64 lines
4.2 KiB
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64 lines
4.2 KiB
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../asio.png"></td></tr></table>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="asio.reference.can_require"></a><a class="link" href="can_require.html" title="can_require">can_require</a>
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</h3></div></div></div>
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<p>
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<a class="indexterm" name="asio.indexterm.can_require"></a>
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</p>
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<p>
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A type trait that determines whether a <code class="computeroutput"><span class="identifier">require</span></code>
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expression is well-formed.
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</p>
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<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span>
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<span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span>
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<span class="keyword">typename</span><span class="special">...</span> <span class="identifier">Properties</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">can_require</span>
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</pre>
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<p>
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Class template <code class="computeroutput"><span class="identifier">can_require</span></code>
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is a trait that is derived from <code class="computeroutput"><span class="identifier">true_type</span></code>
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if the expression <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">require</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">declval</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(),</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">declval</span><span class="special"><</span><span class="identifier">Properties</span><span class="special">>()...)</span></code>
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is well formed; otherwise <code class="computeroutput"><span class="identifier">false_type</span></code>.
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</p>
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<h5>
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<a name="asio.reference.can_require.h0"></a>
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<span><a name="asio.reference.can_require.requirements"></a></span><a class="link" href="can_require.html#asio.reference.can_require.requirements">Requirements</a>
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</h5>
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<p>
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<span class="emphasis"><em>Header: </em></span><code class="literal">asio/require.hpp</code>
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</p>
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<p>
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<span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio.hpp</code>
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</p>
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</div>
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<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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