Re: Generics with concrete and class-wide types

[Georg Bauhaus <rm.tsoh.plus-bug.bauhaus@maps.futureapps.de>]

Maciej Sobczak wrote:
> Consider a generic subprogram that makes sense for arguments of both
> class-wide type and a concrete type.

> -- does not compile:
> procedure SP is new Some_Procedure
>   (T => Integer, Iterator_Type => Iterator_Integer'Class); -- Bang!

FWIW, the following triggers everything from a running
program to an Ada 95 compiler internal assertion failure
(in case the iterator object is initialized in the main
procedure).


with Iterators, Some_Procedure;
procedure Test_Iterators is

   package II is new Iterators(Integer);

   procedure Context_Conc(it: II.Conc_Iter) is
      procedure SP is new Some_Procedure
        (Integer, II, Iterator_Type => II.Conc_Iter);
   begin
      SP(it);
   end Context_Conc;

   procedure Context_Disp(it: II.Iterator'Class) is
      procedure SP is new Some_Procedure
        (Integer, II, Iterator_Type => II.Iterator'Class);
   begin
      SP(it);
   end Context_Disp;

   c: II.Conc_Iter := II.Conc_Iter'(El => new Integer'(42));
begin
   Context_Conc(c);
   Context_Disp(c);
end Test_Iterators;

with Iterators;
generic
   type T is private;
   with package Integer_Iterators is new Iterators(T);
   type Iterator_Type(<>) is new Integer_Iterators.Iterator with private;
procedure Some_Procedure (it: Iterator_Type);


generic
   type T is private;
package Iterators is

   type Iterator is abstract tagged null record;
   function Get(It: Iterator) return T is abstract;

   type T_Ptr is access constant T;
   type Conc_Iter is new Iterator with
      record
         El: T_Ptr;
      end record;

   function Get(It: Conc_Iter) return T;

end Iterators;


procedure Some_Procedure (It: Iterator_Type) is
   use type Integer_Iterators.Iterator;
   Tmp: T;
begin
   Tmp := Get(It);
end Some_Procedure;


package body Iterators is

   function Get (It: Conc_Iter) return T is
   begin
      return It.El.all;
   end Get;

end Iterators;