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Date: Mon, 11 May 2015 15:37:19 -0700 (PDT)
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Subject: Incomplete types used with generics
From: Jeremiah <jeremiah.breeden@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:25817
Date: 2015-05-11T15:37:19-07:00
List-Id: <comp.lang.ada>

One of the things I read about with ada2012 is the ability to use incomplete types as generic parameters.  However, I am having some trouble implementing them.  I'm using GNAT GPL 2014 and have the following dumbed down packages:

generic
   type Item_Type is tagged limited private;
   type Item_Access is access Item_Type;
package Test_Generic is
   type Test is tagged record
      Ref : Item_Access := null;
   end record;
end Test_Generic;


with Test_Generic;

package Test_Nodes is

   type Node3_ptr is null record;

   type Node1_Type is tagged record
      value : Integer := 0;
   end record;
   type Node1_Access is access Node1_Type;

   package N1 is new Test_Generic(Node1_Type,Node1_Access);

   type Node2_Type is tagged;
   type Node2_Access is access Node2_Type;

   package N2 is new Test_Generic(Node2_Type,Node2_Access);

   type Node2_Type is tagged record
      value : Integer := 1;
      Test  : N2.Test;
   end record;

end Test_Nodes;

However, the line 
package N2 is new Test_Generic(Node2_Type,Node2_Access);

fails with:  premature use of incomplete type

I *think* the generic parameter "type Item_Type is tagged limited private;" is considered incomplete as is "type Node2_Type is tagged;".

What am I missing?

Ada2012 incomplete types with generics reference:
http://www.ada-auth.org/standards/12rat/html/Rat12-4-3.html