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=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM autolearn=ham autolearn_force=no version=3.4.4 X-Google-Thread: 103376,54aae3da1cf935cd X-Google-Attributes: gid103376,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news2.google.com!proxad.net!fr.ip.ndsoftware.net!216.196.110.149.MISMATCH!border2.nntp.ams.giganews.com!nntp.giganews.com!news-out.tin.it!news-in.tin.it!news3.tin.it.POSTED!not-for-mail From: Luca Stasio User-Agent: Mozilla Thunderbird 0.7.2 (Windows/20040707) X-Accept-Language: it, en, en-us MIME-Version: 1.0 Newsgroups: comp.lang.ada Subject: Re: Ada Singleton Pattern References: <%Fi1d.245967$OR2.11136154@news3.tin.it> <14p6ezf3vze8j$.j05arkr066wi.dlg@40tude.net> <87llfdgcdf.fsf@deneb.enyo.de> In-Reply-To: <87llfdgcdf.fsf@deneb.enyo.de> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Message-ID: Date: Tue, 14 Sep 2004 15:38:56 GMT NNTP-Posting-Host: 80.181.112.41 X-Complaints-To: "Please send abuse reports to abuse@tin.it and technical notifications to newsmaster@tin.it" X-Trace: news3.tin.it 1095176336 80.181.112.41 (Tue, 14 Sep 2004 17:38:56 MET DST) NNTP-Posting-Date: Tue, 14 Sep 2004 17:38:56 MET DST Organization: TIN Xref: g2news1.google.com comp.lang.ada:3723 Date: 2004-09-14T15:38:56+00:00 List-Id: Florian Weimer ha scritto: > * Dmitry A. Kazakov: > > >>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. > > > This is only a partial solution, unfortunately. > > Ada *requires* that the package initialization code runs before > The_Only_One is accessed. This is different from many other languages > (where the initialization order of global objects is mostly > unspecified and not related to actual usage patterns) and solves a big > chunk of the singleton problem. > > However, you still have to deal with termination on your own: you must > ensure that no client is still using the singleton object before you > destroy it. There is no direct support in the language for this part > of the problem, and you have to use one of the traditional approaches > if this matters to your application (or assignment 8-). > > (I tried to avoid Ada-specific terminology above because Luca probably > isn't familiar with the Ada language.) Hi, is the one from Martin Dowie and Steve a right solution? Thanx a lot. Luca Stasio