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main.py

from dataclasses import dataclass
from typing import TYPE_CHECKING, TypeVar, dataclass_transform, Protocol
from functools import partial

if TYPE_CHECKING:
    T = TypeVar('T')
    
    @dataclass_transform(frozen_default = True)
    def frozen(cls: type[T]) -> type[T]:
        ...
else:
    frozen = dataclass

@frozen
class Foo:
    x: int
    y: int

foo = Foo(1, 2)


class Bar(Protocol):
    x: int

def bar(bar: Bar): ...

bar(foo)