Compling error

[Imadatobanisa]

These examples below certainly are not allowed, why?

a += 10 -= 50;
A - 10 += 33;

[Cubbi]

The first one parses as a += ( 10 -= 50); and the expression 10 -= 50 is not valid because 10 is an rvalue, and compound assignment expects an lvalue on the left.

The second one works fine for most class types that have operator-, but fails for scalars for the same reason: A-10 is an rvalue.

This compiles, for example:

struct S {
    S operator-(int) const { return *this; }
    S& operator+=(int) { return *this; }
};
int main()
{
    int a;
    S A;

    (a += 10) -= 50; // gotta add the parentheses
    A - 10 += 33;   // gotta use a type that overloads the operators
}

[Raezzor]

Hey Cubbi, I'm real happy for you and I'mma let you finish, but won't the operators only work in this case if they return an object (by reference or a copy, either way)?