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  1. Item    2604245                         30-Aug-90        08:33PDT
  2.  
  3. From:   PASCOE1                         Pascoe, Geoff
  4.  
  5. To:     MACAPP.TECH$                    MacApp Technical
  6.  
  7. Sub:    Re: Multiple Inheritance
  8.  
  9. Neal and Jeff,
  10.  
  11. "They are tightly coupled in Object Pascal, but divorced (though still going
  12. out with each other) in C++."
  13.  
  14. I believe Emerald makes this distinction explicit.  I also find separating
  15. "conceptual modeling" (subtype) from "implementation sharing" (subclass) very
  16. useful.  In the case of C++ I think they're going out with each other, but not
  17. really having a good time :)
  18.  
  19. "Too many people are making too many unstated assumptions about the foundations
  20. of OOP and borrowing too many terms unjustifiably."
  21.  
  22. I agree.  My assertion is that a practical O-O language requires four features:
  23.  
  24. 1) Information hiding
  25.  
  26. 2) Data Abstraction
  27.  
  28. 3) Polymorphism
  29.  
  30. 4) Inheritance
  31.  
  32. Incidentally, it might be useful to know that the concept of the "is-a"
  33. relationship differs in the O-O community.  For some, a type-subtype
  34. relationship is a "kind-of" and an instance-type (instance-class) relationship
  35. is an "is-a".  Again, too many unstated assumptions.
  36.  
  37. Geoff
  38.  
  39.