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From: shang@corp.mot.com (David L. Shang)
Subject: Re: OO, C++, and something much better!
Date: 1997/01/30
Message-ID: <1997Jan30.150303.732@schbbs.mot.com>#1/1
X-Deja-AN: 213248905
sender: news@schbbs.mot.com (SCHBBS News Account)
references: <32F07705.289C@concentric.net>
organization: MOTOROLA 
reply-to: shang@corp.mot.com
newsgroups: 
 comp.lang.c++,comp.lang.smalltalk,comp.lang.eiffel,comp.lang.ada,comp.object
Date: 1997-01-30T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <32F07705.289C@concentric.net> Alan Lovejoy  
<alovejoy@concentric.net> writes:
> 
> And I agree that the way static typing is done in Ada, Modula-3
> and Eiffel is quite superior to what C++ does. But I would be even
> happier with the way Ada or Eiffel handle typing if one could 
> simultaneously have two different variables whose static type
> constraint is "Dictionary" but where each is actually an instance 
> of a different class (say HashTable and BinaryTree)--and the only
> class they both have in common in their inheritance hierarchy is
> Object.
> 

The problem with the languges mentioned above is that the type
system supports only a one-way inheritance, and actually we
sometiimes need a reverse inheritance: from existing subclasses
to superclass.

Your "HashTable and BinaryTree" to "Dictionary" is a good example.

In Transframe, you can simply declare:

	class Dictionary is super HashTable, BinaryTree;

Then the class Dictionary (a superclass) inherits all the common
interfaces of HashTable and BinaryTree.

The superclass construct can do something more. For example,
a safe union type, a signature, etc. For detail, refer to
http://www.transframe.com/ at "Forum/SoftwarePatterns" page.

David Shang