| Again, this comma is not wrapped by any parenthesis <code class="computeroutput"><span class="special">()</span></code> |
| so it will cause a preprocessor error. Because this is a value expression |
| (and not a type expression), it can simply be wrapped within an extra set |
| of round parenthesis <code class="computeroutput"><span class="special">()</span></code>: |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> |
| <span class="special">...</span> |
| <span class="keyword">const</span> <span class="identifier">size_t</span><span class="special">&</span> <span class="identifier">factor</span><span class="special">,</span> |
| <span class="keyword">default</span> <span class="special">(</span><span class="identifier">key_sizeof</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>::</span><span class="identifier">value</span><span class="special">),</span> <span class="comment">// OK.</span> |
| <span class="special">...</span> |
| <span class="special">)</span> <span class="special">{</span> |
| <span class="special">...</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> |
| </pre> |
| <p> |
| <span class="bold"><strong>(4)</strong></span> The default parameter value <code class="computeroutput"><span class="identifier">cat</span><span class="special">(</span><span class="string">":"</span><span class="special">,</span> <span class="string">" "</span><span class="special">)</span></code> is instead fine because it contains a comma |
| <code class="computeroutput"><span class="special">,</span></code> which is already wrapped by |
| the parenthesis <code class="computeroutput"><span class="special">()</span></code> of the function |
| call <code class="computeroutput"><span class="identifier">cat</span><span class="special">(...)</span></code>. |
| </p> |
| <p> |
| Consider the following complete example (see also <a href="../../../test/macro_commas.cpp" target="_top"><code class="literal">macro_commas.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> |
| <span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>&))</span> <span class="identifier">m</span><span class="special">,</span> |
| <span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((::</span><span class="identifier">sign_t</span><span class="special">))</span> <span class="identifier">sign</span><span class="special">,</span> |
| <span class="keyword">const</span> <span class="identifier">size_t</span><span class="special">&</span> <span class="identifier">factor</span><span class="special">,</span> |
| <span class="keyword">default</span> <span class="special">(</span><span class="identifier">key_sizeof</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>::</span><span class="identifier">value</span><span class="special">),</span> |
| <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">separator</span><span class="special">,</span> <span class="keyword">default</span> <span class="identifier">cat</span><span class="special">(</span><span class="string">":"</span><span class="special">,</span> <span class="string">" "</span><span class="special">)</span> |
| <span class="special">)</span> <span class="special">{</span> |
| <span class="comment">// Do something...</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_assignments_and_returns"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.assignments_and_returns"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.assignments_and_returns" title="Assignments and Returns">Assignments |
| and Returns</a> |
| </h3></div></div></div> |
| <p> |
| Local functions are function objects so it is possible to assign them to |
| other functors like <a href="http://www.boost.org/libs/function" target="_top">Boost.Function</a>'s |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span></code> in order to store the local function |
| into a variable, pass it as a parameter to another function, or return it |
| from the enclosing function. |
| </p> |
| <p> |
| For example (see also <a href="../../../test/return_assign.cpp" target="_top"><code class="literal">return_assign.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">call1</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)</span> <span class="special">></span> <span class="identifier">f</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">f</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">==</span> <span class="number">5</span><span class="special">);</span> <span class="special">}</span> |
| <span class="keyword">void</span> <span class="identifier">call0</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">void</span><span class="special">)></span> <span class="identifier">f</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">f</span><span class="special">()</span> <span class="special">==</span> <span class="number">5</span><span class="special">);</span> <span class="special">}</span> |
| |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)></span> <span class="identifier">linear</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">slope</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">slope</span><span class="special">,</span> |
| <span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">default</span> <span class="number">1</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">y</span><span class="special">,</span> <span class="keyword">default</span> <span class="number">2</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">slope</span> <span class="special">*</span> <span class="identifier">y</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">lin</span><span class="special">)</span> |
| |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)></span> <span class="identifier">f</span> <span class="special">=</span> <span class="identifier">lin</span><span class="special">;</span> <span class="comment">// Assign to local variable.</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">f</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">)</span> <span class="special">==</span> <span class="number">5</span><span class="special">);</span> |
| |
| <span class="identifier">call1</span><span class="special">(</span><span class="identifier">lin</span><span class="special">);</span> <span class="comment">// Pass to other functions.</span> |
| <span class="identifier">call0</span><span class="special">(</span><span class="identifier">lin</span><span class="special">);</span> |
| |
| <span class="keyword">return</span> <span class="identifier">lin</span><span class="special">;</span> <span class="comment">// Return.</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">void</span> <span class="identifier">call</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)></span> <span class="identifier">f</span> <span class="special">=</span> <span class="identifier">linear</span><span class="special">(</span><span class="number">2</span><span class="special">);</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">f</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">)</span> <span class="special">==</span> <span class="number">5</span><span class="special">);</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <div class="warning"><table border="0" summary="Warning"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td> |
| <th align="left">Warning</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| As with <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a>, programmers are responsible to ensure that bound |
| variables are valid in any scope where the local function object is called. |
| Returning and calling a local function outside its declaration scope will |
| lead to undefined behaviour if any of the bound variable is no longer valid |
| in the scope where the local function is called (see the <a class="link" href="examples.html" title="Examples">Examples</a> |
| section for more examples on the extra care needed when returning a local |
| function as a closure). It is always safe instead to call a local function |
| within its enclosing scope. |
| </p></td></tr> |
| </table></div> |
| <p> |
| In addition, a local function can bind and call other local functions. Local |
| functions should always be bound by constant reference <code class="computeroutput"><span class="keyword">const</span> |
| <span class="identifier">bind</span><span class="special">&</span></code> |
| to avoid unnecessary copies. For example, the following local function <code class="computeroutput"><span class="identifier">inc_sum</span></code> binds the local function <code class="computeroutput"><span class="identifier">inc</span></code> so <code class="computeroutput"><span class="identifier">inc_sum</span></code> |
| can call <code class="computeroutput"><span class="identifier">inc</span></code> (see aslo <a href="../../../test/transform.cpp" target="_top"><code class="literal">transform.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">offset</span> <span class="special">=</span> <span class="number">5</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">v</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">w</span><span class="special">;</span> |
| |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><=</span> <span class="number">2</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">i</span> <span class="special">*</span> <span class="number">10</span><span class="special">);</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="number">10</span><span class="special">);</span> <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="number">20</span><span class="special">);</span> |
| <span class="identifier">w</span><span class="special">.</span><span class="identifier">resize</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">size</span><span class="special">());</span> |
