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| author | Anas Nashif <anas.nashif@intel.com> | 2012-10-30 12:57:26 -0700 |
|---|---|---|
| committer | Anas Nashif <anas.nashif@intel.com> | 2012-10-30 12:57:26 -0700 |
| commit | 1a78a62555be32868418fe52f8e330c9d0f95d5a (patch) | |
| tree | d3765a80e7d3b9640ec2e930743630cd6b9fce2b /libs/type_traits/doc/html/boost_typetraits/reference/has_negate.html | |
| download | boost-1a78a62555be32868418fe52f8e330c9d0f95d5a.tar.gz boost-1a78a62555be32868418fe52f8e330c9d0f95d5a.tar.bz2 boost-1a78a62555be32868418fe52f8e330c9d0f95d5a.zip | |
Imported Upstream version 1.49.0upstream/1.49.0
Diffstat (limited to 'libs/type_traits/doc/html/boost_typetraits/reference/has_negate.html')
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1 files changed, 195 insertions, 0 deletions
diff --git a/libs/type_traits/doc/html/boost_typetraits/reference/has_negate.html b/libs/type_traits/doc/html/boost_typetraits/reference/has_negate.html new file mode 100644 index 0000000000..d397534643 --- /dev/null +++ b/libs/type_traits/doc/html/boost_typetraits/reference/has_negate.html @@ -0,0 +1,195 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>has_negate</title> +<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> +<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits"> +<link rel="up" href="../reference.html" title="Alphabetical Reference"> +<link rel="prev" href="has_multiplies_assign.html" title="has_multiplies_assign"> +<link rel="next" href="has_new_operator.html" title="has_new_operator"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> +<table cellpadding="2" width="100%"><tr> +<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> +<td align="center"><a href="../../../../../../index.html">Home</a></td> +<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> +<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> +<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> +<td align="center"><a href="../../../../../../more/index.htm">More</a></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="has_multiplies_assign.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="has_new_operator.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="boost_typetraits.reference.has_negate"></a><a class="link" href="has_negate.html" title="has_negate">has_negate</a> +</h3></div></div></div> +<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Rhs</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Ret</span><span class="special">=</span><span class="identifier">dont_care</span><span class="special">></span> +<span class="keyword">struct</span> <span class="identifier">has_negate</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span> +</pre> +<p> + <span class="bold"><strong>Inherits:</strong></span> If (i) <code class="computeroutput"><span class="identifier">rhs</span></code> + of type <code class="computeroutput"><span class="identifier">Rhs</span></code> can be used in + expression <code class="computeroutput"><span class="special">-</span><span class="identifier">rhs</span></code>, + and (ii) <code class="computeroutput"><span class="identifier">Ret</span><span class="special">=</span><span class="identifier">dont_care</span></code> or the result of expression + <code class="computeroutput"><span class="special">-</span><span class="identifier">rhs</span></code> + is convertible to <code class="computeroutput"><span class="identifier">Ret</span></code> then + inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>, + otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>. + </p> +<p> + The default behaviour (<code class="computeroutput"><span class="identifier">Ret</span><span class="special">=</span><span class="identifier">dont_care</span></code>) + is to not check for the return value of prefix <code class="computeroutput"><span class="keyword">operator</span><span class="special">-</span></code>. If <code class="computeroutput"><span class="identifier">Ret</span></code> + is different from the default <code class="computeroutput"><span class="identifier">dont_care</span></code> + type, the return value is checked to be convertible to <code class="computeroutput"><span class="identifier">Ret</span></code>. + Convertible to <code class="computeroutput"><span class="identifier">Ret</span></code> means + that the return value of the operator can be used as argument to a function + expecting <code class="computeroutput"><span class="identifier">Ret</span></code>: +</p> +<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">Ret</span><span class="special">);</span> +<span class="identifier">Rhs</span> <span class="identifier">rhs</span><span class="special">;</span> +<span class="identifier">f</span><span class="special">(-</span><span class="identifier">rhs</span><span class="special">);</span> <span class="comment">// is valid if has_negate<Rhs, Ret>::value==true</span> +</pre> +<p> + If <code class="computeroutput"><span class="identifier">Ret</span><span class="special">=</span><span class="keyword">void</span></code>, the return type is checked to be exactly + <code class="computeroutput"><span class="keyword">void</span></code>. + </p> +<p> + <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"><span class="preprocessor">#include</span> + <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">has_negate</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> + or <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">has_operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> + or <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> + </p> +<p> + <span class="bold"><strong>Examples:</strong></span> + </p> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="identifier">Rhs</span><span class="special">,</span> <span class="identifier">Ret</span><span class="special">>::</span><span class="identifier">value_type</span></code> is the type <code class="computeroutput"><span class="keyword">bool</span></code>. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="identifier">Rhs</span><span class="special">,</span> <span class="identifier">Ret</span><span class="special">>::</span><span class="identifier">value</span></code> is a <code class="computeroutput"><span class="keyword">bool</span></code> + integral constant expression. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">value</span></code> is a <code class="computeroutput"><span class="keyword">bool</span></code> + integral constant expression that evaluates to <code class="computeroutput"><span class="keyword">true</span></code>. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="keyword">long</span><span class="special">></span></code> + inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span></code> inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">long</span><span class="special">></span></code> inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">double</span><span class="special">></span></code> + inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span></code> + inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">></span></code> inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. + </p></blockquote></div> +<div class="blockquote"><blockquote class="blockquote"><p> + <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span></code> inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code>. + </p></blockquote></div> +<p> + <span class="bold"><strong>See also:</strong></span> <a class="link" href="../category/value_traits/operators.html" title="Operator Type Traits">Operator + Type Traits</a> + </p> +<p> + <span class="bold"><strong>Limitation:</strong></span> + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> + Requires a compiler with working SFINAE. + </li></ul></div> +<p> + <span class="bold"><strong>Known issues:</strong></span> + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem"> + This