Nested Type should work with TypedDict

[datvo06]

Currently, we would expect nested_type to return a typeddict type annotation on a TypedDict instance.

from typing import TypedDict
from effectful.internals.unification import nested_type

class UserTD(TypedDict):
    name: str
    age: int

print("nested_type(UserTD(name='a', age=1)).value ->", nested_type(UserTD(name='a', age=1)).value)

Result:

nested_type(UserTD(name='a', age=1)).value -> <class 'dict'>

One difficulty is that the TypedDict instance at runtime is just a dict. Inferring types is possible, but we might not be able to recover the schema fully.

[kiranandcode]

Given that the runtime information is erased, this feature would be likely to produce confusing and unexpected behaviours:

# file1
class UserTD1(TypedDict):
   name: str
   age: int

# file2
class UserTD2(TypedDict):
   name: str
   age: int

# file3
from file1 import UserTD1
from file2 import UserTD2

nested_type({'name':"alex", 'age':10}) # which type should be inferred?

[eb8680]

TypedDict subtyping is structural, not nominal, so this behavior would be implemented by constructing a new TypedDict type dynamically via TypedDict('new', {key: nested_type(val).value for key, val in obj.items()}). In some cases it's also possible to recover the original TypedDict at runtime via types.get_original_bases.

It's possible this could still run into soundness issues, but I don't think this should be closed just yet, it's not obviously doomed to fail.

[kiranandcode]

ah, I see, gotcha.