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62 lines
2.6 KiB
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62 lines
2.6 KiB
HTML
<!doctype html public "-//ietf//dtd html//en">
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<html><head><title>boost::mpl::and_</title>
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<link rel="stylesheet" href="../mpl_wiki.css">
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</head><body bgcolor="white">
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<h1><a href="../Table_of_Contents.html"><img src="../mpl_logo.jpg" alt="[Home]" border=0 align="right"></a>and_</h1><h3>Synopsis</h3>
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<p>
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<pre>
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template<
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typename F1
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, typename F2
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, typename F3 = true_
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...
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, typename Fn = true_
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>
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struct and_
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{
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typedef <em>unspecified</em> type;
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};
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</pre>
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<p>
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<h3>Description</h3>
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<p>
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Returns the result of short-circuit <em>logical and</em> (<code>&&</code>) operation on its arguments.
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<p>
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<h3>Definition</h3>
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<p>
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<pre>
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#include "<a href="../../../../../boost/mpl/and.hpp">boost/mpl/and.hpp</a>"
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</pre>
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<p>
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<h3>Parameters</h3>
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<table border="1">
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<tr><th> Parameter </th><th> Requirement </th><th> Description </th></tr>
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<tr><td><code>F1, F2, .., Fn</code></td><td>A model of nullary <a href="../Metafunction.html">Metafunction</a></td><td></td></tr>
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</table>
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<p>
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<h3>Expression semantics</h3>
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<p>
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<table border="1">
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<tr><th> Expression </th><th> Expression type </th><th> Precondition </th><th> Semantics </th><th> Postcondition </th></tr>
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<tr><td><code>and_<f1,f2,..,fn></code></td><td>A model of <code>bool</code> <a href="../Integral_Constant.html">Integral Constant</a></td><td></td><td><code>false_</code> if either of <code>f1::type::value, f2::type::value, .., fn::type::value</code> expressions evaluates to <code>false</code>, and <code>true_</code> otherwise; guarantees left-to-right evaluation; moreover, the operands subsequent to the first <code>fi</code> metafunction that evaluates to <code>false</code> are not evaluated.</td><td></td></tr>
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</table>
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<p>
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<h3>Example</h3>
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<p>
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<pre>
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<span class="cxx-comment">// will generate compile-time error if invoked with T == any fundamental type</span>
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template< typename T > struct fail
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{
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typedef typename T::nonexistent type;
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};
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<p>
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BOOST_STATIC_ASSERT((and_< true_,false_ >::value == false));
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BOOST_STATIC_ASSERT((and_< false_,fail<int> >::value == false)); <span class="cxx-comment">// OK, fail<int> is never invoked</span>
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BOOST_STATIC_ASSERT((and_< true_,false_,fail<int> >::value == false)); <span class="cxx-comment">// OK too</span>
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</pre>
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<p>
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<h3>See also</h3>
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<p>
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<a href="../Metafunctions.html">Metafunctions</a>, <code><a href="../Reference/or.html">or_</a></code>, <code><a href="../Reference/not.html">not_</a></code>
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<p><hr>
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<a href="../Table_of_Contents.html">Table of Contents</a><br>Last edited September 6, 2003 3:13 am</body></html> |