Why? is it to avoid confusion with "equal to"? I like plus_equal because plus is a sign and equal is also a sign too. So I think it is easier to remember.
I also tend to vocalize += as 'plus equal'. I suggested plus_assign because of the assign member function provided by standard containers.
This is not related to the return type. Only to the arguments of the operator.
Oh, I see.
I think it is best to have the default behavior to forget about the return type. Why would you impose return type to be LHS? It is fine for +, -, ... when RHS=LHS but when you start to deal with different types, I think it just adds confusion.
I see your point. And there is also an issue with derived class to base class conversion, where the base class may have overloaded an operator.
has_operator_plus<double, int> would then check for a return type "double" while has_operator_plus<int, double> for a return type int. You would break the symmetry of these operators. Also what about dereference operator?
Yes, it has been a perennial issue. Like in std::max<int,double>. Unfortunately there doesn't seem to be a universally satisfying solution. Fortunately, it is not a first order issue; one can always refuse to use the default for the result type. Thanks and regards Vijayan