1 //! A double-ended queue implemented with a growable ring buffer.
3 //! This queue has *O*(1) amortized inserts and removals from both ends of the
4 //! container. It also has *O*(1) indexing like a vector. The contained elements
5 //! are not required to be copyable, and the queue will be sendable if the
6 //! contained type is sendable.
8 #![stable(feature = "rust1", since = "1.0.0")]
10 use core::cmp::{self, Ordering};
12 use core::hash::{Hash, Hasher};
13 use core::iter::{repeat_with, FromIterator};
14 use core::marker::PhantomData;
15 use core::mem::{self, ManuallyDrop};
16 use core::ops::{Index, IndexMut, Range, RangeBounds};
17 use core::ptr::{self, NonNull};
20 use crate::collections::TryReserveError;
21 use crate::raw_vec::RawVec;
27 #[stable(feature = "drain", since = "1.6.0")]
28 pub use self::drain::Drain;
32 #[stable(feature = "rust1", since = "1.0.0")]
33 pub use self::iter_mut::IterMut;
37 #[stable(feature = "rust1", since = "1.0.0")]
38 pub use self::into_iter::IntoIter;
42 #[stable(feature = "rust1", since = "1.0.0")]
43 pub use self::iter::Iter;
47 use self::pair_slices::PairSlices;
51 use self::ring_slices::RingSlices;
58 const INITIAL_CAPACITY: usize = 7; // 2^3 - 1
59 const MINIMUM_CAPACITY: usize = 1; // 2 - 1
61 const MAXIMUM_ZST_CAPACITY: usize = 1 << (usize::BITS - 1); // Largest possible power of two
63 /// A double-ended queue implemented with a growable ring buffer.
65 /// The "default" usage of this type as a queue is to use [`push_back`] to add to
66 /// the queue, and [`pop_front`] to remove from the queue. [`extend`] and [`append`]
67 /// push onto the back in this manner, and iterating over `VecDeque` goes front
70 /// Since `VecDeque` is a ring buffer, its elements are not necessarily contiguous
71 /// in memory. If you want to access the elements as a single slice, such as for
72 /// efficient sorting, you can use [`make_contiguous`]. It rotates the `VecDeque`
73 /// so that its elements do not wrap, and returns a mutable slice to the
74 /// now-contiguous element sequence.
76 /// [`push_back`]: VecDeque::push_back
77 /// [`pop_front`]: VecDeque::pop_front
78 /// [`extend`]: VecDeque::extend
79 /// [`append`]: VecDeque::append
80 /// [`make_contiguous`]: VecDeque::make_contiguous
81 #[cfg_attr(not(test), rustc_diagnostic_item = "vecdeque_type")]
82 #[stable(feature = "rust1", since = "1.0.0")]
83 pub struct VecDeque<T> {
84 // tail and head are pointers into the buffer. Tail always points
85 // to the first element that could be read, Head always points
86 // to where data should be written.
87 // If tail == head the buffer is empty. The length of the ringbuffer
88 // is defined as the distance between the two.
94 #[stable(feature = "rust1", since = "1.0.0")]
95 impl<T: Clone> Clone for VecDeque<T> {
96 fn clone(&self) -> VecDeque<T> {
97 self.iter().cloned().collect()
100 fn clone_from(&mut self, other: &Self) {
101 self.truncate(other.len());
103 let mut iter = PairSlices::from(self, other);
104 while let Some((dst, src)) = iter.next() {
105 dst.clone_from_slice(&src);
108 if iter.has_remainder() {
109 for remainder in iter.remainder() {
110 self.extend(remainder.iter().cloned());
116 #[stable(feature = "rust1", since = "1.0.0")]
117 unsafe impl<#[may_dangle] T> Drop for VecDeque<T> {
119 /// Runs the destructor for all items in the slice when it gets dropped (normally or
120 /// during unwinding).
121 struct Dropper<'a, T>(&'a mut [T]);
123 impl<'a, T> Drop for Dropper<'a, T> {
126 ptr::drop_in_place(self.0);
131 let (front, back) = self.as_mut_slices();
133 let _back_dropper = Dropper(back);
135 ptr::drop_in_place(front);
137 // RawVec handles deallocation
141 #[stable(feature = "rust1", since = "1.0.0")]
142 impl<T> Default for VecDeque<T> {
143 /// Creates an empty `VecDeque<T>`.
145 fn default() -> VecDeque<T> {
150 impl<T> VecDeque<T> {
151 /// Marginally more convenient
153 fn ptr(&self) -> *mut T {
157 /// Marginally more convenient
159 fn cap(&self) -> usize {
160 if mem::size_of::<T>() == 0 {
161 // For zero sized types, we are always at maximum capacity
168 /// Turn ptr into a slice
170 unsafe fn buffer_as_slice(&self) -> &[T] {
171 unsafe { slice::from_raw_parts(self.ptr(), self.cap()) }
174 /// Turn ptr into a mut slice
176 unsafe fn buffer_as_mut_slice(&mut self) -> &mut [T] {
177 unsafe { slice::from_raw_parts_mut(self.ptr(), self.cap()) }
180 /// Moves an element out of the buffer
182 unsafe fn buffer_read(&mut self, off: usize) -> T {
183 unsafe { ptr::read(self.ptr().add(off)) }
186 /// Writes an element into the buffer, moving it.
188 unsafe fn buffer_write(&mut self, off: usize, value: T) {
190 ptr::write(self.ptr().add(off), value);
194 /// Returns `true` if the buffer is at full capacity.
196 fn is_full(&self) -> bool {
197 self.cap() - self.len() == 1
200 /// Returns the index in the underlying buffer for a given logical element
203 fn wrap_index(&self, idx: usize) -> usize {
204 wrap_index(idx, self.cap())
207 /// Returns the index in the underlying buffer for a given logical element
210 fn wrap_add(&self, idx: usize, addend: usize) -> usize {
211 wrap_index(idx.wrapping_add(addend), self.cap())
214 /// Returns the index in the underlying buffer for a given logical element
215 /// index - subtrahend.
217 fn wrap_sub(&self, idx: usize, subtrahend: usize) -> usize {
218 wrap_index(idx.wrapping_sub(subtrahend), self.cap())
221 /// Copies a contiguous block of memory len long from src to dst
223 unsafe fn copy(&self, dst: usize, src: usize, len: usize) {
225 dst + len <= self.cap(),
226 "cpy dst={} src={} len={} cap={}",
233 src + len <= self.cap(),
234 "cpy dst={} src={} len={} cap={}",
241 ptr::copy(self.ptr().add(src), self.ptr().add(dst), len);
245 /// Copies a contiguous block of memory len long from src to dst
247 unsafe fn copy_nonoverlapping(&self, dst: usize, src: usize, len: usize) {
249 dst + len <= self.cap(),
250 "cno dst={} src={} len={} cap={}",
257 src + len <= self.cap(),
258 "cno dst={} src={} len={} cap={}",
265 ptr::copy_nonoverlapping(self.ptr().add(src), self.ptr().add(dst), len);
269 /// Copies a potentially wrapping block of memory len long from src to dest.
270 /// (abs(dst - src) + len) must be no larger than cap() (There must be at
271 /// most one continuous overlapping region between src and dest).
272 unsafe fn wrap_copy(&self, dst: usize, src: usize, len: usize) {
274 fn diff(a: usize, b: usize) -> usize {
275 if a <= b { b - a } else { a - b }
278 cmp::min(diff(dst, src), self.cap() - diff(dst, src)) + len <= self.cap(),
279 "wrc dst={} src={} len={} cap={}",
286 if src == dst || len == 0 {
290 let dst_after_src = self.wrap_sub(dst, src) < len;
292 let src_pre_wrap_len = self.cap() - src;
293 let dst_pre_wrap_len = self.cap() - dst;
294 let src_wraps = src_pre_wrap_len < len;
295 let dst_wraps = dst_pre_wrap_len < len;
297 match (dst_after_src, src_wraps, dst_wraps) {
298 (_, false, false) => {
299 // src doesn't wrap, dst doesn't wrap
302 // 1 [_ _ A A B B C C _]
303 // 2 [_ _ A A A A B B _]
307 self.copy(dst, src, len);
310 (false, false, true) => {
311 // dst before src, src doesn't wrap, dst wraps
314 // 1 [A A B B _ _ _ C C]
315 // 2 [A A B B _ _ _ A A]
316 // 3 [B B B B _ _ _ A A]
320 self.copy(dst, src, dst_pre_wrap_len);
321 self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len);
324 (true, false, true) => {
325 // src before dst, src doesn't wrap, dst wraps
328 // 1 [C C _ _ _ A A B B]
329 // 2 [B B _ _ _ A A B B]
330 // 3 [B B _ _ _ A A A A]
334 self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len);
335 self.copy(dst, src, dst_pre_wrap_len);
338 (false, true, false) => {
339 // dst before src, src wraps, dst doesn't wrap
342 // 1 [C C _ _ _ A A B B]
343 // 2 [C C _ _ _ B B B B]
344 // 3 [C C _ _ _ B B C C]
348 self.copy(dst, src, src_pre_wrap_len);
349 self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len);
352 (true, true, false) => {
353 // src before dst, src wraps, dst doesn't wrap
356 // 1 [A A B B _ _ _ C C]
357 // 2 [A A A A _ _ _ C C]
358 // 3 [C C A A _ _ _ C C]
362 self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len);
363 self.copy(dst, src, src_pre_wrap_len);
366 (false, true, true) => {
367 // dst before src, src wraps, dst wraps
370 // 1 [A B C D _ E F G H]
371 // 2 [A B C D _ E G H H]
372 // 3 [A B C D _ E G H A]
373 // 4 [B C C D _ E G H A]
376 debug_assert!(dst_pre_wrap_len > src_pre_wrap_len);
377 let delta = dst_pre_wrap_len - src_pre_wrap_len;
379 self.copy(dst, src, src_pre_wrap_len);
380 self.copy(dst + src_pre_wrap_len, 0, delta);
381 self.copy(0, delta, len - dst_pre_wrap_len);
384 (true, true, true) => {
385 // src before dst, src wraps, dst wraps
388 // 1 [A B C D _ E F G H]
389 // 2 [A A B D _ E F G H]
390 // 3 [H A B D _ E F G H]
391 // 4 [H A B D _ E F F G]
394 debug_assert!(src_pre_wrap_len > dst_pre_wrap_len);
395 let delta = src_pre_wrap_len - dst_pre_wrap_len;
397 self.copy(delta, 0, len - src_pre_wrap_len);
398 self.copy(0, self.cap() - delta, delta);
399 self.copy(dst, src, dst_pre_wrap_len);
405 /// Frobs the head and tail sections around to handle the fact that we
406 /// just reallocated. Unsafe because it trusts old_capacity.
