Trait Middleware

Source

pub trait Middleware<S, A>where
    A: Action,{
    // Required methods
    fn before(&mut self, action: &A, state: &S) -> bool;
    fn after(&mut self, action: &A, state_changed: bool, state: &S) -> Vec<A>;
}

Expand description

Middleware trait for intercepting actions

Implement this trait to add logging, persistence, throttling, or other cross-cutting concerns to your store. Middleware can:

Observe: inspect actions and state (logging, analytics, persistence)
Cancel: return false from before() to prevent the action from reaching the reducer
Inject: return follow-up actions from after() that are dispatched through the full pipeline

§Cancel

Return false from before() to cancel the action — the reducer is never called and after() is not invoked. Useful for throttling, validation, and auth guards.

§Inject

Return actions from after() to trigger follow-up dispatches. Injected actions go through the full middleware + reducer pipeline. Dispatch limits prevent runaway loops.

Useful for cascading behavior: moving a card to “Done” triggers a notification, without the move reducer knowing about notifications.