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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Problem with controlled types
Date: 1998/12/14
Message-ID: <EACHUS.98Dec14183231@spectre.mitre.org>#1/1
X-Deja-AN: 422292055
References: <m367beshjr.fsf@mheaney.ni.net>
 <F3z2s2.6CG.0.-s@inmet.camb.inmet.com>
Organization: The Mitre Corp., Bedford, MA.
Newsgroups: comp.lang.ada
Date: 1998-12-14T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <F3z2s2.6CG.0.-s@inmet.camb.inmet.com> stt@houdini.camb.inmet.com (Tucker Taft) writes:

  > Not quite true.  The problem is that *inside* the package private
  > part and the body, Get_B is primitive on two tagged types,
  > and that is not legal.  

  > So ObjectAda wins this round ;-).

   Interesting.  Try the following example:

generic
  type Out_Type is private;
  type In_Type is new Out_Type;
function Conversion(I: In_Type) return Out_Type;

with Ada.Finalization; with Conversion;
 
package Pkg is
 
   type A is private;

   package Inner is

     type B is private;
     function Convert is new Conversion(A,B);
     -- I'd use Ada.Unchecked_Conversion but that has convention Intrinsic.
   private
     type B is new Ada.Finalization.Controlled with record
        ...
     end record;
   end Inner;

private
 
  type A is new Ada.Finalization.Controlled with record
      ...
  end record;

end Pkg;

   Now according to Tucker, in the private part of Pkg, Convert is a
dispatching operation of A, and in the private part of Inner, it is a
dispatching operation of B.  As written there is no body allowed so
the example is legal.  I could add types C and D and other generic
instantiations to play futher with this.

   I don't think I like either interpretation of 3.9.2(12).
Seriously, 3.9.2(12) says: "A given subprogram shall not be a
dispatching operation of two or more distinct tagged types."  It
doesn't say of two visibly tagged types, so I think my example would
also be illegal.
--

					Robert I. Eachus

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