unmovable2.rs

use std::cell::{Cell, RefCell};
use std::kinds::marker::{ContravariantLifetime, NoCopy};

struct Unmovable<'a, T>  {
    data: RefCell<Option<T>>,
    lock: Cell<ContravariantLifetime<'a>>,
    marker: NoCopy,
}

impl<'a, T> Unmovable<'a, T> {
    fn new() -> Unmovable<'a, T> {
        Unmovable {
            data: RefCell::new(None),
            lock: Cell::new(ContravariantLifetime),
            marker: NoCopy,
        }
    }

    fn get(&'a self) -> &'a RefCell<Option<T>> {
        self.lock.set(ContravariantLifetime);
        &self.data
    }
}

fn main(){
    let y = Unmovable::new();
    *y.get().borrow_mut() = Some(5u);
    *y.get().borrow_mut() = Some(6u);

    // error: cannot move out of `y` because it is borrowed
    // let z = y;
}