Re: Instantiating private types with discriminants?

[rick H <rik_nntp@dsl.pipex.com>]

Georg Bauhaus <bauhaus@futureapps.de> wrote:
> 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;
> 
Thanks Georg - I understand now!


Rick