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   4 <title>Struct template fallback_to_default</title>
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  18 <div class="refentry">
  19 <a name="boost.log.fallback_to_default"></a><div class="titlepage"></div>
  20 <div class="refnamediv">
  21 <h2><span class="refentrytitle">Struct template fallback_to_default</span></h2>
  22 <p>boost::log::fallback_to_default</p>
  23 </div>
  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: &lt;<a class="link" href="../../attributes.html#header.boost.log.attributes.fallback_policy_fwd_hpp" title="Header &lt;boost/log/attributes/fallback_policy_fwd.hpp&gt;">boost/log/attributes/fallback_policy_fwd.hpp</a>&gt;
  26
  27 </span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> DefaultT<span class="special">&gt;</span>
  28 <span class="keyword">struct</span> <a class="link" href="fallback_to_default.html" title="Struct template fallback_to_default">fallback_to_default</a> <span class="special">{</span>
  29   <span class="comment">// <a class="link" href="fallback_to_default.html#boost.log.fallback_to_defaultconstruct-copy-destruct">construct/copy/destruct</a></span>
  30   <a class="link" href="fallback_to_default.html#idp35395184-bb"><span class="identifier">fallback_to_default</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
  31   <span class="keyword">explicit</span> <a class="link" href="fallback_to_default.html#idp35395888-bb"><span class="identifier">fallback_to_default</span></a><span class="special">(</span><span class="identifier">default_type</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  32
  33   <span class="comment">// <a class="link" href="fallback_to_default.html#idp35388192-bb">public member functions</a></span>
  34   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> FunT<span class="special">&gt;</span> <span class="keyword">bool</span> <a class="link" href="fallback_to_default.html#idp35388752-bb"><span class="identifier">apply_default</span></a><span class="special">(</span><span class="identifier">FunT</span> <span class="special">&amp;</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  35   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> FunT<span class="special">&gt;</span> <span class="keyword">bool</span> <a class="link" href="fallback_to_default.html#idp35391888-bb"><span class="identifier">apply_default</span></a><span class="special">(</span><span class="identifier">FunT</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  36
  37   <span class="comment">// <a class="link" href="fallback_to_default.html#idp35397568-bb">public static functions</a></span>
  38   <span class="keyword">static</span> <span class="keyword">void</span> <a class="link" href="fallback_to_default.html#idp35398128-bb"><span class="identifier">on_invalid_type</span></a><span class="special">(</span><span class="identifier">type_info_wrapper</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  39   <span class="keyword">static</span> <span class="keyword">void</span> <a class="link" href="fallback_to_default.html#idp35400464-bb"><span class="identifier">on_missing_value</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
  40 <span class="special">}</span><span class="special">;</span></pre></div>
  41 <div class="refsect1">
  42 <a name="idp90246848"></a><h2>Description</h2>
  43 <p>The <code class="computeroutput"><a class="link" href="fallback_to_default.html" title="Struct template fallback_to_default">fallback_to_default</a></code> policy results in a default value if the attribute value cannot be extracted. </p>
  44 <div class="refsect2">
  45 <a name="idp90248832"></a><h3>
  46 <a name="boost.log.fallback_to_defaultconstruct-copy-destruct"></a><code class="computeroutput">fallback_to_default</code>
  47         public
  48        construct/copy/destruct</h3>
  49 <div class="orderedlist"><ol class="orderedlist" type="1">
  50 <li class="listitem">
  51 <pre class="literallayout"><a name="idp35395184-bb"></a><span class="identifier">fallback_to_default</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>
  52 <p>Default constructor. </p>
  53 </li>
  54 <li class="listitem">
  55 <pre class="literallayout"><span class="keyword">explicit</span> <a name="idp35395888-bb"></a><span class="identifier">fallback_to_default</span><span class="special">(</span><span class="identifier">default_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> def_val<span class="special">)</span><span class="special">;</span></pre>
  56 <p>Initializing constructor. </p>
  57 </li>
  58 </ol></div>
  59 </div>
  60 <div class="refsect2">
  61 <a name="idp90261728"></a><h3>
  62 <a name="idp35388192-bb"></a><code class="computeroutput">fallback_to_default</code> public member functions</h3>
  63 <div class="orderedlist"><ol class="orderedlist" type="1">
  64 <li class="listitem">
  65 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> FunT<span class="special">&gt;</span> <span class="keyword">bool</span> <a name="idp35388752-bb"></a><span class="identifier">apply_default</span><span class="special">(</span><span class="identifier">FunT</span> <span class="special">&amp;</span> fun<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
  66 <p>The method is called in order to apply a function object to the default value. </p>
  67 </li>
  68 <li class="listitem">
  69 <pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> FunT<span class="special">&gt;</span> <span class="keyword">bool</span> <a name="idp35391888-bb"></a><span class="identifier">apply_default</span><span class="special">(</span><span class="identifier">FunT</span> <span class="keyword">const</span> <span class="special">&amp;</span> fun<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
  70 <p>The method is called in order to apply a function object to the default value. </p>
  71 </li>
  72 </ol></div>
  73 </div>
  74 <div class="refsect2">
  75 <a name="idp90283232"></a><h3>
  76 <a name="idp35397568-bb"></a><code class="computeroutput">fallback_to_default</code> public static functions</h3>
  77 <div class="orderedlist"><ol class="orderedlist" type="1">
  78 <li class="listitem">
  79 <pre class="literallayout"><span class="keyword">static</span> <span class="keyword">void</span> <a name="idp35398128-bb"></a><span class="identifier">on_invalid_type</span><span class="special">(</span><span class="identifier">type_info_wrapper</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span></pre>
  80 <p>The method is called when value extraction failed because the attribute value has different type than requested. </p>
  81 </li>
  82 <li class="listitem">
  83 <pre class="literallayout"><span class="keyword">static</span> <span class="keyword">void</span> <a name="idp35400464-bb"></a><span class="identifier">on_missing_value</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre>
  84 <p>The method is called when value extraction failed because the attribute value was not found. </p>
  85 </li>
  86 </ol></div>
  87 </div>
  88 </div>
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  91 <td align="left"></td>
  92 <td align="right"><div class="copyright-footer">Copyright &#169; 2007-2014 Andrey Semashev<p>
  93         Distributed under the Boost Software License, Version 1.0. (See accompanying
  94         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>).
  95       </p>
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