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<a name="boost.function"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Class template function</span></h2>
<p>boost::function &#8212; A generalized function pointer that can be used for
callbacks or wrapping function objects.</p>
</div>
<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="../function/reference.html#header.boost.function_hpp" title="Header &lt;boost/function.hpp&gt;">boost/function.hpp</a>&gt;
</span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="comment"> // Function type R (T1, T2, ..., TN)</span>
<span class="special">&gt;</span>
<span class="keyword">class</span> <a class="link" href="function.html" title="Class template function">function</a> <span class="special">:</span> <span class="keyword">public</span> <a class="link" href="functionN.html" title="Class template functionN">functionN</a><span class="special">&lt;</span><span class="identifier">R</span><span class="special">,</span> <span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">&gt;</span> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="comment">// types</span>
<span class="keyword">typedef</span> <span class="identifier">R</span> <a name="boost.function.result_type"></a><span class="identifier">result_type</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">T1</span> <a name="boost.function.argument_type"></a><span class="identifier">argument_type</span><span class="special">;</span> <span class="comment">// If N == 1</span>
<span class="keyword">typedef</span> <span class="identifier">T1</span> <a name="boost.function.first_argument_type"></a><span class="identifier">first_argument_type</span><span class="special">;</span> <span class="comment">// If N == 2</span>
<span class="keyword">typedef</span> <span class="identifier">T2</span> <a name="boost.function.second_argument_type"></a><span class="identifier">second_argument_type</span><span class="special">;</span> <span class="comment">// If N == 2</span>
<span class="keyword">typedef</span> <span class="identifier">T1</span> <a name="boost.function.arg1_type"></a><span class="identifier">arg1_type</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">T2</span> <a name="boost.function.arg2_type"></a><span class="identifier">arg2_type</span><span class="special">;</span>
.
.
.
<span class="keyword">typedef</span> <span class="identifier">TN</span> <a name="boost.function.argN_type"></a><span class="identifier">argN_type</span><span class="special">;</span>
<span class="comment">// static constants</span>
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">arity</span> = <span class="identifier">N</span><span class="special">;</span>
<span class="comment">// member classes/structs/unions</span>
<span class="comment">// <a class="link" href="../lambda.html" title="Chapter&#160;11.&#160;Boost.Lambda">Lambda</a> library support</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Args<span class="special">&gt;</span>
<span class="keyword">struct</span> <a class="link" href="function/sig.html" title="Struct template sig">sig</a> <span class="special">{</span>
<span class="comment">// types</span>
<span class="keyword">typedef</span> <span class="identifier">result_type</span> <a class="link" href="function/sig.html#boost.function.sig.type"><span class="identifier">type</span></a><span class="special">;</span>
<span class="special">}</span><span class="special">;</span>
<span class="comment">// <a class="link" href="function.html#boost.functionconstruct-copy-destruct">construct/copy/destruct</a></span>
<a class="link" href="function.html#id381397-bb"><span class="identifier">function</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<a class="link" href="function.html#id589340-bb"><span class="identifier">function</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="functionN.html" title="Class template functionN">functionN</a><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<a class="link" href="function.html#id415058-bb"><span class="identifier">function</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> F<span class="special">&gt;</span> <a class="link" href="function.html#id387445-bb"><span class="identifier">function</span></a><span class="special">(</span><span class="identifier">F</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> F<span class="special">,</span> <span class="keyword">typename</span> Allocator<span class="special">&gt;</span> <a class="link" href="function.html#id430662-bb"><span class="identifier">function</span></a><span class="special">(</span><span class="identifier">F</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">)</span><span class="special">;</span>
function&amp; <a class="link" href="function.html#id342327-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
function&amp; <a class="link" href="function.html#id382656-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<a class="link" href="function.html#id438534-bb"><span class="special">~</span><span class="identifier">function</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<span class="comment">// <a class="link" href="function.html#id361065-bb">modifiers</a></span>
<span class="keyword">void</span> <a class="link" href="function.html#id361068-bb"><span class="identifier">swap</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">void</span> <a class="link" href="function.html#id375935-bb"><span class="identifier">clear</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<span class="comment">// <a class="link" href="function.html#id439890-bb">capacity</a></span>
