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<title>Macro BOOST_LOCAL_FUNCTION</title>
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<h2><span class="refentrytitle">Macro BOOST_LOCAL_FUNCTION</span></h2>
<p>BOOST_LOCAL_FUNCTION &#8212; This macro is used to start a local function declaration. </p>
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<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="reference.html#header.boost.local_function_hpp" title="Header &lt;boost/local_function.hpp&gt;">boost/local_function.hpp</a>&gt;

</span>BOOST_LOCAL_FUNCTION(declarations)</pre></div>
<div class="refsect1">
<a name="id903895"></a><h2>Description</h2>
<p>This macro must be used within a declarative context, it must follow the local function result type, it must be followed by the local function body code, and then by 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 (see the  <a class="link" href="boost_localfunction/tutorial.html" title="Tutorial"> Tutorial</a> and <a class="link" href="boost_localfunction/advanced_topics.html" title="Advanced Topics"> Advanced Topics</a> sections): </p>
<pre class="programlisting"><span class="special">{</span> <span class="comment">// Some declarative context.</span>
    <span class="special">...</span>
    <span class="identifier">result_type</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="identifier">declarations</span><span class="special">)</span> <span class="special">{</span>
        <span class="special">...</span> <span class="comment">// Body code.</span>
    <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">qualified_name</span><span class="special">)</span>
    <span class="special">...</span>
<span class="special">}</span>
</pre>
<p>As usual, exceptions specifications can be optionally programmed just after the macro and before the body code block <code class="computeroutput">{ ... }</code> (but the exception specifications will only apply to the body code and not to the library code automatically generated by the macro expansion, see the  <a class="link" href="boost_localfunction/advanced_topics.html" title="Advanced Topics"> Advanced Topics</a> section).</p>
<p>Within templates, the special macros <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_TPL">BOOST_LOCAL_FUNCTION_TPL</a></code> and <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_NAME_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_NAME_TPL">BOOST_LOCAL_FUNCTION_NAME_TPL</a></code> must be used.</p>
<p><span class="bold"><strong>Parameters:</strong></span> </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<tbody><tr>
<td><span class="bold"><strong><code class="computeroutput">declarations</code></strong></span></td>
<td>On compilers that support variadic macros, the parameter declarations are defined by the following grammar: <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">declarations</span><span class="special">:</span>
        <span class="keyword">void</span> <span class="special">|</span> <span class="identifier">declaration_tuple</span> <span class="special">|</span> <span class="identifier">declaration_sequence</span>
<span class="identifier">declaration_tuple</span><span class="special">:</span>
        <span class="identifier">declaration</span><span class="special">,</span> <span class="identifier">declaration</span><span class="special">,</span> <span class="special">...</span>
<span class="identifier">declaration_sequence</span><span class="special">:</span>
        <span class="special">(</span><span class="identifier">declaration</span><span class="special">)</span> <span class="special">(</span><span class="identifier">declaration</span><span class="special">)</span> <span class="special">...</span>
<span class="identifier">declaration</span><span class="special">:</span>
        <span class="identifier">bound_variable</span> <span class="special">|</span> <span class="identifier">parameter</span> <span class="special">|</span> <span class="identifier">default_value</span> <span class="special">|</span> <span class="identifier">result_type</span>
<span class="identifier">bound_variable</span><span class="special">:</span>
        <span class="special">[</span><span class="keyword">const</span><span class="special">]</span> <span class="identifier">bind</span> <span class="special">[</span><span class="special">(</span><span class="identifier">variable_type</span><span class="special">)</span><span class="special">]</span> <span class="special">[</span><span class="special">&amp;</span><span class="special">]</span> <span class="identifier">variable_name</span>
<span class="identifier">parameter</span><span class="special">:</span>
        <span class="special">[</span><span class="keyword">auto</span> <span class="special">|</span> <span class="keyword">register</span><span class="special">]</span> <span class="identifier">parameter_type</span> <span class="identifier">parameter_name</span>
<span class="identifier">default_value</span><span class="special">:</span>
        <span class="keyword">default</span> <span class="identifier">parameter_default_value</span>
<span class="identifier">result_type</span><span class="special">:</span>
