Always return a RegionCollection from #subregions

[codeodor]

Prior to this, #load_subregions returned an empty array if there were no subregions. But there is no reason the calling code should have to check the return type before operating on the return value.

[ecbypi]

Looks good. @jim, @cdainmiller any thoughts?

@codeodor, what are your thoughts on adding tests to ensure an empty RegionCollection behaves as expected?

[codeodor]

Since RegionCollection derives from array, unless Carmen is doing something to violate Liskov Substitution Principle (which I would doubt), I think it's safe.

That said, it's also a self-serving assessment because I'm swamped and only made this change because I figured it was probably a 1-liner that I could find in just a minute. 😄

I'll see what I can cook up if I get a few minutes later today.

[ecbypi]

Since RegionCollection derives from array, unless Carmen is doing something to violate Liskov Substitution Principle (which I would doubt), I think it's safe.

Sounds good. Just want to see if @jim or @cdainmiller have any thoughts before merging.

[jim]

Looks good to me.

FWIW, Having RegionCollection subclass Array was probably a mistake on my part. It would have been better to just include Enumerable and delegate each to an internal Array.

[codeodor]

Awesome, thanks! 👍