<span class="keyword">bool</span> <a class="link" href="function.html#id344924-bb"><span class="identifier">empty</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<a class="link" href="function.html#id586940-bb"><span class="keyword">operator</span> <span class="identifier">safe_bool</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id582573-bb"><span class="keyword">operator</span><span class="special">!</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="comment">// <a class="link" href="function.html#id343499-bb">target access</a></span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Functor<span class="special">&gt;</span> <span class="identifier">Functor</span><span class="special">*</span> <a class="link" href="function.html#id462610-bb"><span class="identifier">target</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Functor<span class="special">&gt;</span> <span class="keyword">const</span> <span class="identifier">Functor</span><span class="special">*</span> <a class="link" href="function.html#id363227-bb"><span class="identifier">target</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Functor<span class="special">&gt;</span> <span class="keyword">bool</span> <a class="link" href="function.html#id399914-bb"><span class="identifier">contains</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Functor</span><span class="special">&amp;</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span><span class="special">&amp;</span> <a class="link" href="function.html#id431176-bb"><span class="identifier">target_type</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="comment">// <a class="link" href="function.html#id425390-bb">invocation</a></span>
<span class="identifier">result_type</span> <a class="link" href="function.html#id425393-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">arg1_type</span><span class="special">,</span> <span class="identifier">arg2_type</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">argN_type</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span>
<span class="comment">// <a class="link" href="function.html#id353111-bb">specialized algorithms</a></span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">&gt;</span>
<span class="keyword">void</span> <a class="link" href="function.html#boost.function.swap_id461955"><span class="identifier">swap</span></a><span class="special">(</span><a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">,</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="comment">// <a class="link" href="function.html#id345227-bb">comparison operators</a></span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id442662-bb"><span class="keyword">operator</span><span class="special">==</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">,</span> <span class="identifier">Functor</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id362021-bb"><span class="keyword">operator</span><span class="special">==</span></a><span class="special">(</span><span class="identifier">Functor</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id428493-bb"><span class="keyword">operator</span><span class="special">==</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">,</span> <a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">&lt;</span><span class="identifier">Functor</span><span class="special">&gt;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id410850-bb"><span class="keyword">operator</span><span class="special">==</span></a><span class="special">(</span><a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">&lt;</span><span class="identifier">Functor</span><span class="special">&gt;</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature1<span class="special">,</span> <span class="keyword">typename</span> Signature2<span class="special">&gt;</span>
<span class="keyword">void</span> <a class="link" href="function.html#id356453-bb"><span class="keyword">operator</span><span class="special">==</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature1</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature2</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id578348-bb"><span class="keyword">operator</span><span class="special">!=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">,</span> <span class="identifier">Functor</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id343372-bb"><span class="keyword">operator</span><span class="special">!=</span></a><span class="special">(</span><span class="identifier">Functor</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id403648-bb"><span class="keyword">operator</span><span class="special">!=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">,</span> <a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">&lt;</span><span class="identifier">Functor</span><span class="special">&gt;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a class="link" href="function.html#id440696-bb"><span class="keyword">operator</span><span class="special">!=</span></a><span class="special">(</span><a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">&lt;</span><span class="identifier">Functor</span><span class="special">&gt;</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature1<span class="special">,</span> <span class="keyword">typename</span> Signature2<span class="special">&gt;</span>
