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<a name="callable_traits"></a>CallableTraits</h2></div>
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<div><div class="authorgroup"><div class="author"><h3 class="author">
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<span class="firstname">Barrett</span> <span class="surname">Adair</span>
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<div><p class="copyright">Copyright © 2016 Barrett Adair</p></div>
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<a name="callable_traits.legal"></a><p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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>)
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<p><b>Table of Contents</b></p>
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<dl class="toc">
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<dt><span class="section"><a href="index.html#callable_traits.introduction">Overview</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="index.html#callable_traits.introduction.prereqs">Prerequisite Topics</a></span></dt>
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<dt><span class="section"><a href="index.html#callable_traits.introduction.motivation">Motivation</a></span></dt>
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<dt><span class="section"><a href="index.html#callable_traits.introduction.boost_function_types">Regarding
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<code class="literal">Boost.FunctionTypes</code></a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="callable_traits/compatibility.html">Compatibility</a></span></dt>
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<dt><span class="section"><a href="callable_traits/faq.html">FAQ</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="callable_traits/faq.html#callable_traits.faq.reasons">Why should I use <code class="literal">CallableTraits</code>?</a></span></dt>
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<dt><span class="section"><a href="callable_traits/faq.html#callable_traits.faq.why_does_namespace_scoped_args_a">Why
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does <code class="literal">callable_traits::</code><code class="literal">args</code> alias a <code class="literal">std::tuple</code>?</a></span></dt>
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<dt><span class="section"><a href="callable_traits/faq.html#callable_traits.faq.why_use_reference_collapsing_rul">Why
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use reference collapsing rules when adding member function ref-qualifiers?</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="callable_traits/building.html">Building the test suite</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_add_member_const.html">add_member_const</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_add_member_cv.html">add_member_cv</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_add_member_lvalue_reference.html">add_member_lvalue_reference</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_add_member_rvalue_reference.html">add_member_rvalue_reference</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_add_member_volatile.html">add_member_volatile</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_add_transaction_safe.html">add_transaction_safe</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_add_varargs.html">add_varargs</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_apply_member_pointer.html">apply_member_pointer</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_apply_return.html">apply_return</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_arg_at.html">arg_at</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_args.html">args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_clear_args.html">clear_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_expand_args.html">expand_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_expand_args_left.html">expand_args_left</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_expand_args_right.html">expand_args_right</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_insert_args.html">insert_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_replace_args.html">replace_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_remove_args.html">remove_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_expand_args0.html">expand_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_function_type.html">function_type</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_has_calling_convention.html">has_calling_convention</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_has_varargs.html">has_varargs</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_has_void_return.html">has_void_return</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_is_const_member.html">is_const_member</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_is_cv_member.html">is_cv_member</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_is_lvalue_reference_member.html">is_lvalue_reference_member</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_is_reference_member.html">is_reference_member</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_is_rvalue_reference_member.html">is_rvalue_reference_member</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_has_member_qualifiers.html">has_member_qualifiers</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_is_volatile_member.html">is_volatile_member</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_remove_member_const.html">remove_member_const</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_remove_member_cv.html">remove_member_cv</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_remove_member_pointer.html">remove_member_pointer</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_remove_member_reference.html">remove_member_reference</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_remove_varargs.html">remove_varargs</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_remove_member_volatile.html">remove_member_volatile</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_push_back_args.html">push_back_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_push_front_args.html">push_front_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_pop_back_args.html">pop_back_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_push_front_args0.html">pop_front_args</a></span></dt>
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<dt><span class="section"><a href="callable_traits/ref_result_of.html">result_of</a></span></dt>
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<dt><span class="article"><a href="callable_traits_interface_example.html">Example: Java-style interfaces without inheritance</a></span></dt>
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<dt><span class="section"><a href="callable_traits/contact.html">Contact</a></span></dt>
