]>
Commit | Line | Data |
---|---|---|
7c673cae FG |
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 | <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: if_c</title> | |
8 | <link rel="stylesheet" href="../style.css" type="text/css" /> | |
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="./if.html" class="navigation-link">Prev</a> <a href="./eval-if.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./if.html" class="navigation-link">Back</a> <a href="./eval-if.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./type-selection.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="./type-selection.html" class="navigation-link">Type Selection</a> / <a href="./if-c.html" class="navigation-link">if_c</a></td> | |
13 | </tr></table><div class="header-separator"></div> | |
14 | <div class="section" id="if-c"> | |
15 | <h1><a class="toc-backref" href="./type-selection.html#id1521">if_c</a></h1> | |
16 | <div class="section" id="id866"> | |
17 | <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> | |
18 | <pre class="literal-block"> | |
19 | template< | |
20 | bool c | |
21 | , typename T1 | |
22 | , typename T2 | |
23 | > | |
24 | struct <a href="./if-c.html" class="identifier">if_c</a> | |
25 | { | |
26 | typedef <em>unspecified</em> type; | |
27 | }; | |
28 | </pre> | |
29 | </div> | |
30 | <div class="section" id="id867"> | |
31 | <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> | |
32 | <p>Returns one of its two arguments, <tt class="literal"><span class="pre">T1</span></tt> or <tt class="literal"><span class="pre">T2</span></tt>, depending on the value of | |
33 | integral constant <tt class="literal"><span class="pre">c</span></tt>. <tt class="literal"><span class="pre"><a href="./if-c.html" class="identifier">if_c</a><c,t1,t2>::type</span></tt> is a shorcut notation for | |
34 | <tt class="literal"><span class="pre"><a href="./if.html" class="identifier">if_</a><</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a><c>,t1,t2</span> <span class="pre">>::type</span></tt>.</p> | |
35 | </div> | |
36 | <div class="section" id="id868"> | |
37 | <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> | |
38 | <pre class="literal-block"> | |
39 | #include <<a href="../../../../boost/mpl/if.hpp" class="header">boost/mpl/if.hpp</a>> | |
40 | </pre> | |
41 | </div> | |
42 | <div class="section" id="id869"> | |
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="15%" /> | |
47 | <col width="36%" /> | |
48 | <col width="48%" /> | |
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">c</span></tt></td> | |
58 | <td>An integral constant</td> | |
59 | <td>A selection condition.</td> | |
60 | </tr> | |
61 | <tr><td><tt class="literal"><span class="pre">T1</span></tt>, <tt class="literal"><span class="pre">T2</span></tt></td> | |
62 | <td>Any type</td> | |
63 | <td>Types to select from.</td> | |
64 | </tr> | |
65 | </tbody> | |
66 | </table> | |
67 | </div> | |
68 | <div class="section" id="id870"> | |
69 | <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> | |
70 | <p>For any integral constant <tt class="literal"><span class="pre">c</span></tt> and arbitrary types <tt class="literal"><span class="pre">t1</span></tt>, <tt class="literal"><span class="pre">t2</span></tt>:</p> | |
71 | <pre class="literal-block"> | |
72 | typedef <a href="./if-c.html" class="identifier">if_c</a><c,t1,t2>::type t; | |
73 | </pre> | |
74 | <table class="docutils field-list" frame="void" rules="none"> | |
75 | <col class="field-name" /> | |
76 | <col class="field-body" /> | |
77 | <tbody valign="top"> | |
78 | <tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td> | |
79 | </tr> | |
80 | <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="./if.html" class="identifier">if_</a><</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a><c>,t1,t2</span> <span class="pre">>::type</span> <span class="pre">t;</span></tt></td> | |
81 | </tr> | |
82 | </tbody> | |
83 | </table> | |
84 | </div> | |
85 | <div class="section" id="id871"> | |
86 | <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> | |
87 | <pre class="literal-block"> | |
88 | typedef <a href="./if-c.html" class="identifier">if_c</a><true,char,long>::type t1; | |
89 | typedef <a href="./if-c.html" class="identifier">if_c</a><false,char,long>::type t2; | |
90 | ||
91 | <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same<t1, char> )); | |
92 | <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same<t2, long> )); | |
93 | </pre> | |
94 | <pre class="literal-block"> | |
95 | // allocates space for an object of class T on heap or "inplace" | |
96 | // depending on its <a href="./size.html" class="identifier">size</a> | |
97 | template< typename T > struct lightweight | |
98 | { | |
99 | // ... | |
100 | typedef typename <a href="./if-c.html" class="identifier">if_c</a>< | |
101 | sizeof(T) <= sizeof(T*) | |
102 | , inplace_storage<T> | |
103 | , heap_storage<T> | |
104 | >::type impl_t; | |
105 | ||
106 | impl_t impl; | |
107 | }; | |
108 | </pre> | |
109 | </div> | |
110 | <div class="section" id="id872"> | |
111 | <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> | |
112 | <p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./integral-constant.html">Integral Constant</a>, <a class="reference internal" href="./if.html">if_</a>, <a class="reference internal" href="./eval-if.html">eval_if</a>, <a class="reference internal" href="./bool.html">bool_</a></p> | |
113 | <!-- Metafunctions/Type Selection//eval_if |30 --> | |
114 | </div> | |
115 | </div> | |
116 | ||
117 | <div class="footer-separator"></div> | |
118 | <table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./if.html" class="navigation-link">Prev</a> <a href="./eval-if.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./if.html" class="navigation-link">Back</a> <a href="./eval-if.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./type-selection.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> | |
119 | <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> | |
120 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
121 | 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> | |
122 | </html> |