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state always need to implement Clone (#2972)

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Yann Simon 2024-10-11 10:06:50 +02:00 committed by GitHub
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axum/src/extract/state.rs
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@ -21,9 +21,6 @@ use std::{
/// //
/// // here you can put configuration, database connection pools, or whatever
/// // state you need
/// //
/// // see "When states need to implement `Clone`" for more details on why we need
/// // `#[derive(Clone)]` here.
/// #[derive(Clone)]
/// struct AppState {}
///
@ -247,53 +244,6 @@ use std::{
/// }
/// ```
///
/// # When states need to implement `Clone`
///
/// Your top level state type must implement `Clone` to be extractable with `State`:
///
/// ```
/// use axum::extract::State;
///
/// // no substates, so to extract to `State<AppState>` we must implement `Clone` for `AppState`
/// #[derive(Clone)]
/// struct AppState {}
///
/// async fn handler(State(state): State<AppState>) {
/// // ...
/// }
/// ```
///
/// This works because of [`impl<S> FromRef<S> for S where S: Clone`][`FromRef`].
///
/// This is also true if you're extracting substates, unless you _never_ extract the top level
/// state itself:
///
/// ```
/// use axum::extract::{State, FromRef};
///
/// // we never extract `State<AppState>`, just `State<InnerState>`. So `AppState` doesn't need to
/// // implement `Clone`
/// struct AppState {
/// inner: InnerState,
/// }
///
/// #[derive(Clone)]
/// struct InnerState {}
///
/// impl FromRef<AppState> for InnerState {
/// fn from_ref(app_state: &AppState) -> InnerState {
/// app_state.inner.clone()
/// }
/// }
///
/// async fn api_users(State(inner): State<InnerState>) {
/// // ...
/// }
/// ```
///
/// In general however we recommend you implement `Clone` for all your state types to avoid
/// potential type errors.
///
/// # Shared mutable state
///
/// [As state is global within a `Router`][global] you can't directly get a mutable reference to