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")]
479 pub fn new() -> VecDeque<T> {
480 VecDeque::new_in(Global)
483 /// Creates an empty `VecDeque` with space for at least `capacity` elements.
488 /// use std::collections::VecDeque;
490 /// let vector: VecDeque<u32> = VecDeque::with_capacity(10);
493 #[stable(feature = "rust1", since = "1.0.0")]
495 pub fn with_capacity(capacity: usize) -> VecDeque<T> {
496 Self::with_capacity_in(capacity, Global)
500 impl<T, A: Allocator> VecDeque<T, A> {
501 /// Creates an empty `VecDeque`.
506 /// use std::collections::VecDeque;
508 /// let vector: VecDeque<u32> = VecDeque::new();
511 #[unstable(feature = "allocator_api", issue = "32838")]
512 pub fn new_in(alloc: A) -> VecDeque<T, A> {
513 VecDeque::with_capacity_in(INITIAL_CAPACITY, alloc)
516 /// Creates an empty `VecDeque` with space for at least `capacity` elements.
521 /// use std::collections::VecDeque;
523 /// let vector: VecDeque<u32> = VecDeque::with_capacity(10);
525 #[unstable(feature = "allocator_api", issue = "32838")]
526 pub fn with_capacity_in(capacity: usize, alloc: A) -> VecDeque<T, A> {
527 // +1 since the ringbuffer always leaves one space empty
528 let cap = cmp::max(capacity + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
529 assert!(cap > capacity, "capacity overflow");
531 VecDeque { tail: 0, head: 0, buf: RawVec::with_capacity_in(cap, alloc) }
534 /// Provides a reference to the element at the given index.
536 /// Element at index 0 is the front of the queue.
541 /// use std::collections::VecDeque;
543 /// let mut buf = VecDeque::new();
544 /// buf.push_back(3);
545 /// buf.push_back(4);
546 /// buf.push_back(5);
547 /// assert_eq!(buf.get(1), Some(&4));
549 #[stable(feature = "rust1", since = "1.0.0")]
550 pub fn get(&self, index: usize) -> Option<&T> {
551 if index < self.len() {
552 let idx = self.wrap_add(self.tail, index);
553 unsafe { Some(&*self.ptr().add(idx)) }
559 /// Provides a mutable reference to the element at the given index.
561 /// Element at index 0 is the front of the queue.
566 /// use std::collections::VecDeque;
568 /// let mut buf = VecDeque::new();
569 /// buf.push_back(3);
570 /// buf.push_back(4);
571 /// buf.push_back(5);
572 /// if let Some(elem) = buf.get_mut(1) {
576 /// assert_eq!(buf[1], 7);
578 #[stable(feature = "rust1", since = "1.0.0")]
579 pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
580 if index < self.len() {
581 let idx = self.wrap_add(self.tail, index);
582 unsafe { Some(&mut *self.ptr().add(idx)) }
588 /// Swaps elements at indices `i` and `j`.
590 /// `i` and `j` may be equal.
592 /// Element at index 0 is the front of the queue.
596 /// Panics if either index is out of bounds.
601 /// use std::collections::VecDeque;
603 /// let mut buf = VecDeque::new();
604 /// buf.push_back(3);
605 /// buf.push_back(4);
606 /// buf.push_back(5);
607 /// assert_eq!(buf, [3, 4, 5]);
609 /// assert_eq!(buf, [5, 4, 3]);
611 #[stable(feature = "rust1", since = "1.0.0")]
612 pub fn swap(&mut self, i: usize, j: usize) {
613 assert!(i < self.len());
614 assert!(j < self.len());
615 let ri = self.wrap_add(self.tail, i);
616 let rj = self.wrap_add(self.tail, j);
617 unsafe { ptr::swap(self.ptr().add(ri), self.ptr().add(rj)) }
620 /// Returns the number of elements the `VecDeque` can hold without
626 /// use std::collections::VecDeque;
628 /// let buf: VecDeque<i32> = VecDeque::with_capacity(10);
629 /// assert!(buf.capacity() >= 10);
632 #[stable(feature = "rust1", since = "1.0.0")]
633 pub fn capacity(&self) -> usize {
637 /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
638 /// given `VecDeque`. Does nothing if the capacity is already sufficient.
640 /// Note that the allocator may give the collection more space than it requests. Therefore
641 /// capacity can not be relied upon to be precisely minimal. Prefer [`reserve`] if future
642 /// insertions are expected.
646 /// Panics if the new capacity overflows `usize`.
651 /// use std::collections::VecDeque;
653 /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
654 /// buf.reserve_exact(10);
655 /// assert!(buf.capacity() >= 11);
658 /// [`reserve`]: VecDeque::reserve
659 #[stable(feature = "rust1", since = "1.0.0")]
660 pub fn reserve_exact(&mut self, additional: usize) {
661 self.reserve(additional);
664 /// Reserves capacity for at least `additional` more elements to be inserted in the given
665 /// `VecDeque`. The collection may reserve more space to avoid frequent reallocations.
669 /// Panics if the new capacity overflows `usize`.
