Issue #16993 has been updated by greggzst (Grzegorz Jakubiak). I opened a PR to add this functionality https://github.com/ruby/ruby/pull/12750 ---------------------------------------- Feature #16993: Sets: from hash keys using Hash#key_set https://bugs.ruby-lang.org/issues/16993#change-111962 * Author: marcandre (Marc-Andre Lafortune) * Status: Open ---------------------------------------- To create a set from hash keys currently implies a temporary array for all keys, rehashing all those keys and rebuilding a hash. Instead, the hash could be copied and its values set to `true`. ```ruby h = {a: 1} # Now: Set.new(h.keys) # => Set[:a] # After h.key_set # => Set[:a], efficiently. ``` -- https://bugs.ruby-lang.org/