Fix each* methods to return a receiver itself

[makenowjust]

All each and methods like each should return a receiver itself. For example, current Deque#each returns Range?, it looks like a bug. (But each_cons and some Enumerable methods return nil same as Ruby)

[asterite]

Thank you!

We copied Ruby here when we made each return self. However, now I'm more inclined to make them return nil. I never understood why it's useful to return self. But I'd like others' opinion here :-)

[makenowjust]

@asterite I asked it to matz in twitter, and answered now. https://twitter.com/yukihiro_matz/status/815905904084197376

Matz says "To return self by Array#each and some methods is not big meaning, because returning value is not used almost. But it is better than to return nil."

[makenowjust]

@asterite My question: To return self, does it have effects for optimization? And if returning nil, does it have no effect?

[asterite]

Yes, of course :-)

If a method returns nil then for code generation it returns void in LLVM. Then if you have a method like:

def foo
  some_array.each do
  end
end

then foo now returns the array, but if each returns nil then foo will return nil. This can also prevent some union types.

But this is not the point. I never understood why each (or p, or puts) return something other than nil. This is kind of ugly:

obj.each do
  # ...
end.do_something_else

so maybe I'd like to remove that anti-feature from the standard library.

[ysbaddaden]

I think we can remove it. It's not such a big deal.

[asterite]

Closed in favor of #3826