From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Running a preprocessor from GPS?
Date: Sat, 1 Aug 2015 09:48:16 +0200
Organization: cbb software GmbH
Message-ID: <1skv40112ytpq.1natkyhrl6jk7$.dlg@40tude.net>
References: <e610ca1e-4df6-4fbb-b3a1-ac35694d9072@googlegroups.com>
 <mp645u$abo$1@loke.gir.dk>
 <2df4698f-4c8e-457c-822d-209cb2f8ab5e@googlegroups.com>
 <mp8r8l$fnn$1@loke.gir.dk>
 <014427b1-ff7a-4a69-82e6-0330af77ed96@googlegroups.com>
 <mpbd8f$re$1@loke.gir.dk>
 <d5a73210-a67f-4d21-8b16-536af10ab157@googlegroups.com>
 <mpborl$6b9$1@dont-email.me>
 <91f88d79-197c-419f-84a8-908e05967a2c@googlegroups.com>
 <d1tst3FoastU1@mid.individual.net> <mpcjpo$93v$1@dont-email.me>
 <135c2b00-d13c-4f5d-a586-8aca442d363b@googlegroups.com>
 <87380683vc.fsf@adaheads.sparre-andersen.dk>
 <347c6be9-c918-4bc0-9494-c93cd6740def@googlegroups.com>
 <mpdts2$72e$3@dont-email.me>
 <4cb32c40-f659-490d-bbb6-73585fc069e8@googlegroups.com>
 <mpfm1b$bif$5@dont-email.me> <mpgcma$hup$1@dont-email.me>
 <7e653a88-e690-431a-9df9-3fc691466e08@googlegroups.com>
Reply-To: mailbox@dmitry-kazakov.de
NNTP-Posting-Host: ChlmA4XFxcJoDoqGdDSflw.user.speranza.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: 40tude_Dialog/2.0.15.1
X-Notice: Filtered by postfilter v. 0.8.2
Xref: news.eternal-september.org comp.lang.ada:27287
Date: 2015-08-01T09:48:16+02:00
List-Id: <comp.lang.ada>

On Fri, 31 Jul 2015 11:20:35 -0700 (PDT), EGarrulo wrote:

> On Friday, July 31, 2015 at 7:54:52 PM UTC+2, Jeffrey R. Carter wrote:
>> Many of the "design patterns" are actually implementation patterns to work
>> around deficiencies in the languages used in the book. An obvious example is the
>> "singleton pattern". In Ada, a singleton is simply a pkg. It's only a problem
>> that needs a pattern in languages that lack modules.
> 
> But a singleton would be instantiated when the "Get_Instance" function gets
> called by client code, not when a module gets loaded.  Or does Ada load a package
> at the first call?

Well, since other responses regarding singletons were IMO wrong. Here is an
answer from the OO POV.

In Ada singleton is achieved directly by the language means.

[ When Ada was designed there was no pattern stuff, which Jeffrey correctly
characterized as workarounds.  Yet Ada designers understood the problem,
maybe unconsciously, and resolved it at the language level. ]

Ada's singleton is an object of anonymous type. Many types allow object
declarations of anonymous types, which guarantees single instance, because
the type has no name.

Array singleton:

   Singleton : array (1..3) of Integer;

Task singleton:

   task Singleton is
      ...
   end task;

Protected object singleton:

   protected Singleton is
      ...
   end task;

Access type singleton (note access, not the target):

   Singleton : [not null] access ...;

For other types the singleton pattern is a declaration of the type and the
instance in the package body. This is probably what Jeffrey meant talking
about packages:

package body P is
   type Nobody_See_Me is ...;
   Singleton : Nobody_See_Me;

P.S. Get_Instance is C++ gibberish because it cannot create/return
unconstrained instances. In Ada you declare an object, singleton or not,
and that creates it. End of story.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de