| |
| <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">offset</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">i</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">return</span> <span class="special">++</span><span class="identifier">i</span> <span class="special">+</span> <span class="identifier">offset</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">inc</span><span class="special">)</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">w</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">inc</span><span class="special">);</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">w</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="number">16</span><span class="special">);</span> <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">w</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="number">26</span><span class="special">);</span> |
| |
| <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="identifier">bind</span><span class="special">&</span> <span class="identifier">inc</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">i</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">j</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">inc</span><span class="special">(</span><span class="identifier">i</span> <span class="special">+</span> <span class="identifier">j</span><span class="special">);</span> <span class="comment">// Call the other bound local function.</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">inc_sum</span><span class="special">)</span> |
| |
| <span class="identifier">offset</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">transform</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">w</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">inc_sum</span><span class="special">);</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="number">27</span><span class="special">);</span> <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="number">47</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_nesting"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.nesting"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.nesting" title="Nesting">Nesting</a> |
| </h3></div></div></div> |
| <p> |
| It is possible to nest local functions into one another. For example (see |
| also <a href="../../../test/nesting.cpp" target="_top"><code class="literal">nesting.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><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="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="identifier">bind</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="identifier">bind</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Nested.</span> |
| <span class="identifier">x</span><span class="special">++;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">g</span><span class="special">)</span> |
| |
| <span class="identifier">x</span><span class="special">--;</span> |
| <span class="identifier">g</span><span class="special">();</span> <span class="comment">// Nested local function call.</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> |
| |
| <span class="identifier">f</span><span class="special">();</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_accessing_types__concepts__etc_"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.accessing_types__concepts__etc_"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.accessing_types__concepts__etc_" title="Accessing Types (concepts, etc)">Accessing |
| Types (concepts, etc)</a> |
| </h3></div></div></div> |
| <p> |
| This library never requires to explicitly specify the type of bound variables |
| (e.g., this reduces maintenance because the local function declaration and |
| definition do not have to change even if the bound variable types change |
| as long as the semantics of the local function remain valid). From within |
| local functions, programmers can access the type of a bound variable using |
| the following macro: |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_LOCAL_FUNCTION_TYPEOF</span><span class="special">(</span><span class="emphasis"><em>bound-variable-name</em></span><span class="special">)</span> |
| </pre> |
| <p> |
| The <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_TYPEOF.html" title="Macro BOOST_LOCAL_FUNCTION_TYPEOF">BOOST_LOCAL_FUNCTION_TYPEOF</a></code> |
| macro expands to a type expression that evaluates (at compile-time) to the |
| fully qualified type of the bound variable with the specified name. This |
| type expression is fully qualified in the sense that it will be constant |
| if the variable is bound by constant <code class="computeroutput"><span class="keyword">const</span> |
| <span class="identifier">bind</span><span class="special">[&]</span></code> |
| and it will also be a reference if the variable is bound by reference <code class="computeroutput"><span class="special">[</span><span class="keyword">const</span><span class="special">]</span> |
| <span class="identifier">bind</span><span class="special">&</span></code> |
| (if needed, programmers can remove the <code class="computeroutput"><span class="keyword">const</span></code> |
| and <code class="computeroutput"><span class="special">&</span></code> qualifiers using |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">remove_const</span></code> and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">remove_reference</span></code>, |
| see <a href="http://www.boost.org/libs/type_traits" target="_top">Boost.TypeTraits</a>). |
| </p> |
| <p> |
| The deduced bound type can be used within the body to check concepts, declare |
| local variables, etc. For example (see also <a href="../../../test/typeof.cpp" target="_top"><code class="literal">typeof.cpp</code></a> |
| and <a href="../../../test/addable.hpp" target="_top"><code class="literal">addable.hpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> |
| |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">,</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">{</span> |
| <span class="comment">// Type-of for concept checking.</span> |
| <span class="identifier">BOOST_CONCEPT_ASSERT</span><span class="special">((</span><span class="identifier">Addable</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">remove_reference</span><span class="special"><</span> |
| <span class="identifier">BOOST_LOCAL_FUNCTION_TYPEOF</span><span class="special">(</span><span class="identifier">sum</span><span class="special">)>::</span><span class="identifier">type</span><span class="special">>));</span> |
| <span class="comment">// Type-of for declarations.</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">remove_reference</span><span class="special"><</span><span class="identifier">BOOST_LOCAL_FUNCTION_TYPEOF</span><span class="special">(</span> |
| <span class="identifier">factor</span><span class="special">)>::</span><span class="identifier">type</span> <span class="identifier">mult</span> <span class="special">=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> |
| <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">mult</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> |
| |
| <span class="identifier">add</span><span class="special">(</span><span class="number">6</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Within templates, <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_TYPEOF.html" title="Macro BOOST_LOCAL_FUNCTION_TYPEOF">BOOST_LOCAL_FUNCTION_TYPEOF</a></code> |
| should not be prefixed by the <code class="computeroutput"><span class="keyword">typename</span></code> |
| keyword but eventual type manipulations need the <code class="computeroutput"><span class="keyword">typename</span></code> |
| prefix as usual (see also <a href="../../../test/typeof_template.cpp" target="_top"><code class="literal">typeof_template.cpp</code></a> |
| and <a href="../../../test/addable.hpp" target="_top"><code class="literal">addable.hpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">calculate</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">factor</span><span class="special">)</span> <span class="special">{</span> |
| <span class="identifier">T</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> |
| |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION_TPL</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">,</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">,</span> <span class="identifier">T</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">{</span> |
| <span class="comment">// Local function `TYPEOF` does not need `typename`.</span> |
| <span class="identifier">BOOST_CONCEPT_ASSERT</span><span class="special">((</span><span class="identifier">Addable</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">remove_reference</span><span class="special"><</span> |
| <span class="identifier">BOOST_LOCAL_FUNCTION_TYPEOF</span><span class="special">(</span><span class="identifier">sum</span><span class="special">)>::</span><span class="identifier">type</span><span class="special">>));</span> |
| <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME_TPL</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> |
| |
| <span class="identifier">add</span><span class="special">(</span><span class="number">6</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="identifier">sum</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| In this context, it is best to use the <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_TYPEOF.html" title="Macro BOOST_LOCAL_FUNCTION_TYPEOF">BOOST_LOCAL_FUNCTION_TYPEOF</a></code> |
| macro instead of using <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a> |
