From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!mx05.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
 =?utf-8?Q?=29?=
 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Type vs subtype about visibility of parent's private full definition
Date: Wed, 15 May 2013 10:13:00 +0200
Organization: Ada @ Home
Message-ID: <op.ww383ycoule2fv@cardamome>
NNTP-Posting-Host: ll7JxPeHtfBeoFl5nDW1Dg.user.speranza.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed; delsp=yes
Content-Transfer-Encoding: Quoted-Printable
X-Complaints-To: abuse@aioe.org
User-Agent: Opera Mail/12.15 (Linux)
X-Notice: Filtered by postfilter v. 0.8.2
Xref: news.eternal-september.org comp.lang.ada:15569
Date: 2013-05-15T10:13:00+02:00
List-Id: <comp.lang.ada>

Hi all,

I already encountered something similar in the past, and it's back again=
.  =

I can only solve it using a subtype instead of a type=E2=80=91new where =
I  =

initially want a type=E2=80=91new, so I'm not happy with using subtype.

The case: a child package don't see the full definition of a type from t=
he  =

private part of its parent package when it derives from that type as a  =

type=E2=80=91new.

Below is an example, using a discriminant, which is not required to expo=
se  =

the visibility issue, but which is the reason why I'm not happy to not b=
e  =

able to derive a type=E2=80=91new instead of a subtype: I can't force st=
atic=E2=80=91check  =

as I expected. If the discriminant was not part of the party, I won't  =

bother. That's the reason why the example makes use of a discriminant an=
d  =

I see the case as an issue.


Example:


     package Parents is

        pragma Pure;

        type Discriminant_Type is
           range 1 .. 5;

        type Instance_Type
          (Discriminant : Discriminant_Type) is
           private;

     private

        type Instance_Type
          (Discriminant : Discriminant_Type) is
           record
              Value : Integer;
           end record;

     end Parents;

     package Parents.Childs is

        pragma Pure;

        subtype Parent_Type is
           Parents.Instance_Type;

        type Instance_Type is
           new Parent_Type
             (Discriminant =3D> 2);

        function Value
          (Object : Instance_Type)
           return Integer;

     private

        function Value
          (Object : Instance_Type)
           return Integer
           is (Object.Value); -- << Error here

     end Parents.Childs;


I did not check the RM, however I'm blocked if I do this, as GNAT has  =

complaints with `is (Object.Value)`, and grumbles:


     no selector "Value" for private type derived from "Instance_Type"


I can just work around it, defining `Parents.Childs.Instance_Type` this =
 =

way:


        subtype Instance_Type is
           Parent_Type
             (Discriminant =3D> 2);


=E2=80=A6 instead of this way (as was in the above package definition):


        type Instance_Type is
           new Parent_Type
             (Discriminant =3D> 2);


I may be naive, I believe `Parents.Childs` private part should see the  =

full definition of `Parents.Instance_Type` in both case, not only when  =

deriving a subtype.

What are your opinions about this issue?


-- =

=E2=80=9CSyntactic sugar causes cancer of the semi-colons.=E2=80=9D [1]
=E2=80=9CStructured Programming supports the law of the excluded muddle.=
=E2=80=9D [1]
[1]: Epigrams on Programming =E2=80=94 Alan J. =E2=80=94 P. Yale Univers=
ity