408 unsafe fn handle_capacity_increase(&mut self, old_capacity: usize) {
409 let new_capacity = self.cap();
411 // Move the shortest contiguous section of the ring buffer
413 // [o o o o o o o . ]
415 // A [o o o o o o o . . . . . . . . . ]
417 // [o o . o o o o o ]
419 // B [. . . o o o o o o o . . . . . . ]
421 // [o o o o o . o o ]
423 // C [o o o o o . . . . . . . . . o o ]
425 if self.tail <= self.head {
428 } else if self.head < old_capacity - self.tail {
431 self.copy_nonoverlapping(old_capacity, 0, self.head);
433 self.head += old_capacity;
434 debug_assert!(self.head > self.tail);
437 let new_tail = new_capacity - (old_capacity - self.tail);
439 self.copy_nonoverlapping(new_tail, self.tail, old_capacity - self.tail);
441 self.tail = new_tail;
442 debug_assert!(self.head < self.tail);
444 debug_assert!(self.head < self.cap());
445 debug_assert!(self.tail < self.cap());
446 debug_assert!(self.cap().count_ones() == 1);
450 impl<T> VecDeque<T> {
451 /// Creates an empty `VecDeque`.
456 /// use std::collections::VecDeque;
458 /// let vector: VecDeque<u32> = VecDeque::new();
460 #[stable(feature = "rust1", since = "1.0.0")]
461 pub fn new() -> VecDeque<T> {
462 VecDeque::with_capacity(INITIAL_CAPACITY)
465 /// Creates an empty `VecDeque` with space for at least `capacity` elements.
470 /// use std::collections::VecDeque;
472 /// let vector: VecDeque<u32> = VecDeque::with_capacity(10);
474 #[stable(feature = "rust1", since = "1.0.0")]
475 pub fn with_capacity(capacity: usize) -> VecDeque<T> {
476 // +1 since the ringbuffer always leaves one space empty
477 let cap = cmp::max(capacity + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
478 assert!(cap > capacity, "capacity overflow");
480 VecDeque { tail: 0, head: 0, buf: RawVec::with_capacity(cap) }
483 /// Provides a reference to the element at the given index.
485 /// Element at index 0 is the front of the queue.
490 /// use std::collections::VecDeque;
492 /// let mut buf = VecDeque::new();
493 /// buf.push_back(3);
494 /// buf.push_back(4);
495 /// buf.push_back(5);
496 /// assert_eq!(buf.get(1), Some(&4));
498 #[stable(feature = "rust1", since = "1.0.0")]
499 pub fn get(&self, index: usize) -> Option<&T> {
500 if index < self.len() {
501 let idx = self.wrap_add(self.tail, index);
502 unsafe { Some(&*self.ptr().add(idx)) }
508 /// Provides a mutable reference to the element at the given index.
510 /// Element at index 0 is the front of the queue.
515 /// use std::collections::VecDeque;
517 /// let mut buf = VecDeque::new();
518 /// buf.push_back(3);
519 /// buf.push_back(4);
520 /// buf.push_back(5);
521 /// if let Some(elem) = buf.get_mut(1) {
525 /// assert_eq!(buf[1], 7);
527 #[stable(feature = "rust1", since = "1.0.0")]
528 pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
529 if index < self.len() {
530 let idx = self.wrap_add(self.tail, index);
531 unsafe { Some(&mut *self.ptr().add(idx)) }
537 /// Swaps elements at indices `i` and `j`.
539 /// `i` and `j` may be equal.
541 /// Element at index 0 is the front of the queue.
545 /// Panics if either index is out of bounds.
550 /// use std::collections::VecDeque;
552 /// let mut buf = VecDeque::new();
553 /// buf.push_back(3);
554 /// buf.push_back(4);
555 /// buf.push_back(5);
556 /// assert_eq!(buf, [3, 4, 5]);
558 /// assert_eq!(buf, [5, 4, 3]);
560 #[stable(feature = "rust1", since = "1.0.0")]
561 pub fn swap(&mut self, i: usize, j: usize) {
562 assert!(i < self.len());
563 assert!(j < self.len());
564 let ri = self.wrap_add(self.tail, i);
565 let rj = self.wrap_add(self.tail, j);
566 unsafe { ptr::swap(self.ptr().add(ri), self.ptr().add(rj)) }
569 /// Returns the number of elements the `VecDeque` can hold without
575 /// use std::collections::VecDeque;
577 /// let buf: VecDeque<i32> = VecDeque::with_capacity(10);
578 /// assert!(buf.capacity() >= 10);
581 #[stable(feature = "rust1", since = "1.0.0")]
582 pub fn capacity(&self) -> usize {
586 /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
587 /// given `VecDeque`. Does nothing if the capacity is already sufficient.
589 /// Note that the allocator may give the collection more space than it requests. Therefore
590 /// capacity can not be relied upon to be precisely minimal. Prefer [`reserve`] if future
591 /// insertions are expected.
595 /// Panics if the new capacity overflows `usize`.
600 /// use std::collections::VecDeque;
602 /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
603 /// buf.reserve_exact(10);
604 /// assert!(buf.capacity() >= 11);
607 /// [`reserve`]: VecDeque::reserve
608 #[stable(feature = "rust1", since = "1.0.0")]
609 pub fn reserve_exact(&mut self, additional: usize) {
610 self.reserve(additional);
613 /// Reserves capacity for at least `additional` more elements to be inserted in the given
614 /// `VecDeque`. The collection may reserve more space to avoid frequent reallocations.
618 /// Panics if the new capacity overflows `usize`.
623 /// use std::collections::VecDeque;
625 /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
627 /// assert!(buf.capacity() >= 11);
629 #[stable(feature = "rust1", since = "1.0.0")]
630 pub fn reserve(&mut self, additional: usize) {
631 let old_cap = self.cap();
632 let used_cap = self.len() + 1;
633 let new_cap = used_cap
634 .checked_add(additional)
635 .and_then(|needed_cap| needed_cap.checked_next_power_of_two())
636 .expect("capacity overflow");
638 if new_cap > old_cap {
639 self.buf.reserve_exact(used_cap, new_cap - used_cap);
641 self.handle_capacity_increase(old_cap);
646 /// Tries to reserve the minimum capacity for exactly `additional` more elements to
647 /// be inserted in the given `VecDeque<T>`. After calling `try_reserve_exact`,
648 /// capacity will be greater than or equal to `self.len() + additional`.
649 /// Does nothing if the capacity is already sufficient.
651 /// Note that the allocator may give the collection more space than it
652 /// requests. Therefore, capacity can not be relied upon to be precisely
653 /// minimal. Prefer `reserve` if future insertions are expected.
657 /// If the capacity overflows `usize`, or the allocator reports a failure, then an error
663 /// #![feature(try_reserve)]
664 /// use std::collections::TryReserveError;
665 /// use std::collections::VecDeque;
667 /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> {
668 /// let mut output = VecDeque::new();
670 /// // Pre-reserve the memory, exiting if we can't
671 /// output.try_reserve_exact(data.len())?;
673 /// // Now we know this can't OOM(Out-Of-Memory) in the middle of our complex work
674 /// output.extend(data.iter().map(|&val| {
675 /// val * 2 + 5 // very complicated
680 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
682 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
683 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
684 self.try_reserve(additional)
687 /// Tries to reserve capacity for at least `additional` more elements to be inserted
688 /// in the given `VecDeque<T>`. The collection may reserve more space to avoid
689 /// frequent reallocations. After calling `try_reserve`, capacity will be
690 /// greater than or equal to `self.len() + additional`. Does nothing if
691 /// capacity is already sufficient.
695 /// If the capacity overflows `usize`, or the allocator reports a failure, then an error
701 /// #![feature(try_reserve)]
702 /// use std::collections::TryReserveError;
703 /// use std::collections::VecDeque;
705 /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> {
706 /// let mut output = VecDeque::new();
708 /// // Pre-reserve the memory, exiting if we can't
709 /// output.try_reserve(data.len())?;
711 /// // Now we know this can't OOM in the middle of our complex work
712 /// output.extend(data.iter().map(|&val| {
713 /// val * 2 + 5 // very complicated
718 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
720 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
721 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
722 let old_cap = self.cap();
723 let used_cap = self.len() + 1;
724 let new_cap = used_cap
725 .checked_add(additional)
726 .and_then(|needed_cap| needed_cap.checked_next_power_of_two())
727 .ok_or(TryReserveError::CapacityOverflow)?;
729 if new_cap > old_cap {
730 self.buf.try_reserve_exact(used_cap, new_cap - used_cap)?;
732 self.handle_capacity_increase(old_cap);
738 /// Shrinks the capacity of the `VecDeque` as much as possible.
740 /// It will drop down as close as possible to the length but the allocator may still inform the
741 /// `VecDeque` that there is space for a few more elements.
746 /// use std::collections::VecDeque;
748 /// let mut buf = VecDeque::with_capacity(15);
749 /// buf.extend(0..4);
750 /// assert_eq!(buf.capacity(), 15);
751 /// buf.shrink_to_fit();
752 /// assert!(buf.capacity() >= 4);
754 #[stable(feature = "deque_extras_15", since = "1.5.0")]
755 pub fn shrink_to_fit(&mut self) {
759 /// Shrinks the capacity of the `VecDeque` with a lower bound.
761 /// The capacity will remain at least as large as both the length
762 /// and the supplied value.
764 /// If the current capacity is less than the lower limit, this is a no-op.