674 /// use std::collections::VecDeque;
676 /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
678 /// assert!(buf.capacity() >= 11);
680 #[stable(feature = "rust1", since = "1.0.0")]
681 pub fn reserve(&mut self, additional: usize) {
682 let old_cap = self.cap();
683 let used_cap = self.len() + 1;
684 let new_cap = used_cap
685 .checked_add(additional)
686 .and_then(|needed_cap| needed_cap.checked_next_power_of_two())
687 .expect("capacity overflow");
689 if new_cap > old_cap {
690 self.buf.reserve_exact(used_cap, new_cap - used_cap);
692 self.handle_capacity_increase(old_cap);
697 /// Tries to reserve the minimum capacity for exactly `additional` more elements to
698 /// be inserted in the given `VecDeque<T>`. After calling `try_reserve_exact`,
699 /// capacity will be greater than or equal to `self.len() + additional`.
700 /// Does nothing if the capacity is already sufficient.
702 /// Note that the allocator may give the collection more space than it
703 /// requests. Therefore, capacity can not be relied upon to be precisely
704 /// minimal. Prefer [`reserve`] if future insertions are expected.
706 /// [`reserve`]: VecDeque::reserve
710 /// If the capacity overflows `usize`, or the allocator reports a failure, then an error
716 /// use std::collections::TryReserveError;
717 /// use std::collections::VecDeque;
719 /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> {
720 /// let mut output = VecDeque::new();
722 /// // Pre-reserve the memory, exiting if we can't
723 /// output.try_reserve_exact(data.len())?;
725 /// // Now we know this can't OOM(Out-Of-Memory) in the middle of our complex work
726 /// output.extend(data.iter().map(|&val| {
727 /// val * 2 + 5 // very complicated
732 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
734 #[stable(feature = "try_reserve", since = "1.57.0")]
735 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
736 self.try_reserve(additional)
739 /// Tries to reserve capacity for at least `additional` more elements to be inserted
740 /// in the given `VecDeque<T>`. The collection may reserve more space to avoid
741 /// frequent reallocations. After calling `try_reserve`, capacity will be
742 /// greater than or equal to `self.len() + additional`. Does nothing if
743 /// capacity is already sufficient.
747 /// If the capacity overflows `usize`, or the allocator reports a failure, then an error
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 #[stable(feature = "try_reserve", since = "1.57.0")]
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 '_.
1005 let ring = ptr::slice_from_raw_parts_mut(self.ptr(), self.cap());
1007 unsafe { IterMut::new(ring, self.tail, self.head, PhantomData) }
1010 /// Returns a pair of slices which contain, in order, the contents of the
1013 /// If [`make_contiguous`] was previously called, all elements of the
1014 /// `VecDeque` will be in the first slice and the second slice will be empty.
1016 /// [`make_contiguous`]: VecDeque::make_contiguous
1021 /// use std::collections::VecDeque;
1023 /// let mut vector = VecDeque::new();
1025 /// vector.push_back(0);
1026 /// vector.push_back(1);
1027 /// vector.push_back(2);
1029 /// assert_eq!(vector.as_slices(), (&[0, 1, 2][..], &[][..]));
1031 /// vector.push_front(10);
1032 /// vector.push_front(9);
1034 /// assert_eq!(vector.as_slices(), (&[9, 10][..], &[0, 1, 2][..]));
1037 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1038 pub fn as_slices(&self) -> (&[T], &[T]) {
1040 let buf = self.buffer_as_slice();
1041 RingSlices::ring_slices(buf, self.head, self.tail)
1045 /// Returns a pair of slices which contain, in order, the contents of the
1048 /// If [`make_contiguous`] was previously called, all elements of the
1049 /// `VecDeque` will be in the first slice and the second slice will be empty.
1051 /// [`make_contiguous`]: VecDeque::make_contiguous
1056 /// use std::collections::VecDeque;
1058 /// let mut vector = VecDeque::new();
1060 /// vector.push_back(0);
1061 /// vector.push_back(1);
1063 /// vector.push_front(10);
1064 /// vector.push_front(9);
1066 /// vector.as_mut_slices().0[0] = 42;
1067 /// vector.as_mut_slices().1[0] = 24;
1068 /// assert_eq!(vector.as_slices(), (&[42, 10][..], &[24, 1][..]));
1071 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1072 pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) {
1074 let head = self.head;
1075 let tail = self.tail;
1076 let buf = self.buffer_as_mut_slice();
1077 RingSlices::ring_slices(buf, head, tail)
1081 /// Returns the number of elements in the `VecDeque`.
1086 /// use std::collections::VecDeque;
1088 /// let mut v = VecDeque::new();
1089 /// assert_eq!(v.len(), 0);
1091 /// assert_eq!(v.len(), 1);
1093 #[stable(feature = "rust1", since = "1.0.0")]
1094 pub fn len(&self) -> usize {
1095 count(self.tail, self.head, self.cap())
1098 /// Returns `true` if the `VecDeque` is empty.
1103 /// use std::collections::VecDeque;
1105 /// let mut v = VecDeque::new();
1106 /// assert!(v.is_empty());
1107 /// v.push_front(1);
1108 /// assert!(!v.is_empty());
1110 #[stable(feature = "rust1", since = "1.0.0")]
1111 pub fn is_empty(&self) -> bool {
1112 self.tail == self.head
1115 fn range_tail_head<R>(&self, range: R) -> (usize, usize)
1117 R: RangeBounds<usize>,
1119 let Range { start, end } = slice::range(range, ..self.len());
1120 let tail = self.wrap_add(self.tail, start);
1121 let head = self.wrap_add(self.tail, end);
1125 /// Creates an iterator that covers the specified range in the `VecDeque`.
1129 /// Panics if the starting point is greater than the end point or if
1130 /// the end point is greater than the length of the vector.