| to reduce the number of times that <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a> |
| is invoked (either the library already internally used <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a> |
| once, in which case using this macro will not use <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a> |
| again, or the bound variable type is explicitly specified by programmers |
| as shown be below, in which case using this macro will not use <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a> |
| at all). |
| </p> |
| <p> |
| Furthermore, within the local function body it possible to access the result |
| type using <code class="computeroutput"><span class="identifier">result_type</span></code>, the |
| type of the first parameter using <code class="computeroutput"><span class="identifier">arg1_type</span></code>, |
| the type of the second parameter using <code class="computeroutput"><span class="identifier">arg2_type</span></code>, |
| etc. <sup>[<a name="boost_localfunction.advanced_topics.accessing_types__concepts__etc_.f0" href="#ftn.boost_localfunction.advanced_topics.accessing_types__concepts__etc_.f0" class="footnote">21</a>]</sup> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_specifying_types__no_boost_typeof_"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.specifying_types__no_boost_typeof_"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.specifying_types__no_boost_typeof_" title="Specifying Types (no Boost.Typeof)">Specifying |
| Types (no Boost.Typeof)</a> |
| </h3></div></div></div> |
| <p> |
| While not required, it is possible to explicitly specify the type of bound |
| variables so the library will not internally use <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a> |
| to automatically deduce the types. When specified, the bound variable type |
| must follow the <code class="computeroutput"><span class="identifier">bind</span></code> "keyword" |
| and it must be wrapped within round parenthesis <code class="computeroutput"><span class="special">()</span></code>: |
| </p> |
| <pre class="programlisting"><span class="identifier">bind</span><span class="special">(</span><span class="emphasis"><em>variable-type</em></span><span class="special">)</span> <span class="emphasis"><em>variable-name</em></span> <span class="comment">// Bind by value with explicit type.</span> |
| <span class="identifier">bind</span><span class="special">(</span><span class="emphasis"><em>variable-type</em></span><span class="special">)&</span> <span class="emphasis"><em>variable-name</em></span> <span class="comment">// Bind by reference with explicit type.</span> |
| <span class="keyword">const</span> <span class="identifier">bind</span><span class="special">(</span><span class="emphasis"><em>variable-type</em></span><span class="special">)</span> <span class="emphasis"><em>variable-name</em></span> <span class="comment">// Bind by constant value with explicit type.</span> |
| <span class="keyword">const</span> <span class="identifier">bind</span><span class="special">(</span><span class="emphasis"><em>variable-type</em></span><span class="special">)&</span> <span class="emphasis"><em>variable-name</em></span> <span class="comment">// Bind by constant reference with explicit type.</span> |
| <span class="identifier">bind</span><span class="special">(</span><span class="emphasis"><em>class-type</em></span><span class="special">*)</span> <span class="identifier">this_</span> <span class="comment">// Bind object `this` with explicit type.</span> |
| <span class="keyword">const</span> <span class="identifier">bind</span><span class="special">(</span><span class="emphasis"><em>class-type</em></span><span class="special">*)</span> <span class="identifier">this_</span> <span class="comment">// Bind object `this` by constant with explicit type.</span> |
| </pre> |
| <p> |
| Note that within the local function body it is always possible to abstract |
| the access to the type of a bound variable using <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_TYPEOF.html" title="Macro BOOST_LOCAL_FUNCTION_TYPEOF">BOOST_LOCAL_FUNCTION_TYPEOF</a></code> |
| (even when the bound variable type is explicitly specified in the local function |
| declaration). |
| </p> |
| <p> |
| The library also uses <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a> |
| to determine the local function result type (because this type is specified |
| outside the <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION.html" title="Macro BOOST_LOCAL_FUNCTION">BOOST_LOCAL_FUNCTION</a></code> |
| macro). Thus it is also possible to specify the local function result type |
| as one of the <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION.html" title="Macro BOOST_LOCAL_FUNCTION">BOOST_LOCAL_FUNCTION</a></code> |
| macro parameters prefixing it by <code class="computeroutput"><span class="keyword">return</span></code> |
| so the library will not use <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a> |
| to deduce the result type: |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_LOCAL_FUNCTION_TYPE</span><span class="special">(</span><span class="keyword">return</span> <code class="literal"><span class="emphasis"><em>result-type</em></span></code><span class="special">,</span> <span class="special">...)</span> |
| </pre> |
| <p> |
| Note that the result type must be specified only once either before the macro |
| (without the <code class="computeroutput"><span class="keyword">return</span></code> prefix) |
| or as one of the macro parameters (with the <code class="computeroutput"><span class="keyword">return</span></code> |
| prefix). As always, the result type can be <code class="computeroutput"><span class="keyword">void</span></code> |
| to declare a function that returns nothing (so <code class="computeroutput"><span class="keyword">return</span> |
| <span class="keyword">void</span></code> is allowed when the result type |
| is specified as one of the macro parameters). |
| </p> |
| <p> |
| The following example specifies all bound variables and result types (see |
| also <a href="../../../test/add_typed.cpp" target="_top"><code class="literal">add_typed.cpp</code></a>): |
| <sup>[<a name="boost_localfunction.advanced_topics.specifying_types__no_boost_typeof_.f0" href="#ftn.boost_localfunction.advanced_topics.specifying_types__no_boost_typeof_.f0" class="footnote">22</a>]</sup> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">adder</span> <span class="special">{</span> |
| <span class="identifier">adder</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">sum_</span><span class="special">(</span><span class="number">0</span><span class="special">)</span> <span class="special">{}</span> |
| |
| <span class="keyword">int</span> <span class="identifier">sum</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">>&</span> <span class="identifier">nums</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">)</span> <span class="special">{</span> |
| <span class="comment">// Explicitly specify bound variable and return types (no type-of).</span> |
| <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&)</span> <span class="identifier">factor</span><span class="special">,</span> |
| <span class="identifier">bind</span><span class="special">(</span><span class="identifier">adder</span><span class="special">*)</span> <span class="identifier">this_</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">,</span> <span class="keyword">return</span> <span class="keyword">int</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">this_</span><span class="special">-></span><span class="identifier">sum_</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">nums</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">add</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="identifier">sum_</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">private</span><span class="special">:</span> |
| <span class="keyword">int</span> <span class="identifier">sum_</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Unless necessary, it is recommended to not specify the bound variable and |
| result types. Let the library deduce these types so the local function syntax |
| will be more concise and the local function declaration will not have to |
| change if a bound variable type changes (reducing maintenance). |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| When all bound variable and result types are explicitly specified, the |
| library implementation will not use <a href="http://www.boost.org/libs/typeof" target="_top">Boost.Typeof</a>. |
| </p></td></tr> |
| </table></div> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_inlining"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.inlining"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.inlining" title="Inlining">Inlining</a> |
| </h3></div></div></div> |
| <p> |
| Local functions can be declared <a href="http://en.wikipedia.org/wiki/Inline_function" target="_top">inline</a> |
| to increase the chances that the compiler will be able to reduce the run-time |
| of the local function call by inlining the generated assembly code. A local |
| function is declared inline by prefixing its name with the keyword <code class="computeroutput"><span class="keyword">inline</span></code>: |
| </p> |
| <pre class="programlisting"><span class="emphasis"><em>result-type</em></span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="emphasis"><em>parameters</em></span><span class="special">)</span> <span class="special">{</span> |
| <span class="special">...</span> <span class="comment">// Body.</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="keyword">inline</span> <span class="emphasis"><em>name</em></span><span class="special">)</span> <span class="comment">// Inlining.</span> |
