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Date: Sun, 12 Apr 2020 05:32:41 -0700 (PDT)
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Subject: Generic oddness
From: Per Jakobsen <pdj@knaldgas.dk>
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Xref: reader01.eternal-september.org comp.lang.ada:58348
Date: 2020-04-12T05:32:41-07:00
List-Id: <comp.lang.ada>

Declaring the package List_Type from Doubly_Linked_Lists gives me "abstract=
 subprogram not allowed as generic actual" unless I declare the "A_Intf" ty=
pe in a package separate from the List_Type declaration, or if I instantiat=
e a workaround (dummy) generic before (as in the below MWE):

--- gnatchop ---------------------
generic
   type A is private;
package Gen is
   pragma Pure;
end Gen;
package Intf is
   type Intf_Type is interface;
   procedure Do_Stuff (I : in out Intf_Type) is abstract;
end Intf;
with Ada.Containers.Doubly_Linked_Lists;
with Intf;
with Gen;

package Test is
   use Intf;

   type A_Intf is new Intf_Type with
      record
         A : Natural;
      end record;

   overriding
   procedure Do_Stuff (I : in out A_Intf);

   package Workaround is new Gen (A =3D> A_Intf);
   --  Commenting the above line will cause the
   --  next line to fail !?!?
   package List_Type is
      new Ada.Containers.Doubly_Linked_Lists (Element_Type =3D> A_Intf,
                                              "=3D"          =3D> "=3D");
end Test;
package body Test is

   overriding
   procedure Do_Stuff (I : in out A_Intf) is
   begin
      null;
   end Do_Stuff;

end Test;
--- gnatchop end ---------------------

Unpack with gnatchop, then compile with gnatmake test.adb. Then comment the=
 Workaround package instantiation and recompile.

Using GNATMAKE Community 2019 (20190517-83).

Is there a sane explanation for this behavior?

~Per