1135 /// use std::collections::VecDeque;
1137 /// let v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1138 /// let range = v.range(2..).copied().collect::<VecDeque<_>>();
1139 /// assert_eq!(range, [3]);
1141 /// // A full range covers all contents
1142 /// let all = v.range(..);
1143 /// assert_eq!(all.len(), 3);
1146 #[stable(feature = "deque_range", since = "1.51.0")]
1147 pub fn range<R>(&self, range: R) -> Iter<'_, T>
1149 R: RangeBounds<usize>,
1151 let (tail, head) = self.range_tail_head(range);
1155 // The shared reference we have in &self is maintained in the '_ of Iter.
1156 ring: unsafe { self.buffer_as_slice() },
1160 /// Creates an iterator that covers the specified mutable range in the `VecDeque`.
1164 /// Panics if the starting point is greater than the end point or if
1165 /// the end point is greater than the length of the vector.
1170 /// use std::collections::VecDeque;
1172 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1173 /// for v in v.range_mut(2..) {
1176 /// assert_eq!(v, vec![1, 2, 6]);
1178 /// // A full range covers all contents
1179 /// for v in v.range_mut(..) {
1182 /// assert_eq!(v, vec![2, 4, 12]);
1185 #[stable(feature = "deque_range", since = "1.51.0")]
1186 pub fn range_mut<R>(&mut self, range: R) -> IterMut<'_, T>
1188 R: RangeBounds<usize>,
1190 let (tail, head) = self.range_tail_head(range);
1192 // SAFETY: The internal `IterMut` safety invariant is established because the
1193 // `ring` we create is a dereferencable slice for lifetime '_.
1194 let ring = ptr::slice_from_raw_parts_mut(self.ptr(), self.cap());
1196 unsafe { IterMut::new(ring, tail, head, PhantomData) }
1199 /// Creates a draining iterator that removes the specified range in the
1200 /// `VecDeque` and yields the removed items.
1202 /// Note 1: The element range is removed even if the iterator is not
1203 /// consumed until the end.
1205 /// Note 2: It is unspecified how many elements are removed from the deque,
1206 /// if the `Drain` value is not dropped, but the borrow it holds expires
1207 /// (e.g., due to `mem::forget`).
1211 /// Panics if the starting point is greater than the end point or if
1212 /// the end point is greater than the length of the vector.
1217 /// use std::collections::VecDeque;
1219 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1220 /// let drained = v.drain(2..).collect::<VecDeque<_>>();
1221 /// assert_eq!(drained, [3]);
1222 /// assert_eq!(v, [1, 2]);
1224 /// // A full range clears all contents
1226 /// assert!(v.is_empty());
1229 #[stable(feature = "drain", since = "1.6.0")]
1230 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1232 R: RangeBounds<usize>,
1236 // When the Drain is first created, the source deque is shortened to
1237 // make sure no uninitialized or moved-from elements are accessible at
1238 // all if the Drain's destructor never gets to run.
1240 // Drain will ptr::read out the values to remove.
1241 // When finished, the remaining data will be copied back to cover the hole,
1242 // and the head/tail values will be restored correctly.
1244 let (drain_tail, drain_head) = self.range_tail_head(range);
1246 // The deque's elements are parted into three segments:
1247 // * self.tail -> drain_tail
1248 // * drain_tail -> drain_head
1249 // * drain_head -> self.head
1251 // T = self.tail; H = self.head; t = drain_tail; h = drain_head
1253 // We store drain_tail as self.head, and drain_head and self.head as
1254 // after_tail and after_head respectively on the Drain. This also
1255 // truncates the effective array such that if the Drain is leaked, we
1256 // have forgotten about the potentially moved values after the start of
1260 // [. . . o o x x o o . . .]
1262 let head = self.head;
1264 // "forget" about the values after the start of the drain until after
1265 // the drain is complete and the Drain destructor is run.
1266 self.head = drain_tail;
1268 let deque = NonNull::from(&mut *self);
1272 // Crucially, we only create shared references from `self` here and read from
1273 // it. We do not write to `self` nor reborrow to a mutable reference.
1274 // Hence the raw pointer we created above, for `deque`, remains valid.
1275 ring: unsafe { self.buffer_as_slice() },
1278 unsafe { Drain::new(drain_head, head, iter, deque) }
1281 /// Clears the `VecDeque`, removing all values.
1286 /// use std::collections::VecDeque;
1288 /// let mut v = VecDeque::new();
1291 /// assert!(v.is_empty());
1293 #[stable(feature = "rust1", since = "1.0.0")]
1295 pub fn clear(&mut self) {
1299 /// Returns `true` if the `VecDeque` contains an element equal to the
1305 /// use std::collections::VecDeque;
1307 /// let mut vector: VecDeque<u32> = VecDeque::new();
1309 /// vector.push_back(0);
1310 /// vector.push_back(1);
1312 /// assert_eq!(vector.contains(&1), true);
1313 /// assert_eq!(vector.contains(&10), false);
1315 #[stable(feature = "vec_deque_contains", since = "1.12.0")]
1316 pub fn contains(&self, x: &T) -> bool
1320 let (a, b) = self.as_slices();
1321 a.contains(x) || b.contains(x)
1324 /// Provides a reference to the front element, or `None` if the `VecDeque` is
1330 /// use std::collections::VecDeque;
1332 /// let mut d = VecDeque::new();
1333 /// assert_eq!(d.front(), None);
1337 /// assert_eq!(d.front(), Some(&1));
1339 #[stable(feature = "rust1", since = "1.0.0")]
1340 pub fn front(&self) -> Option<&T> {
1344 /// Provides a mutable reference to the front element, or `None` if the
1345 /// `VecDeque` is empty.
