| 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"> |
|---|
| 3 | <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> |
|---|
| 4 | <!-- Copyright Aleksey Gurtovoy 2006. Distributed under the Boost --> |
|---|
| 5 | <!-- Software License, Version 1.0. (See accompanying --> |
|---|
| 6 | <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> |
|---|
| 7 | <head> |
|---|
| 8 | <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> |
|---|
| 9 | <meta name="generator" content="Docutils 0.3.6: http://docutils.sourceforge.net/" /> |
|---|
| 10 | <title>THE BOOST MPL LIBRARY: Partial Metafunction Application</title> |
|---|
| 11 | <link rel="stylesheet" href="../style.css" type="text/css" /> |
|---|
| 12 | </head> |
|---|
| 13 | <body class="docframe"> |
|---|
| 14 | <table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./more-lambda-capabilities.html" class="navigation-link">Prev</a> <a href="./metafunction-composition.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group">Back <a href="./metafunction-composition.html" class="navigation-link">Along</a></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> |
|---|
| 15 | <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="./partial-metafunction.html" class="navigation-link">Partial Metafunction Application</a></td> |
|---|
| 16 | </tr></table><div class="header-separator"></div> |
|---|
| 17 | <div class="section" id="partial-metafunction"> |
|---|
| 18 | <h1><a class="toc-backref" href="./more-lambda-capabilities.html#id52" name="partial-metafunction">Partial Metafunction Application</a></h1> |
|---|
| 19 | <p>Consider the lambda expression <tt class="literal"><span class="pre">mpl::plus<_1,_1></span></tt>. A single |
|---|
| 20 | argument is directed to both of <tt class="literal"><span class="pre">plus</span></tt>'s parameters, thereby |
|---|
| 21 | adding a number to itself. Thus, a <em>binary</em> metafunction, |
|---|
| 22 | <tt class="literal"><span class="pre">plus</span></tt>, is used to build a <em>unary</em> lambda expression. In other |
|---|
| 23 | words, we've created a whole new computation! We're not done yet, |
|---|
| 24 | though: By supplying a non-placeholder as one of the arguments, we |
|---|
| 25 | can build a unary lambda expression that adds a fixed value, say |
|---|
| 26 | 42, to its argument:</p> |
|---|
| 27 | <pre class="literal-block"> |
|---|
| 28 | mpl::plus<_1, mpl::int_<42> > |
|---|
| 29 | </pre> |
|---|
| 30 | <!-- @ apply_test = 'enum { value = mpl::apply<', ''' >::type::value }; |
|---|
| 31 | BOOST_STATIC_ASSERT(value == %d);''' |
|---|
| 32 | |
|---|
| 33 | example.wrap(apply_test[0], |
|---|
| 34 | ', mpl::int_<3>' + apply_test[1] % 45) |
|---|
| 35 | compile() --> |
|---|
| 36 | <p>The process of binding argument values to a subset of a function's |
|---|
| 37 | parameters is known in the world of functional programming as |
|---|
| 38 | <strong>partial function application</strong>.</p> |
|---|
| 39 | </div> |
|---|
| 40 | |
|---|
| 41 | <div class="footer-separator"></div> |
|---|
| 42 | <table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./more-lambda-capabilities.html" class="navigation-link">Prev</a> <a href="./metafunction-composition.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group">Back <a href="./metafunction-composition.html" class="navigation-link">Along</a></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> |
|---|
| 43 | </tr></table></body> |
|---|
| 44 | </html> |
|---|