769 /// #![feature(shrink_to)]
770 /// use std::collections::VecDeque;
772 /// let mut buf = VecDeque::with_capacity(15);
773 /// buf.extend(0..4);
774 /// assert_eq!(buf.capacity(), 15);
775 /// buf.shrink_to(6);
776 /// assert!(buf.capacity() >= 6);
777 /// buf.shrink_to(0);
778 /// assert!(buf.capacity() >= 4);
780 #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
781 pub fn shrink_to(&mut self, min_capacity: usize) {
782 let min_capacity = cmp::min(min_capacity, self.capacity());
783 // We don't have to worry about an overflow as neither `self.len()` nor `self.capacity()`
784 // can ever be `usize::MAX`. +1 as the ringbuffer always leaves one space empty.
785 let target_cap = cmp::max(cmp::max(min_capacity, self.len()) + 1, MINIMUM_CAPACITY + 1)
786 .next_power_of_two();
788 if target_cap < self.cap() {
789 // There are three cases of interest:
790 // All elements are out of desired bounds
791 // Elements are contiguous, and head is out of desired bounds
792 // Elements are discontiguous, and tail is out of desired bounds
794 // At all other times, element positions are unaffected.
796 // Indicates that elements at the head should be moved.
797 let head_outside = self.head == 0 || self.head >= target_cap;
798 // Move elements from out of desired bounds (positions after target_cap)
799 if self.tail >= target_cap && head_outside {
801 // [. . . . . . . . o o o o o o o . ]
803 // [o o o o o o o . ]
805 self.copy_nonoverlapping(0, self.tail, self.len());
807 self.head = self.len();
809 } else if self.tail != 0 && self.tail < target_cap && head_outside {
811 // [. . . o o o o o o o . . . . . . ]
813 // [o o . o o o o o ]
814 let len = self.wrap_sub(self.head, target_cap);
816 self.copy_nonoverlapping(0, target_cap, len);
819 debug_assert!(self.head < self.tail);
820 } else if self.tail >= target_cap {
822 // [o o o o o . . . . . . . . . o o ]
824 // [o o o o o . o o ]
825 debug_assert!(self.wrap_sub(self.head, 1) < target_cap);
826 let len = self.cap() - self.tail;
827 let new_tail = target_cap - len;
829 self.copy_nonoverlapping(new_tail, self.tail, len);
831 self.tail = new_tail;
832 debug_assert!(self.head < self.tail);
835 self.buf.shrink_to_fit(target_cap);
837 debug_assert!(self.head < self.cap());
838 debug_assert!(self.tail < self.cap());
839 debug_assert!(self.cap().count_ones() == 1);
843 /// Shortens the `VecDeque`, keeping the first `len` elements and dropping
846 /// If `len` is greater than the `VecDeque`'s current length, this has no
852 /// use std::collections::VecDeque;
854 /// let mut buf = VecDeque::new();
855 /// buf.push_back(5);
856 /// buf.push_back(10);
857 /// buf.push_back(15);
858 /// assert_eq!(buf, [5, 10, 15]);
860 /// assert_eq!(buf, [5]);
862 #[stable(feature = "deque_extras", since = "1.16.0")]
863 pub fn truncate(&mut self, len: usize) {
864 /// Runs the destructor for all items in the slice when it gets dropped (normally or
865 /// during unwinding).
866 struct Dropper<'a, T>(&'a mut [T]);
868 impl<'a, T> Drop for Dropper<'a, T> {
871 ptr::drop_in_place(self.0);
878 // * Any slice passed to `drop_in_place` is valid; the second case has
879 // `len <= front.len()` and returning on `len > self.len()` ensures
880 // `begin <= back.len()` in the first case
881 // * The head of the VecDeque is moved before calling `drop_in_place`,
882 // so no value is dropped twice if `drop_in_place` panics
884 if len > self.len() {
887 let num_dropped = self.len() - len;
888 let (front, back) = self.as_mut_slices();
889 if len > front.len() {
890 let begin = len - front.len();
891 let drop_back = back.get_unchecked_mut(begin..) as *mut _;
892 self.head = self.wrap_sub(self.head, num_dropped);
893 ptr::drop_in_place(drop_back);
895 let drop_back = back as *mut _;
896 let drop_front = front.get_unchecked_mut(len..) as *mut _;
897 self.head = self.wrap_sub(self.head, num_dropped);
899 // Make sure the second half is dropped even when a destructor
900 // in the first one panics.
901 let _back_dropper = Dropper(&mut *drop_back);
902 ptr::drop_in_place(drop_front);
907 /// Returns a front-to-back iterator.
912 /// use std::collections::VecDeque;
914 /// let mut buf = VecDeque::new();
915 /// buf.push_back(5);
916 /// buf.push_back(3);
917 /// buf.push_back(4);
918 /// let b: &[_] = &[&5, &3, &4];
919 /// let c: Vec<&i32> = buf.iter().collect();
920 /// assert_eq!(&c[..], b);
922 #[stable(feature = "rust1", since = "1.0.0")]
923 pub fn iter(&self) -> Iter<'_, T> {
924 Iter { tail: self.tail, head: self.head, ring: unsafe { self.buffer_as_slice() } }
927 /// Returns a front-to-back iterator that returns mutable references.
932 /// use std::collections::VecDeque;
934 /// let mut buf = VecDeque::new();
935 /// buf.push_back(5);
936 /// buf.push_back(3);
937 /// buf.push_back(4);
938 /// for num in buf.iter_mut() {
941 /// let b: &[_] = &[&mut 3, &mut 1, &mut 2];
942 /// assert_eq!(&buf.iter_mut().collect::<Vec<&mut i32>>()[..], b);
944 #[stable(feature = "rust1", since = "1.0.0")]
945 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
946 // SAFETY: The internal `IterMut` safety invariant is established because the
947 // `ring` we create is a dereferencable slice for lifetime '_.
951 ring: ptr::slice_from_raw_parts_mut(self.ptr(), self.cap()),
952 phantom: PhantomData,
956 /// Returns a pair of slices which contain, in order, the contents of the
959 /// If [`make_contiguous`] was previously called, all elements of the
960 /// `VecDeque` will be in the first slice and the second slice will be empty.
962 /// [`make_contiguous`]: VecDeque::make_contiguous
967 /// use std::collections::VecDeque;
969 /// let mut vector = VecDeque::new();
971 /// vector.push_back(0);
972 /// vector.push_back(1);
973 /// vector.push_back(2);
975 /// assert_eq!(vector.as_slices(), (&[0, 1, 2][..], &[][..]));
977 /// vector.push_front(10);
978 /// vector.push_front(9);
980 /// assert_eq!(vector.as_slices(), (&[9, 10][..], &[0, 1, 2][..]));
983 #[stable(feature = "deque_extras_15", since = "1.5.0")]
984 pub fn as_slices(&self) -> (&[T], &[T]) {
986 let buf = self.buffer_as_slice();
987 RingSlices::ring_slices(buf, self.head, self.tail)
991 /// Returns a pair of slices which contain, in order, the contents of the
994 /// If [`make_contiguous`] was previously called, all elements of the
995 /// `VecDeque` will be in the first slice and the second slice will be empty.
997 /// [`make_contiguous`]: VecDeque::make_contiguous
1002 /// use std::collections::VecDeque;
1004 /// let mut vector = VecDeque::new();
1006 /// vector.push_back(0);
1007 /// vector.push_back(1);
1009 /// vector.push_front(10);
1010 /// vector.push_front(9);
1012 /// vector.as_mut_slices().0[0] = 42;
1013 /// vector.as_mut_slices().1[0] = 24;
1014 /// assert_eq!(vector.as_slices(), (&[42, 10][..], &[24, 1][..]));
1017 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1018 pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) {
1020 let head = self.head;
1021 let tail = self.tail;
1022 let buf = self.buffer_as_mut_slice();
1023 RingSlices::ring_slices(buf, head, tail)
1027 /// Returns the number of elements in the `VecDeque`.
1032 /// use std::collections::VecDeque;
1034 /// let mut v = VecDeque::new();
1035 /// assert_eq!(v.len(), 0);
1037 /// assert_eq!(v.len(), 1);
1039 #[stable(feature = "rust1", since = "1.0.0")]
1040 pub fn len(&self) -> usize {
1041 count(self.tail, self.head, self.cap())
1044 /// Returns `true` if the `VecDeque` is empty.
1049 /// use std::collections::VecDeque;
1051 /// let mut v = VecDeque::new();
1052 /// assert!(v.is_empty());
1053 /// v.push_front(1);
1054 /// assert!(!v.is_empty());
1056 #[stable(feature = "rust1", since = "1.0.0")]
1057 pub fn is_empty(&self) -> bool {
1058 self.tail == self.head
1061 fn range_tail_head<R>(&self, range: R) -> (usize, usize)
1063 R: RangeBounds<usize>,
1065 let Range { start, end } = slice::range(range, ..self.len());
1066 let tail = self.wrap_add(self.tail, start);
1067 let head = self.wrap_add(self.tail, end);
1071 /// Creates an iterator that covers the specified range in the `VecDeque`.
1075 /// Panics if the starting point is greater than the end point or if
1076 /// the end point is greater than the length of the vector.
1081 /// use std::collections::VecDeque;
1083 /// let v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1084 /// let range = v.range(2..).copied().collect::<VecDeque<_>>();
1085 /// assert_eq!(range, [3]);
1087 /// // A full range covers all contents
1088 /// let all = v.range(..);
1089 /// assert_eq!(all.len(), 3);
1092 #[stable(feature = "deque_range", since = "1.51.0")]
1093 pub fn range<R>(&self, range: R) -> Iter<'_, T>
1095 R: RangeBounds<usize>,
1097 let (tail, head) = self.range_tail_head(range);
1101 // The shared reference we have in &self is maintained in the '_ of Iter.
1102 ring: unsafe { self.buffer_as_slice() },
1106 /// Creates an iterator that covers the specified mutable range in the `VecDeque`.
1110 /// Panics if the starting point is greater than the end point or if
1111 /// the end point is greater than the length of the vector.