1350 /// use std::collections::VecDeque;
1352 /// let mut d = VecDeque::new();
1353 /// assert_eq!(d.front_mut(), None);
1357 /// match d.front_mut() {
1358 /// Some(x) => *x = 9,
1361 /// assert_eq!(d.front(), Some(&9));
1363 #[stable(feature = "rust1", since = "1.0.0")]
1364 pub fn front_mut(&mut self) -> Option<&mut T> {
1368 /// Provides a reference to the back element, or `None` if the `VecDeque` is
1374 /// use std::collections::VecDeque;
1376 /// let mut d = VecDeque::new();
1377 /// assert_eq!(d.back(), None);
1381 /// assert_eq!(d.back(), Some(&2));
1383 #[stable(feature = "rust1", since = "1.0.0")]
1384 pub fn back(&self) -> Option<&T> {
1385 self.get(self.len().wrapping_sub(1))
1388 /// Provides a mutable reference to the back element, or `None` if the
1389 /// `VecDeque` is empty.
1394 /// use std::collections::VecDeque;
1396 /// let mut d = VecDeque::new();
1397 /// assert_eq!(d.back(), None);
1401 /// match d.back_mut() {
1402 /// Some(x) => *x = 9,
1405 /// assert_eq!(d.back(), Some(&9));
1407 #[stable(feature = "rust1", since = "1.0.0")]
1408 pub fn back_mut(&mut self) -> Option<&mut T> {
1409 self.get_mut(self.len().wrapping_sub(1))
1412 /// Removes the first element and returns it, or `None` if the `VecDeque` is
1418 /// use std::collections::VecDeque;
1420 /// let mut d = VecDeque::new();
1424 /// assert_eq!(d.pop_front(), Some(1));
1425 /// assert_eq!(d.pop_front(), Some(2));
1426 /// assert_eq!(d.pop_front(), None);
1428 #[stable(feature = "rust1", since = "1.0.0")]
1429 pub fn pop_front(&mut self) -> Option<T> {
1430 if self.is_empty() {
1433 let tail = self.tail;
1434 self.tail = self.wrap_add(self.tail, 1);
1435 unsafe { Some(self.buffer_read(tail)) }
1439 /// Removes the last element from the `VecDeque` and returns it, or `None` if
1445 /// use std::collections::VecDeque;
1447 /// let mut buf = VecDeque::new();
1448 /// assert_eq!(buf.pop_back(), None);
1449 /// buf.push_back(1);
1450 /// buf.push_back(3);
1451 /// assert_eq!(buf.pop_back(), Some(3));
1453 #[stable(feature = "rust1", since = "1.0.0")]
1454 pub fn pop_back(&mut self) -> Option<T> {
1455 if self.is_empty() {
1458 self.head = self.wrap_sub(self.head, 1);
1459 let head = self.head;
1460 unsafe { Some(self.buffer_read(head)) }
1464 /// Prepends an element to the `VecDeque`.
1469 /// use std::collections::VecDeque;
1471 /// let mut d = VecDeque::new();
1472 /// d.push_front(1);
1473 /// d.push_front(2);
1474 /// assert_eq!(d.front(), Some(&2));
1476 #[stable(feature = "rust1", since = "1.0.0")]
1477 pub fn push_front(&mut self, value: T) {
1482 self.tail = self.wrap_sub(self.tail, 1);
1483 let tail = self.tail;
1485 self.buffer_write(tail, value);
1489 /// Appends an element to the back of the `VecDeque`.
1494 /// use std::collections::VecDeque;
1496 /// let mut buf = VecDeque::new();
1497 /// buf.push_back(1);
1498 /// buf.push_back(3);
1499 /// assert_eq!(3, *buf.back().unwrap());
1501 #[stable(feature = "rust1", since = "1.0.0")]
1502 pub fn push_back(&mut self, value: T) {
1507 let head = self.head;
1508 self.head = self.wrap_add(self.head, 1);
1509 unsafe { self.buffer_write(head, value) }
1513 fn is_contiguous(&self) -> bool {
1514 // FIXME: Should we consider `head == 0` to mean
1515 // that `self` is contiguous?
1516 self.tail <= self.head
1519 /// Removes an element from anywhere in the `VecDeque` and returns it,
1520 /// replacing it with the first element.
1522 /// This does not preserve ordering, but is *O*(1).
1524 /// Returns `None` if `index` is out of bounds.
1526 /// Element at index 0 is the front of the queue.
1531 /// use std::collections::VecDeque;
1533 /// let mut buf = VecDeque::new();
1534 /// assert_eq!(buf.swap_remove_front(0), None);
1535 /// buf.push_back(1);
1536 /// buf.push_back(2);
1537 /// buf.push_back(3);
1538 /// assert_eq!(buf, [1, 2, 3]);
1540 /// assert_eq!(buf.swap_remove_front(2), Some(3));
1541 /// assert_eq!(buf, [2, 1]);
1543 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1544 pub fn swap_remove_front(&mut self, index: usize) -> Option<T> {
1545 let length = self.len();
1546 if length > 0 && index < length && index != 0 {
1547 self.swap(index, 0);
1548 } else if index >= length {
1554 /// Removes an element from anywhere in the `VecDeque` and returns it, replacing it with the
1557 /// This does not preserve ordering, but is *O*(1).
