TITLE: Another take on extendable enums


RESPONSE: (Fergus Henderson) fjh@munta.cs.mu.oz.au


[ I added the missing static keywords in brackets below. -adc ]


A simple and expandable but not fully type-safe method:

	class Base {
	public:
		typedef int Enum;
	protected:
		static Enum new_enum() { return next_enum++; }
	private:
		static Enum next_enum;
	// ...
	};

	class Derived_A : public Base {
	public:
		[static] Enum a1, a2;
	};
	class Derived_B : public Base {
	public:
		[static] Enum b1, b2;
	};

	Base::Enum Derived_A::a1 = Base::new_enum();
	Base::Enum Derived_A::a2 = Base::new_enum();
	Base::Enum Derived_B::b1 = Base::new_enum();
	Base::Enum Derived_B::b2 = Base::new_enum();

You can make this "type-safe" by making Base::Enum a class
rather than a typedef, but I'm not sure that it's worth the
effort.