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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Can't export object of private type
Date: 1999/02/28
Message-ID: <m3ogme197d.fsf@mheaney.ni.net>#1/1
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Sender: matt@mheaney.ni.net
References: <F7JoCB.JxB@syd.csa.com.au> <F7nAwn.on@syd.csa.com.au>
 <7b1k4h$13k6@news3.newsguy.com>
NNTP-Posting-Date: Sun, 28 Feb 1999 13:55:50 PDT
Newsgroups: comp.lang.ada
Date: 1999-02-28T00:00:00+00:00
List-Id: <comp.lang.ada>

Samuel Mize <smize@imagin.net> writes:

> > The best workaround I've been able to come up with is to export an access 
> > variable to the singleton. For example,
> 
> Let me improve your access-based solution.  Changes are in all-caps:
> 
> >   package Singleton is
> > 
> >     type Singleton_Type is tagged private;

Better is to declare this type as limited and indefinite:

  type Singleton_Type (<>) is limited private;

This way, no one can declare instances of the type, nor can they assign
another value to the singleton.

I'm not clear why the type needs to be tagged.  Don't make the type
tagged unless you have a compelling reason for doing do.

A better solution is to not use a type at all.  Just implement the
object as a state machine package.

I often see programmers using tagged types everywhere.  Please do not do
this.