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::alloc::{Allocator, Global};
21 use crate::collections::TryReserveError;
22 use crate::collections::TryReserveErrorKind;
23 use crate::raw_vec::RawVec;
29 #[stable(feature = "drain", since = "1.6.0")]
30 pub use self::drain::Drain;
34 #[stable(feature = "rust1", since = "1.0.0")]
35 pub use self::iter_mut::IterMut;
39 #[stable(feature = "rust1", since = "1.0.0")]
40 pub use self::into_iter::IntoIter;
44 #[stable(feature = "rust1", since = "1.0.0")]
45 pub use self::iter::Iter;
49 use self::pair_slices::PairSlices;
53 use self::ring_slices::RingSlices;
60 const INITIAL_CAPACITY: usize = 7; // 2^3 - 1
61 const MINIMUM_CAPACITY: usize = 1; // 2 - 1
63 const MAXIMUM_ZST_CAPACITY: usize = 1 << (usize::BITS - 1); // Largest possible power of two
65 /// A double-ended queue implemented with a growable ring buffer.
67 /// The "default" usage of this type as a queue is to use [`push_back`] to add to
68 /// the queue, and [`pop_front`] to remove from the queue. [`extend`] and [`append`]
69 /// push onto the back in this manner, and iterating over `VecDeque` goes front
72 /// A `VecDeque` with a known list of items can be initialized from an array:
75 /// use std::collections::VecDeque;
77 /// let deq = VecDeque::from([-1, 0, 1]);
80 /// Since `VecDeque` is a ring buffer, its elements are not necessarily contiguous
81 /// in memory. If you want to access the elements as a single slice, such as for
82 /// efficient sorting, you can use [`make_contiguous`]. It rotates the `VecDeque`
83 /// so that its elements do not wrap, and returns a mutable slice to the
84 /// now-contiguous element sequence.
86 /// [`push_back`]: VecDeque::push_back
87 /// [`pop_front`]: VecDeque::pop_front
88 /// [`extend`]: VecDeque::extend
89 /// [`append`]: VecDeque::append
90 /// [`make_contiguous`]: VecDeque::make_contiguous
91 #[cfg_attr(not(test), rustc_diagnostic_item = "VecDeque")]
92 #[stable(feature = "rust1", since = "1.0.0")]
93 #[rustc_insignificant_dtor]
96 #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
98 // tail and head are pointers into the buffer. Tail always points
99 // to the first element that could be read, Head always points
100 // to where data should be written.
101 // If tail == head the buffer is empty. The length of the ringbuffer
102 // is defined as the distance between the two.
108 #[stable(feature = "rust1", since = "1.0.0")]
109 impl<T: Clone, A: Allocator + Clone> Clone for VecDeque<T, A> {
110 fn clone(&self) -> Self {
111 let mut deq = Self::with_capacity_in(self.len(), self.allocator().clone());
112 deq.extend(self.iter().cloned());
116 fn clone_from(&mut self, other: &Self) {
117 self.truncate(other.len());
119 let mut iter = PairSlices::from(self, other);
120 while let Some((dst, src)) = iter.next() {
121 dst.clone_from_slice(&src);
124 if iter.has_remainder() {
125 for remainder in iter.remainder() {
126 self.extend(remainder.iter().cloned());
132 #[stable(feature = "rust1", since = "1.0.0")]
133 unsafe impl<#[may_dangle] T, A: Allocator> Drop for VecDeque<T, A> {
135 /// Runs the destructor for all items in the slice when it gets dropped (normally or
136 /// during unwinding).
137 struct Dropper<'a, T>(&'a mut [T]);
139 impl<'a, T> Drop for Dropper<'a, T> {
142 ptr::drop_in_place(self.0);
147 let (front, back) = self.as_mut_slices();
149 let _back_dropper = Dropper(back);
151 ptr::drop_in_place(front);
153 // RawVec handles deallocation
157 #[stable(feature = "rust1", since = "1.0.0")]
158 impl<T> Default for VecDeque<T> {
159 /// Creates an empty `VecDeque<T>`.
161 fn default() -> VecDeque<T> {
166 impl<T, A: Allocator> VecDeque<T, A> {
167 /// Marginally more convenient
169 fn ptr(&self) -> *mut T {
173 /// Marginally more convenient
175 fn cap(&self) -> usize {
176 if mem::size_of::<T>() == 0 {
177 // For zero sized types, we are always at maximum capacity
184 /// Turn ptr into a slice
186 unsafe fn buffer_as_slice(&self) -> &[T] {
187 unsafe { slice::from_raw_parts(self.ptr(), self.cap()) }
190 /// Turn ptr into a mut slice
192 unsafe fn buffer_as_mut_slice(&mut self) -> &mut [T] {
193 unsafe { slice::from_raw_parts_mut(self.ptr(), self.cap()) }
196 /// Moves an element out of the buffer
198 unsafe fn buffer_read(&mut self, off: usize) -> T {
199 unsafe { ptr::read(self.ptr().add(off)) }
202 /// Writes an element into the buffer, moving it.
204 unsafe fn buffer_write(&mut self, off: usize, value: T) {
206 ptr::write(self.ptr().add(off), value);
210 /// Returns `true` if the buffer is at full capacity.
212 fn is_full(&self) -> bool {
213 self.cap() - self.len() == 1
216 /// Returns the index in the underlying buffer for a given logical element
219 fn wrap_index(&self, idx: usize) -> usize {
220 wrap_index(idx, self.cap())
223 /// Returns the index in the underlying buffer for a given logical element
226 fn wrap_add(&self, idx: usize, addend: usize) -> usize {
227 wrap_index(idx.wrapping_add(addend), self.cap())
230 /// Returns the index in the underlying buffer for a given logical element
231 /// index - subtrahend.
233 fn wrap_sub(&self, idx: usize, subtrahend: usize) -> usize {
234 wrap_index(idx.wrapping_sub(subtrahend), self.cap())
237 /// Copies a contiguous block of memory len long from src to dst
239 unsafe fn copy(&self, dst: usize, src: usize, len: usize) {
241 dst + len <= self.cap(),
242 "cpy dst={} src={} len={} cap={}",
249 src + len <= self.cap(),
250 "cpy dst={} src={} len={} cap={}",
257 ptr::copy(self.ptr().add(src), self.ptr().add(dst), len);
261 /// Copies a contiguous block of memory len long from src to dst
263 unsafe fn copy_nonoverlapping(&self, dst: usize, src: usize, len: usize) {
265 dst + len <= self.cap(),
266 "cno dst={} src={} len={} cap={}",
273 src + len <= self.cap(),
274 "cno dst={} src={} len={} cap={}",
281 ptr::copy_nonoverlapping(self.ptr().add(src), self.ptr().add(dst), len);
285 /// Copies a potentially wrapping block of memory len long from src to dest.
286 /// (abs(dst - src) + len) must be no larger than cap() (There must be at
287 /// most one continuous overlapping region between src and dest).
288 unsafe fn wrap_copy(&self, dst: usize, src: usize, len: usize) {
290 fn diff(a: usize, b: usize) -> usize {
291 if a <= b { b - a } else { a - b }
294 cmp::min(diff(dst, src), self.cap() - diff(dst, src)) + len <= self.cap(),
295 "wrc dst={} src={} len={} cap={}",
302 if src == dst || len == 0 {
306 let dst_after_src = self.wrap_sub(dst, src) < len;
308 let src_pre_wrap_len = self.cap() - src;
309 let dst_pre_wrap_len = self.cap() - dst;
310 let src_wraps = src_pre_wrap_len < len;
311 let dst_wraps = dst_pre_wrap_len < len;
313 match (dst_after_src, src_wraps, dst_wraps) {
314 (_, false, false) => {
315 // src doesn't wrap, dst doesn't wrap
318 // 1 [_ _ A A B B C C _]
319 // 2 [_ _ A A A A B B _]
323 self.copy(dst, src, len);
326 (false, false, true) => {
327 // dst before src, src doesn't wrap, dst wraps
330 // 1 [A A B B _ _ _ C C]
331 // 2 [A A B B _ _ _ A A]
332 // 3 [B B B B _ _ _ A A]
336 self.copy(dst, src, dst_pre_wrap_len);
337 self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len);
340 (true, false, true) => {
341 // src before dst, src doesn't wrap, dst wraps
344 // 1 [C C _ _ _ A A B B]
345 // 2 [B B _ _ _ A A B B]
346 // 3 [B B _ _ _ A A A A]
350 self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len);
351 self.copy(dst, src, dst_pre_wrap_len);
354 (false, true, false) => {
355 // dst before src, src wraps, dst doesn't wrap
358 // 1 [C C _ _ _ A A B B]
359 // 2 [C C _ _ _ B B B B]
360 // 3 [C C _ _ _ B B C C]
364 self.copy(dst, src, src_pre_wrap_len);
365 self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len);
368 (true, true, false) => {
369 // src before dst, src wraps, dst doesn't wrap
372 // 1 [A A B B _ _ _ C C]
373 // 2 [A A A A _ _ _ C C]
374 // 3 [C C A A _ _ _ C C]
378 self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len);
379 self.copy(dst, src, src_pre_wrap_len);
382 (false, true, true) => {
383 // dst before src, src wraps, dst wraps
386 // 1 [A B C D _ E F G H]
387 // 2 [A B C D _ E G H H]
388 // 3 [A B C D _ E G H A]
389 // 4 [B C C D _ E G H A]
392 debug_assert!(dst_pre_wrap_len > src_pre_wrap_len);
393 let delta = dst_pre_wrap_len - src_pre_wrap_len;
395 self.copy(dst, src, src_pre_wrap_len);
396 self.copy(dst + src_pre_wrap_len, 0, delta);
397 self.copy(0, delta, len - dst_pre_wrap_len);
400 (true, true, true) => {
401 // src before dst, src wraps, dst wraps
404 // 1 [A B C D _ E F G H]
405 // 2 [A A B D _ E F G H]
406 // 3 [H A B D _ E F G H]
407 // 4 [H A B D _ E F F G]
410 debug_assert!(src_pre_wrap_len > dst_pre_wrap_len);
411 let delta = src_pre_wrap_len - dst_pre_wrap_len;
413 self.copy(delta, 0, len - src_pre_wrap_len);
414 self.copy(0, self.cap() - delta, delta);
415 self.copy(dst, src, dst_pre_wrap_len);
421 /// Frobs the head and tail sections around to handle the fact that we
422 /// just reallocated. Unsafe because it trusts old_capacity.
