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From: "Matthew Heaney" <matthew_heaney@acm.org>
Subject: Re: tagged types extensions - language design question
Date: 2000/01/27
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In article <s90mu0hg7q538@corp.supernews.com> , "Vladimir Olensky" 
<vladimir_olensky@yahoo.com> wrote:

Why don't you just declare these types in separate packages?

package P is

  type T is tagged private;

private
  type T is tagged record ...;
end P;

package P.C is

  type T1_Public is
    abstract new T with record
      Something : Some_Other_Type;
    end record;

  type T1 is new T1_Public with private;

private
  type T1 is new T1_Public with record ... ;
end P.C;



> package P is
>
>    type T is tagged private;
>
>    type T1 is new T with
>       record with private
>                  something: some_type;
>       and record;
>
> private
>
>    type T is tagged with
>       record
>            ID : Integer;
>       end record;
>
>    type T1 is new T with
>       record
>           thing : some_other_type;
>       end record;
>
> end P;
>
> Instead I should do this in two steps.
>   1. to extend  private part   and then
>   2. to extend  public part
> or vice versa.
>
> Due to that type T1 has inheritance_depth = 3
> instead of inheritance_depth =  2.
>
> LRM (3.9.1) says:
>   Every type extension is a tagged type,
> and is EITHER a record extension OR a private
> extension of some other tagged type.
>
>     It would be interesting to know what were
> the reasons not to allow to have BOTH a record
> extension AND a private extension at the same time.
>
> Regards,
> Vladimir Olensky
>
>