1116 /// use std::collections::VecDeque;
1118 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1119 /// for v in v.range_mut(2..) {
1122 /// assert_eq!(v, vec![1, 2, 6]);
1124 /// // A full range covers all contents
1125 /// for v in v.range_mut(..) {
1128 /// assert_eq!(v, vec![2, 4, 12]);
1131 #[stable(feature = "deque_range", since = "1.51.0")]
1132 pub fn range_mut<R>(&mut self, range: R) -> IterMut<'_, T>
1134 R: RangeBounds<usize>,
1136 let (tail, head) = self.range_tail_head(range);
1138 // SAFETY: The internal `IterMut` safety invariant is established because the
1139 // `ring` we create is a dereferencable slice for lifetime '_.
1143 ring: ptr::slice_from_raw_parts_mut(self.ptr(), self.cap()),
1144 phantom: PhantomData,
1148 /// Creates a draining iterator that removes the specified range in the
1149 /// `VecDeque` and yields the removed items.
1151 /// Note 1: The element range is removed even if the iterator is not
1152 /// consumed until the end.
1154 /// Note 2: It is unspecified how many elements are removed from the deque,
1155 /// if the `Drain` value is not dropped, but the borrow it holds expires
1156 /// (e.g., due to `mem::forget`).
1160 /// Panics if the starting point is greater than the end point or if
1161 /// the end point is greater than the length of the vector.
1166 /// use std::collections::VecDeque;
1168 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1169 /// let drained = v.drain(2..).collect::<VecDeque<_>>();
1170 /// assert_eq!(drained, [3]);
1171 /// assert_eq!(v, [1, 2]);
1173 /// // A full range clears all contents
1175 /// assert!(v.is_empty());
1178 #[stable(feature = "drain", since = "1.6.0")]
1179 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
1181 R: RangeBounds<usize>,
1185 // When the Drain is first created, the source deque is shortened to
1186 // make sure no uninitialized or moved-from elements are accessible at
1187 // all if the Drain's destructor never gets to run.
1189 // Drain will ptr::read out the values to remove.
1190 // When finished, the remaining data will be copied back to cover the hole,
1191 // and the head/tail values will be restored correctly.
1193 let (drain_tail, drain_head) = self.range_tail_head(range);
1195 // The deque's elements are parted into three segments:
1196 // * self.tail -> drain_tail
1197 // * drain_tail -> drain_head
1198 // * drain_head -> self.head
1200 // T = self.tail; H = self.head; t = drain_tail; h = drain_head
1202 // We store drain_tail as self.head, and drain_head and self.head as
1203 // after_tail and after_head respectively on the Drain. This also
1204 // truncates the effective array such that if the Drain is leaked, we
1205 // have forgotten about the potentially moved values after the start of
1209 // [. . . o o x x o o . . .]
1211 let head = self.head;
1213 // "forget" about the values after the start of the drain until after
1214 // the drain is complete and the Drain destructor is run.
1215 self.head = drain_tail;
1218 deque: NonNull::from(&mut *self),
1219 after_tail: drain_head,
1224 // Crucially, we only create shared references from `self` here and read from
1225 // it. We do not write to `self` nor reborrow to a mutable reference.
1226 // Hence the raw pointer we created above, for `deque`, remains valid.
1227 ring: unsafe { self.buffer_as_slice() },
1232 /// Clears the `VecDeque`, removing all values.
1237 /// use std::collections::VecDeque;
1239 /// let mut v = VecDeque::new();
1242 /// assert!(v.is_empty());
1244 #[stable(feature = "rust1", since = "1.0.0")]
1246 pub fn clear(&mut self) {
1250 /// Returns `true` if the `VecDeque` contains an element equal to the
1256 /// use std::collections::VecDeque;
1258 /// let mut vector: VecDeque<u32> = VecDeque::new();
1260 /// vector.push_back(0);
1261 /// vector.push_back(1);
1263 /// assert_eq!(vector.contains(&1), true);
1264 /// assert_eq!(vector.contains(&10), false);
1266 #[stable(feature = "vec_deque_contains", since = "1.12.0")]
1267 pub fn contains(&self, x: &T) -> bool
1271 let (a, b) = self.as_slices();
1272 a.contains(x) || b.contains(x)
1275 /// Provides a reference to the front element, or `None` if the `VecDeque` is
1281 /// use std::collections::VecDeque;
1283 /// let mut d = VecDeque::new();
1284 /// assert_eq!(d.front(), None);
1288 /// assert_eq!(d.front(), Some(&1));
1290 #[stable(feature = "rust1", since = "1.0.0")]
1291 pub fn front(&self) -> Option<&T> {
1295 /// Provides a mutable reference to the front element, or `None` if the
1296 /// `VecDeque` is empty.
1301 /// use std::collections::VecDeque;
1303 /// let mut d = VecDeque::new();
1304 /// assert_eq!(d.front_mut(), None);
1308 /// match d.front_mut() {
1309 /// Some(x) => *x = 9,
1312 /// assert_eq!(d.front(), Some(&9));
1314 #[stable(feature = "rust1", since = "1.0.0")]
1315 pub fn front_mut(&mut self) -> Option<&mut T> {
1319 /// Provides a reference to the back element, or `None` if the `VecDeque` is
1325 /// use std::collections::VecDeque;
1327 /// let mut d = VecDeque::new();
1328 /// assert_eq!(d.back(), None);
1332 /// assert_eq!(d.back(), Some(&2));
1334 #[stable(feature = "rust1", since = "1.0.0")]
1335 pub fn back(&self) -> Option<&T> {
1336 self.get(self.len().wrapping_sub(1))
1339 /// Provides a mutable reference to the back element, or `None` if the
1340 /// `VecDeque` is empty.
1345 /// use std::collections::VecDeque;
1347 /// let mut d = VecDeque::new();
1348 /// assert_eq!(d.back(), None);
1352 /// match d.back_mut() {
1353 /// Some(x) => *x = 9,
1356 /// assert_eq!(d.back(), Some(&9));
1358 #[stable(feature = "rust1", since = "1.0.0")]
1359 pub fn back_mut(&mut self) -> Option<&mut T> {
1360 self.get_mut(self.len().wrapping_sub(1))
1363 /// Removes the first element and returns it, or `None` if the `VecDeque` is
1369 /// use std::collections::VecDeque;
1371 /// let mut d = VecDeque::new();
1375 /// assert_eq!(d.pop_front(), Some(1));
1376 /// assert_eq!(d.pop_front(), Some(2));
1377 /// assert_eq!(d.pop_front(), None);
1379 #[stable(feature = "rust1", since = "1.0.0")]
1380 pub fn pop_front(&mut self) -> Option<T> {
1381 if self.is_empty() {
1384 let tail = self.tail;
1385 self.tail = self.wrap_add(self.tail, 1);
1386 unsafe { Some(self.buffer_read(tail)) }
1390 /// Removes the last element from the `VecDeque` and returns it, or `None` if
1396 /// use std::collections::VecDeque;
1398 /// let mut buf = VecDeque::new();
1399 /// assert_eq!(buf.pop_back(), None);
1400 /// buf.push_back(1);
1401 /// buf.push_back(3);
1402 /// assert_eq!(buf.pop_back(), Some(3));
1404 #[stable(feature = "rust1", since = "1.0.0")]
1405 pub fn pop_back(&mut self) -> Option<T> {
1406 if self.is_empty() {
1409 self.head = self.wrap_sub(self.head, 1);
1410 let head = self.head;
1411 unsafe { Some(self.buffer_read(head)) }
1415 /// Prepends an element to the `VecDeque`.
1420 /// use std::collections::VecDeque;
1422 /// let mut d = VecDeque::new();
1423 /// d.push_front(1);
1424 /// d.push_front(2);
1425 /// assert_eq!(d.front(), Some(&2));
1427 #[stable(feature = "rust1", since = "1.0.0")]
1428 pub fn push_front(&mut self, value: T) {
1433 self.tail = self.wrap_sub(self.tail, 1);
1434 let tail = self.tail;
1436 self.buffer_write(tail, value);
1440 /// Appends an element to the back of the `VecDeque`.
1445 /// use std::collections::VecDeque;
1447 /// let mut buf = VecDeque::new();
1448 /// buf.push_back(1);
1449 /// buf.push_back(3);
1450 /// assert_eq!(3, *buf.back().unwrap());
1452 #[stable(feature = "rust1", since = "1.0.0")]
1453 pub fn push_back(&mut self, value: T) {
1458 let head = self.head;
1459 self.head = self.wrap_add(self.head, 1);
1460 unsafe { self.buffer_write(head, value) }
1464 fn is_contiguous(&self) -> bool {
1465 // FIXME: Should we consider `head == 0` to mean
1466 // that `self` is contiguous?
1467 self.tail <= self.head
1470 /// Removes an element from anywhere in the `VecDeque` and returns it,
1471 /// replacing it with the first element.
1473 /// This does not preserve ordering, but is *O*(1).
1475 /// Returns `None` if `index` is out of bounds.
1477 /// Element at index 0 is the front of the queue.
1482 /// use std::collections::VecDeque;
1484 /// let mut buf = VecDeque::new();
1485 /// assert_eq!(buf.swap_remove_front(0), None);
1486 /// buf.push_back(1);
1487 /// buf.push_back(2);
1488 /// buf.push_back(3);
1489 /// assert_eq!(buf, [1, 2, 3]);
1491 /// assert_eq!(buf.swap_remove_front(2), Some(3));
1492 /// assert_eq!(buf, [2, 1]);
1494 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1495 pub fn swap_remove_front(&mut self, index: usize) -> Option<T> {
1496 let length = self.len();
1497 if length > 0 && index < length && index != 0 {
1498 self.swap(index, 0);
1499 } else if index >= length {
1505 /// Removes an element from anywhere in the `VecDeque` and returns it, replacing it with the
1508 /// This does not preserve ordering, but is *O*(1).
1510 /// Returns `None` if `index` is out of bounds.
1512 /// Element at index 0 is the front of the queue.