<span class="keyword">void</span> <a class="link" href="function.html#id348511-bb"><span class="keyword">operator</span><span class="special">!=</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature1</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature2</span><span class="special">&gt;</span><span class="special">&amp;</span><span class="special">)</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="id1280492"></a><h2>Description</h2>
<p>Class template <a class="link" href="function.html" title="Class template function">function</a> is a thin
wrapper around the numbered class templates <a class="link" href="functionN.html" title="Class template functionN">function0</a>, <a class="link" href="functionN.html" title="Class template functionN">function1</a>, etc. It accepts a
function type with N arguments and will will derive from
<a class="link" href="functionN.html" title="Class template functionN">functionN</a> instantiated with the arguments
it receives.</p>
<p>The semantics of all operations in class template
<a class="link" href="function.html" title="Class template function">function</a> are equivalent to that of the
underlying <a class="link" href="functionN.html" title="Class template functionN">functionN</a> object, although
additional member functions are required to allow proper copy
construction and copy assignment of function objects.</p>
<div class="refsect2">
<a name="id1280551"></a><h3>
<a name="boost.functionconstruct-copy-destruct"></a><code class="computeroutput">function</code>
public
construct/copy/destruct</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><a name="id381397-bb"></a><span class="identifier">function</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Postconditions:</span></p></td>
<td><code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code></td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><a name="id589340-bb"></a><span class="identifier">function</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="functionN.html" title="Class template functionN">functionN</a><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Postconditions:</span></p></td>
<td>Contains a copy of the <code class="computeroutput">f</code>'s target, if it has one, or is empty if <code class="computeroutput">f.<a class="link" href="function.html#id344924-bb">empty</a>()</code>.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw unless copying the target of <code class="computeroutput">f</code> throws.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><a name="id415058-bb"></a><span class="identifier">function</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Postconditions:</span></p></td>
<td>Contains a copy of the <code class="computeroutput">f</code>'s target, if it has one, or is empty if <code class="computeroutput">f.<a class="link" href="function.html#id344924-bb">empty</a>()</code>.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw unless copying the target of <code class="computeroutput">f</code> throws.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> F<span class="special">&gt;</span> <a name="id387445-bb"></a><span class="identifier">function</span><span class="special">(</span><span class="identifier">F</span> f<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Requires:</span></p></td>
<td>F is a function object Callable from <code class="computeroutput">this</code>.</td>
</tr>
<tr>
<td><p><span class="term">Postconditions:</span></p></td>
<td>
<code class="computeroutput">*this</code> targets a copy of <code class="computeroutput">f</code> if <code class="computeroutput">f</code> is nonempty, or <code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code> if <code class="computeroutput">f</code> is empty.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> F<span class="special">,</span> <span class="keyword">typename</span> Allocator<span class="special">&gt;</span> <a name="id430662-bb"></a><span class="identifier">function</span><span class="special">(</span><span class="identifier">F</span> f<span class="special">,</span> <span class="identifier">Allocator</span> alloc<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Requires:</span></p></td>
<td>F is a function object Callable from <code class="computeroutput">this</code>, Allocator is an allocator. The copy constructor and destructor of Allocator shall not throw.</td>
</tr>
<tr>
<td><p><span class="term">Postconditions:</span></p></td>
<td>
<code class="computeroutput">*this</code> targets a copy of <code class="computeroutput">f</code> if <code class="computeroutput">f</code> is nonempty, or <code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code> if <code class="computeroutput">f</code> is empty.</td>
</tr>
<tr>
<td><p><span class="term">Effects:</span></p></td>
<td>If memory allocation is required, the given allocator (or a copy of it) will be used to allocate that memory.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout">function&amp; <a name="id342327-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term">Postconditions:</span></p></td>
