state_machine.rs

use std::mem;

use self::State::*;
use self::Transaction::*;

fn main() {
    let mut player = Player::new();
    println!("{:?}", player); // state == One

    player.collision(Run); // state == Two
    println!("{:?}", player);

    player.collision(Go); // state = Three
    println!("{:?}", player);

    player.collision(Jump); // state = One
    println!("{:?}", player);

    if let One { active: true, name } = player.state {
        println!("State is One and active = true, name: {name}");
    }
}

#[derive(Debug)]
struct Player {
    state: State,
}

impl Player {
    fn new() -> Self {
        Self {
            state: One { active: true, name: "rust" },
        }
    }

    fn collision(&mut self, transaction: Transaction) {
        self.state(|state| {
            match (state, &transaction) {
                (One { .. }, Run) => Two,
                (Two, Go) => Three,
                (Three, Jump) => One { active: true, name: "rust collision" },
                (state, _) => state,
            }
        });
    }

    fn state(&mut self, mut call: impl FnMut(State) -> State) {
        let default_state = One { active: false, name: "" };
        let curr_state = mem::replace(&mut self.state, default_state);
        self.state = call(curr_state);
    }
}

#[derive(Debug)]
enum State {
    One { active: bool, name: &'static str },
    Two,
    Three,
}


enum Transaction {
    Go,
    Run,
    Jump,
}