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Date: Mon, 26 Sep 2011 11:25:47 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: subprogram must not be deeper than access type
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Date: 2011-09-26T11:25:48+02:00
List-Id: <comp.lang.ada>

On 25.09.11 23:53, Robert A Duff wrote:

> It's really annoying that in Ada you can't write a small example program
> (with a single compilation unit in a single file) that has multiple
> library-level things.  If I ran the circus, there would be no library
> subprograms.  The main procedure would be declared inside a library
> PACKAGE.

It's worth mentioning, I think, that one source text for a single
compilation in a single file can be submitted to GNAT, such that
at the same time it also removes the specific accessibility problem
that Natasha's example exhibits.  To translate with GNAT, switch -z
is required.  Do other compilers support "main packages", too?

with String_Builder_Types;

package Main is
    use String_Builder_Types;

    function Builder (Depth : Positive) return Typ'Class;

    Output : String_Builder_Types.Non_Generic (Builder'Access);
end Main;

package body Main is

    function Builder (Depth : Positive) return Typ'Class is
       pragma Unreferenced (Depth);
    begin
       return String_Builder_Types.Empty_Typ;
    end Builder;

begin
    null;  --  or actually, real code.
end Main;

package String_Builder_Types is

    type Typ is tagged private;
    Empty_Typ : constant Typ;

    type Func is
        access function (Depth : Positive) return Typ'Class;

    type Non_Generic (Builder : Func) is tagged null record;
private
    type Typ is tagged null record;
    Empty_Typ : constant Typ := Typ'(null record);
end String_Builder_Types;