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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
 =?utf-8?Q?=29?=
 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: Ada2012 Invariants and obaque types
Date: Tue, 21 Jun 2011 12:27:56 +0200
Organization: Ada @ Home
Message-ID: <op.vxe8oupoule2fv@douda-yannick>
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Date: 2011-06-21T12:27:56+02:00
List-Id: <comp.lang.ada>

Hi Martin,

Unless I've missed something, I do not see the point. Whether or not you=
  =

use an invariant, if the public view assert the type is tagged, the full=
  =

view must be tagged. This was the same, even prior to Ada 2012. Otherwis=
e,  =

how would you derive from a tagged public view and define class wide vie=
w,  =

 from a type whose private view isn't tagged ?

Just out of curiosity: which GNAT flavor do you use for Ada 2012 ?

Le Tue, 21 Jun 2011 10:53:31 +0200, Martin <martin.dowie@btopenworld.com=
>  =

a =C3=A9crit:

> A fairly common Ada idiom is to define the full view of a private type=

> using an incomplete declaration. Thus leaving the actual
> implementation to the package spec. Trying this out with the public
> view defined with an invariant lead to a compiler error - is this:
>
> a) expected?
> b) an unexpected consequence? or
> c) a compiler bug?
>
> Example:
> package P1 is
>    type T1 is tagged private
>       with Invariant =3D> Is_Valid (T1);
>    function Create               return T1;
>    function Is_Valid (This : T1) return Boolean;
> private
>    type Imp;
>    type T1 is
>       record
>          I : Imp;
>       end record;
> end P1;
>
> gnatmake -ws -c -u -PH:\Ada\test_invariants\test_invariants.gpr p1.ads=

> gcc -c -g -g -gnatE -gnatVn -gnato -fstack-check -gnat12 -gnatf -I- -
> gnatA H:\Ada\test_invariants\src\p1.ads
> p1.ads:11:04: type "Imp" is frozen at line 3 before its full
> declaration
> p1.ads:13:09: full declaration of private type "T1" defined at line 3
> must be a tagged type
> p1.ads:15:14: invalid use of type before its full declaration
> gnatmake: "H:\Ada\test_invariants\src\p1.ads" compilation error
>
> [2011-06-21 09:46:55] process exited with status 4 (elapsed time:
> 00.26s)


-- =

=E2=80=9CSyntactic sugar causes cancer of the semi-colons.=E2=80=9D  [Ep=
igrams on  =

Programming =E2=80=94 Alan J. =E2=80=94 P. Yale University]
=E2=80=9CStructured Programming supports the law of the excluded muddle.=
=E2=80=9D [Idem]
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