1559 /// Returns `None` if `index` is out of bounds.
1561 /// Element at index 0 is the front of the queue.
1566 /// use std::collections::VecDeque;
1568 /// let mut buf = VecDeque::new();
1569 /// assert_eq!(buf.swap_remove_back(0), None);
1570 /// buf.push_back(1);
1571 /// buf.push_back(2);
1572 /// buf.push_back(3);
1573 /// assert_eq!(buf, [1, 2, 3]);
1575 /// assert_eq!(buf.swap_remove_back(0), Some(1));
1576 /// assert_eq!(buf, [3, 2]);
1578 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1579 pub fn swap_remove_back(&mut self, index: usize) -> Option<T> {
1580 let length = self.len();
1581 if length > 0 && index < length - 1 {
1582 self.swap(index, length - 1);
1583 } else if index >= length {
1589 /// Inserts an element at `index` within the `VecDeque`, shifting all elements with indices
1590 /// greater than or equal to `index` towards the back.
1592 /// Element at index 0 is the front of the queue.
1596 /// Panics if `index` is greater than `VecDeque`'s length
1601 /// use std::collections::VecDeque;
1603 /// let mut vec_deque = VecDeque::new();
1604 /// vec_deque.push_back('a');
1605 /// vec_deque.push_back('b');
1606 /// vec_deque.push_back('c');
1607 /// assert_eq!(vec_deque, &['a', 'b', 'c']);
1609 /// vec_deque.insert(1, 'd');
1610 /// assert_eq!(vec_deque, &['a', 'd', 'b', 'c']);
1612 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1613 pub fn insert(&mut self, index: usize, value: T) {
1614 assert!(index <= self.len(), "index out of bounds");
1619 // Move the least number of elements in the ring buffer and insert
1622 // At most len/2 - 1 elements will be moved. O(min(n, n-i))
1624 // There are three main cases:
1625 // Elements are contiguous
1626 // - special case when tail is 0
1627 // Elements are discontiguous and the insert is in the tail section
1628 // Elements are discontiguous and the insert is in the head section
1630 // For each of those there are two more cases:
1631 // Insert is closer to tail
1632 // Insert is closer to head
1634 // Key: H - self.head
1636 // o - Valid element
1637 // I - Insertion element
1638 // A - The element that should be after the insertion point
1639 // M - Indicates element was moved
1641 let idx = self.wrap_add(self.tail, index);
1643 let distance_to_tail = index;
1644 let distance_to_head = self.len() - index;
1646 let contiguous = self.is_contiguous();
1648 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1649 (true, true, _) if index == 0 => {
1654 // [A o o o o o o . . . . . . . . .]
1657 // [A o o o o o o o . . . . . I]
1660 self.tail = self.wrap_sub(self.tail, 1);
1662 (true, true, _) => {
1664 // contiguous, insert closer to tail:
1667 // [. . . o o A o o o o . . . . . .]
1670 // [. . o o I A o o o o . . . . . .]
1673 // contiguous, insert closer to tail and tail is 0:
1677 // [o o A o o o o . . . . . . . . .]
1680 // [o I A o o o o o . . . . . . . o]
1683 let new_tail = self.wrap_sub(self.tail, 1);
1685 self.copy(new_tail, self.tail, 1);
1686 // Already moved the tail, so we only copy `index - 1` elements.
1687 self.copy(self.tail, self.tail + 1, index - 1);
1689 self.tail = new_tail;
1692 (true, false, _) => {
1694 // contiguous, insert closer to head:
1697 // [. . . o o o o A o o . . . . . .]
1700 // [. . . o o o o I A o o . . . . .]
1703 self.copy(idx + 1, idx, self.head - idx);
1704 self.head = self.wrap_add(self.head, 1);
1707 (false, true, true) => {
1709 // discontiguous, insert closer to tail, tail section:
1712 // [o o o o o o . . . . . o o A o o]
1715 // [o o o o o o . . . . o o I A o o]
1718 self.copy(self.tail - 1, self.tail, index);
1722 (false, false, true) => {
1724 // discontiguous, insert closer to head, tail section:
1727 // [o o . . . . . . . o o o o o A o]
1730 // [o o o . . . . . . o o o o o I A]
1733 // copy elements up to new head
1734 self.copy(1, 0, self.head);
1736 // copy last element into empty spot at bottom of buffer
1737 self.copy(0, self.cap() - 1, 1);
1739 // move elements from idx to end forward not including ^ element
1740 self.copy(idx + 1, idx, self.cap() - 1 - idx);
1745 (false, true, false) if idx == 0 => {
1747 // discontiguous, insert is closer to tail, head section,
1748 // and is at index zero in the internal buffer:
1751 // [A o o o o o o o o o . . . o o o]
1754 // [A o o o o o o o o o . . o o o I]
1757 // copy elements up to new tail
1758 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1760 // copy last element into empty spot at bottom of buffer
1761 self.copy(self.cap() - 1, 0, 1);
1766 (false, true, false) => {
1768 // discontiguous, insert closer to tail, head section:
1771 // [o o o A o o o o o o . . . o o o]
1774 // [o o I A o o o o o o . . o o o o]
1777 // copy elements up to new tail
1778 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1780 // copy last element into empty spot at bottom of buffer
1781 self.copy(self.cap() - 1, 0, 1);
1783 // move elements from idx-1 to end forward not including ^ element
1784 self.copy(0, 1, idx - 1);
1789 (false, false, false) => {
1791 // discontiguous, insert closer to head, head section:
1794 // [o o o o A o o . . . . . . o o o]
1797 // [o o o o I A o o . . . . . o o o]
1800 self.copy(idx + 1, idx, self.head - idx);
1806 // tail might've been changed so we need to recalculate
1807 let new_idx = self.wrap_add(self.tail, index);
1809 self.buffer_write(new_idx, value);
1813 /// Removes and returns the element at `index` from the `VecDeque`.
