Rust code shared from the playground

playground.rs

use std::ops::Deref;

struct StateFn(fn(&mut Machine) -> StateFn);

impl Deref for StateFn {
    type Target = fn(&mut Machine) -> StateFn;
    
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

struct Machine {
    decision: bool
}

impl Machine {
    fn start(&mut self) -> StateFn {
        if self.decision {
            StateFn(Self::state2)
        } else {
            StateFn(Self::state3)
        }
    }
    
    fn state2(&mut self) -> StateFn {
        println!("fooo");
        StateFn(Self::state2)
    }
    
    fn state3(&mut self) -> StateFn {
        println!("bar");
        StateFn(Self::state2)
    }
}

fn main() {
    let mut m = Machine { decision: true };
    
    let mut current = StateFn(Machine::start);
    
    for _ in 0..3 {
        current = current(&mut m);
    }
    
    println!("------");
    
    let mut m = Machine { decision: false };
    
    let mut current = StateFn(Machine::start);
    
    for _ in 0..3 {
        current = current(&mut m);
    }
}