SFINAE check for operator+=

Question

I\'m trying to eliminate an overload from an overload set if operator+= is missing.

I know how to check if T+T is legal :

t         


        

Answer 1

I would write the second form as:

template
auto foo(T a, T b, ...) -> decltype( a+=b, void() )
{
  a += b;
}

The deduced type for decltype(a+=b, void()) would be just void if the expression a+=b is valid, else it would result in SFINAE.

Well, even in the first form, I would use the trailing-return type approach.