diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs index 8ef6090c743a9..bbe68e4222a1f 100644 --- a/src/liballoc/boxed.rs +++ b/src/liballoc/boxed.rs @@ -1090,6 +1090,14 @@ impl Clone for Box<[T]> { fn clone(&self) -> Self { self.to_vec().into_boxed_slice() } + + fn clone_from(&mut self, other: &Self) { + if self.len() == other.len() { + self.clone_from_slice(&other); + } else { + *self = other.clone(); + } + } } #[stable(feature = "box_borrow", since = "1.1.0")] diff --git a/src/liballoc/tests/boxed.rs b/src/liballoc/tests/boxed.rs index 66782ecbeb7f6..5377485da8f3b 100644 --- a/src/liballoc/tests/boxed.rs +++ b/src/liballoc/tests/boxed.rs @@ -16,3 +16,36 @@ fn unitialized_zero_size_box() { NonNull::>::dangling().as_ptr(), ); } + +#[derive(Clone, PartialEq, Eq, Debug)] +struct Dummy { + _data: u8, +} + +#[test] +fn box_clone_and_clone_from_equivalence() { + for size in (0..8).map(|i| 2usize.pow(i)) { + let control = vec![Dummy { _data: 42 }; size].into_boxed_slice(); + let clone = control.clone(); + let mut copy = vec![Dummy { _data: 84 }; size].into_boxed_slice(); + copy.clone_from(&control); + assert_eq!(control, clone); + assert_eq!(control, copy); + } +} + +/// This test might give a false positive in case the box realocates, but the alocator keeps the +/// original pointer. +/// +/// On the other hand it won't give a false negative, if it fails than the memory was definitly not +/// reused +#[test] +fn box_clone_from_ptr_stability() { + for size in (0..8).map(|i| 2usize.pow(i)) { + let control = vec![Dummy { _data: 42 }; size].into_boxed_slice(); + let mut copy = vec![Dummy { _data: 84 }; size].into_boxed_slice(); + let copy_raw = copy.as_ptr() as usize; + copy.clone_from(&control); + assert_eq!(copy.as_ptr() as usize, copy_raw); + } +}