operties.
_.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
  obj


# Create a (shallow-cloned) duplicate of an object.
_.clone = (obj) ->
  return obj.slice 0 if _.isArray obj
  _.extend {}