Rust State Machine

state_machine.rs

struct ThingA;

impl ThingA {
    fn do_action_a(self) -> ThingB {
        ThingB
    }
}

struct ThingB;

enum State {
    A(ThingA),
    B(ThingB),
}

struct StateMachine {
    state: State,
}

impl StateMachine {
    fn new() -> StateMachine {
        StateMachine {
            state: State::A(ThingA),
        }
    }
    
    fn nudge(&mut self) {
        self.state = match self.state {
            State::A(my_thing_a) => State::B(my_thing_a.do_action_a()),
            State::B(my_thing_b) => State::B(my_thing_b),
        }
    }
}

fn main() {
    let mut state_machine = StateMachine::new();
    state_machine.nudge();
    
    println!("done.");
}