424 unsafe fn handle_capacity_increase(&mut self, old_capacity: usize) {
425 let new_capacity = self.cap();
427 // Move the shortest contiguous section of the ring buffer
429 // [o o o o o o o . ]
431 // A [o o o o o o o . . . . . . . . . ]
433 // [o o . o o o o o ]
435 // B [. . . o o o o o o o . . . . . . ]
437 // [o o o o o . o o ]
439 // C [o o o o o . . . . . . . . . o o ]
441 if self.tail <= self.head {
444 } else if self.head < old_capacity - self.tail {
447 self.copy_nonoverlapping(old_capacity, 0, self.head);
449 self.head += old_capacity;
450 debug_assert!(self.head > self.tail);
453 let new_tail = new_capacity - (old_capacity - self.tail);
455 self.copy_nonoverlapping(new_tail, self.tail, old_capacity - self.tail);
457 self.tail = new_tail;
458 debug_assert!(self.head < self.tail);
460 debug_assert!(self.head < self.cap());
461 debug_assert!(self.tail < self.cap());
462 debug_assert!(self.cap().count_ones() == 1);
466 impl<T> VecDeque<T> {
467 /// Creates an empty `VecDeque`.
472 /// use std::collections::VecDeque;
474 /// let vector: VecDeque<u32> = VecDeque::new();
477 #[stable(feature = "rust1", since = "1.0.0")]
478 pub fn new() -> VecDeque<T> {
479 VecDeque::new_in(Global)
482 /// Creates an empty `VecDeque` with space for at least `capacity` elements.
487 /// use std::collections::VecDeque;
489 /// let vector: VecDeque<u32> = VecDeque::with_capacity(10);
492 #[stable(feature = "rust1", since = "1.0.0")]
493 pub fn with_capacity(capacity: usize) -> VecDeque<T> {
494 Self::with_capacity_in(capacity, Global)
498 impl<T, A: Allocator> VecDeque<T, A> {
499 /// Creates an empty `VecDeque`.
504 /// use std::collections::VecDeque;
506 /// let vector: VecDeque<u32> = VecDeque::new();
509 #[unstable(feature = "allocator_api", issue = "32838")]
510 pub fn new_in(alloc: A) -> VecDeque<T, A> {
511 VecDeque::with_capacity_in(INITIAL_CAPACITY, alloc)
514 /// Creates an empty `VecDeque` with space for at least `capacity` elements.
519 /// use std::collections::VecDeque;
521 /// let vector: VecDeque<u32> = VecDeque::with_capacity(10);
523 #[unstable(feature = "allocator_api", issue = "32838")]
524 pub fn with_capacity_in(capacity: usize, alloc: A) -> VecDeque<T, A> {
525 // +1 since the ringbuffer always leaves one space empty
526 let cap = cmp::max(capacity + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
527 assert!(cap > capacity, "capacity overflow");
529 VecDeque { tail: 0, head: 0, buf: RawVec::with_capacity_in(cap, alloc) }
532 /// Provides a reference to the element at the given index.
534 /// Element at index 0 is the front of the queue.
539 /// use std::collections::VecDeque;
541 /// let mut buf = VecDeque::new();
542 /// buf.push_back(3);
543 /// buf.push_back(4);
544 /// buf.push_back(5);
545 /// assert_eq!(buf.get(1), Some(&4));
547 #[stable(feature = "rust1", since = "1.0.0")]
548 pub fn get(&self, index: usize) -> Option<&T> {
549 if index < self.len() {
550 let idx = self.wrap_add(self.tail, index);
551 unsafe { Some(&*self.ptr().add(idx)) }
557 /// Provides a mutable reference to the element at the given index.
559 /// Element at index 0 is the front of the queue.
564 /// use std::collections::VecDeque;
566 /// let mut buf = VecDeque::new();
567 /// buf.push_back(3);
568 /// buf.push_back(4);
569 /// buf.push_back(5);
570 /// if let Some(elem) = buf.get_mut(1) {
574 /// assert_eq!(buf[1], 7);
576 #[stable(feature = "rust1", since = "1.0.0")]
577 pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
578 if index < self.len() {
579 let idx = self.wrap_add(self.tail, index);
580 unsafe { Some(&mut *self.ptr().add(idx)) }
586 /// Swaps elements at indices `i` and `j`.
588 /// `i` and `j` may be equal.
590 /// Element at index 0 is the front of the queue.
594 /// Panics if either index is out of bounds.
599 /// use std::collections::VecDeque;
601 /// let mut buf = VecDeque::new();
602 /// buf.push_back(3);
603 /// buf.push_back(4);
604 /// buf.push_back(5);
605 /// assert_eq!(buf, [3, 4, 5]);
607 /// assert_eq!(buf, [5, 4, 3]);
609 #[stable(feature = "rust1", since = "1.0.0")]
610 pub fn swap(&mut self, i: usize, j: usize) {
611 assert!(i < self.len());
612 assert!(j < self.len());
613 let ri = self.wrap_add(self.tail, i);
614 let rj = self.wrap_add(self.tail, j);
615 unsafe { ptr::swap(self.ptr().add(ri), self.ptr().add(rj)) }
618 /// Returns the number of elements the `VecDeque` can hold without
624 /// use std::collections::VecDeque;
626 /// let buf: VecDeque<i32> = VecDeque::with_capacity(10);
627 /// assert!(buf.capacity() >= 10);
630 #[stable(feature = "rust1", since = "1.0.0")]
631 pub fn capacity(&self) -> usize {
635 /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
636 /// given `VecDeque`. Does nothing if the capacity is already sufficient.
638 /// Note that the allocator may give the collection more space than it requests. Therefore
639 /// capacity can not be relied upon to be precisely minimal. Prefer [`reserve`] if future
640 /// insertions are expected.
644 /// Panics if the new capacity overflows `usize`.
649 /// use std::collections::VecDeque;
651 /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
652 /// buf.reserve_exact(10);
653 /// assert!(buf.capacity() >= 11);
656 /// [`reserve`]: VecDeque::reserve
657 #[stable(feature = "rust1", since = "1.0.0")]
658 pub fn reserve_exact(&mut self, additional: usize) {
659 self.reserve(additional);
662 /// Reserves capacity for at least `additional` more elements to be inserted in the given
663 /// `VecDeque`. The collection may reserve more space to avoid frequent reallocations.
667 /// Panics if the new capacity overflows `usize`.
672 /// use std::collections::VecDeque;
674 /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
676 /// assert!(buf.capacity() >= 11);
678 #[stable(feature = "rust1", since = "1.0.0")]
679 pub fn reserve(&mut self, additional: usize) {
680 let old_cap = self.cap();
681 let used_cap = self.len() + 1;
682 let new_cap = used_cap
683 .checked_add(additional)
684 .and_then(|needed_cap| needed_cap.checked_next_power_of_two())
685 .expect("capacity overflow");
687 if new_cap > old_cap {
688 self.buf.reserve_exact(used_cap, new_cap - used_cap);
690 self.handle_capacity_increase(old_cap);
695 /// Tries to reserve the minimum capacity for exactly `additional` more elements to
696 /// be inserted in the given `VecDeque<T>`. After calling `try_reserve_exact`,
697 /// capacity will be greater than or equal to `self.len() + additional`.
698 /// Does nothing if the capacity is already sufficient.
700 /// Note that the allocator may give the collection more space than it
701 /// requests. Therefore, capacity can not be relied upon to be precisely
702 /// minimal. Prefer [`reserve`] if future insertions are expected.
704 /// [`reserve`]: VecDeque::reserve
708 /// If the capacity overflows `usize`, or the allocator reports a failure, then an error
714 /// #![feature(try_reserve)]
715 /// use std::collections::TryReserveError;
716 /// use std::collections::VecDeque;
718 /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> {
719 /// let mut output = VecDeque::new();
721 /// // Pre-reserve the memory, exiting if we can't
722 /// output.try_reserve_exact(data.len())?;
724 /// // Now we know this can't OOM(Out-Of-Memory) in the middle of our complex work
725 /// output.extend(data.iter().map(|&val| {
726 /// val * 2 + 5 // very complicated
731 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
733 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
734 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
735 self.try_reserve(additional)
738 /// Tries to reserve capacity for at least `additional` more elements to be inserted
739 /// in the given `VecDeque<T>`. The collection may reserve more space to avoid
740 /// frequent reallocations. After calling `try_reserve`, capacity will be
741 /// greater than or equal to `self.len() + additional`. Does nothing if
742 /// capacity is already sufficient.
746 /// If the capacity overflows `usize`, or the allocator reports a failure, then an error
752 /// #![feature(try_reserve)]
753 /// use std::collections::TryReserveError;
754 /// use std::collections::VecDeque;
756 /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> {
757 /// let mut output = VecDeque::new();
759 /// // Pre-reserve the memory, exiting if we can't
760 /// output.try_reserve(data.len())?;
762 /// // Now we know this can't OOM in the middle of our complex work
763 /// output.extend(data.iter().map(|&val| {
764 /// val * 2 + 5 // very complicated
769 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
771 #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
772 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
773 let old_cap = self.cap();
774 let used_cap = self.len() + 1;
775 let new_cap = used_cap
776 .checked_add(additional)
777 .and_then(|needed_cap| needed_cap.checked_next_power_of_two())
778 .ok_or(TryReserveErrorKind::CapacityOverflow)?;
780 if new_cap > old_cap {
781 self.buf.try_reserve_exact(used_cap, new_cap - used_cap)?;
783 self.handle_capacity_increase(old_cap);
789 /// Shrinks the capacity of the `VecDeque` as much as possible.
791 /// It will drop down as close as possible to the length but the allocator may still inform the
792 /// `VecDeque` that there is space for a few more elements.
797 /// use std::collections::VecDeque;
799 /// let mut buf = VecDeque::with_capacity(15);
800 /// buf.extend(0..4);
801 /// assert_eq!(buf.capacity(), 15);
802 /// buf.shrink_to_fit();
803 /// assert!(buf.capacity() >= 4);
805 #[stable(feature = "deque_extras_15", since = "1.5.0")]
806 pub fn shrink_to_fit(&mut self) {
810 /// Shrinks the capacity of the `VecDeque` with a lower bound.