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</dl>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="callable_traits.introduction"></a><a class="link" href="index.html#callable_traits.introduction" title="Overview">Overview</a>
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</h2></div></div></div>
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<div class="toc"><dl class="toc">
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<dt><span class="section"><a href="index.html#callable_traits.introduction.prereqs">Prerequisite Topics</a></span></dt>
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<dt><span class="section"><a href="index.html#callable_traits.introduction.motivation">Motivation</a></span></dt>
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<dt><span class="section"><a href="index.html#callable_traits.introduction.boost_function_types">Regarding
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<code class="literal">Boost.FunctionTypes</code></a></span></dt>
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</dl></div>
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<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">callable_traits</span><span class="special">/</span><span class="identifier">callable_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">type_traits</span><span class="special">></span>
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<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">tuple</span><span class="special">></span>
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<span class="keyword">using</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">is_same</span><span class="special">;</span>
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<span class="keyword">using</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">;</span>
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<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">callable_traits</span><span class="special">;</span>
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<span class="keyword">struct</span> <span class="identifier">number</span> <span class="special">{</span>
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<span class="keyword">int</span> <span class="identifier">value</span><span class="special">;</span>
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<span class="keyword">auto</span> <span class="identifier">add</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">value</span> <span class="special">+</span> <span class="identifier">n</span><span class="special">;</span> <span class="special">}</span>
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<span class="special">};</span>
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<span class="keyword">using</span> <span class="identifier">pmf</span> <span class="special">=</span> <span class="keyword">decltype</span><span class="special">(&</span><span class="identifier">number</span><span class="special">::</span><span class="identifier">add</span><span class="special">);</span>
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</pre>
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<p>
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Manipulate member functions pointers with ease:
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</p>
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<pre class="programlisting"><span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">remove_member_const_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>,</span>
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<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)(</span><span class="keyword">int</span><span class="special">)</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">add_member_volatile_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>,</span>
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<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)(</span><span class="keyword">int</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">volatile</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">parent_class_of_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>,</span>
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<span class="identifier">number</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">remove_member_pointer_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>,</span>
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<span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)</span> <span class="keyword">const</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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</pre>
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<p>
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INVOKE-aware metafunctions:
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</p>
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<pre class="programlisting"><span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">args_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>,</span>
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<span class="identifier">tuple</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">number</span><span class="special">&,</span> <span class="keyword">int</span><span class="special">></span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">arg_at_t</span><span class="special"><</span><span class="number">0</span><span class="special">,</span> <span class="identifier">pmf</span><span class="special">>,</span>
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<span class="keyword">const</span> <span class="identifier">number</span><span class="special">&</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">arg_at_t</span><span class="special"><</span><span class="number">1</span><span class="special">,</span> <span class="identifier">pmf</span><span class="special">>,</span>
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<span class="keyword">int</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">result_of_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>,</span>
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<span class="keyword">int</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">function_type_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>,</span>
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<span class="keyword">int</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">number</span><span class="special">&,</span> <span class="keyword">int</span><span class="special">)</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">qualified_parent_class_of_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>,</span>
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<span class="keyword">const</span> <span class="identifier">number</span><span class="special">&</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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</pre>
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<p>
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Here are a few other trait examples:
