Clearly, if you have a &T reference, the actual pointer address of
that memory must remain valid while that reference is in active
use. But how stable are the memory addresses of local variables in
between borrows? Consider:
let x = 22;
foo(&x);
foo(&x);
fn foo(y: &usize) { .. }Is foo guaranteed to be given the same pointer each time? Note that
safe code can observe the pointer value by doing y as *const usize as usize. If, however, the answer is no, that is helpful to the compiler
since it can spill x only while it is borrowed but otherwise simply
store x in a register.
Range of possible answers:
- local variables have stable addresses (de facto true today)
- local variables have stable addresses while borrowed, but may change betwen borrows (would be nice)