812 /// The capacity will remain at least as large as both the length
813 /// and the supplied value.
815 /// If the current capacity is less than the lower limit, this is a no-op.
820 /// use std::collections::VecDeque;
822 /// let mut buf = VecDeque::with_capacity(15);
823 /// buf.extend(0..4);
824 /// assert_eq!(buf.capacity(), 15);
825 /// buf.shrink_to(6);
826 /// assert!(buf.capacity() >= 6);
827 /// buf.shrink_to(0);
828 /// assert!(buf.capacity() >= 4);
830 #[stable(feature = "shrink_to", since = "1.56.0")]
831 pub fn shrink_to(&mut self, min_capacity: usize) {
832 let min_capacity = cmp::min(min_capacity, self.capacity());
833 // We don't have to worry about an overflow as neither `self.len()` nor `self.capacity()`
834 // can ever be `usize::MAX`. +1 as the ringbuffer always leaves one space empty.
835 let target_cap = cmp::max(cmp::max(min_capacity, self.len()) + 1, MINIMUM_CAPACITY + 1)
836 .next_power_of_two();
838 if target_cap < self.cap() {
839 // There are three cases of interest:
840 // All elements are out of desired bounds
841 // Elements are contiguous, and head is out of desired bounds
842 // Elements are discontiguous, and tail is out of desired bounds
844 // At all other times, element positions are unaffected.
846 // Indicates that elements at the head should be moved.
847 let head_outside = self.head == 0 || self.head >= target_cap;
848 // Move elements from out of desired bounds (positions after target_cap)
849 if self.tail >= target_cap && head_outside {
851 // [. . . . . . . . o o o o o o o . ]
853 // [o o o o o o o . ]
855 self.copy_nonoverlapping(0, self.tail, self.len());
857 self.head = self.len();
859 } else if self.tail != 0 && self.tail < target_cap && head_outside {
861 // [. . . o o o o o o o . . . . . . ]
863 // [o o . o o o o o ]
864 let len = self.wrap_sub(self.head, target_cap);
866 self.copy_nonoverlapping(0, target_cap, len);
869 debug_assert!(self.head < self.tail);
870 } else if self.tail >= target_cap {
872 // [o o o o o . . . . . . . . . o o ]
874 // [o o o o o . o o ]
875 debug_assert!(self.wrap_sub(self.head, 1) < target_cap);
876 let len = self.cap() - self.tail;
877 let new_tail = target_cap - len;
879 self.copy_nonoverlapping(new_tail, self.tail, len);
881 self.tail = new_tail;
882 debug_assert!(self.head < self.tail);
885 self.buf.shrink_to_fit(target_cap);
887 debug_assert!(self.head < self.cap());
888 debug_assert!(self.tail < self.cap());
889 debug_assert!(self.cap().count_ones() == 1);
893 /// Shortens the `VecDeque`, keeping the first `len` elements and dropping
896 /// If `len` is greater than the `VecDeque`'s current length, this has no
902 /// use std::collections::VecDeque;
904 /// let mut buf = VecDeque::new();
905 /// buf.push_back(5);
906 /// buf.push_back(10);
907 /// buf.push_back(15);
908 /// assert_eq!(buf, [5, 10, 15]);
910 /// assert_eq!(buf, [5]);
912 #[stable(feature = "deque_extras", since = "1.16.0")]
913 pub fn truncate(&mut self, len: usize) {
914 /// Runs the destructor for all items in the slice when it gets dropped (normally or
915 /// during unwinding).
916 struct Dropper<'a, T>(&'a mut [T]);
918 impl<'a, T> Drop for Dropper<'a, T> {
921 ptr::drop_in_place(self.0);
928 // * Any slice passed to `drop_in_place` is valid; the second case has
929 // `len <= front.len()` and returning on `len > self.len()` ensures
930 // `begin <= back.len()` in the first case
931 // * The head of the VecDeque is moved before calling `drop_in_place`,
932 // so no value is dropped twice if `drop_in_place` panics
934 if len > self.len() {
937 let num_dropped = self.len() - len;
938 let (front, back) = self.as_mut_slices();
939 if len > front.len() {
940 let begin = len - front.len();
941 let drop_back = back.get_unchecked_mut(begin..) as *mut _;
942 self.head = self.wrap_sub(self.head, num_dropped);
943 ptr::drop_in_place(drop_back);
945 let drop_back = back as *mut _;
946 let drop_front = front.get_unchecked_mut(len..) as *mut _;
947 self.head = self.wrap_sub(self.head, num_dropped);
949 // Make sure the second half is dropped even when a destructor
950 // in the first one panics.
951 let _back_dropper = Dropper(&mut *drop_back);
952 ptr::drop_in_place(drop_front);
957 /// Returns a reference to the underlying allocator.
958 #[unstable(feature = "allocator_api", issue = "32838")]
960 pub fn allocator(&self) -> &A {
964 /// Returns a front-to-back iterator.
969 /// use std::collections::VecDeque;
971 /// let mut buf = VecDeque::new();
972 /// buf.push_back(5);
973 /// buf.push_back(3);
974 /// buf.push_back(4);
975 /// let b: &[_] = &[&5, &3, &4];
976 /// let c: Vec<&i32> = buf.iter().collect();
977 /// assert_eq!(&c[..], b);
979 #[stable(feature = "rust1", since = "1.0.0")]
980 pub fn iter(&self) -> Iter<'_, T> {
981 Iter { tail: self.tail, head: self.head, ring: unsafe { self.buffer_as_slice() } }
984 /// Returns a front-to-back iterator that returns mutable references.
989 /// use std::collections::VecDeque;
991 /// let mut buf = VecDeque::new();
992 /// buf.push_back(5);
993 /// buf.push_back(3);
994 /// buf.push_back(4);
995 /// for num in buf.iter_mut() {
998 /// let b: &[_] = &[&mut 3, &mut 1, &mut 2];
999 /// assert_eq!(&buf.iter_mut().collect::<Vec<&mut i32>>()[..], b);
1001 #[stable(feature = "rust1", since = "1.0.0")]
1002 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
1003 // SAFETY: The internal `IterMut` safety invariant is established because the
1004 // `ring` we create is a dereferencable slice for lifetime '_.
1008 ring: ptr::slice_from_raw_parts_mut(self.ptr(), self.cap()),
1009 phantom: PhantomData,
1013 /// Returns a pair of slices which contain, in order, the contents of the
1016 /// If [`make_contiguous`] was previously called, all elements of the
1017 /// `VecDeque` will be in the first slice and the second slice will be empty.
1019 /// [`make_contiguous`]: VecDeque::make_contiguous
1024 /// use std::collections::VecDeque;
1026 /// let mut vector = VecDeque::new();
1028 /// vector.push_back(0);
1029 /// vector.push_back(1);
1030 /// vector.push_back(2);
1032 /// assert_eq!(vector.as_slices(), (&[0, 1, 2][..], &[][..]));
1034 /// vector.push_front(10);
1035 /// vector.push_front(9);
1037 /// assert_eq!(vector.as_slices(), (&[9, 10][..], &[0, 1, 2][..]));
1040 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1041 pub fn as_slices(&self) -> (&[T], &[T]) {
1043 let buf = self.buffer_as_slice();
1044 RingSlices::ring_slices(buf, self.head, self.tail)
1048 /// Returns a pair of slices which contain, in order, the contents of the
1051 /// If [`make_contiguous`] was previously called, all elements of the
1052 /// `VecDeque` will be in the first slice and the second slice will be empty.
1054 /// [`make_contiguous`]: VecDeque::make_contiguous
1059 /// use std::collections::VecDeque;
1061 /// let mut vector = VecDeque::new();
1063 /// vector.push_back(0);
1064 /// vector.push_back(1);
1066 /// vector.push_front(10);
1067 /// vector.push_front(9);
1069 /// vector.as_mut_slices().0[0] = 42;
1070 /// vector.as_mut_slices().1[0] = 24;
1071 /// assert_eq!(vector.as_slices(), (&[42, 10][..], &[24, 1][..]));
1074 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1075 pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) {
1077 let head = self.head;
1078 let tail = self.tail;
1079 let buf = self.buffer_as_mut_slice();
1080 RingSlices::ring_slices(buf, head, tail)
1084 /// Returns the number of elements in the `VecDeque`.
1089 /// use std::collections::VecDeque;
1091 /// let mut v = VecDeque::new();
1092 /// assert_eq!(v.len(), 0);
1094 /// assert_eq!(v.len(), 1);
1096 #[stable(feature = "rust1", since = "1.0.0")]
1097 pub fn len(&self) -> usize {
1098 count(self.tail, self.head, self.cap())
1101 /// Returns `true` if the `VecDeque` is empty.
1106 /// use std::collections::VecDeque;
1108 /// let mut v = VecDeque::new();
1109 /// assert!(v.is_empty());
1110 /// v.push_front(1);
1111 /// assert!(!v.is_empty());
1113 #[stable(feature = "rust1", since = "1.0.0")]
1114 pub fn is_empty(&self) -> bool {
1115 self.tail == self.head
1118 fn range_tail_head<R>(&self, range: R) -> (usize, usize)
1120 R: RangeBounds<usize>,
1122 let Range { start, end } = slice::range(range, ..self.len());
1123 let tail = self.wrap_add(self.tail, start);
1124 let head = self.wrap_add(self.tail, end);
1128 /// Creates an iterator that covers the specified range in the `VecDeque`.
1132 /// Panics if the starting point is greater than the end point or if
1133 /// the end point is greater than the length of the vector.
1138 /// use std::collections::VecDeque;
1140 /// let v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1141 /// let range = v.range(2..).copied().collect::<VecDeque<_>>();
1142 /// assert_eq!(range, [3]);
1144 /// // A full range covers all contents
1145 /// let all = v.range(..);
1146 /// assert_eq!(all.len(), 3);
1149 #[stable(feature = "deque_range", since = "1.51.0")]
1150 pub fn range<R>(&self, range: R) -> Iter<'_, T>
1152 R: RangeBounds<usize>,
1154 let (tail, head) = self.range_tail_head(range);
1158 // The shared reference we have in &self is maintained in the '_ of Iter.
1159 ring: unsafe { self.buffer_as_slice() },
1163 /// Creates an iterator that covers the specified mutable range in the `VecDeque`.
1167 /// Panics if the starting point is greater than the end point or if
1168 /// the end point is greater than the length of the vector.
