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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Running a preprocessor from GPS?
Date: Sat, 01 Aug 2015 08:20:09 +0100
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Date: 2015-08-01T08:20:09+01:00
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EGarrulo <egarrulo@gmail.com> writes:

> 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?

According to Wikipedia, a singleton "is useful when exactly one object
is needed to coordinate actions across the system". And encapsulating
that object in a package meets that criterion.

Isn't a Get_Instance function a way of getting the desired effect in C++
etc, rather than a necessary detail of the pattern? I can see that it
allows you to postpone creating the singleton instance until a time of
your choosing, rather than the Ada way of doing it during package
elaboration in a sequence chosen by the compilation/build engine.

With regard to Carter's point about "instantiation", it's a term that
Ada has specialised to mean creating an instance of a generic. I don't
know if there's an Ada term that means creating an object that is an
instance of a type? I could suggest "reification" :-) but I doubt that
would fly.