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From: Eric Merritt <cyberlync@yahoo.com>
Newsgroups: comp.lang.ada
Subject: Re: List container strawman 1.1
Date: Tue, 6 Nov 2001 10:21:25 -0800 (PST)
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Date: 2001-11-06T10:21:25-08:00

news:mailman.1005002950.9554.comp.lang.ada@ada.eu.org...
> > A singleton is a generally an object of which
> there is
> > only one instance throughout the entire
> application.
> > That means that accessed from anywhere in the
> program
> > it will return the same list, in effect it is only
> > instantiated once. That instance is then returned
> any
> > time a new list is called for. So any elements
> added
> > to the list are available thought the application.
> > Basically a Singleton is a single instance of an
> > object, ie there can never be more then one
> instance
> > singleton object in an application.
> 
> That may be the meaning other languages, but not
> Ada! I intended the word
> ('singleton') in the mathematical sense of a set
> with only one element. Okay
> so we're not talking about a set, but a list, but I
> think the meaning is
> fairly obvious. In a program, code such as:
> 
>    Team(England,Jumping,Ladies) :=
> Singleton(HRH_Princess_Anne);
> 
> would help to emphasise that a list was being
> constructed that comprised
> only one element. It would contrast usefully, I
> think, with a multiple
> constructor:
> 
>    Team(USA,TF_Relay_4x400m,Men) :=
>       To_List((Alvin_Harrison, Antonio_Pettigrew,
> Calvin_Harrison,
> Michael_Johnson));
> 
> Of course, one alternative is not to have a
> 'singleton' constructor. It's
> only a convenience:
> 
>    Team(England,Jumping,Ladies) := To_List((1 =>
> HRH_Princess_Anne));

I was under the impression that we were talking about
the singleton design pattern not a Singleton list.
Actually I have never heard a single element list
refered to as a Singleton. I guess you learn something
every day. thank you.

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