ys or (obj) ->
  return _.range 0, obj.length if _.isArray(obj)
  key for key, val of obj


# Retrieve the values of an object's properties.
_.values = (obj) ->
  _.map obj, _.identity


# Return a sorted list of the function names available in Underscore.
_.functions = (obj) ->
  _.filter(_.keys(obj), (key) -> _.isFunction(obj[key])).sort()


# Extend a given object with all of the properties in a source object.
_.extend = (obj) ->
  for source in _.rest(arguments)
    obj[key] = val for key, val of source