| </pre> |
| <p> |
| When inlining a local function, note the following: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| On <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| compliant compilers, inline local functions always have a run-time comparable |
| to their equivalent implementation that uses local functors (see the |
| <a class="link" href="alternatives.html" title="Annex: Alternatives">Alternatives</a> |
| section). However, inline local functions have the important limitation |
| that they cannot be assigned to other functors (like <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span></code>) |
| and they cannot be passed as template parameters. |
| </li> |
| <li class="listitem"> |
| On <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> |
| compilers, <code class="computeroutput"><span class="keyword">inline</span></code> has no |
| effect because this library will automatically generate code that uses |
| <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> specific |
| features to inline the local function calls whenever possible even if |
| the local function is not declared inline. Furthermore, non <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> |
| local functions can always be passes as template parameters even when |
| they are declared inline. <sup>[<a name="boost_localfunction.advanced_topics.inlining.f0" href="#ftn.boost_localfunction.advanced_topics.inlining.f0" class="footnote">23</a>]</sup> |
| </li> |
| </ul></div> |
| <div class="important"><table border="0" summary="Important"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td> |
| <th align="left">Important</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| It is recommended to not declare a local function inline unless it is strictly |
| necessary for optimizing pure <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| compliant code (because in all other cases this library will automatically |
| take advantage of <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> |
| features to optimize the local function calls while always allowing to |
| pass the local function as a template parameter). |
| </p></td></tr> |
| </table></div> |
| <p> |
| For example, the following local function is declared inline (thus a for-loop |
| needs to be used for portability instead of passing the local function as |
| a template parameter to the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span></code> |
| algorithm, see also <a href="../../../test/add_inline.cpp" target="_top"><code class="literal">add_inline.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> |
| |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">,</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">{</span> |
| <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="keyword">inline</span> <span class="identifier">add</span><span class="special">)</span> <span class="comment">// Inlining.</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="number">100</span><span class="special">);</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">fill</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="number">1</span><span class="special">);</span> |
| |
| <span class="keyword">for</span><span class="special">(</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">size</span><span class="special">();</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">add</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="identifier">i</span><span class="special">]);</span> <span class="comment">// Cannot use for_each.</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_recursion"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.recursion"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.recursion" title="Recursion">Recursion</a> |
| </h3></div></div></div> |
| <p> |
| Local functions can be declared <a href="http://en.wikipedia.org/wiki/Recursion_(computer_science)#Recursive_procedures" target="_top">recursive</a> |
| so a local function can recursively call itself from its body (as usual with |
| C++ functions). A local function is declared recursive by prefixing its name |
| with the <code class="computeroutput"><span class="identifier">recursive</span></code> "keyword" |
| (thus <code class="computeroutput"><span class="identifier">recursive</span></code> cannot be |
| used as a local function name): |
| </p> |
| <pre class="programlisting"><span class="emphasis"><em>result-type</em></span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="emphasis"><em>parameters</em></span><span class="special">)</span> <span class="special">{</span> |
| <span class="special">...</span> <span class="comment">// Body.</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">recursive</span> <span class="emphasis"><em>name</em></span><span class="special">)</span> <span class="comment">// Recursive.</span> |
| </pre> |
| <p> |
| For example, the following local function is used to recursively calculate |
| the factorials of all the numbers in the specified vector (see also <a href="../../../test/factorial.cpp" target="_top"><code class="literal">factorial.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">calculator</span> <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">results</span><span class="special">;</span> |
| |
| <span class="keyword">void</span> <span class="identifier">factorials</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">>&</span> <span class="identifier">nums</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="identifier">bind</span> <span class="identifier">this_</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">,</span> |
| <span class="keyword">bool</span> <span class="identifier">recursion</span><span class="special">,</span> <span class="keyword">default</span> <span class="keyword">false</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> |
| |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">num</span> <span class="special"><=</span> <span class="number">0</span><span class="special">)</span> <span class="identifier">result</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> |
| <span class="keyword">else</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">num</span> <span class="special">*</span> <span class="identifier">factorial</span><span class="special">(</span><span class="identifier">num</span> <span class="special">-</span> <span class="number">1</span><span class="special">,</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// Recursive call.</span> |
| |
| <span class="keyword">if</span><span class="special">(!</span><span class="identifier">recursion</span><span class="special">)</span> <span class="identifier">this_</span><span class="special">-></span><span class="identifier">results</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">result</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">recursive</span> <span class="identifier">factorial</span><span class="special">)</span> <span class="comment">// Recursive.</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">nums</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">factorial</span><span class="special">);</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Compilers have not been observed to be able to inline recursive local function |
| calls not even when the recursive local function is also declared inline: |
| </p> |
| <pre class="programlisting"><span class="special">...</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="keyword">inline</span> <span class="identifier">recursive</span> <span class="identifier">factorial</span><span class="special">)</span> |
| </pre> |
| <p> |
| Recursive local functions should never be called outside their declaration |
| scope. <sup>[<a name="boost_localfunction.advanced_topics.recursion.f0" href="#ftn.boost_localfunction.advanced_topics.recursion.f0" class="footnote">24</a>]</sup> |
| </p> |
| <div class="warning"><table border="0" summary="Warning"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td> |
| <th align="left">Warning</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| If a local function is returned from the enclosing function and called |
| in a different scope, the behaviour is undefined (and it will likely result |
| in a run-time error). |
| </p></td></tr> |
| </table></div> |
| <p> |
| This is not a limitation with respect to <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a> because lambdas can never call themselves recursively |
| (in other words, there is no recursive lambda function that can successfully |
| be called outside its declaration scope because there is no recursive lambda |
| function at all). |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_overloading"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.overloading"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.overloading" title="Overloading">Overloading</a> |
| </h3></div></div></div> |
| <p> |
| Because local functions are functors, it is possible to overload them using |
| the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">overloaded_function</span></code> functor of <a href="http://www.boost.org/libs/functional/overloaded_function" target="_top">Boost.Functional/OverloadedFunction</a> |
| from the <code class="literal">boost/functional/overloaded_function.hpp</code> header |
| (see the <a href="http://www.boost.org/libs/functional/overloaded_function" target="_top">Boost.Functional/OverloadedFunction</a> |
| documentation for details). |
| </p> |
| <p> |
| In the following example, the overloaded function object <code class="computeroutput"><span class="identifier">add</span></code> |
