Re: Diff. between singleton class and static class

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Jeff Louie <jeff_louie@xxxxxxxxx> wrote:
> First, the Singleton Pattern generally creates a single instance of a
> class, but this is not absolute. In fact, you can argue that some of
> the flexibility of the Singleton Pattern is that it allows you the
> programmer to return more than one instance of a class at a later
> date without breaking the client code.

I'd argue that in that case it's a factory. Certainly the GoF book
defines a singleton in terms of only providing one instance. I agree
that using a singleton allows you to change it into a factory at a
later date without breaking client code though. (Assuming the client
code isn't relying on it being a singleton.)

<snip>

> There _are_ advantages to the Singleton pattern and they include:

<snip>

> 3) Allows sub-classing.

It allows the singleton to be a subclass of something else. The normal
patterns that ensure that only a single instance is ever created don't
work well with subclasses. It can be done, but it's somewhat messy.

--
Jon Skeet - <skeet@xxxxxxxxx>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
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