From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Subject: Re: Ada Singleton Pattern
Date: Mon, 13 Sep 2004 20:38:04 +0000 (UTC)
Date: 2004-09-13T20:38:04+00:00 [thread overview]
Message-ID: <ci50fd$kk9$1@a1-hrz.uni-duisburg.de> (raw)
In-Reply-To: hnk1d.246585$OR2.11156430@news3.tin.it
Luca Stasio <stasio2000@tin.it> wrote:
: Dmitry A. Kazakov ha scritto:
:> On Mon, 13 Sep 2004 15:04:27 GMT, Luca Stasio wrote:
:>
:>
:>>Hi, there is a way to implement the Singleton Pattern in Ada?
:>>There are some examples out there?
:>>Thanx.
:>
:>
:> package Foo is
:> type Singleton (<>) is limited private;
:> ... -- Public interface subroutines
:>
:> The_Only_One : constant Singleton; -- The value
:> private
:> type Singleton is new Integer; -- Any implementation you want
:> The_Only_One : constant Singleton := 5;
:>
:> The public view of Singleton is unconstrained and limited, which prevents
:> it from either being copied or declaring new objects of this type.
:>
: Thanx for your answer.
: Know, sorry... but, there is a way to create a Singleton Class from wich
: derive and create concrete singleton classes?
: I mean: (1) a Singleton class (2) a DatbaseAccessSingleton or a
: NetworkAccessSingleton or... heach one with its own methods but sharing
: the Singleton behaviour.
:
The following outlines a solution; in Ada 200Y it will be possible
to have initialised constants of a limited type, which might help,
the experts might tell you.
In the following, the constant is replaced with a function returning
the very same singleton.
with DB; -- database stuff
package Single is
pragma Elaborate_Body;
type Singleton(<>) is tagged limited private;
-- (this should be moved to another package: )
type The_One_And_Only_DB is new Singleton with private;
function DB17 return The_One_And_Only_DB;
-- the database singleton
private
type Singleton is tagged limited null record;
type The_One_And_Only_DB is new Singleton with record
Comp: DB.Stuff := DB.init;
-- note that you can pass The_One_And_Only'Access to DB.init
-- ...
end record;
end Single;
package body Single is
It: The_One_And_Only_DB;
-- with default initialisation, values provided by DB.init
function DB17 return The_One_And_Only_DB is
begin
return It;
end DB17;
end Single;
-- Georg
next prev parent reply other threads:[~2004-09-13 20:38 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 [this message]
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
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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