Improve Void #3823
Description
Current problems
- Code quality tools complain about initializing
Void()as argument defaults
Do we have any other sentinel types like Void? Do we even need a generic pattern?
Can we use Literal in type unions and is in checked to avoid errors and keep code simple?
Otherwise, can we make Void a type alias of an internal class that cannot be initialized? Implement __repr__() on the metaclass to make the type look like its alias.
Otherwise, can we alias Void to be an enum member?
Can we use NewType instead of aliases? Because aliases are resolved by Sphinx and when showing types in errors.