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Date: Mon, 20 Jan 2003 12:39:04 +0100
From: =?ISO-8859-1?Q?Rodrigo_Garc=EDa?= <rodrigo.garcia@epfl.ch>
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Subject: Re: Problem Eliminating constructors
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Date: 2003-01-20T12:39:04+01:00
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Victor Porton wrote:
> package A is
> 
>   type A_Type is tagged
>     record
>       X: Integer;
>     end;
>     
>   function Create(X: Integer) return A_Type; -- guess what is the body
>   
> end A;
> 
> Then I have
> 
> type B_Type is new A.A_Type with
>   record
>     Y: Integer;
>   end;
> 
> Compiler requires me to override Create as the return type changes.
> But it is meaningless as now I need Create with two parameters
> instead of one.
> 
> What to do?

   You do not need a constructor for this simple case. This will create 
an A_Type object and initialize X to value 5.

   declare
      My_A : A.A_Type := (X => 5);

Similarly, this will create a B_Type object with X=5 and Y=6.

   declare
      My_B : B_Type := (X => 5, Y => 6);

Alternatively, you can use discriminants as well:

   type A_Type (I : Integer) is tagged
      record
         X : Integer := I;
      end record;

And then:

   type B_Type (J : Integer; K : Integer) is new A_Type (I => J) with
      record
        Y : Integer := K;
      end record;

With this solution, you are forced to provide initial values in the 
creation.

Rodrigo