1517 /// use std::collections::VecDeque;
1519 /// let mut buf = VecDeque::new();
1520 /// assert_eq!(buf.swap_remove_back(0), None);
1521 /// buf.push_back(1);
1522 /// buf.push_back(2);
1523 /// buf.push_back(3);
1524 /// assert_eq!(buf, [1, 2, 3]);
1526 /// assert_eq!(buf.swap_remove_back(0), Some(1));
1527 /// assert_eq!(buf, [3, 2]);
1529 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1530 pub fn swap_remove_back(&mut self, index: usize) -> Option<T> {
1531 let length = self.len();
1532 if length > 0 && index < length - 1 {
1533 self.swap(index, length - 1);
1534 } else if index >= length {
1540 /// Inserts an element at `index` within the `VecDeque`, shifting all elements with indices
1541 /// greater than or equal to `index` towards the back.
1543 /// Element at index 0 is the front of the queue.
1547 /// Panics if `index` is greater than `VecDeque`'s length
1552 /// use std::collections::VecDeque;
1554 /// let mut vec_deque = VecDeque::new();
1555 /// vec_deque.push_back('a');
1556 /// vec_deque.push_back('b');
1557 /// vec_deque.push_back('c');
1558 /// assert_eq!(vec_deque, &['a', 'b', 'c']);
1560 /// vec_deque.insert(1, 'd');
1561 /// assert_eq!(vec_deque, &['a', 'd', 'b', 'c']);
1563 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1564 pub fn insert(&mut self, index: usize, value: T) {
1565 assert!(index <= self.len(), "index out of bounds");
1570 // Move the least number of elements in the ring buffer and insert
1573 // At most len/2 - 1 elements will be moved. O(min(n, n-i))
1575 // There are three main cases:
1576 // Elements are contiguous
1577 // - special case when tail is 0
1578 // Elements are discontiguous and the insert is in the tail section
1579 // Elements are discontiguous and the insert is in the head section
1581 // For each of those there are two more cases:
1582 // Insert is closer to tail
1583 // Insert is closer to head
1585 // Key: H - self.head
1587 // o - Valid element
1588 // I - Insertion element
1589 // A - The element that should be after the insertion point
1590 // M - Indicates element was moved
1592 let idx = self.wrap_add(self.tail, index);
1594 let distance_to_tail = index;
1595 let distance_to_head = self.len() - index;
1597 let contiguous = self.is_contiguous();
1599 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1600 (true, true, _) if index == 0 => {
1605 // [A o o o o o o . . . . . . . . .]
1608 // [A o o o o o o o . . . . . I]
1611 self.tail = self.wrap_sub(self.tail, 1);
1613 (true, true, _) => {
1615 // contiguous, insert closer to tail:
1618 // [. . . o o A o o o o . . . . . .]
1621 // [. . o o I A o o o o . . . . . .]
1624 // contiguous, insert closer to tail and tail is 0:
1628 // [o o A o o o o . . . . . . . . .]
1631 // [o I A o o o o o . . . . . . . o]
1634 let new_tail = self.wrap_sub(self.tail, 1);
1636 self.copy(new_tail, self.tail, 1);
1637 // Already moved the tail, so we only copy `index - 1` elements.
1638 self.copy(self.tail, self.tail + 1, index - 1);
1640 self.tail = new_tail;
1643 (true, false, _) => {
1645 // contiguous, insert closer to head:
1648 // [. . . o o o o A o o . . . . . .]
1651 // [. . . o o o o I A o o . . . . .]
1654 self.copy(idx + 1, idx, self.head - idx);
1655 self.head = self.wrap_add(self.head, 1);
1658 (false, true, true) => {
1660 // discontiguous, insert closer to tail, tail section:
1663 // [o o o o o o . . . . . o o A o o]
1666 // [o o o o o o . . . . o o I A o o]
1669 self.copy(self.tail - 1, self.tail, index);
1673 (false, false, true) => {
1675 // discontiguous, insert closer to head, tail section:
1678 // [o o . . . . . . . o o o o o A o]
1681 // [o o o . . . . . . o o o o o I A]
1684 // copy elements up to new head
1685 self.copy(1, 0, self.head);
1687 // copy last element into empty spot at bottom of buffer
1688 self.copy(0, self.cap() - 1, 1);
1690 // move elements from idx to end forward not including ^ element
1691 self.copy(idx + 1, idx, self.cap() - 1 - idx);
1696 (false, true, false) if idx == 0 => {
1698 // discontiguous, insert is closer to tail, head section,
1699 // and is at index zero in the internal buffer:
1702 // [A o o o o o o o o o . . . o o o]
1705 // [A o o o o o o o o o . . o o o I]
1708 // copy elements up to new tail
1709 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1711 // copy last element into empty spot at bottom of buffer
1712 self.copy(self.cap() - 1, 0, 1);
1717 (false, true, false) => {
1719 // discontiguous, insert closer to tail, head section:
1722 // [o o o A o o o o o o . . . o o o]
1725 // [o o I A o o o o o o . . o o o o]
1728 // copy elements up to new tail
1729 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1731 // copy last element into empty spot at bottom of buffer
1732 self.copy(self.cap() - 1, 0, 1);
1734 // move elements from idx-1 to end forward not including ^ element
1735 self.copy(0, 1, idx - 1);
1740 (false, false, false) => {
1742 // discontiguous, insert closer to head, head section:
1745 // [o o o o A o o . . . . . . o o o]
1748 // [o o o o I A o o . . . . . o o o]
1751 self.copy(idx + 1, idx, self.head - idx);
1757 // tail might've been changed so we need to recalculate
1758 let new_idx = self.wrap_add(self.tail, index);
1760 self.buffer_write(new_idx, value);
1764 /// Removes and returns the element at `index` from the `VecDeque`.
1765 /// Whichever end is closer to the removal point will be moved to make
1766 /// room, and all the affected elements will be moved to new positions.
1767 /// Returns `None` if `index` is out of bounds.
1769 /// Element at index 0 is the front of the queue.
1774 /// use std::collections::VecDeque;
1776 /// let mut buf = VecDeque::new();
1777 /// buf.push_back(1);
1778 /// buf.push_back(2);
1779 /// buf.push_back(3);
1780 /// assert_eq!(buf, [1, 2, 3]);
1782 /// assert_eq!(buf.remove(1), Some(2));
1783 /// assert_eq!(buf, [1, 3]);
1785 #[stable(feature = "rust1", since = "1.0.0")]
1786 pub fn remove(&mut self, index: usize) -> Option<T> {
1787 if self.is_empty() || self.len() <= index {
1791 // There are three main cases:
1792 // Elements are contiguous
1793 // Elements are discontiguous and the removal is in the tail section
1794 // Elements are discontiguous and the removal is in the head section
1795 // - special case when elements are technically contiguous,
1796 // but self.head = 0
1798 // For each of those there are two more cases:
1799 // Insert is closer to tail
1800 // Insert is closer to head
1802 // Key: H - self.head
1804 // o - Valid element
1805 // x - Element marked for removal
1806 // R - Indicates element that is being removed
1807 // M - Indicates element was moved
1809 let idx = self.wrap_add(self.tail, index);
1811 let elem = unsafe { Some(self.buffer_read(idx)) };
1813 let distance_to_tail = index;
1814 let distance_to_head = self.len() - index;
1816 let contiguous = self.is_contiguous();
1818 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1819 (true, true, _) => {
1821 // contiguous, remove closer to tail:
1824 // [. . . o o x o o o o . . . . . .]
1827 // [. . . . o o o o o o . . . . . .]
1830 self.copy(self.tail + 1, self.tail, index);
1834 (true, false, _) => {
1836 // contiguous, remove closer to head:
1839 // [. . . o o o o x o o . . . . . .]
1842 // [. . . o o o o o o . . . . . . .]
1845 self.copy(idx, idx + 1, self.head - idx - 1);
1849 (false, true, true) => {
1851 // discontiguous, remove closer to tail, tail section:
1854 // [o o o o o o . . . . . o o x o o]
1857 // [o o o o o o . . . . . . o o o o]
1860 self.copy(self.tail + 1, self.tail, index);
1861 self.tail = self.wrap_add(self.tail, 1);
1864 (false, false, false) => {
1866 // discontiguous, remove closer to head, head section:
1869 // [o o o o x o o . . . . . . o o o]
1872 // [o o o o o o . . . . . . . o o o]
1875 self.copy(idx, idx + 1, self.head - idx - 1);
1879 (false, false, true) => {
1881 // discontiguous, remove closer to head, tail section:
1884 // [o o o . . . . . . o o o o o x o]
1887 // [o o . . . . . . . o o o o o o o]
1890 // or quasi-discontiguous, remove next to head, tail section:
1893 // [. . . . . . . . . o o o o o x o]
1896 // [. . . . . . . . . o o o o o o .]
1899 // draw in elements in the tail section
1900 self.copy(idx, idx + 1, self.cap() - idx - 1);
1902 // Prevents underflow.
1904 // copy first element into empty spot
1905 self.copy(self.cap() - 1, 0, 1);
1907 // move elements in the head section backwards
1908 self.copy(0, 1, self.head - 1);
1911 self.head = self.wrap_sub(self.head, 1);
1914 (false, true, false) => {
1916 // discontiguous, remove closer to tail, head section:
1919 // [o o x o o o o o o o . . . o o o]
1922 // [o o o o o o o o o o . . . . o o]
1925 // draw in elements up to idx
1926 self.copy(1, 0, idx);
1928 // copy last element into empty spot
1929 self.copy(0, self.cap() - 1, 1);
1931 // move elements from tail to end forward, excluding the last one
1932 self.copy(self.tail + 1, self.tail, self.cap() - self.tail - 1);
1934 self.tail = self.wrap_add(self.tail, 1);
1942 /// Splits the `VecDeque` into two at the given index.
1944 /// Returns a newly allocated `VecDeque`. `self` contains elements `[0, at)`,
1945 /// and the returned `VecDeque` contains elements `[at, len)`.
1947 /// Note that the capacity of `self` does not change.
1949 /// Element at index 0 is the front of the queue.
1953 /// Panics if `at > len`.
