main.rs

zero_ref_mut!(FOO, u32);

fn main() {
    let mut val: u32 = 2;

    // initialize static FOO
    // fzero acts like a MutexHandle
    // while it's in scope, FOO is used to store &mut val
    let mut fzero = FOO.claim(&mut val).unwrap();

    // but...
    assert_eq!(std::mem::size_of_val(&fzero), 0);

    // fzero.borrow() acts like &val, but...
    let fref = fzero.borrow();
    assert_eq!(std::mem::size_of_val(&fref), 0);
    assert_eq!(*fref, 2);

    // fzero.borrow_mut() acts like &mut val, but...
    let mut fmut = fzero.borrow_mut();
    assert_eq!(std::mem::size_of_val(&fmut), 0);
    *fmut += 2;
    assert_eq!(*fmut, 4);

    // when all is said and done, these changes are reflected in val
    std::mem::drop(fzero);
    assert_eq!(val, 4);
}