🚀 go-pugleaf

In article <CIMSHOP!DAVIDM.91May26223941@uunet.UU.NET> cimshop!davidm@uunet.UU.NET (David S. Masterson) writes:

>>>>> On 25 May 91 07:43:08 GMT, rfg@lupine.ncd.com (Ron Guilmette) said:

Ron> this sounds like a job for ... ta da!  Inheritance!

Ron> 	enum light_color { pink, yellow, aqua };
Ron> 	enum color : light_color { red, green, blue };

David> This is a bit confusing as you would tend to think of Light_Color as a
David> derivative of Color, not vice versa.

Your not alone in this thought.  Cardelli and Wegner define inclusion
polymorphism (or inheritance if you prefer) for variant types (enums
in C++) in this way.  For anyone that is interested in these sorts of
issues, I recommend reading :-

On Understanding Types, Data Abstraction and Polymorphism
L. Cardelli and P. Wegner
Computing Surveys 17(4):480-521 December 1985

and :-

Type Theories and Object-Oriented Programming
Scott Danfor and Chris Tomlinson
Computing Surveys 20(1):29-72 March 1988

Stephen J. Bevan			bevan@cs.man.ac.uk