C++11 static assert for equality comparable type?

问题:

How to static_assert a template type is EqualityComparable concept in C++11?

回答1:

You could use the following type trait:

#include   template struct is_equality_comparable : std::false_type { };  template struct is_equality_comparable() == std::declval(), (void)0)         >::type     > : std::true_type { }; 

Which you would test this way:

struct X { }; struct Y { };  bool operator == (X const&, X const&) { return true; }  int main() {     static_assert(is_equality_comparable::value, "!"); // Does not fire     static_assert(is_equality_comparable::value, "!"); // Does not fire     static_assert(is_equality_comparable::value, "!"); // Fires! } 

Here is a live example.

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