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From: Stephen Leake <stephen_leake@stephe-leake.org>
Newsgroups: comp.lang.ada
Subject: Re: Renaming of procedures in a generic instantiation
References: 
 <f0affc67-0080-410f-9595-b91f893ec6f5@a19g2000yql.googlegroups.com>
Date: Sun, 26 Sep 2010 04:45:18 -0400
Message-ID: <828w2orizl.fsf@stephe-leake.org>
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Date: 2010-09-26T04:45:18-04:00
List-Id: <comp.lang.ada>

Gene <gene.ressler@gmail.com> writes:

> I'm confused about an aspect of renaming. It boils out to this little
> example:
>
> with Ada.Containers.Ordered_Sets;
>
> package Foo is
>
>   type Queue is private;
>
>   procedure Add(Q : in out Queue; Item : in Integer);
>
>   function Is_Empty(Q : Queue) return Boolean;
>
> private
>
>   package Queues is
>     new Ada.Containers.Ordered_Sets(Integer, "<", "=");
>   type Queue is new Queues.Set with null record;

All primitive operations of Queues.Set are implicitly declared here,
with Queue replacing Queues.Set; that includes Set and Is_Empty. That's
what derived types are for.

> end Foo;
>
> package body Foo is
>
>    procedure Add(Q : in out Queue; Item : in Integer)
>       renames Insert;

This 'Insert' resolves to Foo.Insert (Container : in out Foo.Queue; ...);

>    function Is_Empty(Q : Queue) return Boolean
>       renames Queues.Is_Empty;

Queues.Is_Empty expects a Constainer of type Foo.Queues.Set, not Foo.Queue.

If you replace 

   type Queue is new Queues.Set with null record;

with 

   subtype Queue is Queues.Set;

Then the Add renames will fail (because the primitive operations are not
derived), and the Is_Empty will succeed.

-- 
-- Stephe