A way to constrain initializers

[KotlinIsland]

Mypy don't care about the LSP of an initializer:

class A:
    def __init__(self, a: int): ...
class B(A):
    def __init__(self):  # no error
        super().__init__(1)

But what if that's something you wanted? Specifically this would be good for a zero arg constructor (but there are other concrete usecases)

I wonder how we could achieve this?

We could handle the special case of zero arg pretty easily:

from basedtyping import ZeroArgInit

def foo(t: type[ZeroArgInit]) -> ZeroArgInit:
    return t()

class A:
    def __init__(self, a: int): ...
    
class B:
    def __init__(self): ...

foo(A)  # error
foo(B)  # no error

[KotlinIsland]

def foo(t: Callable[[], T]) -> T:
    return t()

from @DetachHead