1814 /// Whichever end is closer to the removal point will be moved to make
1815 /// room, and all the affected elements will be moved to new positions.
1816 /// Returns `None` if `index` is out of bounds.
1818 /// Element at index 0 is the front of the queue.
1823 /// use std::collections::VecDeque;
1825 /// let mut buf = VecDeque::new();
1826 /// buf.push_back(1);
1827 /// buf.push_back(2);
1828 /// buf.push_back(3);
1829 /// assert_eq!(buf, [1, 2, 3]);
1831 /// assert_eq!(buf.remove(1), Some(2));
1832 /// assert_eq!(buf, [1, 3]);
1834 #[stable(feature = "rust1", since = "1.0.0")]
1835 pub fn remove(&mut self, index: usize) -> Option<T> {
1836 if self.is_empty() || self.len() <= index {
1840 // There are three main cases:
1841 // Elements are contiguous
1842 // Elements are discontiguous and the removal is in the tail section
1843 // Elements are discontiguous and the removal is in the head section
1844 // - special case when elements are technically contiguous,
1845 // but self.head = 0
1847 // For each of those there are two more cases:
1848 // Insert is closer to tail
1849 // Insert is closer to head
1851 // Key: H - self.head
1853 // o - Valid element
1854 // x - Element marked for removal
1855 // R - Indicates element that is being removed
1856 // M - Indicates element was moved
1858 let idx = self.wrap_add(self.tail, index);
1860 let elem = unsafe { Some(self.buffer_read(idx)) };
1862 let distance_to_tail = index;
1863 let distance_to_head = self.len() - index;
1865 let contiguous = self.is_contiguous();
1867 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1868 (true, true, _) => {
1870 // contiguous, remove closer to tail:
1873 // [. . . o o x o o o o . . . . . .]
1876 // [. . . . o o o o o o . . . . . .]
1879 self.copy(self.tail + 1, self.tail, index);
1883 (true, false, _) => {
1885 // contiguous, remove closer to head:
1888 // [. . . o o o o x o o . . . . . .]
1891 // [. . . o o o o o o . . . . . . .]
1894 self.copy(idx, idx + 1, self.head - idx - 1);
1898 (false, true, true) => {
1900 // discontiguous, remove closer to tail, tail section:
1903 // [o o o o o o . . . . . o o x o o]
1906 // [o o o o o o . . . . . . o o o o]
1909 self.copy(self.tail + 1, self.tail, index);
1910 self.tail = self.wrap_add(self.tail, 1);
1913 (false, false, false) => {
1915 // discontiguous, remove closer to head, head section:
1918 // [o o o o x o o . . . . . . o o o]
1921 // [o o o o o o . . . . . . . o o o]
1924 self.copy(idx, idx + 1, self.head - idx - 1);
1928 (false, false, true) => {
1930 // discontiguous, remove closer to head, tail section:
1933 // [o o o . . . . . . o o o o o x o]
1936 // [o o . . . . . . . o o o o o o o]
1939 // or quasi-discontiguous, remove next to head, tail section:
1942 // [. . . . . . . . . o o o o o x o]
1945 // [. . . . . . . . . o o o o o o .]
1948 // draw in elements in the tail section
1949 self.copy(idx, idx + 1, self.cap() - idx - 1);
1951 // Prevents underflow.
1953 // copy first element into empty spot
1954 self.copy(self.cap() - 1, 0, 1);
1956 // move elements in the head section backwards
1957 self.copy(0, 1, self.head - 1);
1960 self.head = self.wrap_sub(self.head, 1);
1963 (false, true, false) => {
1965 // discontiguous, remove closer to tail, head section:
1968 // [o o x o o o o o o o . . . o o o]
1971 // [o o o o o o o o o o . . . . o o]
1974 // draw in elements up to idx
1975 self.copy(1, 0, idx);
1977 // copy last element into empty spot
1978 self.copy(0, self.cap() - 1, 1);
1980 // move elements from tail to end forward, excluding the last one
1981 self.copy(self.tail + 1, self.tail, self.cap() - self.tail - 1);
1983 self.tail = self.wrap_add(self.tail, 1);
1991 /// Splits the `VecDeque` into two at the given index.
1993 /// Returns a newly allocated `VecDeque`. `self` contains elements `[0, at)`,
1994 /// and the returned `VecDeque` contains elements `[at, len)`.
1996 /// Note that the capacity of `self` does not change.
1998 /// Element at index 0 is the front of the queue.
2002 /// Panics if `at > len`.
