Exposing agreggate members of a class

["David Botton" <dbotton@hotmail.com>]

Given:

with GCanvas_Package; use GCanvas_Package;

type GWindow_Object is tagged with private;
type GWindow_Pointer is access all GWindow_Object;

private:

type GWindow_Object is tagged
   record
        Canvas : GCanvas_Object;
   end record;

What is the cleanest way to give access to the Canvas by reference in a way
that will not require Unchecked Programming

What I don't want:

    function Get_Canvas( window : in GWindow_Object ) return GCanvas_Pointer
is
    begin
        return window.Canvas'Unchecked_Access;
    end Get_Canvas;

Which on top of the Unchecked_Access issue means that consumers of such a
class would have to dereference first to use the GCanvas_Object methods:

declare
    Canvas : GCanvas_Pointer := Get_Canvas( window );
begin
    Draw_Line(Canvas.all, 10, 10, 100, 100);
end;

Of course you could write the methods to accept GCanvas_Pointer's, but I
want to avoid the use of Access variables when possible.

Thanks,
David Botton