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From: rfg@lupine.ncd.com (Ron Guilmette)
Newsgroups: comp.std.c++
Subject: Inheritance for enum types ???
Message-ID: <5701@lupine.NCD.COM>
Date: 25 May 91 07:43:08 GMT
Sender: rfg@NCD.COM
Organization: Network Computing Devices, Inc., Mt. View, CA
Lines: 40


Somebody over in comp.lang.c++ asked an interesting question about the
case where you have two or more enum types declared in the same scope
and where each enum type contains a declaration of a particular enumerator
name, like:

	enum fruit { apple, orange, banana };
	enum color { red, orange, yellow };


You can't do this because you will get an error on the (re)declaration of
`orange'.

Sometimes though, it would be nice to be able to do something like this,
e.g. when you want to have one type which refers to a whole big range
of enumerator values, and yet another type which represents some "subrange"
of the larger range of enumerator values.

So I was thinking... this sounds like a job for ... ta da!  Inheritance!

Sure.  Why not?

	enum light_color { pink, yellow, aqua };

	enum color : light_color { red, green, blue };


	enum light_color LC;
	enum color C;


		LC = pink;	// ok
		C = pink;	// also ok
		LC = red;	// buzzzzzt... wrong... but thanks for playing


Does anybody (other than me) think that this might be a good idea?

After all, in C++ we *do* now have strict type checking for enum types,
however we *don't* have anything like Pascal subranges.