There should be an inverse of `Type`

Specifically, it would be nice if there was a keyword Instance such that Instance[Type[_T]] is equivalent to _T

I'm thinking about this mostly in the context of working with metaclasses.

Suppose I have a class with a class method that creates an instance of the class written so it can be reused by subclasses. This can be typed in the following way:

_ThingInstance = TypeVar('_ThingInstance', bound='Thing')

class Thing():

    @classmethod
    def make_new(cls: Type[_ThingInstance]) -> _ThingInstance:
        return cls()

And this is automatically usable by subclasses.

What I want is an Instance type such that I can correctly type the same logic defined within a metaclass like so:

_ThingClass = TypeVar('_ThingClass', bound='MetaThing')

class MetaThing(type):

  def make_new(cls: _ThingClass) -> Instance[_ThingClass]:
      return cls()

As far as I can tell, there's no way to correctly annotate this

Partite dall’annotazione proposta Instance[_ThingClass] e confrontatela con il pattern Type[_ThingInstance] mostrato. Definite come dovrebbe comportarsi l’inversa per i metodi della metaclasse e verificate gli esempi con una copertura del type checking; il lavoro è completo quando le annotazioni richieste vengono accettate con i tipi di istanza inferiti previsti.