Using Arc<AppState> with SignedCookieJar

[woile]

Hello, I've been following some examples that were using Arc<AppState> which I was using with with_state(). But I just started using SignedCookieJar and it creates a problem because I have to implement impl FromRef<AppState> for Key {...}.

error[E0277]: the trait bound `Key: FromRef<Arc<AppState>>` is not satisfied
   --> src/main.rs:81:31
    |
81  |         .route("/login", post(login))
    |                          ---- ^^^^^ the trait `FromRef<Arc<AppState>>` is not implemented for `Key`
    |                          |
    |                          required by a bound introduced by this call

The example of the SignedCookieJar uses directly clone, and I was hoping to avoid it.

Any recommendations?

[davidpdrsn]

Since you cannot implement FromRef<Arc<AppState>> for Key I'd recommend a newtype:

#[derive(Clone)]
struct AppState(Arc<InnerState>);

// deref so you can still access the inner fields easily
impl Deref for AppState {
    type Target = InnerState;

    fn deref(&self) -> &Self::Target {
        &*self.0
    }
}

struct InnerState {
    key: Key
}

impl FromRef<AppState> for Key {
    fn from_ref(state: &AppState) -> Self {
        state.0.key.clone()
    }
}

[woile]

Thanks, this works! Does it make sense to update the SignedCookie to reflect this?

[davidpdrsn]

Update it to what?

[woile]

I was thinking of adding your snippet or just a few lines here. To give like a recommendation of what to do:

If you have been using `Arc<AppState>` you cannot implement `FromRef<Arc<AppState>> for Key`.
The recommendation is to use a new type like: `struct AppState(Arc<InnerState>);` and implement `Deref`.

Maybe is something trivial, but when I was following the axum docs it uses Arc and I was not sure which approach to take.

[davidpdrsn]

Sure adding such a note would be good! Do you wanna make a PR?

Maybe is something trivial, but when I was following the axum docs it uses Arc and I was not sure which approach to take.

Yeah we use Arc states a bit inconsistently currently.