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

You need an lvalue on the left hand side of += but your solution has an xvalue. As dyp has stated in the comments, you can use declval to get an lvalue. This works fine (just tested it):

template() += std::declval())>
void foo(T a, T b, ...)
{
}