Creating a composite type from two enum classes, ready for STL map

Question

I would like to create a composite type out of two enum classes.

enum class Color {RED, GREEN, BLUE};
enum class Shape {SQUARE, CIRCLE, TRIANGLE};

         


        

Answer 1

You don't need a linear index, you can simply compare them lexicographically:

friend bool operator< (const Object &lhs, const Object &rhs) {
  if (lhs.color < rhs.color) return true;
  else if (lhs.color > rhs.color) return false;
  else return lhs.shape < rhs.shape;
}