The best feature of `Hash` maintaining insertion order is that `Set` does too, since a `Set` is a `Hash` with all-`true` values: https://github.com/ruby/ruby/bl

The best feature of `Hash` maintaining insertion order is that `Set` does too, since a `Set` is a `Hash` with all-`true` values: https://github.com/ruby/ruby/blob/3539da64fc42d6eb76f1d4c3ccd219c3259ecd8b/lib/set.rb#L522 https://github.com/ruby/ruby/blob/3539da64fc42d6eb76f1d4c3cc...