merde_json_types

Logo by MisiasArt

merde_json_types is a companion crate to merde_json, providing wrapper types that solve two problems at once.

Problem 1: Most crates have types that do not implement the merde_json traits

I'm thinking about the time crate, the chrono crate, camino, etc.

If you have, say, a time::OffsetDateTime in one of your structs, then merde_json's derive macro will not work. You are going to need a wrapper of some sort, and that's the kind of type this crate provides.

If you enable the time-serialize, time-deserialize, and merde_json features, you can do this:

use merde_json::{from_str, JsonSerialize, ToRustValue};
use merde_json_types::time::Rfc3339;

let dt = Rfc3339(time::OffsetDateTime::now_utc());
let serialized = dt.to_json_string();
let deserialized: Rfc3339<time::OffsetDateTime> =
    merde_json::from_str(&serialized).unwrap().to_rust_value().unwrap();
assert_eq!(dt, deserialized);

Problem 2: Keeping merde_json optional

The [time::Rfc3339] type is exported by this crate as soon as the time-types feature is enabled. But merde_json_types doesn't even depend on merde_json (or provide serialization/deserialization implementations) unless you activate its merde_json feature!

That means, you can have your crate unconditionally depend on merde_json_types, and use Rfc3339 in your public structs:

use merde_json::{Fantome, JsonSerialize, ToRustValue};
use merde_json_types::time::Rfc3339;

#[derive(Debug, PartialEq, Eq)]
pub struct Person<'src, 'val> {
    pub name: String,
    pub birth_date: Rfc3339<time::OffsetDateTime>,

    pub _boo: Fantome<'src, 'val>,
}

merde_json::derive! {
    impl (JsonSerialize, JsonDeserialize) for Person { name, birth_date }
}

And still only depend on merde_json when your own feature gets activated:

[dependencies]
merde_json_types = "2"
merde_json = { version = "2", optional = true }

[features]
merde_json = ["dep:merde_json", "merde_json_types/merde_json"]

Of course, for that to work, we need to get rid of any unconditional mention of merde_json in our code, which would become something like:

use std::marker::PhantomData;
use merde_json_types::time::Rfc3339;

#[derive(Debug, PartialEq, Eq)]
pub struct Person<'src, 'val> {
    pub name: String,
    pub birth_date: Rfc3339<time::OffsetDateTime>,

    /// This field still _has_ to be named `_boo`, but we can't use
    /// the `Fantome` type here without pulling in `merde_json`: so,
    /// we use `PhantomData` instead.
    pub _boo: PhantomData<(&'src (), &'val ())>,
}

#[cfg(feature = "merde_json")]
merde_json::derive! {
    impl (JsonSerialize, JsonDeserialize) for Person { name, birth_date }
}