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</p>
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<pre class="programlisting"><span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_const_member</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(!</span><span class="identifier">is_volatile_member</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(!</span><span class="identifier">has_void_return</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(!</span><span class="identifier">has_varargs</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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</pre>
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<p>
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You can use <code class="literal">CallableTraits</code> to manipulate parameter lists
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(not defined in terms of INVOKE, since that wouldn't make sense here):
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</p>
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<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">pmf_2</span> <span class="special">=</span> <span class="identifier">push_back_args_t</span><span class="special"><</span><span class="identifier">pmf</span><span class="special">,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">short</span><span class="special">,</span> <span class="keyword">long</span><span class="special">>;</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">pmf_2</span><span class="special">,</span>
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<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">short</span><span class="special">,</span> <span class="keyword">long</span><span class="special">)</span> <span class="keyword">const</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">pop_front_args_t</span><span class="special"><</span><span class="identifier">pmf_2</span><span class="special">>,</span>
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<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)(</span><span class="keyword">char</span><span class="special">,</span> <span class="keyword">short</span><span class="special">,</span> <span class="keyword">long</span><span class="special">)</span> <span class="keyword">const</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
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<span class="identifier">insert_args_t</span><span class="special"><</span><span class="number">2</span><span class="special">,</span> <span class="identifier">pmf_2</span><span class="special">,</span> <span class="keyword">short</span><span class="special">*,</span> <span class="keyword">long</span><span class="special">*>,</span>
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<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">short</span><span class="special">*,</span> <span class="keyword">long</span><span class="special">*,</span> <span class="keyword">short</span><span class="special">,</span> <span class="keyword">long</span><span class="special">)</span> <span class="keyword">const</span>
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<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
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|
|
<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
|
|
<span class="identifier">replace_args_t</span><span class="special"><</span><span class="number">2</span><span class="special">,</span> <span class="identifier">pmf_2</span><span class="special">,</span> <span class="keyword">short</span><span class="special">*,</span> <span class="keyword">long</span><span class="special">*>,</span>
|
|
<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">short</span><span class="special">*,</span> <span class="keyword">long</span><span class="special">*)</span> <span class="keyword">const</span>
|
|
<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
|
|
|
|
<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
|
|
<span class="identifier">remove_args_t</span><span class="special"><</span><span class="number">2</span><span class="special">,</span> <span class="identifier">pmf_2</span><span class="special">>,</span>
|
|
<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">long</span><span class="special">)</span> <span class="keyword">const</span>
|
|
<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
|
|
|
|
<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
|
|
<span class="identifier">clear_args_t</span><span class="special"><</span><span class="identifier">pmf_2</span><span class="special">>,</span>
|
|
<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)()</span> <span class="keyword">const</span>
|
|
<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
|
|
|
|
<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">is_same</span><span class="special"><</span>
|
|
<span class="identifier">add_varargs_t</span><span class="special"><</span><span class="identifier">pmf_2</span><span class="special">>,</span>
|
|
<span class="keyword">int</span><span class="special">(</span><span class="identifier">number</span><span class="special">::*)(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">short</span><span class="special">,</span> <span class="keyword">long</span><span class="special">,</span> <span class="special">...)</span> <span class="keyword">const</span>
|
|
<span class="special">>{},</span> <span class="string">""</span><span class="special">);</span>
|
|
</pre>
|
|
<p>
|
|
<code class="literal">CallableTraits</code> is a C++11/14/17 header-only library for
|
|
the inspection, synthesis, and decomposition of callable types. From <code class="computeroutput"><span class="keyword">const</span> <span class="keyword">volatile</span> <span class="special">&&</span></code> to container-like manipulation of
|
|
parameter lists, <code class="literal">CallableTraits</code> provides all the tools you
|
|
need to rid your codebase of function type specializations. <code class="literal">CallableTraits</code>
|
|
offers a comprehensive, fine-grained assortment of traits and metafunctions
|
|
for building and ripping apart C++'s most complicated and obscure types with
|
|
ease. <code class="literal">CallableTraits</code> fills the gaps where existing library
|
|
solutions fall short, aiming to be the "complete type manipulation facility
|
|
for function types" mentioned in the last section of <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2015/p0172r0.html" target="_top">p0172</a>,
|
|
the C++17 proposal regarding "abominable function types". <code class="literal">CallableTraits</code>
|
|
currently supports GCC 4.8 and later, Clang 3.5 and later, AppleClang from
|
|
XCode 6.3 and later, and Visual Studio 2015.
|
|
</p>
|
|
<p>
|
|
<code class="literal">CallableTraits</code> is header-only, and does not depend on any
|
|
headers outside the standard library.
|
|
</p>
|
|
<p>
|
|
<code class="literal">CallableTraits</code> is currently hosted at <a href="https://github.com/badair/callable_traits" target="_top">GitHub</a>.