2007 /// use std::collections::VecDeque;
2009 /// let mut buf: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
2010 /// let buf2 = buf.split_off(1);
2011 /// assert_eq!(buf, [1]);
2012 /// assert_eq!(buf2, [2, 3]);
2015 #[must_use = "use `.truncate()` if you don't need the other half"]
2016 #[stable(feature = "split_off", since = "1.4.0")]
2017 pub fn split_off(&mut self, at: usize) -> Self
2021 let len = self.len();
2022 assert!(at <= len, "`at` out of bounds");
2024 let other_len = len - at;
2025 let mut other = VecDeque::with_capacity_in(other_len, self.allocator().clone());
2028 let (first_half, second_half) = self.as_slices();
2030 let first_len = first_half.len();
2031 let second_len = second_half.len();
2033 // `at` lies in the first half.
2034 let amount_in_first = first_len - at;
2036 ptr::copy_nonoverlapping(first_half.as_ptr().add(at), other.ptr(), amount_in_first);
2038 // just take all of the second half.
2039 ptr::copy_nonoverlapping(
2040 second_half.as_ptr(),
2041 other.ptr().add(amount_in_first),
2045 // `at` lies in the second half, need to factor in the elements we skipped
2046 // in the first half.
2047 let offset = at - first_len;
2048 let amount_in_second = second_len - offset;
2049 ptr::copy_nonoverlapping(
2050 second_half.as_ptr().add(offset),
2057 // Cleanup where the ends of the buffers are
2058 self.head = self.wrap_sub(self.head, other_len);
2059 other.head = other.wrap_index(other_len);
2064 /// Moves all the elements of `other` into `self`, leaving `other` empty.
2068 /// Panics if the new number of elements in self overflows a `usize`.
2073 /// use std::collections::VecDeque;
2075 /// let mut buf: VecDeque<_> = vec![1, 2].into_iter().collect();
2076 /// let mut buf2: VecDeque<_> = vec![3, 4].into_iter().collect();
2077 /// buf.append(&mut buf2);
2078 /// assert_eq!(buf, [1, 2, 3, 4]);
2079 /// assert_eq!(buf2, []);
2082 #[stable(feature = "append", since = "1.4.0")]
2083 pub fn append(&mut self, other: &mut Self) {
2085 self.extend(other.drain(..));
2088 /// Retains only the elements specified by the predicate.
2090 /// In other words, remove all elements `e` such that `f(&e)` returns false.
2091 /// This method operates in place, visiting each element exactly once in the
2092 /// original order, and preserves the order of the retained elements.
2097 /// use std::collections::VecDeque;
2099 /// let mut buf = VecDeque::new();
2100 /// buf.extend(1..5);
2101 /// buf.retain(|&x| x % 2 == 0);
2102 /// assert_eq!(buf, [2, 4]);
2105 /// Because the elements are visited exactly once in the original order,
2106 /// external state may be used to decide which elements to keep.
2109 /// use std::collections::VecDeque;
2111 /// let mut buf = VecDeque::new();
2112 /// buf.extend(1..6);
2114 /// let keep = [false, true, true, false, true];
2115 /// let mut iter = keep.iter();
2116 /// buf.retain(|_| *iter.next().unwrap());
2117 /// assert_eq!(buf, [2, 3, 5]);
2119 #[stable(feature = "vec_deque_retain", since = "1.4.0")]
2120 pub fn retain<F>(&mut self, mut f: F)
2122 F: FnMut(&T) -> bool,
2124 let len = self.len();
2128 // Stage 1: All values are retained.
2137 // Stage 2: Swap retained value into current idx.
2144 self.swap(idx, cur);
2148 // Stage 3: Trancate all values after idx.
2154 // This may panic or abort
2156 fn grow(&mut self) {
2158 let old_cap = self.cap();
2159 // Double the buffer size.
2160 self.buf.reserve_exact(old_cap, old_cap);
2161 assert!(self.cap() == old_cap * 2);
2163 self.handle_capacity_increase(old_cap);
2165 debug_assert!(!self.is_full());
2169 /// Modifies the `VecDeque` in-place so that `len()` is equal to `new_len`,
2170 /// either by removing excess elements from the back or by appending
2171 /// elements generated by calling `generator` to the back.
2176 /// use std::collections::VecDeque;
2178 /// let mut buf = VecDeque::new();
2179 /// buf.push_back(5);
2180 /// buf.push_back(10);
2181 /// buf.push_back(15);
2182 /// assert_eq!(buf, [5, 10, 15]);
2184 /// buf.resize_with(5, Default::default);
2185 /// assert_eq!(buf, [5, 10, 15, 0, 0]);
2187 /// buf.resize_with(2, || unreachable!());
2188 /// assert_eq!(buf, [5, 10]);
2190 /// let mut state = 100;
2191 /// buf.resize_with(5, || { state += 1; state });
2192 /// assert_eq!(buf, [5, 10, 101, 102, 103]);
2194 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2195 pub fn resize_with(&mut self, new_len: usize, generator: impl FnMut() -> T) {
2196 let len = self.len();
2199 self.extend(repeat_with(generator).take(new_len - len))
2201 self.truncate(new_len);
2205 /// Rearranges the internal storage of this deque so it is one contiguous
2206 /// slice, which is then returned.
2208 /// This method does not allocate and does not change the order of the
2209 /// inserted elements. As it returns a mutable slice, this can be used to
2212 /// Once the internal storage is contiguous, the [`as_slices`] and
2213 /// [`as_mut_slices`] methods will return the entire contents of the
2214 /// `VecDeque` in a single slice.