<td>If copy construction does not throw, <code class="computeroutput">*this</code> targets a copy of <code class="computeroutput">f</code>'s target, if it has one, or is empty if <code class="computeroutput">f.<a class="link" href="function.html#id344924-bb">empty</a>()</code>. If copy construction does throw, <code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code>.</td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout">function&amp; <a name="id382656-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Postconditions:</span></p></td>
<td>If copy construction of the target of <code class="computeroutput">f</code> does not throw, <code class="computeroutput">*this</code> targets a copy of <code class="computeroutput">f</code>'s target, if it has one, or is empty if <code class="computeroutput">f.<a class="link" href="function.html#id344924-bb">empty</a>()</code>. </td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw when the target of <code class="computeroutput">f</code> is a stateless function object or a reference to the function object. If copy construction does throw, <code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code>.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><a name="id438534-bb"></a><span class="special">~</span><span class="identifier">function</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term">Effects:</span></p></td>
<td>If <code class="computeroutput">!this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code>, destroys the target of <code class="computeroutput">this</code>.</td>
</tr></tbody>
</table></div>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="id1281356"></a><h3>
<a name="id361065-bb"></a><code class="computeroutput">function</code> modifiers</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="keyword">void</span> <a name="id361068-bb"></a><span class="identifier">swap</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term">Effects:</span></p></td>
<td>Interchanges the targets of <code class="computeroutput">*this</code> and <code class="computeroutput">f</code>.</td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">void</span> <a name="id375935-bb"></a><span class="identifier">clear</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Postconditions:</span></p></td>
<td><code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code></td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw.</td>
</tr>
</tbody>
</table></div>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="id1281513"></a><h3>
<a name="id439890-bb"></a><code class="computeroutput">function</code> capacity</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="keyword">bool</span> <a name="id344924-bb"></a><span class="identifier">empty</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td>
<code class="computeroutput">false</code> if <code class="computeroutput">this</code> has a target, and <code class="computeroutput">true</code> otherwise.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><a name="id586940-bb"></a><span class="keyword">operator</span> <span class="identifier">safe_bool</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td>A <code class="computeroutput">safe_bool</code> that evaluates <code class="computeroutput">false</code> in a boolean context when <code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code>, and <code class="computeroutput">true</code> otherwise.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">bool</span> <a name="id582573-bb"></a><span class="keyword">operator</span><span class="special">!</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td><code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code></td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw.</td>
</tr>
</tbody>
</table></div>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="id1281770"></a><h3>
<a name="id343499-bb"></a><code class="computeroutput">function</code> target access</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><a name="id462607-bb"></a><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Functor<span class="special">&gt;</span> <span class="identifier">Functor</span><span class="special">*</span> <a name="id462610-bb"></a><span class="identifier">target</span><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Functor<span class="special">&gt;</span> <span class="keyword">const</span> <span class="identifier">Functor</span><span class="special">*</span> <a name="id363227-bb"></a><span class="identifier">target</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td>If <code class="computeroutput">this</code> stores a target of type
<code class="computeroutput">Functor</code>, returns the address of the
target. Otherwise, returns the NULL
pointer.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Functor<span class="special">&gt;</span> <span class="keyword">bool</span> <a name="id399914-bb"></a><span class="identifier">contains</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Functor</span><span class="special">&amp;</span> f<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term">Returns:</span></p></td>
<td>
<code class="computeroutput">true</code> if <code class="computeroutput">this-&gt;<a class="link" href="function.html#id462607-bb">target</a>&lt;Functor&gt;()</code> is non-NULL and <code class="computeroutput"><a class="link" href="function_equal.html" title="Function template function_equal">function_equal</a>(*(this-&gt;target&lt;Functor&gt;()), f)</code>
