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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Interfaces and private types
Date: Mon, 28 Jan 2008 16:58:25 -0600
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Date: 2008-01-28T16:58:25-06:00
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"Philippe Tarroux" <philippe.tarroux@limsi.fr> wrote in message
news:fnl2in$k49$1@news2.u-psud.fr...
> Hi again,
>
> There is no compilation problem with the following code :
>
> package Test_Interfaces is
>
>    type Int is synchronized interface;
>    procedure Init (I : in out Int) is abstract;
>
>    type T is new Int with private;
>
> private
>
>    task type T is
>       entry Init;
>    end T;
> end Test_Interfaces;

As written, this is illegal because type T does not have the interface Int.
Specifically, it violates 7.3(7.3/2): "the partial view shall be a
descendant of an interface type (see 3.9.4) if and only if the full type is
a descendant of the interface type."

Assuming that this is just a mistake in your interface and you meant

   task type T is new Int with

then your program is legal, and you should complain your your compiler
vendor about the bug. In no case should there be an error on the declaration
of the object, so that makes it pretty clear that there is a compiler bug.

You could work around the bug with something like:

package Test_Interfaces is

   type Int is synchronized interface;
   procedure Init (I : in out Int) is abstract;

   type T is new Int with private;
   overriding procedure Init (I : in out T);

private

   task type T is new Int with
      entry Init;
   end T;
end Test_Interfaces;

and then have
    procedure Init (I : in out T) is
    begin
          I.Init;
    end Init;
in the body. (But note that this runs into a known bug in the Ada standard,
so it isn't clear that the code will work right.)

                              Randy.