Hi -- I'm just wondering about this: >> RUBY_DESCRIPTION => "ruby 1.9.0 (2008-06-03 revision 16244) [i686-darwin9.2.2]" >> require 'set' => true >> s = Set.new(1..10) => #<Set: {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}> >> s.map {|e| e + 10 } => [11, 12, 13, 14, 15, 16, 17, 18, 19, 20] >> s.map! {|e| e + 10 } => #<Set: {11, 12, 13, 14, 15, 16, 17, 18, 19, 20}> I'm just wondering whether it would make more sense for Set to have a #map method that returned a set, rather than an array, as long as that behavior is considered meaningful (as it appears to be since that's how Set#map! is working). Otherwise that aspect of the map/map! distinction seems kind of arbitrary. David -- Rails training from David A. Black and Ruby Power and Light: INTRO TO RAILS June 9-12 Berlin ADVANCING WITH RAILS June 16-19 Berlin See http://www.rubypal.com for details and updates!