Overloading += in c++

Question

If I've overloaded operator+ and operator= do I still need to overload operator+= for something like this to work:

MyClass mc1, mc2;
mc1 += mc2;

Answer 1

operator+= is not a composite of + and =, therefore you do need to overload it explicitly, since compiler do not know to build puzzles for you. but still you do able to benefit from already defined/overloaded operators, by using them inside operator+=.

Answer 2

Yes, you need to define that as well.

A common trick however, is to define operator+=, and then implement operator+ in terms of it, something like this:

MyClass operator+ (MyClass lhs, const MyClass& rhs){
  return lhs += rhs;
}

If you do it the other way around (use + to implement +=), you get an unnecessary copy operation in the += operator which may be a problem i performance-sensitive code.

Answer 3

Yes, you do.

Answer 4

If the real question here is, "I don't want to write a load of repetitive operators, please tell me how to avoid it", then the answer may be:

http://www.boost.org/doc/libs/1_38_0/libs/utility/operators.htm

The syntax looks a little fiddly, though. As I've never used it myself, I can't reassure you that it's simple really.