Re: Overloading for T and T'Class

[dweller@Starbase.NeoSoft.COM (David Weller)]

In article <Cz4H8G.MA@swlvx2.msd.ray.com>,
John Volan <jgv@swl.msd.ray.com> wrote:
>In Ada9X, is it legal to overload the same subprogram name for both
>some tagged type T and its class-wide type T'Class?  For example:
>
>	package P is
>	  type T is tagged ... ;
>	  procedure Op (X : in out T);
>	  procedure Op (X : in out T'Class);
>	  ...
>	end P;
>

My neophyte language-lawerly sense says "No", you can't do this.  The
reason being (I think, don't have my RM with me), is that the
classwide operation declares an implicit operation within the
immediate scope that is identical to your first declaration of Op.

As a compiler, your declarations would confuse me, since the first Op
says "I'm a primitive operation, and thus I may be extended and
modified by descendants", and the second one says, "I'm a classwide
operation, thus any descendant of my type (a member of T'Class) must
execute this subprogram".  A contradiction, from my perspective.

I think GNAT (at the moment) permits this, further confusing the
issue.

Your example was similar to an issue discussed during a presentation
I made on the first version of the Booch COmponents at Tri-Ada.  


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