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From: stt@houdini.camb.inmet.com (Tucker Taft)
Subject: Re: class-wide objects
Date: 1998/12/07
Message-ID: <F3LpHA.Hro.0.-s@inmet.camb.inmet.com>#1/1
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References: <366B1190.C8142307@magic.fr>
Organization: Intermetrics, Inc.
Newsgroups: comp.lang.ada
Date: 1998-12-07T00:00:00+00:00
List-Id: <comp.lang.ada>

Francois Godme (fgodme@magic.fr) wrote:

: ...
: An attribute to get the subtype of the actual tagged parameter would
: solve both problems. May be we could combine
: the two attributes 'Class and 'Tag together:

: procedure P4 (S : in Point'Class;
:               N : in Natural) is

:    Local : Point'Class (S'Tag); -- allocates an object with the tag of S

:    subtype T_Local_Point is Point'Class (S'Tag);

:    Local_Array : array (1 .. N) of T_Local_Point;

: begin
:    ...
: end P4;

: What do you think ? Am I right or am I missing something ? Could the
: GNAT team provide an implementation defined attribute for this ?

Just providing the tag is not enough, because the type might
have discriminants as well, which must be specified at the
point of declaration.  One could imagine some new attribute
like "'Subtype" and then write:

    Local : Point'Class(S'Subtype);

In fact, something like this was proposed during the Ada 9X
revision process, but it didn't make the "cut" among the
various language revision proposals.

: Francois Godme
--
-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
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