        <span class="keyword">return</span> <span class="identifier">function_result_type</span>
</pre> On compilers that do not support variadic macros, <code class="computeroutput">declaration_tuple</code> cannot be used: <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">declarations</span><span class="special">:</span>
        <span class="keyword">void</span> <span class="special">|</span> <span class="identifier">declaration_sequence</span>
</pre>(Lexical conventions: <code class="computeroutput">token1 | token2</code> means either <code class="computeroutput">token1</code> or <code class="computeroutput">token2</code>; <code class="computeroutput">[token]</code> means either <code class="computeroutput">token</code> or nothing; <code class="computeroutput">{expression}</code> means the token resulting from the expression.)  </td>
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<p>
</p>
<p>Note that on compilers that support variadic macros, commas can be used to separate the declarations resembling more closely the usual C++ function declaration syntax (this is the preferred syntax). However, for portability, on all C++ compilers (with and without variadic macros) the same library macros also accept parameter declarations specified as a Boost.Preprocessor sequence separated by round parenthesis <code class="computeroutput">()</code>.</p>
<p>When binding the object <code class="computeroutput">this</code>, the special symbol <code class="computeroutput">this_</code> needs to be used instead of <code class="computeroutput">this</code> as the name of the variable to bind and also within the local function body to access the object. (Mistakenly using <code class="computeroutput">this</code> instead of <code class="computeroutput">this_</code> might not always result in a compiler error and will in general result in undefined behaviour.)</p>
<p>The result type must either be specified just before the macro or within the macro declarations prefixed by <code class="computeroutput">return</code> (but not in both places).</p>
<p>Within the local function body it possible to access the result type using <code class="computeroutput">result_type</code>, the type of the first parameter using <code class="computeroutput">arg1_type</code>, the type of the second parameter using <code class="computeroutput">arg2_type</code>, etc. The bound variable types can be accessed 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>.</p>
<p>This macro cannot be portably expanded multiple times on the same line. In these cases, use 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> macro instead.</p>
<p>The maximum number of local function parameters (excluding bound variables) is specified by the configuration macro  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_CONFIG_ARITY_MAX.html" title="Macro BOOST_LOCAL_FUNCTION_CONFIG_ARITY_MAX">BOOST_LOCAL_FUNCTION_CONFIG_ARITY_MAX</a></code>. The maximum number of bound variables is specified by the configuration macro  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_CONFIG_BIND_MAX.html" title="Macro BOOST_LOCAL_FUNCTION_CONFIG_BIND_MAX">BOOST_LOCAL_FUNCTION_CONFIG_BIND_MAX</a></code>. The configuration macro  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_CONFIG_LOCALS_AS_TPARAMS.html" title="Macro BOOST_LOCAL_FUNCTION_CONFIG_LOCALS_AS_TPARAMS">BOOST_LOCAL_FUNCTION_CONFIG_LOCALS_AS_TPARAMS</a></code> can be used to force optimizations that reduce the local function call run-time overhead.</p>
<p><span class="bold"><strong>Note:</strong></span> Local functions are functors so they can be assigned to other functors like <code class="computeroutput">boost::function</code> (see Boost.Function).</p>
<p><span class="bold"><strong>See:</strong></span> <a class="link" href="boost_localfunction/tutorial.html" title="Tutorial"> Tutorial</a> section,  <a class="link" href="boost_localfunction/advanced_topics.html" title="Advanced Topics"> Advanced Topics</a> section,  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_NAME.html" title="Macro BOOST_LOCAL_FUNCTION_NAME">BOOST_LOCAL_FUNCTION_NAME</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>,  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_NAME_TPL.html" title="Macro BOOST_LOCAL_FUNCTION_NAME_TPL">BOOST_LOCAL_FUNCTION_NAME_TPL</a></code>,  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_TYPEOF.html" title="Macro BOOST_LOCAL_FUNCTION_TYPEOF">BOOST_LOCAL_FUNCTION_TYPEOF</a></code>, <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_ID.html" title="Macro BOOST_LOCAL_FUNCTION_ID">BOOST_LOCAL_FUNCTION_ID</a></code>,  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_CONFIG_ARITY_MAX.html" title="Macro BOOST_LOCAL_FUNCTION_CONFIG_ARITY_MAX">BOOST_LOCAL_FUNCTION_CONFIG_ARITY_MAX</a></code>,  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_CONFIG_BIND_MAX.html" title="Macro BOOST_LOCAL_FUNCTION_CONFIG_BIND_MAX">BOOST_LOCAL_FUNCTION_CONFIG_BIND_MAX</a></code>,  <code class="computeroutput"><a class="link" href="BOOST_LOCAL_FUNCTION_CONFIG_LOCALS_AS_TPARAMS.html" title="Macro BOOST_LOCAL_FUNCTION_CONFIG_LOCALS_AS_TPARAMS">BOOST_LOCAL_FUNCTION_CONFIG_LOCALS_AS_TPARAMS</a></code>. </p>
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