Issue #13933 has been updated by Dan0042 (Daniel DeLorme). akr (Akira Tanaka) wrote in #note-8:

Range#empty? should work with them.

Ok for `Float::INFINITY, [], ""`, but I don't think `true, false, Object.new` are relevant. A Range object normally has a begin and end, and if the values are not comparable (like `"a"..1`) we get "ArgumentError (bad value for range)". With `true..true` we happen to coincidentally pass that validation because `true<=>true` is 0 (and arguably it should be nil but that's another topic). But semantically, as a range, `true..true` doesn't mean anything. The introduction of beginless/endless ranges also mean that we can now create all kinds of ranges that skip the normal validation. `(true..true)` and `(true..)` and `(..true)` are not semantically meaningful ranges, there is no use case for them, and therefore it doesn't matter that `#include?` raises an error, and it shouldn't matter what is returned by `#empty?` But unlike `true`, arrays truly are comparable. The Comparable module is not mixed in, but <=> can return -1 and 1. So `[]` is truly a minimum value for arrays. It could be special-cased. Although I'm not sure it's worth the trouble. Or maybe we can define a range "r" as empty if `r.begin.nil? and r.exclude_end? and r.end.respond_to?(:empty?) and r.end.empty?` Random idea: beginless/endless ranges may only be created for objects that mix in `Comparable`. So `(Time.now..)` is ok but `(Object.new..)` raises "ArgumentError (bad value for range)" ---------------------------------------- Feature #13933: Add Range#empty? https://bugs.ruby-lang.org/issues/13933#change-104711 * Author: ted (Ted Johansson) * Status: Open * Priority: Normal ---------------------------------------- Range already responds to #size. It would be nice if it also responded to predicate #empty? :-) -- https://bugs.ruby-lang.org/