1958 /// use std::collections::VecDeque;
1960 /// let mut buf: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1961 /// let buf2 = buf.split_off(1);
1962 /// assert_eq!(buf, [1]);
1963 /// assert_eq!(buf2, [2, 3]);
1966 #[must_use = "use `.truncate()` if you don't need the other half"]
1967 #[stable(feature = "split_off", since = "1.4.0")]
1968 pub fn split_off(&mut self, at: usize) -> Self {
1969 let len = self.len();
1970 assert!(at <= len, "`at` out of bounds");
1972 let other_len = len - at;
1973 let mut other = VecDeque::with_capacity(other_len);
1976 let (first_half, second_half) = self.as_slices();
1978 let first_len = first_half.len();
1979 let second_len = second_half.len();
1981 // `at` lies in the first half.
1982 let amount_in_first = first_len - at;
1984 ptr::copy_nonoverlapping(first_half.as_ptr().add(at), other.ptr(), amount_in_first);
1986 // just take all of the second half.
1987 ptr::copy_nonoverlapping(
1988 second_half.as_ptr(),
1989 other.ptr().add(amount_in_first),
1993 // `at` lies in the second half, need to factor in the elements we skipped
1994 // in the first half.
1995 let offset = at - first_len;
1996 let amount_in_second = second_len - offset;
1997 ptr::copy_nonoverlapping(
1998 second_half.as_ptr().add(offset),
2005 // Cleanup where the ends of the buffers are
2006 self.head = self.wrap_sub(self.head, other_len);
2007 other.head = other.wrap_index(other_len);
2012 /// Moves all the elements of `other` into `self`, leaving `other` empty.
2016 /// Panics if the new number of elements in self overflows a `usize`.
2021 /// use std::collections::VecDeque;
2023 /// let mut buf: VecDeque<_> = vec![1, 2].into_iter().collect();
2024 /// let mut buf2: VecDeque<_> = vec![3, 4].into_iter().collect();
2025 /// buf.append(&mut buf2);
2026 /// assert_eq!(buf, [1, 2, 3, 4]);
2027 /// assert_eq!(buf2, []);
2030 #[stable(feature = "append", since = "1.4.0")]
2031 pub fn append(&mut self, other: &mut Self) {
2033 self.extend(other.drain(..));
2036 /// Retains only the elements specified by the predicate.
2038 /// In other words, remove all elements `e` such that `f(&e)` returns false.
2039 /// This method operates in place, visiting each element exactly once in the
2040 /// original order, and preserves the order of the retained elements.
2045 /// use std::collections::VecDeque;
2047 /// let mut buf = VecDeque::new();
2048 /// buf.extend(1..5);
2049 /// buf.retain(|&x| x % 2 == 0);
2050 /// assert_eq!(buf, [2, 4]);
2053 /// The exact order may be useful for tracking external state, like an index.
2056 /// use std::collections::VecDeque;
2058 /// let mut buf = VecDeque::new();
2059 /// buf.extend(1..6);
2061 /// let keep = [false, true, true, false, true];
2063 /// buf.retain(|_| (keep[i], i += 1).0);
2064 /// assert_eq!(buf, [2, 3, 5]);
2066 #[stable(feature = "vec_deque_retain", since = "1.4.0")]
2067 pub fn retain<F>(&mut self, mut f: F)
2069 F: FnMut(&T) -> bool,
2071 let len = self.len();
2077 self.swap(i - del, i);
2081 self.truncate(len - del);
2085 // This may panic or abort
2087 fn grow(&mut self) {
2089 let old_cap = self.cap();
2090 // Double the buffer size.
2091 self.buf.reserve_exact(old_cap, old_cap);
2092 assert!(self.cap() == old_cap * 2);
2094 self.handle_capacity_increase(old_cap);
2096 debug_assert!(!self.is_full());
2100 /// Modifies the `VecDeque` in-place so that `len()` is equal to `new_len`,
2101 /// either by removing excess elements from the back or by appending
2102 /// elements generated by calling `generator` to the back.
2107 /// use std::collections::VecDeque;
2109 /// let mut buf = VecDeque::new();
2110 /// buf.push_back(5);
2111 /// buf.push_back(10);
2112 /// buf.push_back(15);
2113 /// assert_eq!(buf, [5, 10, 15]);
2115 /// buf.resize_with(5, Default::default);
2116 /// assert_eq!(buf, [5, 10, 15, 0, 0]);
2118 /// buf.resize_with(2, || unreachable!());
2119 /// assert_eq!(buf, [5, 10]);
2121 /// let mut state = 100;
2122 /// buf.resize_with(5, || { state += 1; state });
2123 /// assert_eq!(buf, [5, 10, 101, 102, 103]);
2125 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2126 pub fn resize_with(&mut self, new_len: usize, generator: impl FnMut() -> T) {
2127 let len = self.len();
2130 self.extend(repeat_with(generator).take(new_len - len))
2132 self.truncate(new_len);
2136 /// Rearranges the internal storage of this deque so it is one contiguous
2137 /// slice, which is then returned.
2139 /// This method does not allocate and does not change the order of the
2140 /// inserted elements. As it returns a mutable slice, this can be used to
2143 /// Once the internal storage is contiguous, the [`as_slices`] and
2144 /// [`as_mut_slices`] methods will return the entire contents of the
2145 /// `VecDeque` in a single slice.
2147 /// [`as_slices`]: VecDeque::as_slices
2148 /// [`as_mut_slices`]: VecDeque::as_mut_slices
2152 /// Sorting the content of a deque.
2155 /// use std::collections::VecDeque;
2157 /// let mut buf = VecDeque::with_capacity(15);
2159 /// buf.push_back(2);
2160 /// buf.push_back(1);
2161 /// buf.push_front(3);
2163 /// // sorting the deque
2164 /// buf.make_contiguous().sort();
2165 /// assert_eq!(buf.as_slices(), (&[1, 2, 3] as &[_], &[] as &[_]));
2167 /// // sorting it in reverse order
2168 /// buf.make_contiguous().sort_by(|a, b| b.cmp(a));
2169 /// assert_eq!(buf.as_slices(), (&[3, 2, 1] as &[_], &[] as &[_]));
2172 /// Getting immutable access to the contiguous slice.
2175 /// use std::collections::VecDeque;
2177 /// let mut buf = VecDeque::new();
2179 /// buf.push_back(2);
2180 /// buf.push_back(1);
2181 /// buf.push_front(3);
2183 /// buf.make_contiguous();
2184 /// if let (slice, &[]) = buf.as_slices() {
2185 /// // we can now be sure that `slice` contains all elements of the deque,
2186 /// // while still having immutable access to `buf`.
2187 /// assert_eq!(buf.len(), slice.len());
2188 /// assert_eq!(slice, &[3, 2, 1] as &[_]);
2191 #[stable(feature = "deque_make_contiguous", since = "1.48.0")]
2192 pub fn make_contiguous(&mut self) -> &mut [T] {
2193 if self.is_contiguous() {
2194 let tail = self.tail;
2195 let head = self.head;
2196 return unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 };
2199 let buf = self.buf.ptr();
2200 let cap = self.cap();
2201 let len = self.len();
2203 let free = self.tail - self.head;
2204 let tail_len = cap - self.tail;
2206 if free >= tail_len {
2207 // there is enough free space to copy the tail in one go,
2208 // this means that we first shift the head backwards, and then
2209 // copy the tail to the correct position.
2211 // from: DEFGH....ABC
2214 ptr::copy(buf, buf.add(tail_len), self.head);
2216 ptr::copy_nonoverlapping(buf.add(self.tail), buf, tail_len);
2222 } else if free > self.head {
2223 // FIXME: We currently do not consider ....ABCDEFGH
2224 // to be contiguous because `head` would be `0` in this
2225 // case. While we probably want to change this it
2226 // isn't trivial as a few places expect `is_contiguous`
2227 // to mean that we can just slice using `buf[tail..head]`.
2229 // there is enough free space to copy the head in one go,
2230 // this means that we first shift the tail forwards, and then
2231 // copy the head to the correct position.
2233 // from: FGH....ABCDE
2236 ptr::copy(buf.add(self.tail), buf.add(self.head), tail_len);
2238 ptr::copy_nonoverlapping(buf, buf.add(self.head + tail_len), self.head);
2241 self.tail = self.head;
2242 self.head = self.wrap_add(self.tail, len);
2245 // free is smaller than both head and tail,
2246 // this means we have to slowly "swap" the tail and the head.
2248 // from: EFGHI...ABCD or HIJK.ABCDEFG
2249 // to: ABCDEFGHI... or ABCDEFGHIJK.
2250 let mut left_edge: usize = 0;
2251 let mut right_edge: usize = self.tail;
2253 // The general problem looks like this
2254 // GHIJKLM...ABCDEF - before any swaps
2255 // ABCDEFM...GHIJKL - after 1 pass of swaps
2256 // ABCDEFGHIJM...KL - swap until the left edge reaches the temp store
2257 // - then restart the algorithm with a new (smaller) store
2258 // Sometimes the temp store is reached when the right edge is at the end
2259 // of the buffer - this means we've hit the right order with fewer swaps!
2262 // ABCDEF.. - after four only swaps we've finished
2263 while left_edge < len && right_edge != cap {
2264 let mut right_offset = 0;
2265 for i in left_edge..right_edge {
2266 right_offset = (i - left_edge) % (cap - right_edge);
2267 let src: isize = (right_edge + right_offset) as isize;
2268 ptr::swap(buf.add(i), buf.offset(src));
2270 let n_ops = right_edge - left_edge;
2272 right_edge += right_offset + 1;
2280 let tail = self.tail;
2281 let head = self.head;
2282 unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 }
2285 /// Rotates the double-ended queue `mid` places to the left.
2288 /// - Rotates item `mid` into the first position.
2289 /// - Pops the first `mid` items and pushes them to the end.
2290 /// - Rotates `len() - mid` places to the right.
2294 /// If `mid` is greater than `len()`. Note that `mid == len()`
2295 /// does _not_ panic and is a no-op rotation.
2299 /// Takes `*O*(min(mid, len() - mid))` time and no extra space.
