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From: rick H <rik_nntp@dsl.pipex.com>
Subject: Re: Instantiating private types with discriminants?
Newsgroups: comp.lang.ada
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Date: Wed, 10 May 2006 15:10:51 GMT
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Date: 2006-05-10T15:10:51+00:00
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Ludovic Brenta <ludovic@ludovic-brenta.org> wrote:
> rick H wrote :
>> Thanks, Ludovic.  Bearing in mind that, in my original example, Var_A is
>> declared as an *access* to the class-wide type, I tried declaring the
>> various Put procedures as you showed, and then simply dereferencing
>> Var_A when calling Put:
>>    Put (Var_A.all);
>> However, the compiler (gnat) complained that I cannot use a class-wide
>> argument in this case.
> 
> This sounds suspicious; it should work. Could you post your full source
> code? I think there may be a small mistake somewhere.
>

with Ada.Integer_Text_IO;
with Ada.Float_Text_IO;

procedure Simple_Case is

   type General_T is tagged null record;
   type Access_T is access General_T'Class;

   type Type_A is new General_T with
   record
      Data : Integer;
   end record;

   type Type_B is new General_T with
   record
      Data : Float;
   end record;

   procedure Put (Item: in General_T) is
   begin
      null;
   end Put;

   procedure Put (Item: in Type_A) is
   begin
      Ada.Integer_Text_IO.Put (Item.Data);
   end Put;

   procedure Put (Item: in Type_B) is
   begin
      Ada.Float_Text_IO.Put (Item.Data);
   end Put;

   Var_A : Access_T; --  could be "new Type_A" or a "new Type_B"
begin

   --  Var_A := new Type_A' (Data => 100);
   Var_A := new Type_B' (Data => 100.0);

   Put (Var_A.all);


end Simple_Case;