def add_method(self, f, name=None):
        """ Add a method to the dispatcher.

        Parameters
        ----------
        f : callable
            Callable to be added.
        name : str, optional
            Name to register (the default is function **f** name)

        Notes
        -----
        When used as a decorator keeps callable object unmodified.

        Examples
        --------

        Use as method

        >>> d = Dispatcher()
        >>> d.add_method(lambda a, b: a + b, name="sum")
        <function __main__.<lambda>>

        Or use as decorator

        >>> d = Dispatcher()
        >>> @d.add_method
            def mymethod(*args, **kwargs):
                print(args, kwargs)

        """
        self.method_map[name or f.__name__] = f
        return f