From: jsa@alexandria.organon.com (Jon S Anthony)
Subject: Re: Which compiler is correct?
Date: 1997/06/20
Date: 1997-06-20T00:00:00+00:00 [thread overview]
Message-ID: <JSA.97Jun20185414@alexandria.organon.com> (raw)
In-Reply-To: ud205z1ifw.fsf@tanana.llnl.gov
In article <ud205z1ifw.fsf@tanana.llnl.gov> woodruff@tanana.llnl.gov (John Woodruff) writes:
> Here is another inquiry of the type "which compiler is correct." It is
> so similar to the issue Bob answered for Tom that I retain the thread
> (and the answer Bob gave is so clear that I imagine that this one will
> be equally easy to understand once I know the answer.)
>
> Let me define a package with a tagged private type:
> package Parent is
> type Obj is tagged private ;
> private
> type Obj is tagged record
> I : Integer ;
> end record ;
> end Parent ;
>
> The package has just one child that extends the type. Depending on the
> specifics of how I derive the new type, I get correct code or code that
> evokes an error message that I don't understand:
>
> package Parent.Child is
> type Good_Obj is new Parent.Obj with private ;
> type Bad_Obj is new Parent.Obj with null record ;
NOTE: at this point
a) Parent's i component is _not_ visible and so not available to this
view of the children.
b) Bad_Obj is _fully_ declared at this point and so will never get the
implicit declaration of Parent's i component.
> procedure Do_Nothing ; -- just to require body
> private
> type Good_Obj is new Parent.Obj with null record ;
At this point, Parent.I is visible and the full declaration of
Good_Obj implicitly declares this component.
> end ;
>
> One of the compilers (compiler "r") is able to compile the body without
> error; the other compiler reports an error in the body when I try to
> reference the component of the parent type.
>
> package body Parent.Child is
> good : Good_Obj ;
> Bad : Bad_Obj ;
> procedure Do_Nothing is
> begin
> null;
> end ;
> begin
> Good.I := 2 ;
> Bad.I := 2 ; -- compiler "g" reports error
> end ;
So, Bad.I is not directly available and compiler "g", I believe, is
correct.
> selector". I am unable to think of a reason why the body of the child
> package can reference the parent's private declaration of Obj for one,
> but not for the other derived types.
I think this all falls out of the rules in 7.3.1, and in particular
pay close attention to what is said in (3).
/Jon
--
Jon Anthony
OMI, Belmont, MA 02178
617.484.3383
"Nightmares - Ha! The way my life's been going lately,
Who'd notice?" -- Londo Mollari
next prev parent reply other threads:[~1997-06-20 0:00 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-06-17 0:00 Which compiler is correct? Tom Moran
1997-06-18 0:00 ` Robert A Duff
1997-06-18 0:00 ` John Woodruff
1997-06-19 0:00 ` Robert A Duff
1997-06-20 0:00 ` Jon S Anthony [this message]
1997-06-21 0:00 ` Robert A Duff
1997-06-26 0:00 ` Jon S Anthony
1997-06-19 0:00 ` Simon Wright
1997-06-20 0:00 ` Jon S Anthony
1997-06-21 0:00 ` Robert A Duff
1997-06-21 0:00 ` Robert A Duff
1997-06-21 0:00 ` Simon Wright
1997-06-23 0:00 ` Mats.Weber
1997-06-24 0:00 ` Jon S Anthony
1997-06-18 0:00 ` Pascal Obry
1997-06-18 0:00 ` Tom Moran
-- strict thread matches above, loose matches on Subject: below --
1996-09-10 0:00 Which compiler is correct?? Robert B. Love
1996-09-10 0:00 ` Robert Dewar
1996-09-11 0:00 ` Robert B. Love
1996-09-10 0:00 ` Robert Dewar
1996-09-11 0:00 ` Robert A Duff
1996-09-12 0:00 ` Ken Cowan
1996-09-12 0:00 ` Ken Cowan
1996-09-13 0:00 ` Jon S Anthony
1996-09-11 0:00 ` Jon S Anthony
1996-09-12 0:00 ` Tucker Taft
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