1173 /// use std::collections::VecDeque;
1175 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1176 /// for v in v.range_mut(2..) {
1179 /// assert_eq!(v, vec![1, 2, 6]);
1181 /// // A full range covers all contents
1182 /// for v in v.range_mut(..) {
1185 /// assert_eq!(v, vec![2, 4, 12]);
1188 #[stable(feature = "deque_range", since = "1.51.0")]
1189 pub fn range_mut<R>(&mut self, range: R) -> IterMut<'_, T>
1191 R: RangeBounds<usize>,
1193 let (tail, head) = self.range_tail_head(range);
1195 // SAFETY: The internal `IterMut` safety invariant is established because the
1196 // `ring` we create is a dereferencable slice for lifetime '_.
1200 ring: ptr::slice_from_raw_parts_mut(self.ptr(), self.cap()),
1201 phantom: PhantomData,
1205 /// Creates a draining iterator that removes the specified range in the
1206 /// `VecDeque` and yields the removed items.
1208 /// Note 1: The element range is removed even if the iterator is not
1209 /// consumed until the end.
1211 /// Note 2: It is unspecified how many elements are removed from the deque,
1212 /// if the `Drain` value is not dropped, but the borrow it holds expires
1213 /// (e.g., due to `mem::forget`).
1217 /// Panics if the starting point is greater than the end point or if
1218 /// the end point is greater than the length of the vector.
1223 /// use std::collections::VecDeque;
1225 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1226 /// let drained = v.drain(2..).collect::<VecDeque<_>>();
1227 /// assert_eq!(drained, [3]);
1228 /// assert_eq!(v, [1, 2]);
1230 /// // A full range clears all contents
1232 /// assert!(v.is_empty());
1235 #[stable(feature = "drain", since = "1.6.0")]
1236 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1238 R: RangeBounds<usize>,
1242 // When the Drain is first created, the source deque is shortened to
1243 // make sure no uninitialized or moved-from elements are accessible at
1244 // all if the Drain's destructor never gets to run.
1246 // Drain will ptr::read out the values to remove.
1247 // When finished, the remaining data will be copied back to cover the hole,
1248 // and the head/tail values will be restored correctly.
1250 let (drain_tail, drain_head) = self.range_tail_head(range);
1252 // The deque's elements are parted into three segments:
1253 // * self.tail -> drain_tail
1254 // * drain_tail -> drain_head
1255 // * drain_head -> self.head
1257 // T = self.tail; H = self.head; t = drain_tail; h = drain_head
1259 // We store drain_tail as self.head, and drain_head and self.head as
1260 // after_tail and after_head respectively on the Drain. This also
1261 // truncates the effective array such that if the Drain is leaked, we
1262 // have forgotten about the potentially moved values after the start of
1266 // [. . . o o x x o o . . .]
1268 let head = self.head;
1270 // "forget" about the values after the start of the drain until after
1271 // the drain is complete and the Drain destructor is run.
1272 self.head = drain_tail;
1275 deque: NonNull::from(&mut *self),
1276 after_tail: drain_head,
1281 // Crucially, we only create shared references from `self` here and read from
1282 // it. We do not write to `self` nor reborrow to a mutable reference.
1283 // Hence the raw pointer we created above, for `deque`, remains valid.
1284 ring: unsafe { self.buffer_as_slice() },
1289 /// Clears the `VecDeque`, removing all values.
1294 /// use std::collections::VecDeque;
1296 /// let mut v = VecDeque::new();
1299 /// assert!(v.is_empty());
1301 #[stable(feature = "rust1", since = "1.0.0")]
1303 pub fn clear(&mut self) {
1307 /// Returns `true` if the `VecDeque` contains an element equal to the
1313 /// use std::collections::VecDeque;
1315 /// let mut vector: VecDeque<u32> = VecDeque::new();
1317 /// vector.push_back(0);
1318 /// vector.push_back(1);
1320 /// assert_eq!(vector.contains(&1), true);
1321 /// assert_eq!(vector.contains(&10), false);
1323 #[stable(feature = "vec_deque_contains", since = "1.12.0")]
1324 pub fn contains(&self, x: &T) -> bool
1328 let (a, b) = self.as_slices();
1329 a.contains(x) || b.contains(x)
1332 /// Provides a reference to the front element, or `None` if the `VecDeque` is
1338 /// use std::collections::VecDeque;
1340 /// let mut d = VecDeque::new();
1341 /// assert_eq!(d.front(), None);
1345 /// assert_eq!(d.front(), Some(&1));
1347 #[stable(feature = "rust1", since = "1.0.0")]
1348 pub fn front(&self) -> Option<&T> {
1352 /// Provides a mutable reference to the front element, or `None` if the
1353 /// `VecDeque` is empty.
1358 /// use std::collections::VecDeque;
1360 /// let mut d = VecDeque::new();
1361 /// assert_eq!(d.front_mut(), None);
1365 /// match d.front_mut() {
1366 /// Some(x) => *x = 9,
1369 /// assert_eq!(d.front(), Some(&9));
1371 #[stable(feature = "rust1", since = "1.0.0")]
1372 pub fn front_mut(&mut self) -> Option<&mut T> {
1376 /// Provides a reference to the back element, or `None` if the `VecDeque` is
1382 /// use std::collections::VecDeque;
1384 /// let mut d = VecDeque::new();
1385 /// assert_eq!(d.back(), None);
1389 /// assert_eq!(d.back(), Some(&2));
1391 #[stable(feature = "rust1", since = "1.0.0")]
1392 pub fn back(&self) -> Option<&T> {
1393 self.get(self.len().wrapping_sub(1))
1396 /// Provides a mutable reference to the back element, or `None` if the
1397 /// `VecDeque` is empty.
1402 /// use std::collections::VecDeque;
1404 /// let mut d = VecDeque::new();
1405 /// assert_eq!(d.back(), None);
1409 /// match d.back_mut() {
1410 /// Some(x) => *x = 9,
1413 /// assert_eq!(d.back(), Some(&9));
1415 #[stable(feature = "rust1", since = "1.0.0")]
1416 pub fn back_mut(&mut self) -> Option<&mut T> {
1417 self.get_mut(self.len().wrapping_sub(1))
1420 /// Removes the first element and returns it, or `None` if the `VecDeque` is
1426 /// use std::collections::VecDeque;
1428 /// let mut d = VecDeque::new();
1432 /// assert_eq!(d.pop_front(), Some(1));
1433 /// assert_eq!(d.pop_front(), Some(2));
1434 /// assert_eq!(d.pop_front(), None);
1436 #[stable(feature = "rust1", since = "1.0.0")]
1437 pub fn pop_front(&mut self) -> Option<T> {
1438 if self.is_empty() {
1441 let tail = self.tail;
1442 self.tail = self.wrap_add(self.tail, 1);
1443 unsafe { Some(self.buffer_read(tail)) }
1447 /// Removes the last element from the `VecDeque` and returns it, or `None` if
1453 /// use std::collections::VecDeque;
1455 /// let mut buf = VecDeque::new();
1456 /// assert_eq!(buf.pop_back(), None);
1457 /// buf.push_back(1);
1458 /// buf.push_back(3);
1459 /// assert_eq!(buf.pop_back(), Some(3));
1461 #[stable(feature = "rust1", since = "1.0.0")]
1462 pub fn pop_back(&mut self) -> Option<T> {
1463 if self.is_empty() {
1466 self.head = self.wrap_sub(self.head, 1);
1467 let head = self.head;
1468 unsafe { Some(self.buffer_read(head)) }
1472 /// Prepends an element to the `VecDeque`.
1477 /// use std::collections::VecDeque;
1479 /// let mut d = VecDeque::new();
1480 /// d.push_front(1);
1481 /// d.push_front(2);
1482 /// assert_eq!(d.front(), Some(&2));
1484 #[stable(feature = "rust1", since = "1.0.0")]
1485 pub fn push_front(&mut self, value: T) {
1490 self.tail = self.wrap_sub(self.tail, 1);
1491 let tail = self.tail;
1493 self.buffer_write(tail, value);
1497 /// Appends an element to the back of the `VecDeque`.
1502 /// use std::collections::VecDeque;
1504 /// let mut buf = VecDeque::new();
1505 /// buf.push_back(1);
1506 /// buf.push_back(3);
1507 /// assert_eq!(3, *buf.back().unwrap());
1509 #[stable(feature = "rust1", since = "1.0.0")]
1510 pub fn push_back(&mut self, value: T) {
1515 let head = self.head;
1516 self.head = self.wrap_add(self.head, 1);
1517 unsafe { self.buffer_write(head, value) }
1521 fn is_contiguous(&self) -> bool {
1522 // FIXME: Should we consider `head == 0` to mean
1523 // that `self` is contiguous?
1524 self.tail <= self.head
1527 /// Removes an element from anywhere in the `VecDeque` and returns it,
1528 /// replacing it with the first element.
1530 /// This does not preserve ordering, but is *O*(1).
1532 /// Returns `None` if `index` is out of bounds.
1534 /// Element at index 0 is the front of the queue.
1539 /// use std::collections::VecDeque;
1541 /// let mut buf = VecDeque::new();
1542 /// assert_eq!(buf.swap_remove_front(0), None);
1543 /// buf.push_back(1);
1544 /// buf.push_back(2);
1545 /// buf.push_back(3);
1546 /// assert_eq!(buf, [1, 2, 3]);
1548 /// assert_eq!(buf.swap_remove_front(2), Some(3));
1549 /// assert_eq!(buf, [2, 1]);
1551 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1552 pub fn swap_remove_front(&mut self, index: usize) -> Option<T> {
1553 let length = self.len();
1554 if length > 0 && index < length && index != 0 {
1555 self.swap(index, 0);
1556 } else if index >= length {
1562 /// Removes an element from anywhere in the `VecDeque` and returns it, replacing it with the
1565 /// This does not preserve ordering, but is *O*(1).
1567 /// Returns `None` if `index` is out of bounds.
1569 /// Element at index 0 is the front of the queue.
