[RFC][plugin]: make PluginObjectStore a singleton.

[Deepak Bhole]

* Denis Lila <dlila at redhat.com> [2011-03-31 15:29]:
> 
> > I particularly like this comment ;) Do you have a source for this? I
> > would prefer it if this was an actual class. It's not behaviourally an
> > enum, so it should not be marked as such.
> 
> Effective Java, second edition.
> I don't have the book with me, and I forget what Joshua Bloch's
> arguments for enum singletons were (except for how much easier
> the singleton property is to enfoce (which is more than enough
> of a reason by itself, but there were others)), but they were
> very good ones.
> 

I've read this before too. The top things if I recall correctly are that
an enum cannot be constructed, not even via reflection and it is 
implicitly final.

Cheers,
Deepak

> > It's not behaviourally an enum
> 
> I disagree with this. I agree that it's not behaviourally
> a C++ enum, but Java enums are fundamentally different. In Java
> an enum is simply a class with a compile-time constant number of
> instances. That's exactly what a singleton is (except a singleton
> is a special case of that, where that constant number is 1).
> 
> And besides, I see no practical problem with making this an
> enum, but I do see practical benefits, so why not use it?
> (unless someone else can see such problems, of course)
> 
> Regards,
> Denis.
> 
> ----- Original Message -----
> > On 03/31/2011 03:03 PM, Deepak Bhole wrote:
> > > * Denis Lila<dlila at redhat.com> [2011-03-31 14:54]:
> > >> >  The attached patch does what the subject says.
> > >> >
> > >> >  Ok to push?
> > >> >
> > > Please rename the instance to INSTANCE and method to getInstance to
> > > make
> > > it clearer that it is a singleton in the caller as well.
> > >
> > 
> > I agree with what Deepak said.
> > 
> > >> >  +// Enums are the best way to implement singletons.
> > 
> 
> > 
> > >> >  +enum PluginObjectStore {
> > >> >  + THE_STORE;
> > >> >
> > 
> > Thanks,
> > Omair