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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Type invariants and private extensions?
Date: Mon, 2 Oct 2017 18:16:16 -0500
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:48296
Date: 2017-10-02T18:16:16-05:00
List-Id: <comp.lang.ada>

"Victor Porton" <porton@narod.ru> wrote in message 
news:op6v4m$tmm$1@gioia.aioe.org...
> Egil H H wrote:
>
>> On Monday, September 11, 2017 at 10:48:46 PM UTC+2, Victor Porton wrote:
>>> > The Invariant will then be inherited by all derived types
>>>
>>> It is not what I want. I want different invariants for different derived
>>> types.
>>>
>>
>> You can add new invariants in addition to the ones inherited
>
> I cannot: the compiler gives an error:
>
> package P is
>
>  type T is tagged private;
>
> private
>
>  type T is tagged null record;
>
> end P;
>
> with P; use P;
>
> package P1 is
>
>  type T1 is new T with null record
>    with Type_Invariant => True;
>
> end P1;

Right, but you can define a private extension:

package P1 is

    type T1 is new T with private;

private

    type T1 is new T with null record
       with Type_Invariant => True;

 end P1;

The semantics is the same as with a plain record extension, and the 
invariant makes more sense.

                                      Randy.