projects / ceph.git / blame
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1 | <?xml version="1.0" encoding="utf-8" ?> |
| 2 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> | |
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| 4 | <head> | |
| 5 | <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> | |
| 6 | <meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> | |
| 7 | <title>The MPL Reference Manual: identity</title> | |
| 8 | <link rel="stylesheet" href="../style.css" type="text/css" /> | |
| 9 | </head> | |
| 10 | <body class="docframe refmanual"> | |
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| 12 | <td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./metafunctions.html" class="navigation-link">Metafunctions</a> / <a href="./miscellaneous.html" class="navigation-link">Miscellaneous</a> / <a href="./identity.html" class="navigation-link">identity</a></td> | |
| 13 | </tr></table><div class="header-separator"></div> | |
| 14 | <div class="section" id="identity"> | |
| 15 | <h1><a class="toc-backref" href="./miscellaneous.html#id1564">identity</a></h1> | |
| 16 | <div class="section" id="id1146"> | |
| 17 | <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> | |
| 18 | <pre class="literal-block"> | |
| 19 | template< | |
| 20 | typename X | |
| 21 | > | |
| 22 | struct <a href="./identity.html" class="identifier">identity</a> | |
| 23 | { | |
| 24 | typedef X type; | |
| 25 | }; | |
| 26 | </pre> | |
| 27 | </div> | |
| 28 | <div class="section" id="id1147"> | |
| 29 | <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> | |
| 30 | <p>The <a class="reference external" href="http://mathworld.wolfram.com/IdentityFunction.html" target="_top">identity</a> metafunction. Returns <tt class="literal"><span class="pre">X</span></tt> unchanged.</p> | |
| 31 | </div> | |
| 32 | <div class="section" id="id1149"> | |
| 33 | <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> | |
| 34 | <pre class="literal-block"> | |
| 35 | #include <<a href="../../../../boost/mpl/identity.hpp" class="header">boost/mpl/identity.hpp</a>> | |
| 36 | </pre> | |
| 37 | </div> | |
| 38 | <div class="section" id="id1150"> | |
| 39 | <h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3> | |
| 40 | <p><a class="reference internal" href="./metafunction.html">Metafunction</a></p> | |
| 41 | </div> | |
| 42 | <div class="section" id="id1151"> | |
| 43 | <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> | |
| 44 | <table border="1" class="docutils table"> | |
| 45 | <colgroup> | |
| 46 | <col width="22%" /> | |
| 47 | <col width="28%" /> | |
| 48 | <col width="51%" /> | |
| 49 | </colgroup> | |
| 50 | <thead valign="bottom"> | |
| 51 | <tr><th class="head">Parameter</th> | |
| 52 | <th class="head">Requirement</th> | |
| 53 | <th class="head">Description</th> | |
| 54 | </tr> | |
| 55 | </thead> | |
| 56 | <tbody valign="top"> | |
| 57 | <tr><td><tt class="literal"><span class="pre">X</span></tt></td> | |
| 58 | <td>Any type</td> | |
| 59 | <td>An argument to be returned.</td> | |
| 60 | </tr> | |
| 61 | </tbody> | |
| 62 | </table> | |
| 63 | </div> | |
| 64 | <div class="section" id="id1152"> | |
| 65 | <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> | |
| 66 | <p>For an arbitrary type <tt class="literal"><span class="pre">x</span></tt>:</p> | |
| 67 | <pre class="literal-block"> | |
| 68 | typedef <a href="./identity.html" class="identifier">identity</a><x>::type r; | |
| 69 | </pre> | |
| 70 | <table class="docutils field-list" frame="void" rules="none"> | |
| 71 | <col class="field-name" /> | |
| 72 | <col class="field-body" /> | |
| 73 | <tbody valign="top"> | |
| 74 | <tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">A type.</p> | |
| 75 | </td> | |
| 76 | </tr> | |
| 77 | <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p> | |
| 78 | <pre class="literal-block"> | |
| 79 | typedef x r; | |
| 80 | </pre> | |
| 81 | </td> | |
| 82 | </tr> | |
| 83 | <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><p class="first last"><tt class="literal"><span class="pre">is_same<r,x>::value</span> <span class="pre">==</span> <span class="pre">true</span></tt>.</p> | |
| 84 | </td> | |
| 85 | </tr> | |
| 86 | </tbody> | |
| 87 | </table> | |
| 88 | </div> | |
| 89 | <div class="section" id="id1153"> | |
| 90 | <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> | |
| 91 | <pre class="literal-block"> | |
| 92 | typedef <a href="./apply.html" class="identifier">apply</a>< <a href="./identity.html" class="identifier">identity</a><<a href="./placeholders.html" class="identifier">_1</a>>, char >::type t1; | |
| 93 | typedef <a href="./apply.html" class="identifier">apply</a>< <a href="./identity.html" class="identifier">identity</a><<a href="./placeholders.html" class="identifier">_2</a>>, char,int >::type t2; | |
| 94 | ||
| 95 | <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< t1, char > )); | |
| 96 | <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< t2, int > )); | |
| 97 | </pre> | |
| 98 | </div> | |
| 99 | <div class="section" id="id1154"> | |
| 100 | <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> | |
| 101 | <p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./placeholders.html">Placeholders</a>, <a class="reference internal" href="./trivial.html#label-metafunctions-trivial">Trivial Metafunctions</a>, <a class="reference internal" href="./always.html">always</a>, <a class="reference internal" href="./apply.html">apply</a></p> | |
| 102 | <!-- Metafunctions/Miscellaneous//always |20 --> | |
| 103 | </div> | |
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| 105 | ||
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| 108 | <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> | |
| 109 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 110 | file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> | |
| 111 | </html> |