Trait edfsm::Fsm

pub trait Fsm {
    type S;
    type C;
    type E;
    type SE;

    // Required methods
    fn for_command(s: &Self::S, c: Self::C, se: &mut Self::SE) -> Option<Self::E>;
    fn on_event(s: &mut Self::S, e: &Self::E) -> bool;

    // Provided methods
    fn on_entry(_s: &Self::S, _se: &mut Self::SE) { ... }
    fn step(s: &mut Self::S, c: Self::C, se: &mut Self::SE) -> Option<Self::E> { ... }
}

Describes the behavior of a Finite State Machine (FSM) that can receive commands and produce events. Along the way, effects can be performed given the receipt of a command. State can be reconsituted by replaying events.

Note that effects are represented by a separate structure so that they can be consolidated, and also to help structure the code. Further, it is possible to have multiple implementations of effects e.g. different ones when testing.

Effects are also synchronous. If an effect handler must communicate, say, with a task in a non-blocking fashion, then the state machine should represent this intermediate state. For example, a channel could be used to communicate with such a task with try_send being used and then causing a state transition in relation to that result. While this approach adds steps to a state machine, it does allow them to remain responsive to receiving more commands.

Required Associated Types

type S

The state managed by the FSM

type C

The command(s) that are able to be processed by the FSM

type E

The event emitted having performed a command

type SE

The side effect handler

Required Methods

fn for_command(s: &Self::S, c: Self::C, se: &mut Self::SE) -> Option<Self::E>

Given a state and command, optionally emit an event. Can perform side effects along the way. This function is generally only called from the run function.

fn on_event(s: &mut Self::S, e: &Self::E) -> bool

Given a state and event, modify state, which could indicate transition to the next state. No side effects are to be performed. Can be used to replay events to attain a new state i.e. the major function of event sourcing.

Provided Methods

fn on_entry(_s: &Self::S, _se: &mut Self::SE)

Optional effect on entering a state i.e. transitioning in to state S from another.

fn step(s: &mut Self::S, c: Self::C, se: &mut Self::SE) -> Option<Self::E>

This is the main entry point to the event driven FSM. Runs the state machine for a command, optionally performing effects, possibly producing an event and possibly transitioning to a new state. Also applies any “Entry/” processing when arriving at a new state.

Implementors