Re: Renaming of procedures in a generic instantiation

[Stephen Leake <stephen_leake@stephe-leake.org>]

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