Is Destructured unable to handle default arguments or am I misunderstanding its purpose?

[michaelfortunato]

Hey,
I have a CLI command with many arguments. As such I grouped common ones into a dataclass, and figured I could use Destructured to present all the arguments to the user as one flat structure. I noticed though that I was unable to get my group to be populated after calling parse, even though I had attached default values to every field in the gubgruop. See the following: I expect cli.other to be of type Other and fully populated after I called parse(CLI). Should we expect these classes to be populated with their defaults or is that not supported yet? Or is destructured used from something else?

from dataclasses import dataclass
from functools import partial
from typing import Annotated

import cappa
from cappa import Arg as cArg
from cappa import parse
from cappa.destructure import Destructured

Arg = partial(cArg, short=False, long=True)


@dataclass(frozen=True, slots=True)
class Other:
    arg2: Annotated[int, Arg(default=2 * 3)]
    arg3: Annotated[str, Arg(default="value3")]


@cappa.command(
    help="Testing Destrictured",
    name="Test",
)
@dataclass(frozen=True, slots=True)
class CLI:
    arg1: Annotated[str, Arg(default="value1")]
    other: Destructured[Other]


if __name__ == "__main__":
    cli = parse(CLI)
    print(cli)
    assert cli.other is not None, (
        "Shouldn't cli.other be populated given the `Arg(default=...` "
        "provided in its fields?"
    )

Thanks!

[DanCardin]

Hi, thanks for the question!

To make this work today, you would do other: Destructured[Other] = field(default_factory=Other).

but ultimately yes, i think there is a bug here because other should not be None, since it violates the declared type.

I guess the question is whether it makes sense to directly infer that in absence of a predefined default...I think likely yes.

I was initially going to say lacking the above default essentially makes it programmer error, since you didn't declare a default, how are we supposed to know what to do? But it seems like a pretty safe default to me. if the class doesn't allow zero-argument construction by way of a required arg, then it would automatically produce a user error for the missing argument.

[DanCardin]

#237 Implements that as default behavior, and additionally implements Other | None implying None