1574 /// use std::collections::VecDeque;
1576 /// let mut buf = VecDeque::new();
1577 /// assert_eq!(buf.swap_remove_back(0), None);
1578 /// buf.push_back(1);
1579 /// buf.push_back(2);
1580 /// buf.push_back(3);
1581 /// assert_eq!(buf, [1, 2, 3]);
1583 /// assert_eq!(buf.swap_remove_back(0), Some(1));
1584 /// assert_eq!(buf, [3, 2]);
1586 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1587 pub fn swap_remove_back(&mut self, index: usize) -> Option<T> {
1588 let length = self.len();
1589 if length > 0 && index < length - 1 {
1590 self.swap(index, length - 1);
1591 } else if index >= length {
1597 /// Inserts an element at `index` within the `VecDeque`, shifting all elements with indices
1598 /// greater than or equal to `index` towards the back.
1600 /// Element at index 0 is the front of the queue.
1604 /// Panics if `index` is greater than `VecDeque`'s length
1609 /// use std::collections::VecDeque;
1611 /// let mut vec_deque = VecDeque::new();
1612 /// vec_deque.push_back('a');
1613 /// vec_deque.push_back('b');
1614 /// vec_deque.push_back('c');
1615 /// assert_eq!(vec_deque, &['a', 'b', 'c']);
1617 /// vec_deque.insert(1, 'd');
1618 /// assert_eq!(vec_deque, &['a', 'd', 'b', 'c']);
1620 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1621 pub fn insert(&mut self, index: usize, value: T) {
1622 assert!(index <= self.len(), "index out of bounds");
1627 // Move the least number of elements in the ring buffer and insert
1630 // At most len/2 - 1 elements will be moved. O(min(n, n-i))
1632 // There are three main cases:
1633 // Elements are contiguous
1634 // - special case when tail is 0
1635 // Elements are discontiguous and the insert is in the tail section
1636 // Elements are discontiguous and the insert is in the head section
1638 // For each of those there are two more cases:
1639 // Insert is closer to tail
1640 // Insert is closer to head
1642 // Key: H - self.head
1644 // o - Valid element
1645 // I - Insertion element
1646 // A - The element that should be after the insertion point
1647 // M - Indicates element was moved
1649 let idx = self.wrap_add(self.tail, index);
1651 let distance_to_tail = index;
1652 let distance_to_head = self.len() - index;
1654 let contiguous = self.is_contiguous();
1656 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1657 (true, true, _) if index == 0 => {
1662 // [A o o o o o o . . . . . . . . .]
1665 // [A o o o o o o o . . . . . I]
1668 self.tail = self.wrap_sub(self.tail, 1);
1670 (true, true, _) => {
1672 // contiguous, insert closer to tail:
1675 // [. . . o o A o o o o . . . . . .]
1678 // [. . o o I A o o o o . . . . . .]
1681 // contiguous, insert closer to tail and tail is 0:
1685 // [o o A o o o o . . . . . . . . .]
1688 // [o I A o o o o o . . . . . . . o]
1691 let new_tail = self.wrap_sub(self.tail, 1);
1693 self.copy(new_tail, self.tail, 1);
1694 // Already moved the tail, so we only copy `index - 1` elements.
1695 self.copy(self.tail, self.tail + 1, index - 1);
1697 self.tail = new_tail;
1700 (true, false, _) => {
1702 // contiguous, insert closer to head:
1705 // [. . . o o o o A o o . . . . . .]
1708 // [. . . o o o o I A o o . . . . .]
1711 self.copy(idx + 1, idx, self.head - idx);
1712 self.head = self.wrap_add(self.head, 1);
1715 (false, true, true) => {
1717 // discontiguous, insert closer to tail, tail section:
1720 // [o o o o o o . . . . . o o A o o]
1723 // [o o o o o o . . . . o o I A o o]
1726 self.copy(self.tail - 1, self.tail, index);
1730 (false, false, true) => {
1732 // discontiguous, insert closer to head, tail section:
1735 // [o o . . . . . . . o o o o o A o]
1738 // [o o o . . . . . . o o o o o I A]
1741 // copy elements up to new head
1742 self.copy(1, 0, self.head);
1744 // copy last element into empty spot at bottom of buffer
1745 self.copy(0, self.cap() - 1, 1);
1747 // move elements from idx to end forward not including ^ element
1748 self.copy(idx + 1, idx, self.cap() - 1 - idx);
1753 (false, true, false) if idx == 0 => {
1755 // discontiguous, insert is closer to tail, head section,
1756 // and is at index zero in the internal buffer:
1759 // [A o o o o o o o o o . . . o o o]
1762 // [A o o o o o o o o o . . o o o I]
1765 // copy elements up to new tail
1766 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1768 // copy last element into empty spot at bottom of buffer
1769 self.copy(self.cap() - 1, 0, 1);
1774 (false, true, false) => {
1776 // discontiguous, insert closer to tail, head section:
1779 // [o o o A o o o o o o . . . o o o]
1782 // [o o I A o o o o o o . . o o o o]
1785 // copy elements up to new tail
1786 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1788 // copy last element into empty spot at bottom of buffer
1789 self.copy(self.cap() - 1, 0, 1);
1791 // move elements from idx-1 to end forward not including ^ element
1792 self.copy(0, 1, idx - 1);
1797 (false, false, false) => {
1799 // discontiguous, insert closer to head, head section:
1802 // [o o o o A o o . . . . . . o o o]
1805 // [o o o o I A o o . . . . . o o o]
1808 self.copy(idx + 1, idx, self.head - idx);
1814 // tail might've been changed so we need to recalculate
1815 let new_idx = self.wrap_add(self.tail, index);
1817 self.buffer_write(new_idx, value);
1821 /// Removes and returns the element at `index` from the `VecDeque`.
1822 /// Whichever end is closer to the removal point will be moved to make
1823 /// room, and all the affected elements will be moved to new positions.
1824 /// Returns `None` if `index` is out of bounds.
1826 /// Element at index 0 is the front of the queue.
1831 /// use std::collections::VecDeque;
1833 /// let mut buf = VecDeque::new();
1834 /// buf.push_back(1);
1835 /// buf.push_back(2);
1836 /// buf.push_back(3);
1837 /// assert_eq!(buf, [1, 2, 3]);
1839 /// assert_eq!(buf.remove(1), Some(2));
1840 /// assert_eq!(buf, [1, 3]);
1842 #[stable(feature = "rust1", since = "1.0.0")]
1843 pub fn remove(&mut self, index: usize) -> Option<T> {
1844 if self.is_empty() || self.len() <= index {
1848 // There are three main cases:
1849 // Elements are contiguous
1850 // Elements are discontiguous and the removal is in the tail section
1851 // Elements are discontiguous and the removal is in the head section
1852 // - special case when elements are technically contiguous,
1853 // but self.head = 0
1855 // For each of those there are two more cases:
1856 // Insert is closer to tail
1857 // Insert is closer to head
1859 // Key: H - self.head
1861 // o - Valid element
1862 // x - Element marked for removal
1863 // R - Indicates element that is being removed
1864 // M - Indicates element was moved
1866 let idx = self.wrap_add(self.tail, index);
1868 let elem = unsafe { Some(self.buffer_read(idx)) };
1870 let distance_to_tail = index;
1871 let distance_to_head = self.len() - index;
1873 let contiguous = self.is_contiguous();
1875 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1876 (true, true, _) => {
1878 // contiguous, remove closer to tail:
1881 // [. . . o o x o o o o . . . . . .]
1884 // [. . . . o o o o o o . . . . . .]
1887 self.copy(self.tail + 1, self.tail, index);
1891 (true, false, _) => {
1893 // contiguous, remove closer to head:
1896 // [. . . o o o o x o o . . . . . .]
1899 // [. . . o o o o o o . . . . . . .]
1902 self.copy(idx, idx + 1, self.head - idx - 1);
1906 (false, true, true) => {
1908 // discontiguous, remove closer to tail, tail section:
1911 // [o o o o o o . . . . . o o x o o]
1914 // [o o o o o o . . . . . . o o o o]
1917 self.copy(self.tail + 1, self.tail, index);
1918 self.tail = self.wrap_add(self.tail, 1);
1921 (false, false, false) => {
1923 // discontiguous, remove closer to head, head section:
1926 // [o o o o x o o . . . . . . o o o]
1929 // [o o o o o o . . . . . . . o o o]
1932 self.copy(idx, idx + 1, self.head - idx - 1);
1936 (false, false, true) => {
1938 // discontiguous, remove closer to head, tail section:
1941 // [o o o . . . . . . o o o o o x o]
1944 // [o o . . . . . . . o o o o o o o]
1947 // or quasi-discontiguous, remove next to head, tail section:
1950 // [. . . . . . . . . o o o o o x o]
1953 // [. . . . . . . . . o o o o o o .]
1956 // draw in elements in the tail section
1957 self.copy(idx, idx + 1, self.cap() - idx - 1);
1959 // Prevents underflow.
1961 // copy first element into empty spot
1962 self.copy(self.cap() - 1, 0, 1);
1964 // move elements in the head section backwards
1965 self.copy(0, 1, self.head - 1);
1968 self.head = self.wrap_sub(self.head, 1);
1971 (false, true, false) => {
1973 // discontiguous, remove closer to tail, head section:
1976 // [o o x o o o o o o o . . . o o o]
1979 // [o o o o o o o o o o . . . . o o]
1982 // draw in elements up to idx
1983 self.copy(1, 0, idx);
1985 // copy last element into empty spot
1986 self.copy(0, self.cap() - 1, 1);
1988 // move elements from tail to end forward, excluding the last one
1989 self.copy(self.tail + 1, self.tail, self.cap() - self.tail - 1);
1991 self.tail = self.wrap_add(self.tail, 1);
1999 /// Splits the `VecDeque` into two at the given index.
2001 /// Returns a newly allocated `VecDeque`. `self` contains elements `[0, at)`,
2002 /// and the returned `VecDeque` contains elements `[at, len)`.
2004 /// Note that the capacity of `self` does not change.
2006 /// Element at index 0 is the front of the queue.
2010 /// Panics if `at > len`.
2015 /// use std::collections::VecDeque;
2017 /// let mut buf: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
2018 /// let buf2 = buf.split_off(1);
2019 /// assert_eq!(buf, [1]);
2020 /// assert_eq!(buf2, [2, 3]);
2023 #[must_use = "use `.truncate()` if you don't need the other half"]
2024 #[stable(feature = "split_off", since = "1.4.0")]
2025 pub fn split_off(&mut self, at: usize) -> Self
2029 let len = self.len();
2030 assert!(at <= len, "`at` out of bounds");
2032 let other_len = len - at;
2033 let mut other = VecDeque::with_capacity_in(other_len, self.allocator().clone());
2036 let (first_half, second_half) = self.as_slices();
2038 let first_len = first_half.len();
2039 let second_len = second_half.len();
2041 // `at` lies in the first half.
