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18 <div class="refentry">
19 <a name="boost.log.attributes.function"></a><div class="titlepage"></div>
20 <div class="refnamediv">
21 <h2><span class="refentrytitle">Class template function</span></h2>
22 <p>boost::log::attributes::function — A class of an attribute that acquires its value from a third-party function object. </p>
24 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
25 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../../../attributes.html#header.boost.log.attributes.function_hpp" title="Header <boost/log/attributes/function.hpp>">boost/log/attributes/function.hpp</a>>
27 </span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> R<span class="special">></span>
28 <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> <span class="identifier">attribute</span> <span class="special">{</span>
29 <span class="keyword">public</span><span class="special">:</span>
30 <span class="comment">// types</span>
31 <span class="keyword">typedef</span> <span class="identifier">R</span> <a name="boost.log.attributes.function.value_type"></a><span class="identifier">value_type</span><span class="special">;</span> <span class="comment">// The attribute value type. </span>
33 <span class="comment">// member classes/structs/unions</span>
35 <span class="comment">// Base class for factory implementation.</span>
37 <span class="keyword">class</span> <a class="link" href="function/impl.html" title="Class impl">impl</a> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">attribute</span><span class="special">::</span><span class="identifier">impl</span> <span class="special">{</span>
38 <span class="special">}</span><span class="special">;</span>
40 <span class="comment">// Factory implementation.</span>
41 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
42 <span class="keyword">class</span> <a class="link" href="function/impl_template.html" title="Class template impl_template">impl_template</a> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">function</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span><span class="special">::</span><span class="identifier">impl</span> <span class="special">{</span>
43 <span class="keyword">public</span><span class="special">:</span>
44 <span class="comment">// <a class="link" href="function/impl_template.html#boost.log.attributes.function.impl_templateconstruct-copy-destruct">construct/copy/destruct</a></span>
45 <span class="keyword">explicit</span> <a class="link" href="function/impl_template.html#idm45711348701808-bb"><span class="identifier">impl_template</span></a><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
47 <span class="comment">// <a class="link" href="function/impl_template.html#idm45711348704864-bb">public member functions</a></span>
48 <span class="keyword">virtual</span> <a class="link" href="../attribute_value.html" title="Class attribute_value">attribute_value</a> <a class="link" href="function/impl_template.html#idm45711348704304-bb"><span class="identifier">get_value</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
49 <span class="special">}</span><span class="special">;</span>
51 <span class="comment">// <a class="link" href="function.html#boost.log.attributes.functionconstruct-copy-destruct">construct/copy/destruct</a></span>
52 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="keyword">explicit</span> <a class="link" href="function.html#idm45711348695392-bb"><span class="identifier">function</span></a><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
53 <span class="keyword">explicit</span> <a class="link" href="function.html#idm45711348692864-bb"><span class="identifier">function</span></a><span class="special">(</span><a class="link" href="cast_source.html" title="Class cast_source">cast_source</a> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
55 <span class="comment">// <a class="link" href="function.html#idm45711348698960-bb">private member functions</a></span>
56 <a class="link" href="function.html#idm45711348698384-bb"><span class="identifier">BOOST_STATIC_ASSERT_MSG</span></a><span class="special">(</span><span class="special">!</span><span class="identifier">is_void</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span><span class="special">::</span><span class="identifier">value</span><span class="special">,</span>
57 <span class="string">"Boost.Log: Function object return type must not be void"</span><span class="special">)</span><span class="special">;</span>
58 <span class="special">}</span><span class="special">;</span></pre></div>
59 <div class="refsect1">
60 <a name="idm45554751831248"></a><h2>Description</h2>
61 <p>The attribute calls a stored nullary function object to acquire each value. The result type of the function object is the attribute value type.</p>
62 <p>It is not recommended to use this class directly. Use <code class="computeroutput">make_function</code> convenience functions to construct the attribute instead. </p>
63 <div class="refsect2">
64 <a name="idm45554751829328"></a><h3>
65 <a name="boost.log.attributes.functionconstruct-copy-destruct"></a><code class="computeroutput">function</code>
67 construct/copy/destruct</h3>
68 <div class="orderedlist"><ol class="orderedlist" type="1">
70 <pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="keyword">explicit</span> <a name="idm45711348695392-bb"></a><span class="identifier">function</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span> fun<span class="special">)</span><span class="special">;</span></pre>
71 <p>Initializing constructor </p>
74 <pre class="literallayout"><span class="keyword">explicit</span> <a name="idm45711348692864-bb"></a><span class="identifier">function</span><span class="special">(</span><a class="link" href="cast_source.html" title="Class cast_source">cast_source</a> <span class="keyword">const</span> <span class="special">&</span> source<span class="special">)</span><span class="special">;</span></pre>
75 <p>Constructor for casting support </p>
79 <div class="refsect2">
80 <a name="idm45554751810976"></a><h3>
81 <a name="idm45711348698960-bb"></a><code class="computeroutput">function</code> private member functions</h3>
82 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><pre class="literallayout"> <a name="idm45711348698384-bb"></a><span class="identifier">BOOST_STATIC_ASSERT_MSG</span><span class="special">(</span><span class="special">!</span><span class="identifier">is_void</span><span class="special"><</span> <span class="identifier">R</span> <span class="special">></span><span class="special">::</span><span class="identifier">value</span><span class="special">,</span>
83 <span class="string">"Boost.Log: Function object return type must not be void"</span><span class="special">)</span><span class="special">;</span></pre></li></ol></div>
87 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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89 <td align="right"><div class="copyright-footer">Copyright © 2007-2016 Andrey Semashev<p>
90 Distributed under the Boost Software License, Version 1.0. (See accompanying
91 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>).
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