Question

I use my own class as a key type for std::map. How the map implementation determines when two objects are equal?

I know that I can determine operator< or Comp type to arrange elements. But I can find nothing about equality.

Answer 1

It’s possible to make the comparison using just operator<, so it doesn’t require you to define operator== as well. Basically, if one is not less than the other, and the other is not less than the first, they must be equal. This is a possible utility function implementation of such:

bool isEqual(const Type &arg1, const Type &arg2) const {
    return !(arg1 < arg2) && !(arg2 < arg1);
}