// Question: when does simply taking the address of something
// invoke undefined behavior?

// (run in miri)
// Answer:

fn main() { unsafe {
    let mut a = 0;
    let b = &mut a as *mut _;
    let c = &mut *b;
    let addr = &a as *const _ as usize;
    *c = 2;
} }

// The answer in C is "Never! That would be crazy."
//
// But according to the "Stacked Borrows" memory model, whenever a variable
// is borrowed exclusively - even indirect borrowing through a raw pointer
// like this case - that borrow only remains valid if the address of the
// variable isn't taken.
//
// That's kinda like saying that the address ceases to exist.  And that's
// *really* strange.  And how does it generalize to multiple threads?