1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>FAQ</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="CallableTraits"> 8<link rel="up" href="../index.html" title="CallableTraits"> 9<link rel="prev" href="reference.html" title="Reference Documentation"> 10<link rel="next" href="building.html" title="Building the test suite"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="reference.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="building.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="callable_traits.faq"></a><a class="link" href="faq.html" title="FAQ">FAQ</a> 28</h2></div></div></div> 29<h4> 30<a name="callable_traits.faq.h0"></a> 31 <span class="phrase"><a name="callable_traits.faq.reasons"></a></span><a class="link" href="faq.html#callable_traits.faq.reasons">Why 32 should I use <code class="literal">Boost.CallableTraits</code>?</a> 33 </h4> 34<p> 35 If you are not writing generic code, you should not use <code class="literal">Boost.CallableTraits</code>. 36 </p> 37<p> 38 If you <span class="emphasis"><em>are</em></span> writing generic code, take a moment to skim 39 your header files, and see if you can find code that looks like this: 40 </p> 41<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Return</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">First</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Second</span><span class="special">></span> 42<span class="keyword">class</span> <span class="identifier">foo</span><span class="special"><</span><span class="identifier">Return</span><span class="special">(</span><span class="identifier">First</span><span class="special">,</span> <span class="identifier">Second</span><span class="special">)></span> <span class="special">{</span> 43 <span class="comment">// ^^^^^^^^^^^^^^^^^^^^^</span> 44<span class="special">};</span> 45</pre> 46<p> 47 Or maybe something like this: 48 </p> 49<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Return</span><span class="special">,</span> <span class="keyword">class</span> <span class="special">...</span><span class="identifier">Args</span><span class="special">></span> 50<span class="keyword">class</span> <span class="identifier">foo</span><span class="special"><</span><span class="identifier">Return</span><span class="special">(*)(</span><span class="identifier">Args</span><span class="special">...)></span> <span class="special">{</span> 51 <span class="comment">// ^^^^^^^^^^^^^^^^^^</span> 52<span class="special">};</span> 53</pre> 54<p> 55 Or, if you are <span class="bold"><strong>really</strong></span> unlucky, something like 56 this: 57 </p> 58<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Return</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="special">...</span><span class="identifier">Args</span><span class="special">></span> 59<span class="keyword">class</span> <span class="identifier">foo</span><span class="special"><</span><span class="identifier">Return</span><span class="special">(</span><span class="identifier">T</span><span class="special">::*)(</span><span class="identifier">Args</span><span class="special">...,</span> <span class="special">...)</span> <span class="keyword">const</span> <span class="keyword">volatile</span> <span class="special">&</span> <span class="keyword">noexcept</span><span class="special">></span> <span class="special">{</span> 60 <span class="comment">// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^</span> 61<span class="special">};</span> 62</pre> 63<p> 64 With <code class="literal">Boost.CallableTraits</code>, you can get rid of all of these 65 template specializations (unless you deal with platform-specific calling conventions, 66 for now). Even if you are only specializing a simple function type like <code class="computeroutput"><span class="identifier">Return</span><span class="special">(</span><span class="identifier">Args</span><span class="special">...)</span></code>, <code class="literal">Boost.CallableTraits</code> 67 might be useful to you. You may find that <code class="literal">Boost.CallableTraits</code> 68 can help make your code more readable, more maintainable, more generic, and 69 less error-prone. 70 </p> 71<p> 72 <code class="literal">Boost.CallableTraits</code> is well-tested on many platforms. 73 <code class="literal">Boost.CallableTraits</code> correctly handles many corner cases 74 that are often overlooked. The need for a proper library solution grows as 75 more features are added to C++. 76 </p> 77<h4> 78<a name="callable_traits.faq.h1"></a> 79 <span class="phrase"><a name="callable_traits.faq.boost_is_a_massive_dependency_do"></a></span><a class="link" href="faq.html#callable_traits.faq.boost_is_a_massive_dependency_do">Boost 80 is a massive dependency. Do I really need it?</a> 81 </h4> 82<p> 83 Nope! <code class="literal">Boost.CallableTraits</code> doesn't have any dependencies, 84 so all you need are the <code class="literal">Boost.CallableTraits</code> headers. 85 </p> 86<h4> 87<a name="callable_traits.faq.h2"></a> 88 <span class="phrase"><a name="callable_traits.faq.why_use_reference_collapsing_rul"></a></span><a class="link" href="faq.html#callable_traits.faq.why_use_reference_collapsing_rul">Why 89 use reference collapsing rules when adding member function ref-qualifiers?</a> 90 </h4> 91<p> 92 Although arbitrary, the reference collapsing rules are well-defined and already 93 known to many template metaprogrammers. Anything else would be a burden to 94 memorize. This also parallels the metafunctions provided in <code class="computeroutput"><span class="special"><</span><span class="identifier">type_traits</span><span class="special">></span></code>. 95 </p> 96<h4> 97<a name="callable_traits.faq.h3"></a> 98 <span class="phrase"><a name="callable_traits.faq.many_features_in_this_library_ca"></a></span><a class="link" href="faq.html#callable_traits.faq.many_features_in_this_library_ca">Many 99 features in this library cause a "substitution failure" when the 100 template constraints are violated. Does this mean that I can violate the constraints 101 in a SFINAE context, as long as there is another legal substitute?</a> 102 </h4> 103<p> 104 Yes. The SFINAE-ability of violated constraints has been tested extensively 105 on supported compilers. Achieving this required some messy code in the public 106 header files. 107 </p> 108<h4> 109<a name="callable_traits.faq.h4"></a> 110 <span class="phrase"><a name="callable_traits.faq.what_about_calling_conventions"></a></span><a class="link" href="faq.html#callable_traits.faq.what_about_calling_conventions">What 111 about calling conventions?</a> 112 </h4> 113<p> 114 I originally implemented features for these. However, these features necessitated 115 many, many more platform-specific test cases. The code is still designed to 116 accommodate such features, so I would consider adding them in the future if 117 there is sufficient interest. 118 </p> 119</div> 120<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 121<td align="left"></td> 122<td align="right"><div class="copyright-footer">Copyright © 2016-2018 Barrett Adair<p> 123 Distributed under the Boost Software License, Version 1.0. (See accompanying 124 file LICENSE.md or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 125 </p> 126</div></td> 127</tr></table> 128<hr> 129<div class="spirit-nav"> 130<a accesskey="p" href="reference.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="building.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 131</div> 132</body> 133</html> 134
