Macro mutify 

macro_rules! mutify {
    ($expr: expr) => { ... };
}

Coerce a mut var: T or var: &mut T into a &mut T.

Example

fn plus_one(n: &mut i32) {
    *n += 1;
}

let mut a = 3;
plus_one(mutify!(a));
assert_eq!(a, 4);

let b = &mut a;
plus_one(mutify!(b));
assert_eq!(a, 5);