diff options
Diffstat (limited to '')
| -rw-r--r-- | src/vec.rs | 25 |
1 files changed, 18 insertions, 7 deletions
@@ -263,13 +263,24 @@ impl<T, const N: usize> Vec<T, N> { /// Shortens the vector, keeping the first `len` elements and dropping the rest. pub fn truncate(&mut self, len: usize) { - // drop any extra elements - while len < self.len { - // decrement len before the drop_in_place(), so a panic on Drop - // doesn't re-drop the just-failed value. - self.len -= 1; - let len = self.len; - unsafe { ptr::drop_in_place(self.as_mut_slice().get_unchecked_mut(len)) }; + // This is safe because: + // + // * the slice passed to `drop_in_place` is valid; the `len > self.len` + // case avoids creating an invalid slice, and + // * the `len` of the vector is shrunk before calling `drop_in_place`, + // such that no value will be dropped twice in case `drop_in_place` + // were to panic once (if it panics twice, the program aborts). + unsafe { + // Note: It's intentional that this is `>` and not `>=`. + // Changing it to `>=` has negative performance + // implications in some cases. See rust-lang/rust#78884 for more. + if len > self.len { + return; + } + let remaining_len = self.len - len; + let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len); + self.len = len; + ptr::drop_in_place(s); } } |