docs: def vectorize(*args, **kwargs):
      """
      Allows using `@vectorize` as well as `@vectorize()`.
      """
      if args and callable(args[0]):
          # Guessing the argument is the method.
          return _vectorize(args[0])
      else:
          # Wait for the second call.
          return lambda m: _vectorize(m, *args, **kwargs)