2304 /// use std::collections::VecDeque;
2306 /// let mut buf: VecDeque<_> = (0..10).collect();
2308 /// buf.rotate_left(3);
2309 /// assert_eq!(buf, [3, 4, 5, 6, 7, 8, 9, 0, 1, 2]);
2311 /// for i in 1..10 {
2312 /// assert_eq!(i * 3 % 10, buf[0]);
2313 /// buf.rotate_left(3);
2315 /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
2317 #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
2318 pub fn rotate_left(&mut self, mid: usize) {
2319 assert!(mid <= self.len());
2320 let k = self.len() - mid;
2322 unsafe { self.rotate_left_inner(mid) }
2324 unsafe { self.rotate_right_inner(k) }
2328 /// Rotates the double-ended queue `k` places to the right.
2331 /// - Rotates the first item into position `k`.
2332 /// - Pops the last `k` items and pushes them to the front.
2333 /// - Rotates `len() - k` places to the left.
2337 /// If `k` is greater than `len()`. Note that `k == len()`
2338 /// does _not_ panic and is a no-op rotation.
2342 /// Takes `*O*(min(k, len() - k))` time and no extra space.
2347 /// use std::collections::VecDeque;
2349 /// let mut buf: VecDeque<_> = (0..10).collect();
2351 /// buf.rotate_right(3);
2352 /// assert_eq!(buf, [7, 8, 9, 0, 1, 2, 3, 4, 5, 6]);
2354 /// for i in 1..10 {
2355 /// assert_eq!(0, buf[i * 3 % 10]);
2356 /// buf.rotate_right(3);
2358 /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
2360 #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
2361 pub fn rotate_right(&mut self, k: usize) {
2362 assert!(k <= self.len());
2363 let mid = self.len() - k;
2365 unsafe { self.rotate_right_inner(k) }
2367 unsafe { self.rotate_left_inner(mid) }
2371 // SAFETY: the following two methods require that the rotation amount
2372 // be less than half the length of the deque.
2374 // `wrap_copy` requires that `min(x, cap() - x) + copy_len <= cap()`,
2375 // but than `min` is never more than half the capacity, regardless of x,
2376 // so it's sound to call here because we're calling with something
2377 // less than half the length, which is never above half the capacity.
2379 unsafe fn rotate_left_inner(&mut self, mid: usize) {
2380 debug_assert!(mid * 2 <= self.len());
2382 self.wrap_copy(self.head, self.tail, mid);
2384 self.head = self.wrap_add(self.head, mid);
2385 self.tail = self.wrap_add(self.tail, mid);
2388 unsafe fn rotate_right_inner(&mut self, k: usize) {
2389 debug_assert!(k * 2 <= self.len());
2390 self.head = self.wrap_sub(self.head, k);
2391 self.tail = self.wrap_sub(self.tail, k);
2393 self.wrap_copy(self.tail, self.head, k);
2397 /// Binary searches this sorted `VecDeque` for a given element.
2399 /// If the value is found then [`Result::Ok`] is returned, containing the
2400 /// index of the matching element. If there are multiple matches, then any
2401 /// one of the matches could be returned. If the value is not found then
2402 /// [`Result::Err`] is returned, containing the index where a matching
2403 /// element could be inserted while maintaining sorted order.
2405 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2407 /// [`binary_search_by`]: VecDeque::binary_search_by
2408 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2409 /// [`partition_point`]: VecDeque::partition_point
2413 /// Looks up a series of four elements. The first is found, with a
2414 /// uniquely determined position; the second and third are not
2415 /// found; the fourth could match any position in `[1, 4]`.
2418 /// use std::collections::VecDeque;
2420 /// let deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2422 /// assert_eq!(deque.binary_search(&13), Ok(9));
2423 /// assert_eq!(deque.binary_search(&4), Err(7));
2424 /// assert_eq!(deque.binary_search(&100), Err(13));
2425 /// let r = deque.binary_search(&1);
2426 /// assert!(matches!(r, Ok(1..=4)));
2429 /// If you want to insert an item to a sorted `VecDeque`, while maintaining
2433 /// use std::collections::VecDeque;
2435 /// let mut deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2437 /// let idx = deque.binary_search(&num).unwrap_or_else(|x| x);
2438 /// deque.insert(idx, num);
2439 /// assert_eq!(deque, &[0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2441 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2443 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2447 self.binary_search_by(|e| e.cmp(x))
2450 /// Binary searches this sorted `VecDeque` with a comparator function.
2452 /// The comparator function should implement an order consistent
2453 /// with the sort order of the underlying `VecDeque`, returning an
2454 /// order code that indicates whether its argument is `Less`,
2455 /// `Equal` or `Greater` than the desired target.
2457 /// If the value is found then [`Result::Ok`] is returned, containing the
2458 /// index of the matching element. If there are multiple matches, then any
2459 /// one of the matches could be returned. If the value is not found then
2460 /// [`Result::Err`] is returned, containing the index where a matching
2461 /// element could be inserted while maintaining sorted order.
2463 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2465 /// [`binary_search`]: VecDeque::binary_search
2466 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2467 /// [`partition_point`]: VecDeque::partition_point
2471 /// Looks up a series of four elements. The first is found, with a
2472 /// uniquely determined position; the second and third are not
2473 /// found; the fourth could match any position in `[1, 4]`.
2476 /// use std::collections::VecDeque;
2478 /// let deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2480 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&13)), Ok(9));
2481 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&4)), Err(7));
2482 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&100)), Err(13));
2483 /// let r = deque.binary_search_by(|x| x.cmp(&1));
2484 /// assert!(matches!(r, Ok(1..=4)));
2486 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2487 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2489 F: FnMut(&'a T) -> Ordering,
2491 let (front, back) = self.as_slices();
2492 let cmp_back = back.first().map(|elem| f(elem));
2494 if let Some(Ordering::Equal) = cmp_back {
2496 } else if let Some(Ordering::Less) = cmp_back {
2497 back.binary_search_by(f).map(|idx| idx + front.len()).map_err(|idx| idx + front.len())
2499 front.binary_search_by(f)
2503 /// Binary searches this sorted `VecDeque` with a key extraction function.
2505 /// Assumes that the `VecDeque` is sorted by the key, for instance with
2506 /// [`make_contiguous().sort_by_key()`] using the same key extraction function.
2508 /// If the value is found then [`Result::Ok`] is returned, containing the
2509 /// index of the matching element. If there are multiple matches, then any
2510 /// one of the matches could be returned. If the value is not found then
2511 /// [`Result::Err`] is returned, containing the index where a matching
2512 /// element could be inserted while maintaining sorted order.
2514 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2516 /// [`make_contiguous().sort_by_key()`]: VecDeque::make_contiguous
2517 /// [`binary_search`]: VecDeque::binary_search
2518 /// [`binary_search_by`]: VecDeque::binary_search_by
2519 /// [`partition_point`]: VecDeque::partition_point
2523 /// Looks up a series of four elements in a slice of pairs sorted by
2524 /// their second elements. The first is found, with a uniquely
2525 /// determined position; the second and third are not found; the
2526 /// fourth could match any position in `[1, 4]`.
2529 /// use std::collections::VecDeque;
2531 /// let deque: VecDeque<_> = vec![(0, 0), (2, 1), (4, 1), (5, 1),
2532 /// (3, 1), (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2533 /// (1, 21), (2, 34), (4, 55)].into();
2535 /// assert_eq!(deque.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2536 /// assert_eq!(deque.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2537 /// assert_eq!(deque.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2538 /// let r = deque.binary_search_by_key(&1, |&(a, b)| b);
2539 /// assert!(matches!(r, Ok(1..=4)));
2541 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2543 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2545 F: FnMut(&'a T) -> B,
2548 self.binary_search_by(|k| f(k).cmp(b))
2551 /// Returns the index of the partition point according to the given predicate
2552 /// (the index of the first element of the second partition).
2554 /// The deque is assumed to be partitioned according to the given predicate.
2555 /// This means that all elements for which the predicate returns true are at the start of the deque
2556 /// and all elements for which the predicate returns false are at the end.
2557 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
2558 /// (all odd numbers are at the start, all even at the end).
2560 /// If this deque is not partitioned, the returned result is unspecified and meaningless,
2561 /// as this method performs a kind of binary search.
2563 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
2565 /// [`binary_search`]: VecDeque::binary_search
2566 /// [`binary_search_by`]: VecDeque::binary_search_by
2567 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2572 /// use std::collections::VecDeque;
2574 /// let deque: VecDeque<_> = vec![1, 2, 3, 3, 5, 6, 7].into();
2575 /// let i = deque.partition_point(|&x| x < 5);
2577 /// assert_eq!(i, 4);
2578 /// assert!(deque.iter().take(i).all(|&x| x < 5));
2579 /// assert!(deque.iter().skip(i).all(|&x| !(x < 5)));
2581 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2582 pub fn partition_point<P>(&self, mut pred: P) -> usize
2584 P: FnMut(&T) -> bool,
2586 let (front, back) = self.as_slices();
2588 if let Some(true) = back.first().map(|v| pred(v)) {
2589 back.partition_point(pred) + front.len()
2591 front.partition_point(pred)
2596 impl<T: Clone> VecDeque<T> {
2597 /// Modifies the `VecDeque` in-place so that `len()` is equal to new_len,
2598 /// either by removing excess elements from the back or by appending clones of `value`
2604 /// use std::collections::VecDeque;
2606 /// let mut buf = VecDeque::new();
2607 /// buf.push_back(5);
2608 /// buf.push_back(10);
2609 /// buf.push_back(15);
2610 /// assert_eq!(buf, [5, 10, 15]);
2612 /// buf.resize(2, 0);
2613 /// assert_eq!(buf, [5, 10]);
2615 /// buf.resize(5, 20);
2616 /// assert_eq!(buf, [5, 10, 20, 20, 20]);
2618 #[stable(feature = "deque_extras", since = "1.16.0")]
2619 pub fn resize(&mut self, new_len: usize, value: T) {
2620 self.resize_with(new_len, || value.clone());
2624 /// Returns the index in the underlying buffer for a given logical element index.
