I am not sure what is happening here:

with open('storage.json', 'w') as f:
        json.dump(johnny.to_json(), f)

johnny.to_json already returns a string. If you do f.write(johnny.to_json()), do you still have an issue?

johnny.to_json already returns a string. If you do f.write(johnny.to_json()), do you still have an issue?

Yes, the reason I am writing to a file in this example is that Person.from_json(johnny.to_json()) would indeed work as expected, the reason being that johnny.to_json would not change the names inner elements to string, it would leave them as they are and therefore would not convert them back in the from_json function.

When this is written to a file, the text: '{"names": ["John Doe"]}' is dumped into it. when attempting to convert that into Person via the Person.from_json function, the type of the names elements will indeed be incorrect.

In short, the writing into a file is not required and the following will also reproduce this bug:

from dataclasses import dataclass
from dataclasses_json import DataClassJsonMixin


class Name(str):
    ...


@dataclass
class Person(DataClassJsonMixin):
    names: list[Name]


if __name__ == '__main__':
    js = '{"names": ["John Doe"]}'
    print(isinstance(Person.from_json(js).names[0], Name))  # prints: False

I'll retest this on latest commit tomorrow to see if this is some similar issue with 3.10 as with self-types