2042 let amount_in_first = first_len - at;
2044 ptr::copy_nonoverlapping(first_half.as_ptr().add(at), other.ptr(), amount_in_first);
2046 // just take all of the second half.
2047 ptr::copy_nonoverlapping(
2048 second_half.as_ptr(),
2049 other.ptr().add(amount_in_first),
2053 // `at` lies in the second half, need to factor in the elements we skipped
2054 // in the first half.
2055 let offset = at - first_len;
2056 let amount_in_second = second_len - offset;
2057 ptr::copy_nonoverlapping(
2058 second_half.as_ptr().add(offset),
2065 // Cleanup where the ends of the buffers are
2066 self.head = self.wrap_sub(self.head, other_len);
2067 other.head = other.wrap_index(other_len);
2072 /// Moves all the elements of `other` into `self`, leaving `other` empty.
2076 /// Panics if the new number of elements in self overflows a `usize`.
2081 /// use std::collections::VecDeque;
2083 /// let mut buf: VecDeque<_> = vec![1, 2].into_iter().collect();
2084 /// let mut buf2: VecDeque<_> = vec![3, 4].into_iter().collect();
2085 /// buf.append(&mut buf2);
2086 /// assert_eq!(buf, [1, 2, 3, 4]);
2087 /// assert_eq!(buf2, []);
2090 #[stable(feature = "append", since = "1.4.0")]
2091 pub fn append(&mut self, other: &mut Self) {
2093 self.extend(other.drain(..));
2096 /// Retains only the elements specified by the predicate.
2098 /// In other words, remove all elements `e` such that `f(&e)` returns false.
2099 /// This method operates in place, visiting each element exactly once in the
2100 /// original order, and preserves the order of the retained elements.
2105 /// use std::collections::VecDeque;
2107 /// let mut buf = VecDeque::new();
2108 /// buf.extend(1..5);
2109 /// buf.retain(|&x| x % 2 == 0);
2110 /// assert_eq!(buf, [2, 4]);
2113 /// Because the elements are visited exactly once in the original order,
2114 /// external state may be used to decide which elements to keep.
2117 /// use std::collections::VecDeque;
2119 /// let mut buf = VecDeque::new();
2120 /// buf.extend(1..6);
2122 /// let keep = [false, true, true, false, true];
2123 /// let mut iter = keep.iter();
2124 /// buf.retain(|_| *iter.next().unwrap());
2125 /// assert_eq!(buf, [2, 3, 5]);
2127 #[stable(feature = "vec_deque_retain", since = "1.4.0")]
2128 pub fn retain<F>(&mut self, mut f: F)
2130 F: FnMut(&T) -> bool,
2132 let len = self.len();
2136 // Stage 1: All values are retained.
2145 // Stage 2: Swap retained value into current idx.
2152 self.swap(idx, cur);
2156 // Stage 3: Trancate all values after idx.
2162 // This may panic or abort
2164 fn grow(&mut self) {
2166 let old_cap = self.cap();
2167 // Double the buffer size.
2168 self.buf.reserve_exact(old_cap, old_cap);
2169 assert!(self.cap() == old_cap * 2);
2171 self.handle_capacity_increase(old_cap);
2173 debug_assert!(!self.is_full());
2177 /// Modifies the `VecDeque` in-place so that `len()` is equal to `new_len`,
2178 /// either by removing excess elements from the back or by appending
2179 /// elements generated by calling `generator` to the back.
2184 /// use std::collections::VecDeque;
2186 /// let mut buf = VecDeque::new();
2187 /// buf.push_back(5);
2188 /// buf.push_back(10);
2189 /// buf.push_back(15);
2190 /// assert_eq!(buf, [5, 10, 15]);
2192 /// buf.resize_with(5, Default::default);
2193 /// assert_eq!(buf, [5, 10, 15, 0, 0]);
2195 /// buf.resize_with(2, || unreachable!());
2196 /// assert_eq!(buf, [5, 10]);
2198 /// let mut state = 100;
2199 /// buf.resize_with(5, || { state += 1; state });
2200 /// assert_eq!(buf, [5, 10, 101, 102, 103]);
2202 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2203 pub fn resize_with(&mut self, new_len: usize, generator: impl FnMut() -> T) {
2204 let len = self.len();
2207 self.extend(repeat_with(generator).take(new_len - len))
2209 self.truncate(new_len);
2213 /// Rearranges the internal storage of this deque so it is one contiguous
2214 /// slice, which is then returned.
2216 /// This method does not allocate and does not change the order of the
2217 /// inserted elements. As it returns a mutable slice, this can be used to
2220 /// Once the internal storage is contiguous, the [`as_slices`] and
2221 /// [`as_mut_slices`] methods will return the entire contents of the
2222 /// `VecDeque` in a single slice.
2224 /// [`as_slices`]: VecDeque::as_slices
2225 /// [`as_mut_slices`]: VecDeque::as_mut_slices
2229 /// Sorting the content of a deque.
2232 /// use std::collections::VecDeque;
2234 /// let mut buf = VecDeque::with_capacity(15);
2236 /// buf.push_back(2);
2237 /// buf.push_back(1);
2238 /// buf.push_front(3);
2240 /// // sorting the deque
2241 /// buf.make_contiguous().sort();
2242 /// assert_eq!(buf.as_slices(), (&[1, 2, 3] as &[_], &[] as &[_]));
2244 /// // sorting it in reverse order
2245 /// buf.make_contiguous().sort_by(|a, b| b.cmp(a));
2246 /// assert_eq!(buf.as_slices(), (&[3, 2, 1] as &[_], &[] as &[_]));
2249 /// Getting immutable access to the contiguous slice.
2252 /// use std::collections::VecDeque;
2254 /// let mut buf = VecDeque::new();
2256 /// buf.push_back(2);
2257 /// buf.push_back(1);
2258 /// buf.push_front(3);
2260 /// buf.make_contiguous();
2261 /// if let (slice, &[]) = buf.as_slices() {
2262 /// // we can now be sure that `slice` contains all elements of the deque,
2263 /// // while still having immutable access to `buf`.
2264 /// assert_eq!(buf.len(), slice.len());
2265 /// assert_eq!(slice, &[3, 2, 1] as &[_]);
2268 #[stable(feature = "deque_make_contiguous", since = "1.48.0")]
2269 pub fn make_contiguous(&mut self) -> &mut [T] {
2270 if self.is_contiguous() {
2271 let tail = self.tail;
2272 let head = self.head;
2273 return unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 };
2276 let buf = self.buf.ptr();
2277 let cap = self.cap();
2278 let len = self.len();
2280 let free = self.tail - self.head;
2281 let tail_len = cap - self.tail;
2283 if free >= tail_len {
2284 // there is enough free space to copy the tail in one go,
2285 // this means that we first shift the head backwards, and then
2286 // copy the tail to the correct position.
2288 // from: DEFGH....ABC
2291 ptr::copy(buf, buf.add(tail_len), self.head);
2293 ptr::copy_nonoverlapping(buf.add(self.tail), buf, tail_len);
2299 } else if free > self.head {
2300 // FIXME: We currently do not consider ....ABCDEFGH
2301 // to be contiguous because `head` would be `0` in this
2302 // case. While we probably want to change this it
2303 // isn't trivial as a few places expect `is_contiguous`
2304 // to mean that we can just slice using `buf[tail..head]`.
2306 // there is enough free space to copy the head in one go,
2307 // this means that we first shift the tail forwards, and then
2308 // copy the head to the correct position.
2310 // from: FGH....ABCDE
2313 ptr::copy(buf.add(self.tail), buf.add(self.head), tail_len);
2315 ptr::copy_nonoverlapping(buf, buf.add(self.head + tail_len), self.head);
2318 self.tail = self.head;
2319 self.head = self.wrap_add(self.tail, len);
2322 // free is smaller than both head and tail,
2323 // this means we have to slowly "swap" the tail and the head.
2325 // from: EFGHI...ABCD or HIJK.ABCDEFG
2326 // to: ABCDEFGHI... or ABCDEFGHIJK.
2327 let mut left_edge: usize = 0;
2328 let mut right_edge: usize = self.tail;
2330 // The general problem looks like this
2331 // GHIJKLM...ABCDEF - before any swaps
2332 // ABCDEFM...GHIJKL - after 1 pass of swaps
2333 // ABCDEFGHIJM...KL - swap until the left edge reaches the temp store
2334 // - then restart the algorithm with a new (smaller) store
2335 // Sometimes the temp store is reached when the right edge is at the end
2336 // of the buffer - this means we've hit the right order with fewer swaps!
2339 // ABCDEF.. - after four only swaps we've finished
2340 while left_edge < len && right_edge != cap {
2341 let mut right_offset = 0;
2342 for i in left_edge..right_edge {
2343 right_offset = (i - left_edge) % (cap - right_edge);
2344 let src: isize = (right_edge + right_offset) as isize;
2345 ptr::swap(buf.add(i), buf.offset(src));
2347 let n_ops = right_edge - left_edge;
2349 right_edge += right_offset + 1;
2357 let tail = self.tail;
2358 let head = self.head;
2359 unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 }
2362 /// Rotates the double-ended queue `mid` places to the left.
2365 /// - Rotates item `mid` into the first position.
2366 /// - Pops the first `mid` items and pushes them to the end.
2367 /// - Rotates `len() - mid` places to the right.
2371 /// If `mid` is greater than `len()`. Note that `mid == len()`
2372 /// does _not_ panic and is a no-op rotation.
2376 /// Takes `*O*(min(mid, len() - mid))` time and no extra space.
2381 /// use std::collections::VecDeque;
2383 /// let mut buf: VecDeque<_> = (0..10).collect();
2385 /// buf.rotate_left(3);
2386 /// assert_eq!(buf, [3, 4, 5, 6, 7, 8, 9, 0, 1, 2]);
2388 /// for i in 1..10 {
2389 /// assert_eq!(i * 3 % 10, buf[0]);
2390 /// buf.rotate_left(3);
2392 /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
2394 #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
2395 pub fn rotate_left(&mut self, mid: usize) {
2396 assert!(mid <= self.len());
2397 let k = self.len() - mid;
2399 unsafe { self.rotate_left_inner(mid) }
2401 unsafe { self.rotate_right_inner(k) }
2405 /// Rotates the double-ended queue `k` places to the right.
