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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| 6 | <meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> | |
| 7 | <title>The MPL Reference Manual: Placeholder Expression</title> | |
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| 9 | </head> | |
| 10 | <body class="docframe refmanual"> | |
| 11 | <table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./lambda-expression.html" class="navigation-link">Prev</a> <a href="./tag-dispatched-metafunction.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./lambda-expression.html" class="navigation-link">Back</a> <a href="./tag-dispatched-metafunction.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> | |
| 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="./metafunctions-concepts.html" class="navigation-link">Concepts</a> / <a href="./placeholder-expression.html" class="navigation-link">Placeholder Expression</a></td> | |
| 13 | </tr></table><div class="header-separator"></div> | |
| 14 | <div class="section" id="placeholder-expression"> | |
| 15 | <h1><a class="toc-backref" href="./metafunctions-concepts.html#id1515">Placeholder Expression</a></h1> | |
| 16 | <div class="section" id="id835"> | |
| 17 | <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> | |
| 18 | <p>A <a class="reference internal" href="./placeholder-expression.html">Placeholder Expression</a> is a type that is either a <a class="reference internal" href="./placeholders.html#placeholder">placeholder</a> or a class | |
| 19 | template specialization with at least one argument that itself is a | |
| 20 | <a class="reference internal" href="./placeholder-expression.html">Placeholder Expression</a>.</p> | |
| 21 | </div> | |
| 22 | <div class="section" id="id836"> | |
| 23 | <h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3> | |
| 24 | <p>If <tt class="literal"><span class="pre">X</span></tt> is a class template, and <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt> are arbitrary types, then | |
| 25 | <tt class="literal"><span class="pre">X<a1,...,an></span></tt> is a <a class="reference internal" href="./placeholder-expression.html">Placeholder Expression</a> if and only if all of the following | |
| 26 | conditions hold:</p> | |
| 27 | <ul class="simple"> | |
| 28 | <li>At least one of the template arguments <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt> is a <a class="reference internal" href="./placeholders.html#placeholder">placeholder</a> | |
| 29 | or a <a class="reference internal" href="./placeholder-expression.html">Placeholder Expression</a>.</li> | |
| 30 | <li>All of <tt class="literal"><span class="pre">X</span></tt>'s template parameters, including the default ones, are types.</li> | |
| 31 | <li>The number of <tt class="literal"><span class="pre">X</span></tt>'s template parameters, including the default ones, is | |
| 32 | less or equal to the value of <tt class="literal"><span class="pre"><a href="./limit-metafunction-arity.html" class="identifier">BOOST_MPL_LIMIT_METAFUNCTION_ARITY</a></span></tt> | |
| 33 | <a class="reference internal" href="./configuration.html">configuration macro</a>.</li> | |
| 34 | </ul> | |
| 35 | </div> | |
| 36 | <div class="section" id="id838"> | |
| 37 | <h3><a class="subsection-title" href="#models" name="models">Models</a></h3> | |
| 38 | <ul class="simple"> | |
| 39 | <li><a class="reference internal" href="./placeholders.html">_1</a></li> | |
| 40 | <li><tt class="literal"><span class="pre"><a href="./plus.html" class="identifier">plus</a><_,</span> <span class="pre"><a href="./int.html" class="identifier">int_</a><2></span> <span class="pre">></span></tt></li> | |
| 41 | <li><tt class="literal"><span class="pre"><a href="./if.html" class="identifier">if_</a><</span> <span class="pre"><a href="./less.html" class="identifier">less</a><<a href="./placeholders.html" class="identifier">_1</a>,</span> <span class="pre"><a href="./int.html" class="identifier">int_</a><7></span> <span class="pre">>,</span> <span class="pre"><a href="./plus.html" class="identifier">plus</a><<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>>,</span> <span class="pre"><a href="./placeholders.html" class="identifier">_1</a></span> <span class="pre">></span></tt></li> | |
| 42 | </ul> | |
| 43 | </div> | |
| 44 | <div class="section" id="id839"> | |
| 45 | <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> | |
| 46 | <p><a class="reference internal" href="./lambda-expression.html">Lambda Expression</a>, <a class="reference internal" href="./placeholders.html">Placeholders</a>, <a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./apply.html">apply</a>, <a class="reference internal" href="./lambda.html">lambda</a></p> | |
| 47 | <!-- Metafunctions/Concepts//Tag Dispatched Metafunction |50 --> | |
| 48 | </div> | |
| 49 | </div> | |
| 50 | ||
| 51 | <div class="footer-separator"></div> | |
| 52 | <table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./lambda-expression.html" class="navigation-link">Prev</a> <a href="./tag-dispatched-metafunction.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./lambda-expression.html" class="navigation-link">Back</a> <a href="./tag-dispatched-metafunction.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> | |
| 53 | <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> | |
| 54 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 55 | 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> | |
| 56 | </html> |