2626 fn wrap_index(index: usize, size: usize) -> usize {
2627 // size is always a power of 2
2628 debug_assert!(size.is_power_of_two());
2632 /// Calculate the number of elements left to be read in the buffer
2634 fn count(tail: usize, head: usize, size: usize) -> usize {
2635 // size is always a power of 2
2636 (head.wrapping_sub(tail)) & (size - 1)
2639 #[stable(feature = "rust1", since = "1.0.0")]
2640 impl<A: PartialEq> PartialEq for VecDeque<A> {
2641 fn eq(&self, other: &VecDeque<A>) -> bool {
2642 if self.len() != other.len() {
2645 let (sa, sb) = self.as_slices();
2646 let (oa, ob) = other.as_slices();
2647 if sa.len() == oa.len() {
2648 sa == oa && sb == ob
2649 } else if sa.len() < oa.len() {
2650 // Always divisible in three sections, for example:
2651 // self: [a b c|d e f]
2652 // other: [0 1 2 3|4 5]
2653 // front = 3, mid = 1,
2654 // [a b c] == [0 1 2] && [d] == [3] && [e f] == [4 5]
2655 let front = sa.len();
2656 let mid = oa.len() - front;
2658 let (oa_front, oa_mid) = oa.split_at(front);
2659 let (sb_mid, sb_back) = sb.split_at(mid);
2660 debug_assert_eq!(sa.len(), oa_front.len());
2661 debug_assert_eq!(sb_mid.len(), oa_mid.len());
2662 debug_assert_eq!(sb_back.len(), ob.len());
2663 sa == oa_front && sb_mid == oa_mid && sb_back == ob
2665 let front = oa.len();
2666 let mid = sa.len() - front;
2668 let (sa_front, sa_mid) = sa.split_at(front);
2669 let (ob_mid, ob_back) = ob.split_at(mid);
2670 debug_assert_eq!(sa_front.len(), oa.len());
2671 debug_assert_eq!(sa_mid.len(), ob_mid.len());
2672 debug_assert_eq!(sb.len(), ob_back.len());
2673 sa_front == oa && sa_mid == ob_mid && sb == ob_back
2678 #[stable(feature = "rust1", since = "1.0.0")]
2679 impl<A: Eq> Eq for VecDeque<A> {}
2681 __impl_slice_eq1! { [] VecDeque<A>, Vec<B>, }
2682 __impl_slice_eq1! { [] VecDeque<A>, &[B], }
2683 __impl_slice_eq1! { [] VecDeque<A>, &mut [B], }
2684 __impl_slice_eq1! { [const N: usize] VecDeque<A>, [B; N], }
2685 __impl_slice_eq1! { [const N: usize] VecDeque<A>, &[B; N], }
2686 __impl_slice_eq1! { [const N: usize] VecDeque<A>, &mut [B; N], }
2688 #[stable(feature = "rust1", since = "1.0.0")]
2689 impl<A: PartialOrd> PartialOrd for VecDeque<A> {
2690 fn partial_cmp(&self, other: &VecDeque<A>) -> Option<Ordering> {
2691 self.iter().partial_cmp(other.iter())
2695 #[stable(feature = "rust1", since = "1.0.0")]
2696 impl<A: Ord> Ord for VecDeque<A> {
2698 fn cmp(&self, other: &VecDeque<A>) -> Ordering {
2699 self.iter().cmp(other.iter())
2703 #[stable(feature = "rust1", since = "1.0.0")]
2704 impl<A: Hash> Hash for VecDeque<A> {
2705 fn hash<H: Hasher>(&self, state: &mut H) {
2706 self.len().hash(state);
2707 // It's not possible to use Hash::hash_slice on slices
2708 // returned by as_slices method as their length can vary
2709 // in otherwise identical deques.
2711 // Hasher only guarantees equivalence for the exact same
2712 // set of calls to its methods.
2713 self.iter().for_each(|elem| elem.hash(state));
2717 #[stable(feature = "rust1", since = "1.0.0")]
2718 impl<A> Index<usize> for VecDeque<A> {
2722 fn index(&self, index: usize) -> &A {
2723 self.get(index).expect("Out of bounds access")
2727 #[stable(feature = "rust1", since = "1.0.0")]
2728 impl<A> IndexMut<usize> for VecDeque<A> {
2730 fn index_mut(&mut self, index: usize) -> &mut A {
2731 self.get_mut(index).expect("Out of bounds access")
2735 #[stable(feature = "rust1", since = "1.0.0")]
2736 impl<A> FromIterator<A> for VecDeque<A> {
2737 fn from_iter<T: IntoIterator<Item = A>>(iter: T) -> VecDeque<A> {
2738 let iterator = iter.into_iter();
2739 let (lower, _) = iterator.size_hint();
2740 let mut deq = VecDeque::with_capacity(lower);
2741 deq.extend(iterator);
2746 #[stable(feature = "rust1", since = "1.0.0")]
2747 impl<T> IntoIterator for VecDeque<T> {
2749 type IntoIter = IntoIter<T>;
2751 /// Consumes the `VecDeque` into a front-to-back iterator yielding elements by
2753 fn into_iter(self) -> IntoIter<T> {
2754 IntoIter { inner: self }
2758 #[stable(feature = "rust1", since = "1.0.0")]
2759 impl<'a, T> IntoIterator for &'a VecDeque<T> {
2761 type IntoIter = Iter<'a, T>;
2763 fn into_iter(self) -> Iter<'a, T> {
2768 #[stable(feature = "rust1", since = "1.0.0")]
2769 impl<'a, T> IntoIterator for &'a mut VecDeque<T> {
2770 type Item = &'a mut T;
2771 type IntoIter = IterMut<'a, T>;
2773 fn into_iter(self) -> IterMut<'a, T> {
2778 #[stable(feature = "rust1", since = "1.0.0")]
2779 impl<A> Extend<A> for VecDeque<A> {
2780 fn extend<T: IntoIterator<Item = A>>(&mut self, iter: T) {
2781 // This function should be the moral equivalent of:
2783 // for item in iter.into_iter() {
2784 // self.push_back(item);
2786 let mut iter = iter.into_iter();
2787 while let Some(element) = iter.next() {
2788 if self.len() == self.capacity() {
2789 let (lower, _) = iter.size_hint();
2790 self.reserve(lower.saturating_add(1));
2793 let head = self.head;
2794 self.head = self.wrap_add(self.head, 1);
2796 self.buffer_write(head, element);
2802 fn extend_one(&mut self, elem: A) {
2803 self.push_back(elem);
2807 fn extend_reserve(&mut self, additional: usize) {
2808 self.reserve(additional);
2812 #[stable(feature = "extend_ref", since = "1.2.0")]
2813 impl<'a, T: 'a + Copy> Extend<&'a T> for VecDeque<T> {
2814 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2815 self.extend(iter.into_iter().cloned());
2819 fn extend_one(&mut self, &elem: &T) {
2820 self.push_back(elem);
2824 fn extend_reserve(&mut self, additional: usize) {
2825 self.reserve(additional);
2829 #[stable(feature = "rust1", since = "1.0.0")]
2830 impl<T: fmt::Debug> fmt::Debug for VecDeque<T> {
2831 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2832 f.debug_list().entries(self).finish()
2836 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2837 impl<T> From<Vec<T>> for VecDeque<T> {
2838 /// Turn a [`Vec<T>`] into a [`VecDeque<T>`].
2840 /// [`Vec<T>`]: crate::vec::Vec
2841 /// [`VecDeque<T>`]: crate::collections::VecDeque
2843 /// This avoids reallocating where possible, but the conditions for that are
2844 /// strict, and subject to change, and so shouldn't be relied upon unless the
2845 /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated.
2846 fn from(mut other: Vec<T>) -> Self {
2847 let len = other.len();
2848 if mem::size_of::<T>() == 0 {
2849 // There's no actual allocation for ZSTs to worry about capacity,
2850 // but `VecDeque` can't handle as much length as `Vec`.
2851 assert!(len < MAXIMUM_ZST_CAPACITY, "capacity overflow");
2853 // We need to resize if the capacity is not a power of two, too small or
2854 // doesn't have at least one free space. We do this while it's still in
2855 // the `Vec` so the items will drop on panic.
2856 let min_cap = cmp::max(MINIMUM_CAPACITY, len) + 1;
2857 let cap = cmp::max(min_cap, other.capacity()).next_power_of_two();
2858 if other.capacity() != cap {
2859 other.reserve_exact(cap - len);
2864 let (other_buf, len, capacity) = other.into_raw_parts();
2865 let buf = RawVec::from_raw_parts(other_buf, capacity);
2866 VecDeque { tail: 0, head: len, buf }
2871 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2872 impl<T> From<VecDeque<T>> for Vec<T> {
2873 /// Turn a [`VecDeque<T>`] into a [`Vec<T>`].
2875 /// [`Vec<T>`]: crate::vec::Vec
2876 /// [`VecDeque<T>`]: crate::collections::VecDeque
2878 /// This never needs to re-allocate, but does need to do *O*(*n*) data movement if
2879 /// the circular buffer doesn't happen to be at the beginning of the allocation.
2884 /// use std::collections::VecDeque;
2886 /// // This one is *O*(1).
2887 /// let deque: VecDeque<_> = (1..5).collect();
2888 /// let ptr = deque.as_slices().0.as_ptr();
2889 /// let vec = Vec::from(deque);
2890 /// assert_eq!(vec, [1, 2, 3, 4]);
2891 /// assert_eq!(vec.as_ptr(), ptr);
2893 /// // This one needs data rearranging.
2894 /// let mut deque: VecDeque<_> = (1..5).collect();
2895 /// deque.push_front(9);
2896 /// deque.push_front(8);
2897 /// let ptr = deque.as_slices().1.as_ptr();
2898 /// let vec = Vec::from(deque);
2899 /// assert_eq!(vec, [8, 9, 1, 2, 3, 4]);
2900 /// assert_eq!(vec.as_ptr(), ptr);
2902 fn from(mut other: VecDeque<T>) -> Self {
2903 other.make_contiguous();
2906 let other = ManuallyDrop::new(other);
2907 let buf = other.buf.ptr();
2908 let len = other.len();
2909 let cap = other.cap();
2911 if other.tail != 0 {
2912 ptr::copy(buf.add(other.tail), buf, len);
2914 Vec::from_raw_parts(buf, len, cap)