library/alloc/tests/boxed.rs

   1 use std::cell::Cell;
   2 use std::mem::MaybeUninit;
   3 use std::ptr::NonNull;
   4
   5 #[test]
   6 fn unitialized_zero_size_box() {
   7     assert_eq!(
   8         &*Box::<()>::new_uninit() as *const _,
   9         NonNull::<MaybeUninit<()>>::dangling().as_ptr(),
  10     );
  11     assert_eq!(
  12         Box::<[()]>::new_uninit_slice(4).as_ptr(),
  13         NonNull::<MaybeUninit<()>>::dangling().as_ptr(),
  14     );
  15     assert_eq!(
  16         Box::<[String]>::new_uninit_slice(0).as_ptr(),
  17         NonNull::<MaybeUninit<String>>::dangling().as_ptr(),
  18     );
  19 }
  20
  21 #[derive(Clone, PartialEq, Eq, Debug)]
  22 struct Dummy {
  23     _data: u8,
  24 }
  25
  26 #[test]
  27 fn box_clone_and_clone_from_equivalence() {
  28     for size in (0..8).map(|i| 2usize.pow(i)) {
  29         let control = vec![Dummy { _data: 42 }; size].into_boxed_slice();
  30         let clone = control.clone();
  31         let mut copy = vec![Dummy { _data: 84 }; size].into_boxed_slice();
  32         copy.clone_from(&control);
  33         assert_eq!(control, clone);
  34         assert_eq!(control, copy);
  35     }
  36 }
  37
  38 /// This test might give a false positive in case the box realocates, but the alocator keeps the
  39 /// original pointer.
  40 ///
  41 /// On the other hand it won't give a false negative, if it fails than the memory was definitely not
  42 /// reused
  43 #[test]
  44 fn box_clone_from_ptr_stability() {
  45     for size in (0..8).map(|i| 2usize.pow(i)) {
  46         let control = vec![Dummy { _data: 42 }; size].into_boxed_slice();
  47         let mut copy = vec![Dummy { _data: 84 }; size].into_boxed_slice();
  48         let copy_raw = copy.as_ptr() as usize;
  49         copy.clone_from(&control);
  50         assert_eq!(copy.as_ptr() as usize, copy_raw);
  51     }
  52 }
  53
  54 #[test]
  55 fn box_deref_lval() {
  56     let x = Box::new(Cell::new(5));
  57     x.set(1000);
  58     assert_eq!(x.get(), 1000);
  59 }