|
|
<span class="bold"><strong><code class="literal">CallableTraits</code> is not a Boost library.</strong></span>
|
|
</p>
|
|
<div class="section">
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
<a name="callable_traits.introduction.prereqs"></a><a class="link" href="index.html#callable_traits.introduction.prereqs" title="Prerequisite Topics">Prerequisite Topics</a>
|
|
</h3></div></div></div>
|
|
<p>
|
|
This documentation will be most beneficial to readers who posess a basic
|
|
understanding of the following C++ features:
|
|
</p>
|
|
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/language/partial_specialization" target="_top">template
|
|
specializations</a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/language/sfinae" target="_top">SFINAE</a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/utility/functional/invoke" target="_top"><code class="literal"><span class="emphasis"><em>INVOKE</em></span></code></a>
|
|
rules
|
|
</li>
|
|
<li class="listitem">
|
|
function types
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/language/pointer#Pointers_to_functions" target="_top">function
|
|
pointers</a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://stackoverflow.com/questions/480248/function-references" target="_top">function
|
|
references</a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/language/pointer#Pointers_to_member_functions" target="_top">pointers
|
|
to member functions</a> (a.k.a. PMFs)
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/language/pointer#Pointers_to_data_members" target="_top">pointers
|
|
to data members</a> (a.k.a. PMDs)
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/language/operators#Function_call_operator" target="_top">the
|
|
function call operator, <code class="literal">operator()</code></a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="https://isocpp.org/blog/2012/11/universal-references-in-c11-scott-meyers" target="_top">universal
|
|
references</a> and <a href="http://stackoverflow.com/questions/13725747/concise-explanation-of-reference-collapsing-rules-requested-1-a-a-2" target="_top">reference
|
|
collapsing rules</a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/language/member_functions#const-.2C_volatile-.2C_and_ref-qualified_member_functions" target="_top">cv-qualified
|
|
and ref-qualified member functions</a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0172r0.html" target="_top">"abominable"
|
|
function types</a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/cpp/language/overloaded_address" target="_top">taking
|
|
the address of overloaded functions</a>
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="http://en.cppreference.com/w/c/language/variadic" target="_top">C-style
|
|
variadics</a>, a.k.a. varargs
|
|
</li>
|
|
<li class="listitem">
|
|
<a href="https://en.wikipedia.org/wiki/X86_calling_conventions" target="_top">calling
|
|
conventions</a>
|
|
</li>
|
|
</ul></div>
|
|
</div>
|
|
<div class="section">
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
<a name="callable_traits.introduction.motivation"></a><a class="link" href="index.html#callable_traits.introduction.motivation" title="Motivation">Motivation</a>
|
|
</h3></div></div></div>
|
|
<div class="blockquote"><blockquote class="blockquote">
|
|
<p>
|
|
<span class="bold"><strong><span class="emphasis"><em><span class="quote">“<span class="quote">Don't try to write helper code to
|
|
detect PMFs/PMDs and dispatch on them -- it is an <span class="underline">absolute
|
|
nightmare</span>. PMF types are the worst types by far in the core
|
|
language.</span>”</span></em></span></strong></span>
|
|
</p>
|
|
<p>
|
|
-- Stephan T. Lavavej, CppCon 2015, <a href="https://www.youtube.com/watch?v=zt7ThwVfap0&t=11m40s" target="_top">"functional:
|
|
What's New, And Proper Usage"</a>
|
|
</p>
|
|
</blockquote></div>
|
|
<p>
|
|
Consider for a moment the class template below, which defines all <span class="red"><span class="bold"><strong>48</strong></span></span> template specializations
|
|
necessary to account for all valid function types and member function pointer
|
|
types in C++11 and C++14:
|
|
</p>
|
|
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">foo</span><span class="special">;</span>
|
|
|
|
<span class="comment">//function type without varargs</span>
|
|
<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> <span class="keyword">struct</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>
|
|
<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> <span class="keyword">struct</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> <span class="special">{};</span>
|
|
<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> <span class="keyword">struct</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> <span class="special">{};</span>
|
|
<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> <span class="keyword">struct</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="keyword">const</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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="keyword">const</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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="keyword">const</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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="keyword">const</span> <span class="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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="keyword">const</span> <span class="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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="keyword">const</span> <span class="keyword">volatile</span> <span class="special">&&></span> <span class="special">{};</span>
|
|
|
|
<span class="comment">//function type with varargs</span>
|
|
<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> <span class="keyword">struct</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> <span class="special">{};</span>
|
|
<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> <span class="keyword">struct</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> <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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">const</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">const</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">const</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">const</span> <span class="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">const</span> <span class="keyword">volatile</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">Return</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">struct</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> <span class="keyword">const</span> <span class="keyword">volatile</span> <span class="special">&&></span> <span class="special">{};</span>
