use &mut T, Box<T> and &mut dyn T in one function

ref_mut.rs

use std::ops::DerefMut;
use std::thread::sleep;
use std::time::Duration;

trait DigitalInput {
    fn set_state(&mut self, _new_state: bool);
}

trait Mutable<T: ?Sized> {
    fn ref_mut(&mut self) -> &mut T;
}

impl<'a, T: ?Sized> Mutable<T> for &'a mut T {
    fn ref_mut(&mut self) -> &'_ mut T {
        self
    }
}

impl<T: ?Sized> Mutable<T> for Box<T> {
    fn ref_mut(&mut self) -> &'_ mut T {
        self.deref_mut()
    }
}

fn flash_periodically<L: Mutable<P>, P: DigitalInput + ?Sized>(mut lamp: L, interval: Duration) {
    let mut current_state = false;

    loop {
        lamp.ref_mut().set_state(current_state);
        current_state = !current_state;
        sleep(interval);
    }
}

struct Pin;

impl DigitalInput for Pin {
    fn set_state(&mut self, _new_state: bool) {
        unimplemented!()
    }
}

fn main() {
    let pin: &mut Pin = &mut Pin;
    flash_periodically(pin, Duration::from_millis(100));

    let pin: Box<dyn DigitalInput> = Box::new(Pin);
    flash_periodically(pin, Duration::from_millis(100));

    let pin: &mut dyn DigitalInput = &mut Pin;
    flash_periodically(pin, Duration::from_millis(100));
}