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From: dgibson@thalamus.cis.ohio-state.edu (david scott gibson)
Subject: Re: Extending A Generic Signature Package
Date: 1997/03/21
Message-ID: <5guuehINN6iq@thalamus.cis.ohio-state.edu>#1/1
X-Deja-AN: 227359944
References: <5gkv23INN3rn@thalamus.cis.ohio-state.edu>
 <5gn90o$gm1@sutton.cs.columbia.edu> <5gtvbv$1nj@pandora.cs.utwente.nl>
 <JSA.97Mar21135016@alexandria>
Organization: The Ohio State University,
 Department of Computer and Information Science
Newsgroups: comp.lang.ada
Date: 1997-03-21T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <JSA.97Mar21135016@alexandria>,
Jon S Anthony <jsa@alexandria> wrote:

>Just to be clear, "pointers" are only indirectly relevant to
>dispatching.  The key is passing a class wide type argument(s) to a
>controlling operand(s) of a primitive operation.  For example, there
>is no need of a pointer in your above example:
>
>    declare
>       X : Base'Class := Get_Object;
>    begin
>       Op1(X);
>    end;

So in this case it's clear to us and the compiler what specific type
derived from Base Get_Object returns.  It may or may not be an access
type.  If an access type, Op1 could have an access parameter formal
and still dispatch.  However, Get_Object must return a tagged type and
thus the value returned must be returned by reference in either case,
right?  So whether explicit or not X, the value of X must be a pointer
to some object.  Is that right?  If Get_Object doesn't return an acces
type and we don't use Unchecked_Access or aliased variables anywhere
in the program, does Ada guarantee that the object to which X points
cannot be aliased?

Dave
--
dgibson@cis.ohio-state.edu