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70 lines
3.6 KiB
HTML
<!doctype html public "-//ietf//dtd html//en">
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<html><head><title>boost::mpl::Reference/copy</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_Content.html"><img src="../mpl_logo.jpg" alt="[Home]" border=0 align="right"></a>copy</h1><h3>Synopsis</h3>
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<p>
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<pre>
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template<
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typename Sequence
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, typename State
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, typename BinaryOp
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>
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struct copy
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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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<code>copy</code> is, in fact, just another name for <code><a href="../Reference/fold.html">fold</a></code>. It was introduced for symmetry with <code><a href="../Reference/copy_if.html">copy_if</a></code> [<a href="#1">1</a>], and because it's a nice name for one of the typical <code>fold</code> applications, that is, copying the content of one sequence into another - see the example below.
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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/copy.hpp">boost/mpl/copy.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>Sequence</code></td><td>A model of <a href="../Sequence.html">Sequence</a></td><td>A sequence to iterate. </td></tr>
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<tr><td><code>State</code></td><td>A type</td><td>The initial state for the first <code>BinaryOp</code> application. </td></tr>
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<tr><td><code>BinaryOp</code></td><td>A model of [Lambda Function]</td><td>The operation to be executed on forward traversal. </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>typedef copy<Sequence,T,Op>::type s;</code></td><td>A type</td><td></td><td>Equivalent to <code>typedef fold< Sequence,T,Op >::type s;</code>.</td><td></td></tr>
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</table>
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<p>
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<h3>Complexity</h3>
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<p>
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Linear. Exactly <code><a href="../Reference/size.html">size</a><Sequence>::type::value</code> applications of <code>BinaryOp</code>.
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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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typedef <a href="../Reference/vector_c.html">vector_c</a><int,0,1,2,3,4,5,6,7,8,9> numbers;
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typedef copy<
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<a href="../Reference/range_c.html">range_c</a><int,10,20>
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, <a href="../Reference/push_back.html">push_back</a><_,_>
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, numbers
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>::type result;
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<p>
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BOOST_STATIC_ASSERT(<a href="../Reference/size.html">size</a><result>::value == 20);
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BOOST_STATIC_ASSERT((<a href="../Reference/equal.html">equal</a>< result,<a href="../Reference/range_c.html">range_c</a><int,0,20> >::type::value));
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</pre>
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<p>
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<h3>Notes</h3>
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<p>
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[<a name="1">1</a>] In case if you wonder why <code><a href="../Reference/copy_if.html">copy_if</a></code>, in its turn, wasn't just called <code>fold_if</code>, - something that would allow to eliminate the family of <code>copy</code> algorithms completely - these two have quite different semantics.<br>
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<p>
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<h3>See also</h3>
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<p>
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<a href="../Algorithms.html">Algorithms</a>, <code><a href="../Reference/copy_if.html">copy_if</a></code>, <code><a href="../Reference/copy_backward.html">copy_backward</a></code>, <code><a href="../Reference/copy_backward_if.html">copy_backward_if</a></code>, <code><a href="../Reference/fold.html">fold</a></code>, <code><a href="../Reference/fold_backward.html">fold_backward</a></code>
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<p><hr>
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<a href="../Table_of_Content.html">Table of Content</a> | <a href="../Reference.html">Reference</a><br>Last edited July 19, 2002 2:10 am</body></html> |