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,
	WEIRD_PORT autolearn=unavailable autolearn_force=no version=3.4.4
X-Received: by 10.98.141.152 with SMTP id p24mr6498844pfk.41.1495317328697;
        Sat, 20 May 2017 14:55:28 -0700 (PDT)
X-Received: by 10.157.35.104 with SMTP id k37mr342015otd.14.1495317328552;
 Sat, 20 May 2017 14:55:28 -0700 (PDT)
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!news.glorb.com!67no1015714itx.0!news-out.google.com!m134ni4240itb.0!nntp.google.com!67no1014861itx.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Sat, 20 May 2017 14:55:28 -0700 (PDT)
In-Reply-To: <88d90508-a6ce-445f-b2a1-519a64a741b2@googlegroups.com>
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com;
 posting-host=173.71.201.205;
 posting-account=QF6XPQoAAABce2NyPxxDAaKdAkN6RgAf
NNTP-Posting-Host: 173.71.201.205
References: <bd5b3107-709d-46b9-b29b-fd15e8a6e265@googlegroups.com>
 <88d90508-a6ce-445f-b2a1-519a64a741b2@googlegroups.com>
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <55306f0a-8b60-4940-af19-e99a74e3fb3b@googlegroups.com>
Subject: Re: Preventing private procedure visibility being made public through
 extension
From: Jere <jhb.chat@gmail.com>
Injection-Date: Sat, 20 May 2017 21:55:28 +0000
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Xref: news.eternal-september.org comp.lang.ada:46827
Date: 2017-05-20T14:55:28-07:00
List-Id: <comp.lang.ada>

On Saturday, May 20, 2017 at 4:13:10 PM UTC-4, AdaMagica wrote:
> > with Base;
> >=20
> > package Derived is
> >   =20
> >    type Derived_Param is new Base.Base_Param with null record;
> >   =20
> >    type Derived_Type is new Base.Base_Type with private;
> >   =20
> >    procedure Something
> >       (Obj : in out Derived_Type;=20
> >        Value : Derived_Param'Class)
> >    is null;
> >   =20
> > private
> >   =20
> >    type Derived_Type is new Base.Base_Type with null record;
> >   =20
> >    overriding
> >    procedure Something
> >       (Obj : in out Derived_Type;=20
> >        Value : Base.Base_Param'Class)=20
> >    is null;
> >   =20
> > end Derived;
>=20
> Here you are wrong. Hiding the overriding does not prevent the client fro=
m calling the operation. It nearly makes no difference whether you override=
 an inherited operation in the public or in the private part. (There are a =
few syntactic diffrences though.)
>=20
> > *************************************************
> >=20
> > This is all well and good.  Variables of Derived_Type=20
> > can only call the version of something that I specified=20
> > publicly and the overriden one cannot be called.
>=20
> As I said, this is wrong.
>=20
> >=20
> > However, variables of More_Derived_Type have public=20
> > visibility to both versions of Something.  I would=20
> > have hoped that the version hidden by Derived_Type=20
> > would keep it hidden, but extending the type makes
> > the private procedure visible again.
> >=20
> > Example main:
> >=20
> > main.adb
> > *************************************************
> > with Base;
> > with Derived; use Derived;
> >=20
> > procedure Main is
> >    p : Derived_Param;
> >    d : Derived_Type;
> >    m : More_Derived_Type;
> > begin
> >    d.Something(p);  -- Works as expected
>=20
> I think your compiler is in error here. This call is (IMHO) also ambiguou=
s.
> Both of these operations are visible here:

Perhaps a compiler bug, but it is even more than just not=20
ambiguous, it cannot call the version of the procedure that I=20
put in the private section (for variables of type Derived_Type). =20

If I declare a variable:

b : Base.Base_Param;

and try to call

d.Something(b);

It will fail with an error:
Expected type "Derived_Param'Class" defined at derived.ads:5
expected type "Derived_Param'Class" defined at derived.ads:5
found type "Base_Param" defined at base.ads:3

I even tried casting b to Base_Param'Class with similar=20
results (compiler error).  It is acting like the=20
procedure is not publicly visible for variable d.

Now if I didn't have a procedure named Something declared,=20
it acts as you described.  Is this a compiler bug?