simplify

[dpep]

I was trying to understand the Singleton code (neat!) and saw a few ways we could simplify. If we roll Singleton.__init__ into included, it means we don't have to expose that helper method to the public and creates a single entry point (include Singleton). We could also simplify the instance method to have only a single return statement, at the end. I also added some tests that helped me catch a regression during development.

(ported from ruby/ruby#7890 and thanks to @jeremyevans and @ioquatix for taking a first pass!)

Would this help?

[ioquatix]

This looks good to me, can you considerate feedback of #clone - do we need to add a test to confirm it's working correctly?

[dpep]

@ioquatix if I understand @jeremyevans's feedback around #clone, then this new test catches the regression he pointed out and confirms this change is working correctly, ie. that cloning a singleton class creates a new singleton class with it's own unique instance. (note that I added back in @singleton__instance__ = nil to resolve this)

does that address your concern or is there another test case we should add?

[hsbt]

I reverted this change because this break Rails CI.

see https://bugs.ruby-lang.org/issues/19711

[ioquatix]

@hsbt thanks.

[ioquatix]

@dpep your change was reverted because it broke Rails. That means the behaviour of your implementation changed, and unfortunately it was not covered by a test in this repository.

https://bugs.ruby-lang.org/issues/19711

It looks like Rails expects subclasses of a Singleton to be instantiatable.

If you have time, can you investigate?

[dpep]

whoops, sorry about that! see #9 for a retry with improved test coverage to guard against this corner case