|
|
|
|
<span class="comment">//member function pointer type without varargs</span>
|
|
<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> <span class="keyword">struct</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">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> <span class="keyword">struct</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="special">{};</span>
|
|
<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> <span class="keyword">struct</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="special">{};</span>
|
|
<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> <span class="keyword">struct</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="keyword">const</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">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> <span class="keyword">struct</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="keyword">const</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">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> <span class="keyword">struct</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="keyword">const</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">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> <span class="keyword">struct</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="keyword">volatile</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">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> <span class="keyword">struct</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="keyword">volatile</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">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> <span class="keyword">struct</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="keyword">volatile</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">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> <span class="keyword">struct</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="keyword">const</span> <span class="keyword">volatile</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">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> <span class="keyword">struct</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="keyword">const</span> <span class="keyword">volatile</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">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> <span class="keyword">struct</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="keyword">const</span> <span class="keyword">volatile</span> <span class="special">&&></span> <span class="special">{};</span>
|
|
|
|
<span class="comment">//member function pointer type with varargs</span>
|
|
<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> <span class="keyword">struct</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="special">{};</span>
|
|
<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> <span class="keyword">struct</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="special">&></span> <span class="special">{};</span>
|
|
<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> <span class="keyword">struct</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="special">&&></span> <span class="special">{};</span>
|
|
<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> <span class="keyword">struct</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="special">></span> <span class="special">{};</span>
|
|
<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> <span class="keyword">struct</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="special">&></span> <span class="special">{};</span>
|
|
<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> <span class="keyword">struct</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="special">&&></span> <span class="special">{};</span>
|
|
<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> <span class="keyword">struct</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">volatile</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">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> <span class="keyword">struct</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">volatile</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">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> <span class="keyword">struct</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">volatile</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">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> <span class="keyword">struct</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="special">{};</span>
|
|
<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> <span class="keyword">struct</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="special">{};</span>
|
|
<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> <span class="keyword">struct</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="special">{};</span>
|
|
</pre>
|
|
<p>
|
|
Use cases for such obscure specializations are vitually nonexistent in run-of-the-mill
|
|
application codebases. Even in library code, these are exceedingly rare.
|
|
However, there are a handful of very specific metaprogramming scenarios that
|
|
can only be solved with such template "spam". While these use cases
|
|
are indeed rare, the writing and testing of these templates is incredibly
|
|
tedious and time consuming. On this premise, <code class="literal">CallableTraits</code>
|
|
offers a final and decisive library-level solution, so that authors of generic
|
|
code will <span class="bold"><strong>never again</strong></span> need to write these
|
|
specializations, for <span class="emphasis"><em>any</em></span> reason.
|
|
</p>
|
|
<p>
|
|
Template specializations like those in the code snippet above <span class="emphasis"><em>still</em></span>
|
|
do not account for function pointers, function references, function objects/lambdas,
|
|
or calling conventions. <code class="literal">CallableTraits</code> goes the extra
|
|
mile by accounting for all of them.