2408 /// - Rotates the first item into position `k`.
2409 /// - Pops the last `k` items and pushes them to the front.
2410 /// - Rotates `len() - k` places to the left.
2414 /// If `k` is greater than `len()`. Note that `k == len()`
2415 /// does _not_ panic and is a no-op rotation.
2419 /// Takes `*O*(min(k, len() - k))` time and no extra space.
2424 /// use std::collections::VecDeque;
2426 /// let mut buf: VecDeque<_> = (0..10).collect();
2428 /// buf.rotate_right(3);
2429 /// assert_eq!(buf, [7, 8, 9, 0, 1, 2, 3, 4, 5, 6]);
2431 /// for i in 1..10 {
2432 /// assert_eq!(0, buf[i * 3 % 10]);
2433 /// buf.rotate_right(3);
2435 /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
2437 #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
2438 pub fn rotate_right(&mut self, k: usize) {
2439 assert!(k <= self.len());
2440 let mid = self.len() - k;
2442 unsafe { self.rotate_right_inner(k) }
2444 unsafe { self.rotate_left_inner(mid) }
2448 // SAFETY: the following two methods require that the rotation amount
2449 // be less than half the length of the deque.
2451 // `wrap_copy` requires that `min(x, cap() - x) + copy_len <= cap()`,
2452 // but than `min` is never more than half the capacity, regardless of x,
2453 // so it's sound to call here because we're calling with something
2454 // less than half the length, which is never above half the capacity.
2456 unsafe fn rotate_left_inner(&mut self, mid: usize) {
2457 debug_assert!(mid * 2 <= self.len());
2459 self.wrap_copy(self.head, self.tail, mid);
2461 self.head = self.wrap_add(self.head, mid);
2462 self.tail = self.wrap_add(self.tail, mid);
2465 unsafe fn rotate_right_inner(&mut self, k: usize) {
2466 debug_assert!(k * 2 <= self.len());
2467 self.head = self.wrap_sub(self.head, k);
2468 self.tail = self.wrap_sub(self.tail, k);
2470 self.wrap_copy(self.tail, self.head, k);
2474 /// Binary searches this sorted `VecDeque` for a given element.
2476 /// If the value is found then [`Result::Ok`] is returned, containing the
2477 /// index of the matching element. If there are multiple matches, then any
2478 /// one of the matches could be returned. If the value is not found then
2479 /// [`Result::Err`] is returned, containing the index where a matching
2480 /// element could be inserted while maintaining sorted order.
2482 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2484 /// [`binary_search_by`]: VecDeque::binary_search_by
2485 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2486 /// [`partition_point`]: VecDeque::partition_point
2490 /// Looks up a series of four elements. The first is found, with a
2491 /// uniquely determined position; the second and third are not
2492 /// found; the fourth could match any position in `[1, 4]`.
2495 /// use std::collections::VecDeque;
2497 /// let deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2499 /// assert_eq!(deque.binary_search(&13), Ok(9));
2500 /// assert_eq!(deque.binary_search(&4), Err(7));
2501 /// assert_eq!(deque.binary_search(&100), Err(13));
2502 /// let r = deque.binary_search(&1);
2503 /// assert!(matches!(r, Ok(1..=4)));
2506 /// If you want to insert an item to a sorted `VecDeque`, while maintaining
2510 /// use std::collections::VecDeque;
2512 /// let mut deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2514 /// let idx = deque.binary_search(&num).unwrap_or_else(|x| x);
2515 /// deque.insert(idx, num);
2516 /// assert_eq!(deque, &[0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2518 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2520 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2524 self.binary_search_by(|e| e.cmp(x))
2527 /// Binary searches this sorted `VecDeque` with a comparator function.
2529 /// The comparator function should implement an order consistent
2530 /// with the sort order of the underlying `VecDeque`, returning an
2531 /// order code that indicates whether its argument is `Less`,
2532 /// `Equal` or `Greater` than the desired target.
2534 /// If the value is found then [`Result::Ok`] is returned, containing the
2535 /// index of the matching element. If there are multiple matches, then any
2536 /// one of the matches could be returned. If the value is not found then
2537 /// [`Result::Err`] is returned, containing the index where a matching
2538 /// element could be inserted while maintaining sorted order.
2540 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2542 /// [`binary_search`]: VecDeque::binary_search
2543 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2544 /// [`partition_point`]: VecDeque::partition_point
2548 /// Looks up a series of four elements. The first is found, with a
2549 /// uniquely determined position; the second and third are not
2550 /// found; the fourth could match any position in `[1, 4]`.
2553 /// use std::collections::VecDeque;
2555 /// let deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2557 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&13)), Ok(9));
2558 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&4)), Err(7));
2559 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&100)), Err(13));
2560 /// let r = deque.binary_search_by(|x| x.cmp(&1));
2561 /// assert!(matches!(r, Ok(1..=4)));
2563 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2564 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2566 F: FnMut(&'a T) -> Ordering,
2568 let (front, back) = self.as_slices();
2569 let cmp_back = back.first().map(|elem| f(elem));
2571 if let Some(Ordering::Equal) = cmp_back {
2573 } else if let Some(Ordering::Less) = cmp_back {
2574 back.binary_search_by(f).map(|idx| idx + front.len()).map_err(|idx| idx + front.len())
2576 front.binary_search_by(f)
2580 /// Binary searches this sorted `VecDeque` with a key extraction function.
2582 /// Assumes that the `VecDeque` is sorted by the key, for instance with
2583 /// [`make_contiguous().sort_by_key()`] using the same key extraction function.
2585 /// If the value is found then [`Result::Ok`] is returned, containing the
2586 /// index of the matching element. If there are multiple matches, then any
2587 /// one of the matches could be returned. If the value is not found then
2588 /// [`Result::Err`] is returned, containing the index where a matching
2589 /// element could be inserted while maintaining sorted order.
2591 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2593 /// [`make_contiguous().sort_by_key()`]: VecDeque::make_contiguous
2594 /// [`binary_search`]: VecDeque::binary_search
2595 /// [`binary_search_by`]: VecDeque::binary_search_by
2596 /// [`partition_point`]: VecDeque::partition_point
2600 /// Looks up a series of four elements in a slice of pairs sorted by
2601 /// their second elements. The first is found, with a uniquely
2602 /// determined position; the second and third are not found; the
2603 /// fourth could match any position in `[1, 4]`.
2606 /// use std::collections::VecDeque;
2608 /// let deque: VecDeque<_> = vec![(0, 0), (2, 1), (4, 1), (5, 1),
2609 /// (3, 1), (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2610 /// (1, 21), (2, 34), (4, 55)].into();
2612 /// assert_eq!(deque.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2613 /// assert_eq!(deque.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2614 /// assert_eq!(deque.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2615 /// let r = deque.binary_search_by_key(&1, |&(a, b)| b);
2616 /// assert!(matches!(r, Ok(1..=4)));
2618 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2620 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2622 F: FnMut(&'a T) -> B,
2625 self.binary_search_by(|k| f(k).cmp(b))
2628 /// Returns the index of the partition point according to the given predicate
2629 /// (the index of the first element of the second partition).
2631 /// The deque is assumed to be partitioned according to the given predicate.
2632 /// This means that all elements for which the predicate returns true are at the start of the deque
2633 /// and all elements for which the predicate returns false are at the end.
2634 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
2635 /// (all odd numbers are at the start, all even at the end).
2637 /// If this deque is not partitioned, the returned result is unspecified and meaningless,
2638 /// as this method performs a kind of binary search.
2640 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
2642 /// [`binary_search`]: VecDeque::binary_search
2643 /// [`binary_search_by`]: VecDeque::binary_search_by
2644 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2649 /// use std::collections::VecDeque;
2651 /// let deque: VecDeque<_> = vec![1, 2, 3, 3, 5, 6, 7].into();
2652 /// let i = deque.partition_point(|&x| x < 5);
2654 /// assert_eq!(i, 4);
2655 /// assert!(deque.iter().take(i).all(|&x| x < 5));
2656 /// assert!(deque.iter().skip(i).all(|&x| !(x < 5)));
2658 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2659 pub fn partition_point<P>(&self, mut pred: P) -> usize
2661 P: FnMut(&T) -> bool,
2663 let (front, back) = self.as_slices();
2665 if let Some(true) = back.first().map(|v| pred(v)) {
2666 back.partition_point(pred) + front.len()
2668 front.partition_point(pred)
2673 impl<T: Clone, A: Allocator> VecDeque<T, A> {
2674 /// Modifies the `VecDeque` in-place so that `len()` is equal to new_len,
2675 /// either by removing excess elements from the back or by appending clones of `value`
2681 /// use std::collections::VecDeque;
2683 /// let mut buf = VecDeque::new();
2684 /// buf.push_back(5);
2685 /// buf.push_back(10);
2686 /// buf.push_back(15);
2687 /// assert_eq!(buf, [5, 10, 15]);
2689 /// buf.resize(2, 0);
2690 /// assert_eq!(buf, [5, 10]);
2692 /// buf.resize(5, 20);
2693 /// assert_eq!(buf, [5, 10, 20, 20, 20]);
2695 #[stable(feature = "deque_extras", since = "1.16.0")]
2696 pub fn resize(&mut self, new_len: usize, value: T) {
2697 self.resize_with(new_len, || value.clone());
2701 /// Returns the index in the underlying buffer for a given logical element index.
