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From: =?ISO-8859-1?Q?Yannick_Duch=EAne_Hibou57?= <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: Discriminant and type extensions
Date: Tue, 6 Oct 2009 23:20:15 -0700 (PDT)
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Date: 2009-10-06T23:20:15-07:00
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On 6 oct, 01:08, Adam Beneschan <a...@irvine.com> wrote:
> then take the (Discriminant =3D> Discriminant) off the *private*
> extension declaration. =A0I.e.:
>
> =A0 type Extension_Type (Discriminant : Natural) is
> =A0 =A0 =A0new P1.T_Type
> =A0 =A0 =A0with private;
>
> But leave it on the full declaration:
>
> =A0 type Extension_Type (Discriminant : Natural) is
> =A0 =A0 =A0new P1.T_Type (Discriminant =3D> Discriminant)
> =A0 =A0 =A0with null record;
>
> See if that works.

Yes, it works

The message was indeed about statically matching constraint


Just beside, not directly related to this topic, but related to making
things explicit, I've found an nice way to recall about abstract
methods to be implemented by derived type.

If a base type is defined in a package and it is derived in a second
package, if it leaves some abstract methods undefined (still to be
given a concrete implementation), it can be show using both the
Overriding and Abstract clauses on the same declaration.

Here is an working example :


package P1 is

   type Base_Type is
      abstract
      tagged
      private;

   procedure Abstract_Method
     (Entity : Base_Type) is
      abstract;

private

   type Base_Type is
      abstract
      tagged
      null record;

end P1;

with P1;

package P2 is

   type Derived_Type is
      abstract
      new P1.Base_Type
      with private;

   overriding procedure Abstract_Method
     (Entity : Derived_Type) is
      abstract;
   -- Recalls about the inherited abstract method.
   -- Using both =93 overriding =94 and =93 abstract =94 is
   -- handled as expected : it does not create an
   -- homonymous method and really makes reference
   -- to the inherited one, thanks to the =93 overriding =94,
   -- and clearly states it has no concrete implementation
   -- thanks to the =93 abstract =94.

private

   type Derived_Type is
      abstract
      new P1.Base_Type
      with null record;

end P2;