Derive Macro Recall 

#[derive(Recall)]
{
    // Attributes available to this derive:
    #[recallable]
}

Derive macro that generates the Recall trait implementation.

For plain fields, recall assigns the memento value directly. For fields annotated with #[recallable], it recursively calls recall on the nested value. Fields marked #[recallable(skip)] are left untouched. For #[recallable] fields, replace/merge behavior comes from the field type’s own Recall implementation.

Lifetime parameters are supported only when the generated memento can stay owned: non-skipped fields may not borrow one of the struct’s lifetimes. Skipped borrowed fields and lifetime-only markers such as PhantomData<&'a T> are allowed.

This example requires the serde feature.

use recallable::{Recall, Recallable};

#[derive(Clone, Debug, serde::Serialize, Recallable, Recall)]
struct State {
    score: i32,
    #[recallable(skip)]
    cached_label: String,
}

let mut state = State { score: 0, cached_label: "stale".into() };
let memento: <State as Recallable>::Memento =
    serde_json::from_str(r#"{"score":42}"#).unwrap();
state.recall(memento);
assert_eq!(state.score, 42);
assert_eq!(state.cached_label, "stale"); // skip preserves the value

Derive macro that generates the Recall trait implementation.

The generated recall method:

• assigns fields directly by default,
• recursively calls recall on fields marked with #[recallable],
• respects #[recallable(skip)] by omitting those fields from recalling.

For #[recallable] fields, replace/merge behavior comes from the field type’s own Recall implementation.