|
|
</p>
|
|
<div class="note"><table border="0" summary="Note">
|
|
<tr>
|
|
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../src/images/note.png"></td>
|
|
<th align="left">Note</th>
|
|
</tr>
|
|
<tr><td align="left" valign="top"><p>
|
|
The upcoming ISO standard for C++17 includes a <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0012r1.html" target="_top">change
|
|
to the core language</a> which adds the <code class="literal">noexcept</code>
|
|
qualifier to the type system. If the author's understanding is correct,
|
|
this would increase the the count of necessary template specializations
|
|
to <span class="red"><span class="bold"><strong>96</strong></span></span> (<a class="link" href="callable_traits/contact.html" title="Contact">?</a>). Currently, C++17 <code class="computeroutput"><span class="keyword">noexcept</span></code> qualifiers are not handled in
|
|
<code class="literal">CallableTraits</code>, because compiler vendors have not implemented
|
|
support for this feature (to best of the author's knowledge). However,
|
|
features to account for and manipulate <code class="computeroutput"><span class="keyword">noexcept</span></code>
|
|
qualifiers are planned in <code class="literal">CallableTraits</code>, as soon as
|
|
feature is implemented by a compiler vendor. Of course, the <code class="literal">CallableTraits</code>
|
|
feature additions will be non-breaking for currently supported compiler
|
|
versions.
|
|
</p></td></tr>
|
|
</table></div>
|
|
</div>
|
|
<div class="section">
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
<a name="callable_traits.introduction.boost_function_types"></a><a class="link" href="index.html#callable_traits.introduction.boost_function_types" title="Regarding Boost.FunctionTypes">Regarding
|
|
<code class="literal">Boost.FunctionTypes</code></a>
|
|
</h3></div></div></div>
|
|
<p>
|
|
The use cases for <code class="literal">CallableTraits</code> are closely related to
|
|
those of <a href="http://www.boost.org/doc/libs/1_61_0/libs/function_types/doc/html/index.html" target="_top"><code class="literal">Boost.FunctionTypes</code></a>.
|
|
Here are some reasons why you might prefer <code class="literal">CallableTraits</code>:
|
|
</p>
|
|
<div class="orderedlist"><ol class="orderedlist" type="1">
|
|
<li class="listitem">
|
|
<code class="literal">Boost.FunctionTypes</code> is tightly coupled to <a href="http://www.boost.org/doc/libs/1_60_0/libs/mpl/doc/index.html" target="_top"><code class="literal">Boost.MPL</code></a>
|
|
sequences, while <code class="literal">CallableTraits</code> generally takes a
|
|
lower-level approach. No knowledge of MPL terminology is needed to use
|
|
<code class="literal">CallableTraits</code>.
|
|
</li>
|
|
<li class="listitem">
|
|
Other types in C++ receive fine-grained, low-level attention in <code class="literal">Boost.TypeTraits</code>
|
|
and <code class="literal"><type_traits></code>. <code class="literal">CallableTraits</code>
|
|
gives callable types similar attention, without additional metaprogramming
|
|
dependencies.
|
|
</li>
|
|
<li class="listitem">
|
|
<code class="literal">CallableTraits</code> aims to eliminate function type template
|
|
specializations. <code class="literal">Boost.FunctionTypes</code> does not.
|
|
</li>
|
|
<li class="listitem">
|
|
<code class="literal">CallableTraits</code> targets C++11/14/17 features. <code class="literal">Boost.FunctionTypes</code>
|
|
does not.
|
|
</li>
|
|
<li class="listitem">
|
|
The <code class="literal">Boost.FunctionTypes</code> interface relies heavily on
|
|
tag types. <code class="literal">CallableTraits</code> does not.
|
|
</li>
|
|
</ol></div>
|
|
<p>
|
|
<code class="literal">Boost.FunctionTypes</code> is a good tool for projects already
|
|
dependent on the MPL, which must also support very old compilers. However,
|
|
the <code class="literal">Boost.FunctionTypes</code> interface is unpleasant. It relies
|
|
heavily on both the MPL and tag types, for problems that are more simply
|
|
solved with neither. Using <code class="literal">Boost.FunctionTypes</code> requires
|
|
an understanding of the library's "big picture."
|
|
</p>
|
|
<p>
|
|
<code class="literal">CallableTraits</code> borrows and extends much of the functionality
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found in <code class="literal">Boost.FunctionTypes</code>, re-packaging it in a more
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accessible <code class="computeroutput"><span class="identifier">type_traits</span></code>-style
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interface. There is nothing inherently wrong with <code class="literal">Boost.FunctionTypes</code>,
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but an MPL sequence-based solution with no C++11/14/17 support should not
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be the only library option for inspecting and manipulating callable types.
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