[Bug] PEP 484- and 585-compliant nested generics are broken af, bro

I think this will be easiest to understand from an example:

from beartype import beartype

RowIndex = int 
ColIndex = int 

@beartype
def fn(a: RowIndex) -> ColIndex:
    return a

fn(RowIndex(1))

I want this call to fn() to fail (due to beartype, obviously). Clearly it can’t be done in exactly the way I’ve written, so either this bit:

RowIndex = int 
ColIndex = int 

or this bit:

RowIndex(1)

must be done differently. I am open to any ideas! Of course we could write a class that subtypes int, but that is extremely clumsy and annoying. I want to do the aliasing and the instantiation from the supertype (i.e. the RowIndex(1)) in the least obtrusive way possible.

You could also use dataclasses, and then beartype will check the constructor, but then you have to do row_idx.val every time you want the value, which is highly annoying.

[langfield]

Ohgodnoes. Actually, you are supposed to subclass subscripted type hints. You’re absolutely in the right and fully compliant with typing standards like PEP 484 and 585 here. You’re doing good things.

Wow, my record is currently 0-2 for claiming things are true ‘no doubt’ this week. I should really stop saying that, lol.

Pleased to hear this is something you intend to support! Yeah, I had imported List with from beartype.typing import List so it was using the 585-style hints under the hood. No exception raised, as you said.

[langfield]

Sadly, there is this

class Board(List[List[str]]): pass

@beartype
def get_board() -> Board:
    return Board([1])

get_board()

No doubt you are not supposed to subclass subscripted type hints. But it’s too bad this does not work.

The other annoyance is that anyone using black to autoformat code will not be able to define these aliases/classes in one line.