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From: koehnema@enuxsa.eas.asu.edu (Harry Koehnemann)
Subject: Re: Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG)
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References: <36eebb$jn5@disunms.epfl.ch> <Cwyzx4.H3K@irvine.com>
 <1994Oct2.164105.13127@swlvx2.msd.ray.com>
Date: Mon, 3 Oct 1994 20:29:00 GMT
Xref: bga.com comp.lang.ada:6430 comp.object:7029 comp.lang.c++:31541
Date: 1994-10-03T20:29:00+00:00
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In article <1994Oct2.164105.13127@swlvx2.msd.ray.com> jgv@swl.msd.ray.com (John Volan) writes:
>
>That's my fear as well.  That's why I've been trying very hard to find
>an Ada9X solution.  Eiffel can do decoupled mutual recursion standing on its
>head.  Smalltalk virtually swims in a sea of decoupled mutual recursion 
>(trivial in a typeless language).  I suspect C++ can actually manage it as well.
>(Can any C++ folks confirm this?  Realize what I mean: Can you forward-declare 
>a class and then *not* complete its declaration in the same header file, and 
>yet complete the declaration of a client class?  Or do you *have* to declare 
>both classes in the same header file?)

Yes.  See the example.

	class A;
	Class B {
	    A *a;		// legal
	    ...
	    a -> print();	// illegal
	};

However, the body of B cannot perform any operations on 'a' since they
are not visible.  I think this would also work in Ada9X, except that
multiple pointer declarations would be incompatible with one another
due to Ada's typing mechanism.

>From what I remember of Eiffel and Smalltalk (it's been a while), one
can invoke an operation from a class that has not yet been declared.
However, both C++ and Ada9X require a function (or operation) be
declared before it be used.  I think this is the feature you seek,
which is more than simply a forward declaration.

Hope this helps.
--
Harry Koehnemann			Arizona State University
hek@asu.edu				Computer Science Department