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Date: Tue, 09 May 2006 15:45:32 +0200
From: Georg Bauhaus <bauhaus@futureapps.de>
Organization: future apps GmbH
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Newsgroups: comp.lang.ada
Subject: Re: Instantiating private types with discriminants?
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Date: 2006-05-09T15:45:27+02:00
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rick H wrote:


> So, my question to the experts is: Why does "privatising" a type's
> details change the way that you "new" instantiations of it?

You cannot write down the private components of a private type
anywhere they are invisible. Even though your private type Type_B
doesn't actually have private components, that isn't known outside
Discrim's private part, i.e. in procedure Use_Discrim . Consider:

with Discrim; use Discrim;
procedure Use_Discrim is
   A_Thing: Type_A;
   B_Thing: Type_B;
   Another_B_Thing: Type_B(Param => 42);  -- declaring with constraint
   A : Type_A_Ptr;                   --  public  implementation
   B : Type_B_Ptr;                   --  private implementation
begin
   A_Thing := (Param => 100);
   B_Thing := (Param => 100);  -- what about the private components?
   A_Thing := Type_A'(Param => 100);
   A_Thing := Type_A (Param => 100);
   A := new Type_A'(Param => 100);   --  qualified expression
   B := new Type_B (Param => 123);   --  ?
end Use_Discrim;