Provides a .to static constexpr function object.
When creating a binary function object of type Algo whose signature is Object x Object -> Return, nested_to<Algo> can be used as a base class of Algo. Doing so will provide a static constexpr member called to, which has the following signature:
Note that the function object Algo must be default-constructible, since the algorithm will be called as Algo{}(arguments...).