2703 fn wrap_index(index: usize, size: usize) -> usize {
2704 // size is always a power of 2
2705 debug_assert!(size.is_power_of_two());
2709 /// Calculate the number of elements left to be read in the buffer
2711 fn count(tail: usize, head: usize, size: usize) -> usize {
2712 // size is always a power of 2
2713 (head.wrapping_sub(tail)) & (size - 1)
2716 #[stable(feature = "rust1", since = "1.0.0")]
2717 impl<T: PartialEq, A: Allocator> PartialEq for VecDeque<T, A> {
2718 fn eq(&self, other: &Self) -> bool {
2719 if self.len() != other.len() {
2722 let (sa, sb) = self.as_slices();
2723 let (oa, ob) = other.as_slices();
2724 if sa.len() == oa.len() {
2725 sa == oa && sb == ob
2726 } else if sa.len() < oa.len() {
2727 // Always divisible in three sections, for example:
2728 // self: [a b c|d e f]
2729 // other: [0 1 2 3|4 5]
2730 // front = 3, mid = 1,
2731 // [a b c] == [0 1 2] && [d] == [3] && [e f] == [4 5]
2732 let front = sa.len();
2733 let mid = oa.len() - front;
2735 let (oa_front, oa_mid) = oa.split_at(front);
2736 let (sb_mid, sb_back) = sb.split_at(mid);
2737 debug_assert_eq!(sa.len(), oa_front.len());
2738 debug_assert_eq!(sb_mid.len(), oa_mid.len());
2739 debug_assert_eq!(sb_back.len(), ob.len());
2740 sa == oa_front && sb_mid == oa_mid && sb_back == ob
2742 let front = oa.len();
2743 let mid = sa.len() - front;
2745 let (sa_front, sa_mid) = sa.split_at(front);
2746 let (ob_mid, ob_back) = ob.split_at(mid);
2747 debug_assert_eq!(sa_front.len(), oa.len());
2748 debug_assert_eq!(sa_mid.len(), ob_mid.len());
2749 debug_assert_eq!(sb.len(), ob_back.len());
2750 sa_front == oa && sa_mid == ob_mid && sb == ob_back
2755 #[stable(feature = "rust1", since = "1.0.0")]
2756 impl<T: Eq, A: Allocator> Eq for VecDeque<T, A> {}
2758 __impl_slice_eq1! { [] VecDeque<T, A>, Vec<U, A>, }
2759 __impl_slice_eq1! { [] VecDeque<T, A>, &[U], }
2760 __impl_slice_eq1! { [] VecDeque<T, A>, &mut [U], }
2761 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, [U; N], }
2762 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &[U; N], }
2763 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &mut [U; N], }
2765 #[stable(feature = "rust1", since = "1.0.0")]
2766 impl<T: PartialOrd, A: Allocator> PartialOrd for VecDeque<T, A> {
2767 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2768 self.iter().partial_cmp(other.iter())
2772 #[stable(feature = "rust1", since = "1.0.0")]
2773 impl<T: Ord, A: Allocator> Ord for VecDeque<T, A> {
2775 fn cmp(&self, other: &Self) -> Ordering {
2776 self.iter().cmp(other.iter())
2780 #[stable(feature = "rust1", since = "1.0.0")]
2781 impl<T: Hash, A: Allocator> Hash for VecDeque<T, A> {
2782 fn hash<H: Hasher>(&self, state: &mut H) {
2783 self.len().hash(state);
2784 // It's not possible to use Hash::hash_slice on slices
2785 // returned by as_slices method as their length can vary
2786 // in otherwise identical deques.
2788 // Hasher only guarantees equivalence for the exact same
2789 // set of calls to its methods.
2790 self.iter().for_each(|elem| elem.hash(state));
2794 #[stable(feature = "rust1", since = "1.0.0")]
2795 impl<T, A: Allocator> Index<usize> for VecDeque<T, A> {
2799 fn index(&self, index: usize) -> &T {
2800 self.get(index).expect("Out of bounds access")
2804 #[stable(feature = "rust1", since = "1.0.0")]
2805 impl<T, A: Allocator> IndexMut<usize> for VecDeque<T, A> {
2807 fn index_mut(&mut self, index: usize) -> &mut T {
2808 self.get_mut(index).expect("Out of bounds access")
2812 #[stable(feature = "rust1", since = "1.0.0")]
2813 impl<T> FromIterator<T> for VecDeque<T> {
2814 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> VecDeque<T> {
2815 let iterator = iter.into_iter();
2816 let (lower, _) = iterator.size_hint();
2817 let mut deq = VecDeque::with_capacity(lower);
2818 deq.extend(iterator);
2823 #[stable(feature = "rust1", since = "1.0.0")]
2824 impl<T, A: Allocator> IntoIterator for VecDeque<T, A> {
2826 type IntoIter = IntoIter<T, A>;
2828 /// Consumes the `VecDeque` into a front-to-back iterator yielding elements by
2830 fn into_iter(self) -> IntoIter<T, A> {
2835 #[stable(feature = "rust1", since = "1.0.0")]
2836 impl<'a, T, A: Allocator> IntoIterator for &'a VecDeque<T, A> {
2838 type IntoIter = Iter<'a, T>;
2840 fn into_iter(self) -> Iter<'a, T> {
2845 #[stable(feature = "rust1", since = "1.0.0")]
2846 impl<'a, T, A: Allocator> IntoIterator for &'a mut VecDeque<T, A> {
2847 type Item = &'a mut T;
2848 type IntoIter = IterMut<'a, T>;
2850 fn into_iter(self) -> IterMut<'a, T> {
2855 #[stable(feature = "rust1", since = "1.0.0")]
2856 impl<T, A: Allocator> Extend<T> for VecDeque<T, A> {
2857 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2858 // This function should be the moral equivalent of:
2860 // for item in iter.into_iter() {
2861 // self.push_back(item);
2863 let mut iter = iter.into_iter();
2864 while let Some(element) = iter.next() {
2865 if self.len() == self.capacity() {
2866 let (lower, _) = iter.size_hint();
2867 self.reserve(lower.saturating_add(1));
2870 let head = self.head;
2871 self.head = self.wrap_add(self.head, 1);
2873 self.buffer_write(head, element);
2879 fn extend_one(&mut self, elem: T) {
2880 self.push_back(elem);
2884 fn extend_reserve(&mut self, additional: usize) {
2885 self.reserve(additional);
2889 #[stable(feature = "extend_ref", since = "1.2.0")]
2890 impl<'a, T: 'a + Copy, A: Allocator> Extend<&'a T> for VecDeque<T, A> {
2891 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2892 self.extend(iter.into_iter().cloned());
2896 fn extend_one(&mut self, &elem: &T) {
2897 self.push_back(elem);
2901 fn extend_reserve(&mut self, additional: usize) {
2902 self.reserve(additional);
2906 #[stable(feature = "rust1", since = "1.0.0")]
2907 impl<T: fmt::Debug, A: Allocator> fmt::Debug for VecDeque<T, A> {
2908 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2909 f.debug_list().entries(self).finish()
2913 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2914 impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A> {
2915 /// Turn a [`Vec<T>`] into a [`VecDeque<T>`].
2917 /// [`Vec<T>`]: crate::vec::Vec
2918 /// [`VecDeque<T>`]: crate::collections::VecDeque
2920 /// This avoids reallocating where possible, but the conditions for that are
2921 /// strict, and subject to change, and so shouldn't be relied upon unless the
2922 /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated.
2923 fn from(mut other: Vec<T, A>) -> Self {
2924 let len = other.len();
2925 if mem::size_of::<T>() == 0 {
2926 // There's no actual allocation for ZSTs to worry about capacity,
2927 // but `VecDeque` can't handle as much length as `Vec`.
2928 assert!(len < MAXIMUM_ZST_CAPACITY, "capacity overflow");
2930 // We need to resize if the capacity is not a power of two, too small or
2931 // doesn't have at least one free space. We do this while it's still in
2932 // the `Vec` so the items will drop on panic.
2933 let min_cap = cmp::max(MINIMUM_CAPACITY, len) + 1;
2934 let cap = cmp::max(min_cap, other.capacity()).next_power_of_two();
2935 if other.capacity() != cap {
2936 other.reserve_exact(cap - len);
2941 let (other_buf, len, capacity, alloc) = other.into_raw_parts_with_alloc();
2942 let buf = RawVec::from_raw_parts_in(other_buf, capacity, alloc);
2943 VecDeque { tail: 0, head: len, buf }
2948 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2949 impl<T, A: Allocator> From<VecDeque<T, A>> for Vec<T, A> {
2950 /// Turn a [`VecDeque<T>`] into a [`Vec<T>`].
2952 /// [`Vec<T>`]: crate::vec::Vec
2953 /// [`VecDeque<T>`]: crate::collections::VecDeque
2955 /// This never needs to re-allocate, but does need to do *O*(*n*) data movement if
2956 /// the circular buffer doesn't happen to be at the beginning of the allocation.
2961 /// use std::collections::VecDeque;
2963 /// // This one is *O*(1).
2964 /// let deque: VecDeque<_> = (1..5).collect();
2965 /// let ptr = deque.as_slices().0.as_ptr();
2966 /// let vec = Vec::from(deque);
2967 /// assert_eq!(vec, [1, 2, 3, 4]);
2968 /// assert_eq!(vec.as_ptr(), ptr);
2970 /// // This one needs data rearranging.
2971 /// let mut deque: VecDeque<_> = (1..5).collect();
2972 /// deque.push_front(9);
2973 /// deque.push_front(8);
2974 /// let ptr = deque.as_slices().1.as_ptr();
2975 /// let vec = Vec::from(deque);
2976 /// assert_eq!(vec, [8, 9, 1, 2, 3, 4]);
2977 /// assert_eq!(vec.as_ptr(), ptr);
2979 fn from(mut other: VecDeque<T, A>) -> Self {
2980 other.make_contiguous();
2983 let other = ManuallyDrop::new(other);
2984 let buf = other.buf.ptr();
2985 let len = other.len();
2986 let cap = other.cap();
2987 let alloc = ptr::read(other.allocator());
2989 if other.tail != 0 {
2990 ptr::copy(buf.add(other.tail), buf, len);
2992 Vec::from_raw_parts_in(buf, len, cap, alloc)
2997 #[stable(feature = "std_collections_from_array", since = "1.56.0")]
2998 impl<T, const N: usize> From<[T; N]> for VecDeque<T> {
3000 /// use std::collections::VecDeque;
3002 /// let deq1 = VecDeque::from([1, 2, 3, 4]);
3003 /// let deq2: VecDeque<_> = [1, 2, 3, 4].into();
3004 /// assert_eq!(deq1, deq2);
3006 fn from(arr: [T; N]) -> Self {
3007 let mut deq = VecDeque::with_capacity(N);
3008 let arr = ManuallyDrop::new(arr);
3009 if mem::size_of::<T>() != 0 {
3010 // SAFETY: VecDeque::with_capacity ensures that there is enough capacity.
3012 ptr::copy_nonoverlapping(arr.as_ptr(), deq.ptr(), N);