| can be called with signatures from either the local function <code class="computeroutput"><span class="identifier">add_s</span></code>, or the local function <code class="computeroutput"><span class="identifier">add_d</span></code>, or the local function <code class="computeroutput"><span class="identifier">add_d</span></code> with its extra default parameter, |
| or the function pointer <code class="computeroutput"><span class="identifier">add_i</span></code> |
| (see also <a href="../../../test/overload.cpp" target="_top"><code class="literal">overload.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">add_i</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">y</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">;</span> <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">s</span> <span class="special">=</span> <span class="string">"abc"</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> |
| <span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">s</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">s</span> <span class="special">+</span> <span class="identifier">x</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add_s</span><span class="special">)</span> |
| |
| <span class="keyword">double</span> <span class="identifier">d</span> <span class="special">=</span> <span class="number">1.23</span><span class="special">;</span> |
| <span class="keyword">double</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">d</span><span class="special">,</span> <span class="keyword">double</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">double</span> <span class="identifier">y</span><span class="special">,</span> <span class="keyword">default</span> <span class="number">0</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">d</span> <span class="special">+</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add_d</span><span class="special">)</span> |
| |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">overloaded_function</span><span class="special"><</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&)</span> |
| <span class="special">,</span> <span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">)</span> |
| <span class="special">,</span> <span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">double</span><span class="special">)</span> <span class="comment">// Overload giving default param.</span> |
| <span class="special">,</span> <span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)</span> |
| <span class="special">></span> <span class="identifier">add</span><span class="special">(</span><span class="identifier">add_s</span><span class="special">,</span> <span class="identifier">add_d</span><span class="special">,</span> <span class="identifier">add_d</span><span class="special">,</span> <span class="identifier">add_i</span><span class="special">);</span> <span class="comment">// Overloaded function object.</span> |
| |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">add</span><span class="special">(</span><span class="string">"xyz"</span><span class="special">)</span> <span class="special">==</span> <span class="string">"abcxyz"</span><span class="special">);</span> <span class="comment">// Call `add_s`.</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">((</span><span class="number">4.44</span> <span class="special">-</span> <span class="identifier">add</span><span class="special">(</span><span class="number">3.21</span><span class="special">))</span> <span class="special"><=</span> <span class="number">0.001</span><span class="special">);</span> <span class="comment">// Call `add_d` (no default).</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">((</span><span class="number">44.44</span> <span class="special">-</span> <span class="identifier">add</span><span class="special">(</span><span class="number">3.21</span><span class="special">,</span> <span class="number">40.0</span><span class="special">))</span> <span class="special"><=</span> <span class="number">0.001</span><span class="special">);</span> <span class="comment">// Call `add_d`.</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">)</span> <span class="special">==</span> <span class="number">3</span><span class="special">);</span> <span class="comment">// Call `add_i`.</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_exception_specifications"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.exception_specifications"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.exception_specifications" title="Exception Specifications">Exception |
| Specifications</a> |
| </h3></div></div></div> |
| <p> |
| It is possible to program exception specifications for local functions by |
| specifying them after the <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION.html" title="Macro BOOST_LOCAL_FUNCTION">BOOST_LOCAL_FUNCTION</a></code> |
| macro and before the body code block <code class="computeroutput"><span class="special">{</span> |
| <span class="special">...</span> <span class="special">}</span></code>. |
| </p> |
| <div class="important"><table border="0" summary="Important"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td> |
| <th align="left">Important</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Note that the exception specifications only apply to the body code specified |
| by programmers and they do not apply to the rest of the code automatically |
| generated by the macro expansions to implement local functions. For example, |
| even if the body code is specified to throw no exception using <code class="computeroutput"><span class="keyword">throw</span> <span class="special">()</span> <span class="special">{</span> <span class="special">...</span> <span class="special">}</span></code>, |
| the execution of the library code automatically generated by the macros |
| could still throw (if there is no memory, etc). |
| </p></td></tr> |
| </table></div> |
| <p> |
| For example (see also <a href="../../../test/add_except.cpp" target="_top"><code class="literal">add_except.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">double</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0.0</span><span class="special">;</span> |
| <span class="keyword">int</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> |
| |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">,</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">,</span> |
| <span class="keyword">double</span> <span class="identifier">num</span><span class="special">)</span> <span class="keyword">throw</span><span class="special">()</span> <span class="special">{</span> <span class="comment">// Throw nothing.</span> |
| <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> |
| |
| <span class="identifier">add</span><span class="special">(</span><span class="number">100</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_storage_classifiers"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.storage_classifiers"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.storage_classifiers" title="Storage Classifiers">Storage |
| Classifiers</a> |
| </h3></div></div></div> |
| <p> |
| Local function parameters support the storage classifiers as usual in <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a>. |
| The <code class="computeroutput"><span class="keyword">auto</span></code> storage classifier |
| is specified as: <sup>[<a name="boost_localfunction.advanced_topics.storage_classifiers.f0" href="#ftn.boost_localfunction.advanced_topics.storage_classifiers.f0" class="footnote">25</a>]</sup> |
| </p> |
| <pre class="programlisting"><span class="keyword">auto</span> <span class="emphasis"><em>parameter-type parameter-name</em></span> |
| </pre> |
| <p> |
| The <code class="computeroutput"><span class="keyword">register</span></code> storage classifier |
| is specified as: |
| </p> |
| <pre class="programlisting"><span class="keyword">register</span> <span class="emphasis"><em>parameter-type parameter-name</em></span> |
| </pre> |
| <p> |
| For example (see also <a href="../../../test/add_classifiers.cpp" target="_top"><code class="literal">add_classifiers.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">auto</span> <span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">register</span> <span class="keyword">int</span> <span class="identifier">y</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Classifiers.</span> |
| <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_same_line_expansions"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.same_line_expansions"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.same_line_expansions" title="Same Line Expansions">Same |
| Line Expansions</a> |
| </h3></div></div></div> |
| <p> |
| In general, it is not possible to expand the <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION.html" title="Macro BOOST_LOCAL_FUNCTION">BOOST_LOCAL_FUNCTION</a></code>, |
| <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_TPL">BOOST_LOCAL_FUNCTION_TPL</a></code> |
| macros multiple times on the same line. <sup>[<a name="boost_localfunction.advanced_topics.same_line_expansions.f0" href="#ftn.boost_localfunction.advanced_topics.same_line_expansions.f0" class="footnote">26</a>]</sup> |
| </p> |
| <p> |
| Therefore, this library provides additional macros <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_ID.html" title="Macro BOOST_LOCAL_FUNCTION_ID">BOOST_LOCAL_FUNCTION_ID</a></code> |
| and <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_ID_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_ID_TPL">BOOST_LOCAL_FUNCTION_ID_TPL</a></code> |
| which can be expanded multiple times on the same line as long as programmers |
