From: beckwb@ois.com (R. William Beckwith)
Subject: Re: Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG)
Date: Thu, 29 Sep 1994 18:10:42 GMT
Date: 1994-09-29T18:10:42+00:00 [thread overview]
Message-ID: <CwwL5u.6HD@ois.com> (raw)
In-Reply-To: 1994Sep29.014611.20263@swlvx2.msd.ray.com
John Volan (jgv@swl.msd.ray.com) wrote:
: MAB = mab@dst17.wdl.loral.com (Mark A Biggar) writes:
snip
: ... The only way the
: client could get to that information would be to use an unchecked conversion to
: change this "opaque" pointer into a pointer to the "non-opaque" Office subclass
: below. (I think folks in the other languages would call this "downcasting".)
: But this practice breaks type-safety!
Actually the cool term is now `narrowing'. Narrowing the access type from
access all Abstract_Office'class
to
access all Office'class
does not break type saftey. Since Abstract_Office is abstract, there can be
no objects of type Abstract_Office. Thus, Abstract_Office'class is always
safely convertable to Office'class.
This issue (we call it the "withing problem") is addressed in the CORBA
IDL to Ada 9X mapping document. This mapping provides a nice solution
to this issue that is very similiar to Mark's. The CORBA IDL to C++
mapping document defines C++ classes that are much more complex and
cumbersome (IMHAARO) than non-CORBA C++ classes. I think the IDL to
Ada 9X mapping provides a nice way to code Ada 9X even if you're not
using CORBA.
... Bill
--
e-mail: Bill.Beckwith@ois.com | Team Ada
Objective Interface Systems, Inc. | dist, full O-O
1895 Preston White Drive, Suite 250 | multithreading
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next prev parent reply other threads:[~1994-09-29 18:10 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
1994-09-27 16:52 Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG) John Volan
1994-09-27 18:48 ` Mark A Biggar
1994-09-29 1:46 ` John Volan
1994-09-29 13:57 ` Tucker Taft
1994-09-29 17:20 ` Bjarne Stroustrup <9758-26353> 0112760
1994-09-30 1:38 ` Tucker Taft
1994-09-30 12:33 ` Bjarne Stroustrup <9758-26353> 0112760
1994-09-29 18:37 ` John Volan
1994-09-29 19:34 ` David Weller
1994-09-30 22:13 ` John Volan
1994-10-02 3:31 ` Andrew Lees
1994-09-30 1:47 ` Tucker Taft
1994-09-30 13:30 ` John Volan
1994-09-29 18:10 ` R. William Beckwith [this message]
1994-10-03 0:33 ` Cyrille Comar
1994-09-28 14:01 ` Norman H. Cohen
1994-09-29 2:12 ` John Volan
1994-09-29 14:01 ` Tucker Taft
1994-09-29 18:37 ` Norman H. Cohen
1994-09-29 9:48 ` Magnus Kempe
1994-09-29 13:10 ` Magnus Kempe
1994-09-29 18:05 ` Tucker Taft
1994-09-30 10:20 ` Mut. Recurs. in Ada9X w/o Breaking Encaps.? Magnus Kempe
1994-09-30 13:22 ` Tucker Taft
1994-10-01 1:24 ` Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG) Adam Beneschan
1994-10-01 12:01 ` Magnus Kempe
1994-10-01 18:43 ` Mark A Biggar
1994-10-02 16:41 ` John Volan
1994-10-02 23:33 ` Matt Kennel
1994-10-03 8:07 ` Mut. Recurs. in Ada9X w/o Breaking Encaps.? Magnus Kempe
1994-10-03 12:14 ` Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG) Robert I. Eachus
1994-10-04 2:12 ` R. William Beckwith
1994-10-04 16:00 ` John Volan
1994-10-05 11:42 ` Robert I. Eachus
1994-10-05 21:09 ` Matt Kennel
1994-10-03 20:29 ` Harry Koehnemann
1994-09-29 13:35 ` John Volan
1994-09-30 20:27 ` Norman H. Cohen
1994-10-01 1:47 ` John Volan
1994-10-01 20:44 ` Tucker Taft
1994-10-03 11:29 ` Robert I. Eachus
1994-09-30 22:46 ` Matt Kennel
1994-10-01 2:11 ` John Volan
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