Please no, I'm against that change. It means this doesn't work:

set1 = Set{1, 2, 3}
set2 = Set{3, 2, 1}

case set1
when set2
  puts "Works!"
else
  puts "Doesn't work!"
end

With this PR it will print "Doesn't work!", totally unpredictable.

There's also the thing that I never, ever have seen a set being used in a when condition. And doing includes? is much more explicit and understandable.

@asterite print "Works!" due to def ===(object : T).

Ooooooooh... I didn't see that. Yes, that's better than the Ruby version. So maybe it's good :-)

But then, should Array also behave like this? What makes Set so special that it deserves a ===?

IMO, ordered (indexed) collection should not be redefine === and unordered collection should be redefine ===. Because ordered collection's item is characterized by key-value pair, not value only.

And another thought: Why Set#=== is not redefined, though Range#=== is redefined? Range is pioneer which is redefine === as includes?.

ping.

@makenowjust Could some docs like in Range#=== be added so the use case is shown in code?

@bcardiff Added.

Thanks @makenowjust !