123456789101112131415161718192021222324252627282930313233343536373839404142 |
- <?xml version="1.0" encoding="utf-8" ?>
- <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
- <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
- <!-- Copyright Aleksey Gurtovoy 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <head>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
- <meta name="generator" content="Docutils 0.3.6: http://docutils.sourceforge.net/" />
- <title>THE BOOST MPL LIBRARY: Metafunction Composition</title>
- <link rel="stylesheet" href="../style.css" type="text/css" />
- </head>
- <body class="docframe">
- <table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./partial-metafunction.html" class="navigation-link">Prev</a> <a href="./lambda-details.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./partial-metafunction.html" class="navigation-link">Back</a> Along</span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./more-lambda-capabilities.html" class="navigation-link">Up</a> <a href="../index.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./tutorial_toc.html" class="navigation-link">Full TOC</a></span></td>
- <td class="header-group page-location"><a href="../index.html" class="navigation-link">Front Page</a> / <a href="./tutorial-metafunctions.html" class="navigation-link">Tutorial: Metafunctions and Higher-Order Metaprogramming</a> / <a href="./more-lambda-capabilities.html" class="navigation-link">More Lambda Capabilities</a> / <a href="./metafunction-composition.html" class="navigation-link">Metafunction Composition</a></td>
- </tr></table><div class="header-separator"></div>
- <div class="section" id="metafunction-composition">
- <h1><a class="toc-backref" href="./more-lambda-capabilities.html#id53" name="metafunction-composition">Metafunction Composition</a></h1>
- <p>Lambda expressions can also be used to assemble more interesting
- computations from simple metafunctions. For example, the following
- expression, which multiplies the sum of two numbers by their
- difference, is a <strong>composition</strong> of the three metafunctions <tt class="literal"><span class="pre">multiplies</span></tt>,
- <tt class="literal"><span class="pre">plus</span></tt>, and <tt class="literal"><span class="pre">minus</span></tt>:</p>
- <pre class="literal-block">
- mpl::multiplies<mpl::plus<_1,_2>, mpl::minus<_1,_2> >
- </pre>
- <!-- @ example.wrap(apply_test[0],
- ', mpl::int_<5>,mpl::int_<3>' + apply_test[1] % 16)
- # Can't exactly justify this yet, but there's no way to get
- # it into the text
- prefix += ['#include <boost/mpl/multiplies.hpp>']
- compile() -->
- <p>When evaluating a lambda expression, MPL checks to see if any of its
- arguments are themselves lambda expressions, and evaluates each one
- that it finds. The results of these inner evaluations are substituted
- into the outer expression before it is evaluated.</p>
- </div>
- <div class="footer-separator"></div>
- <table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./partial-metafunction.html" class="navigation-link">Prev</a> <a href="./lambda-details.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./partial-metafunction.html" class="navigation-link">Back</a> Along</span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./more-lambda-capabilities.html" class="navigation-link">Up</a> <a href="../index.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./tutorial_toc.html" class="navigation-link">Full TOC</a></span></td>
- </tr></table></body>
- </html>
|