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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: constructor in abstract tagged types
Date: Wed, 8 May 2019 21:26:05 +0200
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Xref: reader01.eternal-september.org comp.lang.ada:56262
Date: 2019-05-08T21:26:05+02:00
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On 2019-05-08 20:37, Daniel wrote:

> Hello, im trying to know how can i use abstract tagged types and constructors at the same time.

Ada does not have proper constructors. But there are various software 
patterns to work this around.

> I have this
> 
> package FATHERS is
>    type Father is abstract tagged record
>       Years : Natural;
>       field1 : Natural;
> --    .....and 15 more fields
>    end record;
> 
>    function F_build(Years :Natural) return Father is abstract;
>    procedure F_forced_to_do_it is abstract;

private
    --
    -- Class-wide initialization of Father's fields
    --
    procedure Initialize (Object : in out Father'Class; Years : Natural);

> end FATHERS;
> 
> package FATHERS.SONS is
> type Son is new father with record
>     skate : boolean;
> end Son;
> 
> function F_Build(Years :Natural) return Son;
> procedure F_Forced_to_do_it;
> end FATHERS.SONS;
> 
> package body FATHERS.SONS is
> 
> function F_Build(Years : Natural) return Son is
> begin
      return Result : Son do
         Initialize (Result, Years); -- Parent's "constructor"
         Result.Skate := True;
      end return;
> end F_Build;
> 
> end FATHERS.SONS;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de