Planet
navi homePPSaboutscreenshotsdownloaddevelopmentforum

source: downloads/boost_1_34_1/libs/mpl/doc/refmanual/eval-if-c.html @ 29

Last change on this file since 29 was 29, checked in by landauf, 17 years ago

updated boost from 1_33_1 to 1_34_1
File size: 7.8 KB
Line 
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 MPL Reference Manual: eval_if_c</title>
11<link rel="stylesheet" href="../style.css" type="text/css" />
12</head>
13<body class="docframe refmanual">
14<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./eval-if.html" class="navigation-link">Prev</a>&nbsp;<a href="./invocation.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./eval-if.html" class="navigation-link">Back</a>&nbsp;Along</span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./type-selection.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
15<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="./type-selection.html" class="navigation-link">Type Selection</a> / <a href="./eval-if-c.html" class="navigation-link">eval_if_c</a></td>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="eval-if-c">
18<h1><a class="toc-backref" href="./type-selection.html#id449" name="eval-if-c">eval_if_c</a></h1>
19<div class="section" id="type-eval-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22template&lt; 
23      bool c
24    , typename F1
25    , typename F2
26    &gt;
27struct <a href="./eval-if-c.html" class="identifier">eval_if_c</a>
28{
29    typedef <em>unspecified</em> type;
30};
31</pre>
32</div>
33<div class="section" id="type-eval-description">
34<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
35<p>Evaluates one of its two <a class="reference" href="./metafunction.html#nullary-metafunction">nullary-metafunction</a> arguments, <tt class="literal"><span class="pre">F1</span></tt> or <tt class="literal"><span class="pre">F2</span></tt>, depending
36on the value of integral constant <tt class="literal"><span class="pre">c</span></tt>. <tt class="literal"><span class="pre"><a href="./eval-if-c.html" class="identifier">eval_if_c</a>&lt;c,f1,f2&gt;::type</span></tt> is a shorcut
37notation for <tt class="literal"><span class="pre"><a href="./eval-if.html" class="identifier">eval_if</a>&lt;</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a>&lt;c&gt;,f1,f2</span> <span class="pre">&gt;::type</span></tt>.</p>
38</div>
39<div class="section" id="type-eval-header">
40<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
41<pre class="literal-block">
42#include &lt;<a href="../../../../boost/mpl/eval_if.hpp" class="header">boost/mpl/eval_if.hpp</a>&gt;
43</pre>
44</div>
45<div class="section" id="type-eval-parameters">
46<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
47<table border="1" class="table">
48<colgroup>
49<col width="15%" />
50<col width="36%" />
51<col width="48%" />
52</colgroup>
53<thead valign="bottom">
54<tr><th>Parameter</th>
55<th>Requirement</th>
56<th>Description</th>
57</tr>
58</thead>
59<tbody valign="top">
60<tr><td><tt class="literal"><span class="pre">c</span></tt></td>
61<td>An integral constant</td>
62<td>An evaluation condition.</td>
63</tr>
64<tr><td><tt class="literal"><span class="pre">F1</span></tt>, <tt class="literal"><span class="pre">F2</span></tt></td>
65<td>Nullary <a class="reference" href="./metafunction.html">Metafunction</a></td>
66<td>Metafunctions to select for evaluation from.</td>
67</tr>
68</tbody>
69</table>
70</div>
71<div class="section" id="type-eval-expression-semantics">
72<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
73<p>For any integral constant <tt class="literal"><span class="pre">c</span></tt> and nullary <a class="reference" href="./metafunction.html">Metafunction</a>s <tt class="literal"><span class="pre">f1</span></tt>, <tt class="literal"><span class="pre">f2</span></tt>:</p>
74<pre class="literal-block">
75typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a>&lt;c,f1,f2&gt;::type t;
76</pre>
77<table class="field-list" frame="void" rules="none">
78<col class="field-name" />
79<col class="field-body" />
80<tbody valign="top">
81<tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td>
82</tr>
83<tr class="field"><th class="field-name">Semantics:</th><td class="field-body">Equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre"><a href="./eval-if.html" class="identifier">eval_if</a>&lt;</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a>&lt;c&gt;,f1,f2</span> <span class="pre">&gt;::type</span> <span class="pre">t;</span></tt></td>
84</tr>
85</tbody>
86</table>
87</div>
88<div class="section" id="type-eval-example">
89<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
90<pre class="literal-block">
91typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a>&lt; true, <a href="./identity.html" class="identifier">identity</a>&lt;char&gt;, <a href="./identity.html" class="identifier">identity</a>&lt;long&gt; &gt;::type t1;
92typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a>&lt; false, <a href="./identity.html" class="identifier">identity</a>&lt;char&gt;, <a href="./identity.html" class="identifier">identity</a>&lt;long&gt; &gt;::type t2;
93
94<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;t1,char&gt; ));
95<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;t2,long&gt; ));
96</pre>
97</div>
98<div class="section" id="type-eval-see-also">
99<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
100<p><a class="reference" href="./metafunctions.html">Metafunctions</a>, <a class="reference" href="./integral-constant.html">Integral Constant</a>, <a class="refentry reference" href="./eval-if.html"><tt class="refentry literal"><span class="pre">eval_if</span></tt></a>, <a class="refentry reference" href="./if.html"><tt class="refentry literal"><span class="pre">if_</span></tt></a>, <a class="refentry reference" href="./bool.html"><tt class="refentry literal"><span class="pre">bool_</span></tt></a></p>
101<!-- modtime: November 10, 2004 04:42:25 +0000 -->
102</div>
103</div>
104
105<div class="footer-separator"></div>
106<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./eval-if.html" class="navigation-link">Prev</a>&nbsp;<a href="./invocation.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./eval-if.html" class="navigation-link">Back</a>&nbsp;Along</span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./type-selection.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
107</tr></table></body>
108</html>
Note: See TracBrowser for help on using the repository browser.