diff options
Diffstat (limited to 'src/liballoc')
| -rw-r--r-- | src/liballoc/collections/vec_deque.rs | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs index 31e49d06a7b..71faf672962 100644 --- a/src/liballoc/collections/vec_deque.rs +++ b/src/liballoc/collections/vec_deque.rs @@ -2709,6 +2709,11 @@ impl<T: fmt::Debug> fmt::Debug for VecDeque<T> { #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")] impl<T> From<Vec<T>> for VecDeque<T> { + /// Turn a [`Vec<T>`] into a [`VecDeque<T>`]. + /// + /// This avoids reallocating where possible, but the conditions for that are + /// strict, and subject to change, and so shouldn't be relied upon unless the + /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated. fn from(mut other: Vec<T>) -> Self { unsafe { let other_buf = other.as_mut_ptr(); @@ -2735,6 +2740,32 @@ impl<T> From<Vec<T>> for VecDeque<T> { #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")] impl<T> From<VecDeque<T>> for Vec<T> { + /// Turn a [`VecDeque<T>`] into a [`Vec<T>`]. + /// + /// This never needs to re-allocate, but does need to do O(n) data movement if + /// the circular buffer doesn't happen to be at the beginning of the allocation. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// // This one is O(1). + /// let deque: VecDeque<_> = (1..5).collect(); + /// let ptr = deque.as_slices().0.as_ptr(); + /// let vec = Vec::from(deque); + /// assert_eq!(vec, [1, 2, 3, 4]); + /// assert_eq!(vec.as_ptr(), ptr); + /// + /// // This one needs data rearranging. + /// let mut deque: VecDeque<_> = (1..5).collect(); + /// deque.push_front(9); + /// deque.push_front(8); + /// let ptr = deque.as_slices().1.as_ptr(); + /// let vec = Vec::from(deque); + /// assert_eq!(vec, [8, 9, 1, 2, 3, 4]); + /// assert_eq!(vec.as_ptr(), ptr); + /// ``` fn from(other: VecDeque<T>) -> Self { unsafe { let buf = other.buf.ptr(); |