Re: Overloading for T and T'Class

[bobduff@dsd.camb.inmet.com (Bob Duff)]

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:

Yes, but not particularly useful.

>	package P is
>	  type T is tagged ... ;
>	  procedure Op (X : in out T);
>	  procedure Op (X : in out T'Class);
>	  ...
>	end P;

This is legal, but calls to Op will tend to be ambiguous.  For example,
if Y is of type T, then Op(Y) might mean either one of the Ops, and
would therefore be ambiguous (and therefore illegal).

We considered making the above declarations be homographs, and therefore
illegal in the above case, but that caused some subtle semantic problems
(I can't remember the details right now), so we decided to allow it.
It's not necessary to make every useless thing illegal.

Anyway, don't do it.  ;-)

- Bob
-- 
Bob Duff                                bobduff@inmet.com
Oak Tree Software, Inc.
Ada 9X Mapping/Revision Team (Intermetrics, Inc.)