TITLE: Expandable enums?


PROBLEM: scottb@satb.cnde.iastate.edu (Scott Bilas)

Hello all.  I'm wondering about something with enum's.  I have a base
class that declares an enum type, and I use this in that class and any
derived classes as an argument (as a command code).  What I'd like to be
able to do is expand this enum inside of derived classes...sort of have
each derived class add its own little set of allowable commands to the
enum type.  a) Is this possible,

or b) is there a much easier and more straightforward yet still type-safe
method of passing codes to functions (that's expandable).  Probably b,
right?  


RESPONSE: p j l @graceland.att.com (Paul J. Lucas), AT&T Bell Laboratories


No. [ Part a) is not possible. ]


[ For part b), ] Not really.  I just use ints and don't screw up:

	struct A {
		enum { a1, a2, a3, a4, next };
	};

	struct B : A {
		enum { b1 = A::next, b2, b3, b4, next };
	};

	// ...

	Note: the enums are "typeless" on purpose.

[ Another way to look at this problem is to defer some "type checking"
  to run-time. For example, the base class could define an "int set" and
  load it with the legal values for the base. Derived classes could
  add more members to this set. This would allow run-time, instead of
  compile-time, checking for legal values. -adc ]