From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: 'Protected' abstract subprograms
Date: Sat, 11 Jan 2014 09:59:11 +0100
Date: 2014-01-11T09:59:11+01:00 [thread overview]
Message-ID: <zlias3msw59.e73qre8brldl$.dlg@40tude.net> (raw)
In-Reply-To: 839fee13-2743-49f6-a7f3-f95578386201@googlegroups.com
On Fri, 10 Jan 2014 14:00:31 -0800 (PST), sbelmont700@gmail.com wrote:
> I find it to be a fairly common occurrence and, depending on who you ask,
> a programming best practice to have a publically visible non-abstract
> dispatching operation re-dispatch to an abstract subprogram (i.e. the
> 'template pattern').
Fortunately, in Ada you don't need to re-dispatch because Ada directly
supports composing operations out of primitive operations. That is what
class-wide operations are for.
type T is abstract ...;
procedure Bar (X : T) is abstract; -- Primitive operation
procedure Foo (X : T'Class); -- Class-wide operation
procedure Foo (X : T'Class) is
begin
...
Bar (X); -- This dispatches
...
end Foo;
> In any case, does anyone know of a workaround to achieve the same sort of
> behavior?
First, and foremost, never re-dispatch, that is semantically broken [*],
potentially unmaintainable (due to substitutability hell) and inefficient
too.
Secondly. There is another method of hiding operations. You pack it into a
set of implementation packages. The packages declare the operation public,
but the type itself is from some ancestor without the operation:
type T is new Public_View with private;
private
type T is new Implementation_View with ...;
The user of T does not know about Implementation_View, which itself is
public of course.
The drawback of this model is construction of new objects derived from T.
But since that is completely broken in Ada, anyway, I mean the mess of
limited aggregates, constructing functions etc, you will have fight that in
any case.
---------
* When you dispatch in a body of an operation that means that the body is
valid for more than one type. Many types = class. Operation for all class =
class-wide operation. It cannot be primitive, per definition. Re-dispatch
breaks this model and effectively makes your design un/weakly typed.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2014-01-11 8:59 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-10 22:00 'Protected' abstract subprograms sbelmont700
2014-01-10 22:30 ` Randy Brukardt
2014-01-11 16:12 ` sbelmont700
2014-01-14 3:45 ` Randy Brukardt
2014-01-14 9:05 ` Dmitry A. Kazakov
2014-01-15 0:36 ` Randy Brukardt
2014-01-15 9:17 ` Dmitry A. Kazakov
2014-01-15 14:11 ` Robert A Duff
2014-01-15 15:40 ` adambeneschan
2014-01-15 21:21 ` Robert A Duff
2014-01-15 23:10 ` Randy Brukardt
2014-01-16 0:51 ` Robert A Duff
2014-01-16 10:43 ` AdaMagica
2014-01-16 16:32 ` adambeneschan
2014-01-17 1:49 ` Robert A Duff
2014-01-17 23:23 ` Randy Brukardt
2014-01-19 21:07 ` Robert A Duff
2014-01-20 8:40 ` Dmitry A. Kazakov
2014-01-21 14:37 ` Robert A Duff
2014-01-22 8:27 ` Dmitry A. Kazakov
2014-01-21 1:21 ` Randy Brukardt
2014-01-21 14:35 ` Robert A Duff
2014-01-15 23:17 ` Randy Brukardt
2014-01-16 8:52 ` Dmitry A. Kazakov
2014-01-11 8:41 ` J-P. Rosen
2014-01-11 8:59 ` Dmitry A. Kazakov [this message]
2014-01-11 13:42 ` Niklas Holsti
2014-01-11 19:35 ` Dmitry A. Kazakov
2014-01-12 9:19 ` Niklas Holsti
2014-01-12 10:22 ` Dmitry A. Kazakov
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