trait cannot detect whether prefix <code class="computeroutput"><span class="keyword">operator</span><span class="special">-</span></code> is public or not: if <code class="computeroutput"><span class="keyword">operator</span><span class="special">-</span></code> is defined as a private member of <code class="computeroutput"><span class="identifier">Rhs</span></code> then instantiating <code class="computeroutput"><span class="identifier">has_negate</span><span class="special"><</span><span class="identifier">Rhs</span><span class="special">></span></code> + will produce a compiler error. For this reason <code class="computeroutput"><span class="identifier">has_negate</span></code> + cannot be used to determine whether a type has a public <code class="computeroutput"><span class="keyword">operator</span><span class="special">-</span></code> + or not. +<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">A</span> <span class="special">{</span> <span class="keyword">private</span><span class="special">:</span> <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">-();</span> <span class="special">};</span> +<span class="identifier">boost</span><span class="special">::</span><span class="identifier">has_negate</span><span class="special"><</span><span class="identifier">A</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// error: A::operator-() is private</span> +</pre> + </li> +<li class="listitem"> + There is an issue if the operator exists only for type <code class="computeroutput"><span class="identifier">A</span></code> and <code class="computeroutput"><span class="identifier">B</span></code> + is convertible to <code class="computeroutput"><span class="identifier">A</span></code>. + In this case, the compiler will report an ambiguous overload. +<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">A</span> <span class="special">{</span> <span class="special">};</span> +<span class="keyword">void</span> <span class="keyword">operator</span><span class="special">-(</span><span class="keyword">const</span> <span class="identifier">A</span><span class="special">&);</span> +<span class="keyword">struct</span> <span class="identifier">B</span> <span class="special">{</span> <span class="keyword">operator</span> <span class="identifier">A</span><span class="special">();</span> <span class="special">};</span> +<span class="identifier">boost</span><span class="special">::</span><span class="identifier">has_negate</span><span class="special"><</span><span class="identifier">A</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// this is fine</span> +<span class="identifier">boost</span><span class="special">::</span><span class="identifier">has_negate</span><span class="special"><</span><span class="identifier">B</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// error: ambiguous overload</span> +</pre> + </li> +<li class="listitem"> + There is an issue when applying this trait to template classes. If <code class="computeroutput"><span class="keyword">operator</span><span class="special">-</span></code> + is defined but does not bind for a given template type, it is still detected + by the trait which returns <code class="computeroutput"><span class="keyword">true</span></code> + instead of <code class="computeroutput"><span class="keyword">false</span></code>. Example: + +<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">has_negate</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> +<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> + +<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> +<span class="keyword">struct</span> <span class="identifier">contains</span> <span class="special">{</span> <span class="identifier">T</span> <span class="identifier">data</span><span class="special">;</span> <span class="special">};</span> + +<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> +<span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">-(</span><span class="keyword">const</span> <span class="identifier">contains</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">&</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">{</span> + <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">data</span><span class="special">);</span> +<span class="special">}</span> + +<span class="keyword">class</span> <span class="identifier">bad</span> <span class="special">{</span> <span class="special">};</span> +<span class="keyword">class</span> <span class="identifier">good</span> <span class="special">{</span> <span class="special">};</span> +<span class="keyword">bool</span> <span class="identifier">f</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">good</span><span class="special">&)</span> <span class="special">{</span> <span class="special">}</span> + +<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> <span class="special">{</span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special"><<</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">boolalpha</span><span class="special">;</span> + <span class="comment">// works fine for contains<good></span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special"><<</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">has_negate</span><span class="special"><</span> <span class="identifier">contains</span><span class="special"><</span> <span class="identifier">good</span> <span class="special">></span> <span class="special">>::</span><span class="identifier">value</span><span class="special"><<</span><span class="char">'\n'</span><span class="special">;</span> <span class="comment">// true</span> + <span class="identifier">contains</span><span class="special"><</span><span class="identifier">good</span><span class="special">></span> <span class="identifier">g</span><span class="special">;</span> + <span class="special">-</span><span class="identifier">g</span><span class="special">;</span> <span class="comment">// ok</span> + <span class="comment">// does not work for contains<bad></span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special"><<</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">has_negate</span><span class="special"><</span> <span class="identifier">contains</span><span class="special"><</span> <span class="identifier">bad</span> <span class="special">></span> <span class="special">>::</span><span class="identifier">value</span><span class="special"><<</span><span class="char">'\n'</span><span class="special">;</span> <span class="comment">// true, should be false</span> + <span class="identifier">contains</span><span class="special"><</span><span class="identifier">bad</span><span class="special">></span> <span class="identifier">b</span><span class="special">;</span> + <span class="special">-</span><span class="identifier">b</span><span class="special">;</span> <span class="comment">// compile time error</span> + <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> +<span class="special">}</span> +</pre> + </li> +<li class="listitem"> + <code class="computeroutput"><span class="keyword">volatile</span></code> qualifier is not + properly handled and would lead to undefined behavior + </li> +</ul></div> +</div> +<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> +<td align="left"></td> +<td align="right"><div class="copyright-footer">Copyright © 2000, 2011 Adobe Systems Inc, David Abrahams, + Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, + Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten + Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven + Watanabe<p> + Distributed under the Boost Software License, Version 1.0. (See accompanying + file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) + </p> +</div></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="has_multiplies_assign.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="has_new_operator.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |