Support for object arguments in _.memoize()

obj_memoize.coffee

# Adds support for using object arguments with _.memoize().
nextMemoizeObjKey = 1
memoizeObjectArg = (func) ->
  _.memoize func, (obj) ->
    key = obj._memoizeObjKey
    unless key?
      key = obj._memoizeObjKey = nextMemoizeObjKey++
    key

# Example:
fooFunc = memoizeObjectArg (obj) -> Object.keys(obj)
arg = {foo: 'bar'}
fooFunc(arg) # => ['foo']
# The same memoized value is returned regardless of changes.
arg.foo = 'bar2'
fooFunc(arg) # => ['foo']