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POChecking a member exists, possibly in a base class, C++11 version
 

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    <p>In <a href="https://stackoverflow.com/a/1967183/134841">https://stackoverflow.com/a/1967183/134841</a>, a solution is provided for statically checking whether a member exists, possibly in a subclass of a type:</p> <pre><code>template &lt;typename Type&gt; class has_resize_method { class yes { char m;}; class no { yes m[2];}; struct BaseMixin { void resize(int){} }; struct Base : public Type, public BaseMixin {}; template &lt;typename T, T t&gt; class Helper{}; template &lt;typename U&gt; static no deduce(U*, Helper&lt;void (BaseMixin::*)(), &amp;U::foo&gt;* = 0); static yes deduce(...); public: static const bool result = sizeof(yes) == sizeof(deduce((Base*)(0))); }; </code></pre> <p>However, it doesn't work on C++11 <code>final</code> classes, because it inherits from the class under test, which <code>final</code> prevents.</p> <p>OTOH, this one:</p> <pre><code>template &lt;typename C&gt; struct has_reserve_method { private: struct No {}; struct Yes { No no[2]; }; template &lt;typename T, typename I, void(T::*)(I) &gt; struct sfinae {}; template &lt;typename T&gt; static No check( ... ); template &lt;typename T&gt; static Yes check( sfinae&lt;T,int, &amp;T::reserve&gt; * ); template &lt;typename T&gt; static Yes check( sfinae&lt;T,size_t,&amp;T::reserve&gt; * ); public: static const bool value = sizeof( check&lt;C&gt;(0) ) == sizeof( Yes ) ; }; </code></pre> <p>fails to find the <code>reserve(int/size_t)</code> method in baseclasses.</p> <p>Is there an implementation of this metafunction that both finds <code>reserved()</code> in baseclasses of <code>T</code> and still works if <code>T</code> is <code>final</code>?</p>
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    1. USMarc Mutz - mmutz
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      1. USJim Jeffries
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    1. COOn C++11 you can just use "sfinae for expressions" instead of doing this roundabout way needed in C++03.
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      1. USJohannes Schaub - litb
    2. CO@JohannesSchaub-litb Request for solution! I'd love to see the difference it makes for this kind of example.
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      1. USstinky472
 

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