Ron Buckton (2014-08-12T01:45:09.000Z)
domenic at domenicdenicola.com (2014-08-18T18:35:53.564Z)
Sorry for the short reply here, as I'm not at my PC. Would having an @@isValue (Map) and @@isKey (Set/Map) work? ```js Set.prototype[@@isValue] = value => true; // default ``` Built -in Set operations would check values against @@isValue and throw. You can then override it in your subclass and make it non-configurable. Alternatively, there could be an options argument on the Set constructor where you could supply a value filter.