| specify unique identifiers as the macros' first parameters. The unique identifier |
| can be any token (not just numeric) that can be successfully concatenated |
| by the preprocessor (e.g., <code class="computeroutput"><span class="identifier">local_function_number_1_at_line_123</span></code>). |
| <sup>[<a name="boost_localfunction.advanced_topics.same_line_expansions.f1" href="#ftn.boost_localfunction.advanced_topics.same_line_expansions.f1" class="footnote">27</a>]</sup> |
| </p> |
| <p> |
| The <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_ID.html" title="Macro BOOST_LOCAL_FUNCTION_ID">BOOST_LOCAL_FUNCTION_ID</a></code> |
| and <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_ID_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_ID_TPL">BOOST_LOCAL_FUNCTION_ID_TPL</a></code> |
| macros accept local function parameter declaration lists using the exact |
| same syntax as <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION.html" title="Macro BOOST_LOCAL_FUNCTION">BOOST_LOCAL_FUNCTION</a></code>. |
| For example (see also <a href="../../../test/same_line.cpp" target="_top"><code class="literal">same_line.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">LOCAL_INC_DEC</span><span class="special">(</span><span class="identifier">offset</span><span class="special">)</span> <span class="special">\</span> |
| <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION_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> |
| <span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">offset</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span> |
| <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">inc</span><span class="special">)</span> <span class="special">\</span> |
| <span class="special">\</span> |
| <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION_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> |
| <span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">offset</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span> |
| <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">-</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">dec</span><span class="special">)</span> |
| |
| <span class="preprocessor">#define</span> <span class="identifier">LOCAL_INC_DEC_TPL</span><span class="special">(</span><span class="identifier">offset</span><span class="special">)</span> <span class="special">\</span> |
| <span class="identifier">T</span> <span class="identifier">BOOST_LOCAL_FUNCTION_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> |
| <span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">offset</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span> |
| <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME_TPL</span><span class="special">(</span><span class="identifier">inc</span><span class="special">)</span> <span class="special">\</span> |
| <span class="special">\</span> |
| <span class="identifier">T</span> <span class="identifier">BOOST_LOCAL_FUNCTION_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> |
| <span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">offset</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="special">\</span> |
| <span class="keyword">return</span> <span class="identifier">x</span> <span class="special">-</span> <span class="identifier">offset</span><span class="special">;</span> <span class="special">\</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME_TPL</span><span class="special">(</span><span class="identifier">dec</span><span class="special">)</span> |
| |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">delta</span><span class="special">)</span> <span class="special">{</span> |
| <span class="identifier">LOCAL_INC_DEC_TPL</span><span class="special">(</span><span class="identifier">delta</span><span class="special">)</span> <span class="comment">// Multiple local functions on same line.</span> |
| <span class="comment">/** @todo back to BOOST_TEST(dec(inc(123)) == 123)) and doc that on vacpp compiler composition doesn't work */</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">inc</span><span class="special">(</span><span class="number">123</span><span class="special">)</span> <span class="special">==</span> <span class="number">123</span> <span class="special">+</span> <span class="identifier">delta</span><span class="special">);</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">dec</span><span class="special">(</span><span class="number">123</span><span class="special">)</span> <span class="special">==</span> <span class="number">123</span> <span class="special">-</span> <span class="identifier">delta</span><span class="special">);</span> |
| <span class="special">}</span> |
| |
| <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> |
| <span class="keyword">int</span> <span class="identifier">delta</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> |
| |
| <span class="identifier">LOCAL_INC_DEC</span><span class="special">(</span><span class="identifier">delta</span><span class="special">)</span> <span class="comment">// Multiple local functions on same line.</span> |
| <span class="comment">/** @todo back to BOOST_TEST(dec(inc(123)) == 123)) and doc that on vacpp compiler composition doesn't work */</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">inc</span><span class="special">(</span><span class="number">123</span><span class="special">)</span> <span class="special">==</span> <span class="number">123</span> <span class="special">+</span> <span class="identifier">delta</span><span class="special">);</span> |
| <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">dec</span><span class="special">(</span><span class="number">123</span><span class="special">)</span> <span class="special">==</span> <span class="number">123</span> <span class="special">-</span> <span class="identifier">delta</span><span class="special">);</span> |
| |
| <span class="identifier">f</span><span class="special">(</span><span class="identifier">delta</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| As shown by the example above, the <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_ID.html" title="Macro BOOST_LOCAL_FUNCTION_ID">BOOST_LOCAL_FUNCTION_ID</a></code> |
| and <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_ID_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_ID_TPL">BOOST_LOCAL_FUNCTION_ID_TPL</a></code> |
| macros are especially useful when it is necessary to invoke them multiple |
| times within a user-defined macro (because the preprocessor expands all nested |
| macros on the same line). |
| </p> |
| </div> |
| <div class="section boost_localfunction_advanced_topics_limitations__operators__etc_"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_localfunction.advanced_topics.limitations__operators__etc_"></a><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.limitations__operators__etc_" title="Limitations (operators, etc)">Limitations |
| (operators, etc)</a> |
| </h3></div></div></div> |
| <p> |
| The following table summarizes all C++ function features indicating those |
| features that are not supported by this library for local functions. |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| C++ Function Feature |
| </p> |
| </th> |
| <th> |
| <p> |
| Local Function Support |
| </p> |
| </th> |
| <th> |
| <p> |
| Comment |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">export</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| No. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is not supported because local functions cannot be templates |
| (plus most C++ compilers do not implement <code class="computeroutput"><span class="keyword">export</span></code> |
| at all). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span></code><code class="literal"><span class="emphasis"><em>template-parameter-list</em></span></code><code class="computeroutput"><span class="special">></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| No. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is not supported because local functions are implemented using |
| local classes and <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| local classes cannot be templates. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">explicit</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| No. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is not supported because local functions are not constructors. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">inline</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Yes. |
| </p> |
| </td> |
| <td> |
| <p> |
| Local functions can be specified <code class="computeroutput"><span class="keyword">inline</span></code> |
| to improve the chances that <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| compilers can optimize the local function call run-time (but <code class="computeroutput"><span class="keyword">inline</span></code> local functions cannot be |
| passed as template parameters on <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| compilers, see the <a class="link" href="advanced_topics.html" title="Advanced Topics">Advanced |
| Topics</a> section). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">extern</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| No. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is not supported because local functions are always defined |
| locally within the enclosing scope and together with their declarations. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">static</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| No. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is not supported because local functions are not member functions. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">virtual</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| No. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is not supported because local functions are not member functions. |
