From: Luca Stasio <stasio2000@tin.it>
Subject: Re: Ada Singleton Pattern
Date: Wed, 15 Sep 2004 19:38:51 GMT
Date: 2004-09-15T19:38:51+00:00 [thread overview]
Message-ID: <fT02d.328253$5D1.14478004@news4.tin.it> (raw)
In-Reply-To: <uk6uwezty.fsf@earthlink.net>
Matthew Heaney ha scritto:
> Luca Stasio <stasio2000@tin.it> writes:
>
>
>>Hi, there is a way to implement the Singleton Pattern in Ada? There
>>are some examples out there? Thanx.
>
>
> I prefer to do it this way:
>
> package P is
> pragma Elaborate_Body;
>
> type T (<>) is limited private;
> type T_Access is access all T;
>
> function Object return T_Access;
>
> procedure Op (O : access T);
> ...
> private
> type T is limited record ... end record;
> end;
>
> package body P is
> State : aliased T;
>
> function Object return T_Access is
> begin
> return State'Access;
> end;
> ...
> end P;
>
> Technically, since there's only one object, then you don't really need
> to declare the state as components of type T. T can just be a dummy
> type (type T is limited null record;), and operations (like Op) can just
> ignore the object passed as a parameter, and manipulate package state
> directly.
>
> But all of this is just syntactic overhead. You can always get rid of
> the type declaration, and just let the operations manipulate the package
> state. (Booch calls this an "abstract state machine.")
>
> Of course, if this is a type hierarchy, then you probably do need a type
> (since packages aren't "first class citizens," to use Wegner's phrase).
>
Hi... thank you too !!!
next prev parent reply other threads:[~2004-09-15 19:38 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-13 15:04 Ada Singleton Pattern Luca Stasio
2004-09-13 15:33 ` Dmitry A. Kazakov
2004-09-13 16:18 ` Luca Stasio
2004-09-13 17:01 ` Luca Stasio
2004-09-13 18:43 ` Martin Dowie
2004-09-13 19:37 ` Martin Dowie
2004-09-14 2:29 ` Steve
2004-09-14 8:52 ` Martin Dowie
2004-09-14 12:46 ` Jim Rogers
2004-09-14 13:57 ` Luca Stasio
2004-09-13 20:38 ` Georg Bauhaus
2004-09-14 8:17 ` Dmitry A. Kazakov
2004-09-14 13:56 ` Luca Stasio
2004-09-14 14:21 ` Florian Weimer
2004-09-14 14:48 ` Dmitry A. Kazakov
2004-09-14 15:04 ` Florian Weimer
2004-09-15 7:33 ` Dmitry A. Kazakov
2004-09-16 6:48 ` Florian Weimer
2004-09-16 7:45 ` Dmitry A. Kazakov
2004-09-14 15:38 ` Luca Stasio
2004-09-14 16:32 ` Florian Weimer
2004-09-14 17:43 ` Luca Stasio
2004-09-15 7:27 ` Martin Dowie
2004-09-15 19:38 ` Luca Stasio
2004-09-15 5:43 ` Matthew Heaney
2004-09-15 19:38 ` Luca Stasio [this message]
2004-09-18 21:47 ` Pylinius
2004-09-19 4:19 ` Matthew Heaney
2004-09-20 3:03 ` Pylinius
2004-09-23 7:35 ` Luca Stasio
2004-09-27 5:22 ` Pylinius
2004-09-27 8:05 ` Luca Stasio
2004-10-05 17:55 ` Luca Stasio
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