Is there a way to deserialize an empty list as None?

[drewlwhitney]

Basically, if I have

struct Thing {
    list: Option<Vec<u32>>,
    other: u32,
}

and the JSON

{
    "list": [],
    "other": 0
}

I want it to deserialize it into

Thing {
    list: None,
    other: 0,
}

so empty lists are mapped to None, similar to NoneAsEmptyString.

Obviously I can just write a helper function for this and use with = (...), but I wanted to see if something like this already exists.

If this does not exist but you'd be interested in something like it (maybe #[serde_as(as = "NoneAsEmptyList")]) I could look into making a pull request.

Thank you!

[jonasbb]

Hi, no that is not currently implemented. It's implementation probably has to differ a bit from NoneAsEmptyString. For one I am not sure if a simple visitor like that is possible or if deserialization just always has to create the Vec. At least for submission to this crate it should be possible to customize the inner type of the Vec.
I am open to adding this to the crate. While I'm not sure how frequently used this pattern is, the implementation is likely just a couple of lines plus docs and tests.

[drewlwhitney]

Understood! I'll work on a PR in the next few weeks