</td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span><span class="special">&amp;</span> <a name="id431176-bb"></a><span class="identifier">target_type</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td>
<code class="computeroutput">typeid</code> of the target function object, or <code class="computeroutput">typeid(void)</code> if <code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code>.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>Will not throw.</td>
</tr>
</tbody>
</table></div>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="id1282167"></a><h3>
<a name="id425390-bb"></a><code class="computeroutput">function</code> invocation</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="identifier">result_type</span> <a name="id425393-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">arg1_type</span> a1<span class="special">,</span> <span class="identifier">arg2_type</span> a2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">argN_type</span> aN<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Effects:</span></p></td>
<td>
<code class="computeroutput">f(a1, a2, ..., aN)</code>, where <code class="computeroutput">f</code> is the target of <code class="computeroutput">*this</code>.</td>
</tr>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td>if <code class="computeroutput">R</code> is <code class="computeroutput">void</code>, nothing is returned; otherwise, the return value of the call to <code class="computeroutput">f</code> is returned.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>
<code class="computeroutput"><a class="link" href="bad_function_call.html" title="Class bad_function_call">bad_function_call</a></code> if <code class="computeroutput">this-&gt;<a class="link" href="function.html#id344924-bb">empty</a>()</code>. Otherwise, may through any exception thrown by the target function <code class="computeroutput">f</code>.</td>
</tr>
</tbody>
</table></div>
</li></ol></div>
</div>
<div class="refsect2">
<a name="id1282492"></a><h3>
<a name="id353111-bb"></a><code class="computeroutput">function</code> specialized algorithms</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">&gt;</span>
<span class="keyword">void</span> <a name="boost.function.swap_id461955"></a><span class="identifier">swap</span><span class="special">(</span><a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f1<span class="special">,</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f2<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term">Effects:</span></p></td>
<td><code class="computeroutput">f1.<a class="link" href="function.html#id361068-bb">swap</a>(f2)</code></td>
</tr></tbody>
</table></div>
</li></ol></div>
</div>
<div class="refsect2">
<a name="id1282643"></a><h3>
<a name="id345227-bb"></a><code class="computeroutput">function</code> comparison operators</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<p><a name="boost.function.operator==_id442658"></a></p>
<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a name="id442662-bb"></a><span class="keyword">operator</span><span class="special">==</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f<span class="special">,</span> <span class="identifier">Functor</span> g<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a name="id362021-bb"></a><span class="keyword">operator</span><span class="special">==</span><span class="special">(</span><span class="identifier">Functor</span> g<span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a name="id428493-bb"></a><span class="keyword">operator</span><span class="special">==</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f<span class="special">,</span> <a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">&lt;</span><span class="identifier">Functor</span><span class="special">&gt;</span> g<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a name="id410850-bb"></a><span class="keyword">operator</span><span class="special">==</span><span class="special">(</span><a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">&lt;</span><span class="identifier">Functor</span><span class="special">&gt;</span> g<span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature1<span class="special">,</span> <span class="keyword">typename</span> Signature2<span class="special">&gt;</span>
<span class="keyword">void</span> <a name="id356453-bb"></a><span class="keyword">operator</span><span class="special">==</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature1</span><span class="special">&gt;</span><span class="special">&amp;</span> f1<span class="special">,</span>
<span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature2</span><span class="special">&gt;</span><span class="special">&amp;</span> f2<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td>True when <code class="computeroutput">f</code> stores an object of
type <code class="computeroutput">Functor</code> and one of the following conditions applies:
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
<code class="computeroutput">g</code> is of type
<code class="computeroutput"><a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a>&lt;Functor&gt;</code>
and <code class="computeroutput">f.target&lt;Functor&gt;() == g.<a class="link" href="reference_wrapper.html#id1138615-bb">get_pointer</a>()</code>.</li>
<li class="listitem">
<code class="computeroutput">g</code> is not of type
<code class="computeroutput"><a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a>&lt;Functor&gt;</code>