| <sup>[<a name="boost_localfunction.advanced_topics.limitations__operators__etc_.f0" href="#ftn.boost_localfunction.advanced_topics.limitations__operators__etc_.f0" class="footnote">a</a>]</sup> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="literal"><span class="emphasis"><em>result-type</em></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Yes. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is supported (see the <a class="link" href="tutorial.html" title="Tutorial">Tutorial</a> |
| section). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="literal"><span class="emphasis"><em>function-name</em></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Yes. |
| </p> |
| </td> |
| <td> |
| <p> |
| Local functions are named and they can call themselves recursively |
| but they cannot be operators (see the <a class="link" href="tutorial.html" title="Tutorial">Tutorial</a> |
| and <a class="link" href="advanced_topics.html" title="Advanced Topics">Advanced |
| Topics</a> sections). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="literal"><span class="emphasis"><em>parameter-list</em></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Yes. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is supported and it also supports the <code class="computeroutput"><span class="keyword">auto</span></code> |
| and <code class="computeroutput"><span class="keyword">register</span></code> storage |
| classifiers, default parameters, and binding of variables in scope |
| (see the <a class="link" href="tutorial.html" title="Tutorial">Tutorial</a> |
| and <a class="link" href="advanced_topics.html" title="Advanced Topics">Advanced |
| Topics</a> sections). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| Trailing <code class="computeroutput"><span class="keyword">const</span></code> qualifier |
| </p> |
| </td> |
| <td> |
| <p> |
| No. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is not supported because local functions are not member functions. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| Trailing <code class="computeroutput"><span class="keyword">volatile</span></code> |
| qualifier |
| </p> |
| </td> |
| <td> |
| <p> |
| No. |
| </p> |
| </td> |
| <td> |
| <p> |
| This is not supported because local functions are not member functions. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| <tbody class="footnotes"><tr><td colspan="3"><div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.limitations__operators__etc_.f0" href="#boost_localfunction.advanced_topics.limitations__operators__etc_.f0" class="para">a</a>] </sup> |
| <span class="bold"><strong>Rationale.</strong></span> It would be possible |
| to make a local function class inherit from another local function |
| class. However, this "inheritance" feature is not implemented |
| because it seemed of <a href="http://lists.boost.org/Archives/boost/2010/09/170895.php" target="_top">no |
| use</a> given that local functions can be bound to one another |
| thus they can simply call each other directly without recurring |
| to dynamic binding or base function calls. |
| </p></div></td></tr></tbody> |
| </table></div> |
| <h5> |
| <a name="boost_localfunction.advanced_topics.limitations__operators__etc_.h0"></a> |
| <span><a name="boost_localfunction.advanced_topics.limitations__operators__etc_.operators"></a></span><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.limitations__operators__etc_.operators">Operators</a> |
| </h5> |
| <p> |
| Local functions cannot be operators. Naming a local function <code class="computeroutput"><span class="keyword">operator</span><span class="special">...</span></code> |
| will generate a compile-time error. <sup>[<a name="boost_localfunction.advanced_topics.limitations__operators__etc_.f1" href="#ftn.boost_localfunction.advanced_topics.limitations__operators__etc_.f1" class="footnote">28</a>]</sup> |
| </p> |
| <p> |
| For example, the following code does not compile (see also <a href="../../../test/operator_error.cpp" target="_top"><code class="literal">operator_error.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">bool</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">point</span><span class="special">&</span> <span class="identifier">p</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">point</span><span class="special">&</span> <span class="identifier">q</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">x</span> <span class="special">==</span> <span class="identifier">q</span><span class="special">.</span><span class="identifier">x</span> <span class="special">&&</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">y</span> <span class="special">==</span> <span class="identifier">q</span><span class="special">.</span><span class="identifier">y</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="keyword">operator</span><span class="special">==)</span> <span class="comment">// Error: Cannot use `operator...`.</span> |
| </pre> |
| <p> |
| </p> |
| <h5> |
| <a name="boost_localfunction.advanced_topics.limitations__operators__etc_.h1"></a> |
| <span><a name="boost_localfunction.advanced_topics.limitations__operators__etc_.goto"></a></span><a class="link" href="advanced_topics.html#boost_localfunction.advanced_topics.limitations__operators__etc_.goto">Goto</a> |
| </h5> |
| <p> |
| It is possible to jump with a <code class="computeroutput"><span class="keyword">goto</span></code> |
| within the local function body. For example, the following compiles (see |
| also <a href="../../../test/goto.cpp" target="_top"><code class="literal">goto.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">error</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">y</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">z</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">z</span> <span class="special">></span> <span class="number">0</span><span class="special">)</span> <span class="keyword">goto</span> <span class="identifier">success</span><span class="special">;</span> <span class="comment">// OK: Can jump within local function.</span> |
| <span class="keyword">return</span> <span class="special">-</span><span class="number">1</span><span class="special">;</span> |
| <span class="identifier">success</span><span class="special">:</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">validate</span><span class="special">)</span> |
| |
| <span class="keyword">return</span> <span class="identifier">validate</span><span class="special">(</span><span class="identifier">x</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">);</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| However, it is not possible to jump with a <code class="computeroutput"><span class="keyword">goto</span></code> |
| from within the local function body to to a label defined in the enclosing |
| scope. For example, the following does not compile (see also <a href="../../../test/goto_error.cpp" target="_top"><code class="literal">goto_error.cpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">error</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">y</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">z</span><span class="special">)</span> <span class="special">{</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">z</span> <span class="special"><=</span> <span class="number">0</span><span class="special">)</span> <span class="keyword">goto</span> <span class="identifier">failure</span><span class="special">;</span> <span class="comment">// Error: Cannot jump to enclosing scope.</span> |
| <span class="keyword">else</span> <span class="keyword">goto</span> <span class="identifier">success</span><span class="special">;</span> <span class="comment">// OK: Can jump within local function.</span> |
| <span class="identifier">success</span><span class="special">:</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">validate</span><span class="special">)</span> |
| |
| <span class="keyword">return</span> <span class="identifier">validate</span><span class="special">(</span><span class="identifier">x</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">);</span> |
| <span class="identifier">failure</span><span class="special">:</span> |
| <span class="keyword">return</span> <span class="special">-</span><span class="number">1</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| <div class="footnotes"> |
| <br><hr width="100" align="left"> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.default_parameters.f0" href="#boost_localfunction.advanced_topics.default_parameters.f0" class="para">17</a>] </sup> |
| <span class="bold"><strong>Rationale.</strong></span> The assignment symbol <code class="computeroutput"><span class="special">=</span></code> cannot be used to specify default parameter |
| values because default values are not part of the parameter type so they |
| cannot be handled using template meta-programming. Default parameter values |
| need to be separated from the rest of the parameter declaration using the |
| preprocessor. Specifically, this library needs to use preprocessor meta-programming |
| to remove default values when constructing the local function type and |
| also to count the number of default values to provide the correct set of |
| call operators for the local functor. Therefore, the symbol <code class="computeroutput"><span class="special">=</span></code> cannot be used because it cannot be handled |
| by preprocessor meta-programming (non-alphanumeric symbols cannot be detected |
| by preprocessor meta-programming because they cannot be concatenated by |
