C++11 ways of finding if a type has member function or supports operator?

Question

There is a (seemingly) nice C++03 way of finding out if a type has a member function or operator:

https://github.com/jaredhoberock/is_call_possible/blob/master/is_ca

Answer 1

This works with all test cases given in the GitHub (Demo: http://ideone.com/ZLGp4R):

#include 

template 
struct is_call_possible : public std::false_type {};

template 
struct is_call_possible::value ||
        std::is_convertible().operator()(std::declval()...)
            //                ^^^^^^^^^^ replace this with the member you need.
        ), R>::value
    >::type
> : public std::true_type {};