Struct StateTransition

pub struct StateTransition<S> {
    pub trigger: Pin<Box<dyn Future<Output = Value> + Send + 'static>>,
    pub transition: Arc<dyn for<'a> Fn(&'a mut ClientSMDatabaseTransaction<'_, '_>, Value, S) -> BoxFuture<'a, S> + Send + Sync>,
}

Represents one or multiple possible state transitions triggered in a common way

Fields

trigger: Pin<Box<dyn Future<Output = Value> + Send + 'static>>

Future that will block until a state transition is possible.

The trigger future must be idempotent since it might be re-run if the client is restarted.

To wait for a possible state transition it can query external APIs, subscribe to events emitted by other state machines, etc. Optionally, it can also return some data that will be given to the state transition function, see the transition docs for details.

transition: Arc<dyn for<'a> Fn(&'a mut ClientSMDatabaseTransaction<'_, '_>, Value, S) -> BoxFuture<'a, S> + Send + Sync>

State transition function that, using the output of the trigger, performs the appropriate state transition.

This function shall not block on network IO or similar things as all actual state transitions are run serially.

Since the this function can return different output states depending on the Value returned by the trigger future it can be used to model multiple possible state transition at once. E.g. instead of having two state transitions querying the same API endpoint and each waiting for a specific value to be returned to trigger their respective state transition we can have one trigger future querying the API and depending on the return value run different state transitions, saving network requests.

Implementations

impl<S> StateTransition<S>

pub fn new<V, Trigger, TransitionFn>( trigger: Trigger, transition: TransitionFn, ) -> StateTransition<S>

where S: MaybeSend + MaybeSync + Clone + 'static, V: Serialize + DeserializeOwned + Send, Trigger: Future<Output = V> + MaybeSend + 'static, TransitionFn: for<'a> Fn(&'a mut ClientSMDatabaseTransaction<'_, '_>, V, S) -> BoxFuture<'a, S> + MaybeSend + MaybeSync + Clone + 'static,

Creates a new StateTransition where the trigger future returns a value of type V that is then given to the transition function.