and <code class="computeroutput">function_equals(*(f.target&lt;Functor&gt;()), g)</code>.</li>
</ul></div>
</td>
</tr>
<tr>
<td><p><span class="term">Notes:</span></p></td>
<td>
<code class="computeroutput"><a class="link" href="function.html" title="Class template function">function</a></code>
objects are not
<a class="link" href="../EqualityComparable.html" title="Concept EqualityComparable">EqualityComparable</a>.</td>
</tr>
<tr>
<td><p><span class="term">Rationale:</span></p></td>
<td>The <code class="computeroutput">safe_bool</code> conversion
opens a loophole whereby two <code class="computeroutput">function</code>
instances can be compared via <code class="computeroutput">==</code>, although this
is not feasible to implement. The undefined <code class="computeroutput">void
operator==</code> closes the loophole and ensures a
compile-time or link-time error.</td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<p><a name="boost.function.operator!=_id365908"></a></p>
<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a name="id578348-bb"></a><span class="keyword">operator</span><span class="special">!=</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f<span class="special">,</span> <span class="identifier">Functor</span> g<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a name="id343372-bb"></a><span class="keyword">operator</span><span class="special">!=</span><span class="special">(</span><span class="identifier">Functor</span> g<span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a name="id403648-bb"></a><span class="keyword">operator</span><span class="special">!=</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f<span class="special">,</span> <a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">&lt;</span><span class="identifier">Functor</span><span class="special">&gt;</span> g<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature<span class="special">,</span> <span class="keyword">typename</span> Functor<span class="special">&gt;</span>
<span class="keyword">bool</span> <a name="id440696-bb"></a><span class="keyword">operator</span><span class="special">!=</span><span class="special">(</span><a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">&lt;</span><span class="identifier">Functor</span><span class="special">&gt;</span> g<span class="special">,</span> <span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature</span><span class="special">&gt;</span><span class="special">&amp;</span> f<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Signature1<span class="special">,</span> <span class="keyword">typename</span> Signature2<span class="special">&gt;</span>
<span class="keyword">void</span> <a name="id348511-bb"></a><span class="keyword">operator</span><span class="special">!=</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature1</span><span class="special">&gt;</span><span class="special">&amp;</span> f1<span class="special">,</span>
<span class="keyword">const</span> <a class="link" href="function.html" title="Class template function">function</a><span class="special">&lt;</span><span class="identifier">Signature2</span><span class="special">&gt;</span><span class="special">&amp;</span> f2<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td>True when <code class="computeroutput">f</code> does not store an
object of type <code class="computeroutput">Functor</code> or it stores an object of
type <code class="computeroutput">Functor</code> and one of the following conditions
applies:
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
<code class="computeroutput">g</code> is of type
<code class="computeroutput"><a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a>&lt;Functor&gt;</code>
and <code class="computeroutput">f.target&lt;Functor&gt;() != g.<a class="link" href="reference_wrapper.html#id1138615-bb">get_pointer</a>()</code>.</li>
<li class="listitem">
<code class="computeroutput">g</code> is not of type
<code class="computeroutput"><a class="link" href="reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a>&lt;Functor&gt;</code>
and <code class="computeroutput">!function_equals(*(f.target&lt;Functor&gt;()), g)</code>.</li>
</ul></div>
</td>
</tr>
<tr>
<td><p><span class="term">Notes:</span></p></td>
<td>
<code class="computeroutput"><a class="link" href="function.html" title="Class template function">function</a></code>
objects are not
<a class="link" href="../EqualityComparable.html" title="Concept EqualityComparable">EqualityComparable</a>.</td>
</tr>
<tr>
<td><p><span class="term">Rationale:</span></p></td>
<td>The <code class="computeroutput">safe_bool</code> conversion
opens a loophole whereby two <code class="computeroutput">function</code>
instances can be compared via <code class="computeroutput">!=</code>, although this
is not feasible to implement. The undefined <code class="computeroutput">void
operator!=</code> closes the loophole and ensures a
compile-time or link-time error.</td>
</tr>
</tbody>
</table></div>
</li>
</ol></div>
</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 &#169; 2001-2004 Douglas Gregor<p>Use, modification and distribution is subject to the Boost
Software License, Version 1.0. (See accompanying file
<code class="filename">LICENSE_1_0.txt</code> or 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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