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From: Robb.Nebbe@di.epfl.ch (Robb Nebbe)
Newsgroups: comp.lang.ada
Subject: Re: Is Ada the future? [was: Is C++ the future?]
Date: 14 Oct 1994 10:16:41 GMT
Organization: Ecole Polytechnique Federale de Lausanne
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Date: 1994-10-14T10:16:41+00:00
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mbk@inls1.ucsd.edu (Matt Kennel) writes:

|> 
|> The core issue:  doing this should be possible.  (Indeed it
|> was hard for me to imagine that it should ever have been
|> not possible).
|> 
|> -- Obvious Eiffel construction.
|> class ONE is
|>  	a:TWO;
|> end;
|> 
|> class TWO is
|> 	b:ONE;
|> end;
|> 

To do this ONE and TWO must have an implicit level of indirection.
If you use expanded types if Eiffel, which corespond to normal
types in Ada, you can't do this.

In Ada you can write:

type TWO_Implementation;

type TWO is access TWO_Implementation;

type ONE_Implementation is
   record
      a : TWO;
   end record;

type ONE is access ONE_Implementation;

type TWO_Implementation is
   record
      b : ONE;
   end record;

Which is more or less the same thing as your Eiffel example. The
problem is not declaring it, it is distributing it over multiple
packages. In Ada the assumption that a type will be handled through
a pointer is not valid.

- Robb Nebbe