| the preprocessor). |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.default_parameters.f1" href="#boost_localfunction.advanced_topics.default_parameters.f1" class="para">18</a>] </sup> |
| The authors do not personally find the use of the <code class="computeroutput"><span class="identifier">WITH_DEFAULT</span></code> |
| macro more readable and they prefer to use the <code class="computeroutput"><span class="keyword">default</span></code> |
| keyword directly. Furthermore, <code class="computeroutput"><span class="identifier">WITH_DEFAULT</span></code> |
| needs to be defined differently for compilers without variadic macros |
| <code class="computeroutput"><span class="preprocessor">#define</span> <span class="identifier">WITH_DEFAULT</span> |
| <span class="special">(</span><span class="keyword">default</span><span class="special">)</span></code> so it can only be defined by programmers |
| based on the syntax they decide to use (see the <a class="link" href="no_variadic_macros.html" title="Annex: No Variadic Macros">No |
| Variadic Macros</a> section). |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.commas_and_symbols_in_macros.f0" href="#boost_localfunction.advanced_topics.commas_and_symbols_in_macros.f0" class="para">19</a>] </sup> |
| <span class="bold"><strong>Rationale.</strong></span> This limitation is because |
| this library uses preprocessor token concatenation <code class="literal">##</code> |
| to inspect the macro parameters (to distinguish between function parameters, |
| bound variables, etc) and the C++ preprocessor does not allow to concatenate |
| non-alphanumeric tokens. |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.commas_and_symbols_in_macros.f1" href="#boost_localfunction.advanced_topics.commas_and_symbols_in_macros.f1" class="para">20</a>] </sup> |
| The preprocessor always interprets unwrapped commas as separating macro |
| parameters. Thus in this case the comma will indicate to the preprocessor |
| that the first macro parameter is <code class="computeroutput"><span class="keyword">const</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">tring</span></code>, the second macro parameter is |
| <code class="computeroutput"><span class="identifier">size_t</span><span class="special">>&</span> |
| <span class="identifier">m</span></code>, etc instead of passing <code class="computeroutput"><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">>&</span> <span class="identifier">m</span></code> |
| as a single macro parameter. |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.accessing_types__concepts__etc_.f0" href="#boost_localfunction.advanced_topics.accessing_types__concepts__etc_.f0" class="para">21</a>] </sup> |
| <span class="bold"><strong>Rationale.</strong></span> The type names <code class="computeroutput"><span class="identifier">result_type</span></code> and <code class="computeroutput"><span class="identifier">arg</span></code><code class="literal"><span class="emphasis"><em>N</em></span></code><code class="computeroutput"><span class="identifier">_type</span></code> follow the <a href="http://www.boost.org/libs/type_traits" target="_top">Boost.TypeTraits</a> |
| naming conventions for function traits. |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.specifying_types__no_boost_typeof_.f0" href="#boost_localfunction.advanced_topics.specifying_types__no_boost_typeof_.f0" class="para">22</a>] </sup> |
| In the examples of this documentation, bound variables, function parameters, |
| and the result type are specified in this order because this is the order |
| used by <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a>. However, the library accepts bound variables, |
| function parameters, and the result type in any order. |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.inlining.f0" href="#boost_localfunction.advanced_topics.inlining.f0" class="para">23</a>] </sup> |
| <span class="bold"><strong>Rationale.</strong></span> This library uses an indirect |
| function call via a function pointer in order to pass the local function |
| as a template parameter (see the <a class="link" href="implementation.html" title="Annex: Implementation">Implementation</a> |
| section). No compiler has yet been observed to be able to inline function |
| calls when they use such indirect function pointer calls. Therefore, |
| inline local functions do not use such indirect function pointer call |
| (so they are more likely to be optimized) but because of that they |
| cannot be passed as template parameters. The indirect function pointer |
| call is needed on <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| but it is not needed on <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> |
| (see <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm" target="_top">[N2657]</a> |
| and <a href="http://www.boost.org/libs/chrono" target="_top">Boost.Config</a>'s |
| <code class="computeroutput"><span class="identifier">BOOST_NO_LOCAL_CLASS_TEMPLATE_PARAMETERS</span></code>) |
| thus this library automatically generates local function calls that |
| can be inline on <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> |
| compilers (even when the local function is not declared inline). |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.recursion.f0" href="#boost_localfunction.advanced_topics.recursion.f0" class="para">24</a>] </sup> |
| <span class="bold"><strong>Rationale.</strong></span> This limitation comes from |
| the fact that the global functor used to pass the local function as a template |
| parameter (and eventually returned outside the declarations scope) does |
| not know the local function name so the local function name used for recursive |
| call cannot be set in the global functor. This limitation together with |
| preventing the possibility for inlining are the reasons why local functions |
| are not recursive unless programmers explicitly declare them <code class="computeroutput"><span class="identifier">recursive</span></code>. |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.storage_classifiers.f0" href="#boost_localfunction.advanced_topics.storage_classifiers.f0" class="para">25</a>] </sup> |
| The <code class="computeroutput"><span class="keyword">auto</span></code> storage classifier |
| is part of the <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| standard and therefore supported by this library. However, the meaning |
| and usage of the <code class="computeroutput"><span class="keyword">auto</span></code> keyword |
| changed in <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a>. |
| Therefore, use the <code class="computeroutput"><span class="keyword">auto</span></code> storage |
| classifier with the usual care in order to avoid writing <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> |
| code that might not work on <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a>. |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.same_line_expansions.f0" href="#boost_localfunction.advanced_topics.same_line_expansions.f0" class="para">26</a>] </sup> |
| <span class="bold"><strong>Rationale.</strong></span> The <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION.html" title="Macro BOOST_LOCAL_FUNCTION">BOOST_LOCAL_FUNCTION</a></code> |
| and <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_TPL">BOOST_LOCAL_FUNCTION_TPL</a></code> |
| macros internally use <code class="computeroutput"><span class="identifier">__LINE__</span></code> |
| to generate unique identifiers. Therefore, if these macros are expanded |
| more than on time on the same line, the generated identifiers will no longer |
| be unique and the code will not compile. (This restriction does not apply |
| to MSVC and other compilers that provide the non-standard <code class="computeroutput"><span class="identifier">__COUNTER__</span></code> macro.) Note that the <code class="computeroutput"><a class="link" href="../BOOST_LOCAL_FUNCTION_NAME.html" title="Macro BOOST_LOCAL_FUNCTION_NAME">BOOST_LOCAL_FUNCTION_NAME</a></code> macro |
| can always be expanded multiple times on the same line because the unique |
| local function name (and not <code class="computeroutput"><span class="identifier">__LINE__</span></code>) |
| is used by this macro to generate unique identifiers (so there is no need |
| for a <code class="computeroutput"><span class="identifier">BOOST_LOCAL_FUNCTION_NAME_ID</span></code> |
| macro). |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.same_line_expansions.f1" href="#boost_localfunction.advanced_topics.same_line_expansions.f1" class="para">27</a>] </sup> |
| Because there are restrictions on the set of tokens that the preprocessor |
| can concatenate and because not all compilers correctly implement these |
| restrictions, it is in general recommended to specify unique identifiers |
| as a combination of alphanumeric tokens. |
| </p></div> |
| <div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.advanced_topics.limitations__operators__etc_.f1" href="#boost_localfunction.advanced_topics.limitations__operators__etc_.f1" class="para">28</a>] </sup> |
| <span class="bold"><strong>Rationale.</strong></span> This is the because a local |
| function name must be a valid local variable name (the local variable used |
| to hold the local functor) and operators cannot be used as local variable |
| names. |
| </p></div> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2009-2012 Lorenzo |
| Caminiti<p> |
| Distributed under the Boost Software License, Version 1.0 (see accompanying |
| 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>) |
| </p> |
| </div></td> |
| </tr></table> |
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