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| <h2><span class="refentrytitle">Struct template extract_or_default</span></h2> |
| <p>boost::log::result_of::extract_or_default — A metafunction that allows to acquire the result of the value extraction. </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: <<a class="link" href="../../../attributes.html#header.boost.log.attributes.value_extraction_hpp" title="Header <boost/log/attributes/value_extraction.hpp>">boost/log/attributes/value_extraction.hpp</a>> |
| |
| </span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">,</span> <span class="keyword">typename</span> DefaultT<span class="special">,</span> <span class="keyword">typename</span> TagT<span class="special">></span> |
| <span class="keyword">struct</span> <a class="link" href="extract_or_default.html" title="Struct template extract_or_default">extract_or_default</a> <span class="special">{</span> |
| <span class="comment">// types</span> |
| <span class="keyword">typedef</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">eval_if</span><span class="special"><</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">is_sequence</span><span class="special"><</span> <span class="identifier">T</span> <span class="special">></span><span class="special">,</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">eval_if</span><span class="special"><</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">contains</span><span class="special"><</span> <span class="identifier">T</span><span class="special">,</span> <span class="identifier">DefaultT</span> <span class="special">></span><span class="special">,</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">identity</span><span class="special"><</span> <span class="identifier">T</span> <span class="special">></span><span class="special">,</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">push_back</span><span class="special"><</span> <span class="identifier">T</span><span class="special">,</span> <span class="identifier">DefaultT</span> <span class="special">></span> <span class="special">></span><span class="special">,</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">if_</span><span class="special"><</span> <span class="identifier">is_same</span><span class="special"><</span> <span class="identifier">T</span><span class="special">,</span> <span class="identifier">DefaultT</span> <span class="special">></span><span class="special">,</span> <span class="identifier">T</span><span class="special">,</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector2</span><span class="special"><</span> <span class="identifier">T</span><span class="special">,</span> <span class="identifier">DefaultT</span> <span class="special">></span> <span class="special">></span> <span class="special">></span><span class="special">::</span><span class="identifier">type</span> <a name="boost.log.result_of.extract_or_default.extracted_type"></a><span class="identifier">extracted_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">if_</span><span class="special"><</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">is_sequence</span><span class="special"><</span> <span class="identifier">extracted_type</span> <span class="special">></span><span class="special">,</span> <span class="identifier">value_ref</span><span class="special"><</span> <span class="identifier">extracted_type</span><span class="special">,</span> <span class="identifier">TagT</span> <span class="special">></span><span class="special">,</span> <span class="identifier">extracted_type</span> <span class="keyword">const</span> <span class="special">&</span> <span class="special">></span><span class="special">::</span><span class="identifier">type</span> <a name="boost.log.result_of.extract_or_default.type"></a><span class="identifier">type</span><span class="special">;</span> |
| <span class="special">}</span><span class="special">;</span></pre></div> |
| <div class="refsect1"> |
| <a name="idp109733728"></a><h2>Description</h2> |
| <p>The metafunction results in a type that is in form of <code class="computeroutput">T const&</code>, if <code class="computeroutput">T</code> is not an MPL type sequence and <code class="computeroutput">DefaultT</code> is the same as <code class="computeroutput">T</code>, or <code class="computeroutput">value_ref< TypesT, TagT ></code> otherwise, with <code class="computeroutput">TypesT</code> being a type sequence comprising the types from sequence <code class="computeroutput">T</code> and <code class="computeroutput">DefaultT</code>, if it is not present in <code class="computeroutput">T</code> already. </p> |
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| <td align="right"><div class="copyright-footer">Copyright © 2007-2015 Andrey |
| Semashev<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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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