#![allow(unused_variables)] // This makes a ref that was passed to us via &mut alias with things it should not alias with fn retarget(x: &mut &u32, target: &mut u32) { unsafe { *x = &mut *(target as *mut _); } } fn main() { let target = &mut 42; let mut target_alias = &42; // initial dummy value retarget(&mut target_alias, target); // now `target_alias` points to the same thing as `target` *target = 13; let _val = *target_alias; //~ ERROR does not exist on the stack }