2216 /// [`as_slices`]: VecDeque::as_slices
2217 /// [`as_mut_slices`]: VecDeque::as_mut_slices
2221 /// Sorting the content of a deque.
2224 /// use std::collections::VecDeque;
2226 /// let mut buf = VecDeque::with_capacity(15);
2228 /// buf.push_back(2);
2229 /// buf.push_back(1);
2230 /// buf.push_front(3);
2232 /// // sorting the deque
2233 /// buf.make_contiguous().sort();
2234 /// assert_eq!(buf.as_slices(), (&[1, 2, 3] as &[_], &[] as &[_]));
2236 /// // sorting it in reverse order
2237 /// buf.make_contiguous().sort_by(|a, b| b.cmp(a));
2238 /// assert_eq!(buf.as_slices(), (&[3, 2, 1] as &[_], &[] as &[_]));
2241 /// Getting immutable access to the contiguous slice.
2244 /// use std::collections::VecDeque;
2246 /// let mut buf = VecDeque::new();
2248 /// buf.push_back(2);
2249 /// buf.push_back(1);
2250 /// buf.push_front(3);
2252 /// buf.make_contiguous();
2253 /// if let (slice, &[]) = buf.as_slices() {
2254 /// // we can now be sure that `slice` contains all elements of the deque,
2255 /// // while still having immutable access to `buf`.
2256 /// assert_eq!(buf.len(), slice.len());
2257 /// assert_eq!(slice, &[3, 2, 1] as &[_]);
2260 #[stable(feature = "deque_make_contiguous", since = "1.48.0")]
2261 pub fn make_contiguous(&mut self) -> &mut [T] {
2262 if self.is_contiguous() {
2263 let tail = self.tail;
2264 let head = self.head;
2265 return unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 };
2268 let buf = self.buf.ptr();
2269 let cap = self.cap();
2270 let len = self.len();
2272 let free = self.tail - self.head;
2273 let tail_len = cap - self.tail;
2275 if free >= tail_len {
2276 // there is enough free space to copy the tail in one go,
2277 // this means that we first shift the head backwards, and then
2278 // copy the tail to the correct position.
2280 // from: DEFGH....ABC
2283 ptr::copy(buf, buf.add(tail_len), self.head);
2285 ptr::copy_nonoverlapping(buf.add(self.tail), buf, tail_len);
2291 } else if free > self.head {
2292 // FIXME: We currently do not consider ....ABCDEFGH
2293 // to be contiguous because `head` would be `0` in this
2294 // case. While we probably want to change this it
2295 // isn't trivial as a few places expect `is_contiguous`
2296 // to mean that we can just slice using `buf[tail..head]`.
2298 // there is enough free space to copy the head in one go,
2299 // this means that we first shift the tail forwards, and then
2300 // copy the head to the correct position.
2302 // from: FGH....ABCDE
2305 ptr::copy(buf.add(self.tail), buf.add(self.head), tail_len);
2307 ptr::copy_nonoverlapping(buf, buf.add(self.head + tail_len), self.head);
2310 self.tail = self.head;
2311 self.head = self.wrap_add(self.tail, len);
2314 // free is smaller than both head and tail,
2315 // this means we have to slowly "swap" the tail and the head.
2317 // from: EFGHI...ABCD or HIJK.ABCDEFG
2318 // to: ABCDEFGHI... or ABCDEFGHIJK.
2319 let mut left_edge: usize = 0;
2320 let mut right_edge: usize = self.tail;
2322 // The general problem looks like this
2323 // GHIJKLM...ABCDEF - before any swaps
2324 // ABCDEFM...GHIJKL - after 1 pass of swaps
2325 // ABCDEFGHIJM...KL - swap until the left edge reaches the temp store
2326 // - then restart the algorithm with a new (smaller) store
2327 // Sometimes the temp store is reached when the right edge is at the end
2328 // of the buffer - this means we've hit the right order with fewer swaps!
2331 // ABCDEF.. - after four only swaps we've finished
2332 while left_edge < len && right_edge != cap {
2333 let mut right_offset = 0;
2334 for i in left_edge..right_edge {
2335 right_offset = (i - left_edge) % (cap - right_edge);
2336 let src: isize = (right_edge + right_offset) as isize;
2337 ptr::swap(buf.add(i), buf.offset(src));
2339 let n_ops = right_edge - left_edge;
2341 right_edge += right_offset + 1;
2349 let tail = self.tail;
2350 let head = self.head;
2351 unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 }
2354 /// Rotates the double-ended queue `mid` places to the left.
2357 /// - Rotates item `mid` into the first position.
2358 /// - Pops the first `mid` items and pushes them to the end.
2359 /// - Rotates `len() - mid` places to the right.
2363 /// If `mid` is greater than `len()`. Note that `mid == len()`
2364 /// does _not_ panic and is a no-op rotation.
2368 /// Takes `*O*(min(mid, len() - mid))` time and no extra space.
2373 /// use std::collections::VecDeque;
2375 /// let mut buf: VecDeque<_> = (0..10).collect();
2377 /// buf.rotate_left(3);
2378 /// assert_eq!(buf, [3, 4, 5, 6, 7, 8, 9, 0, 1, 2]);
2380 /// for i in 1..10 {
2381 /// assert_eq!(i * 3 % 10, buf[0]);
2382 /// buf.rotate_left(3);
2384 /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
2386 #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
2387 pub fn rotate_left(&mut self, mid: usize) {
2388 assert!(mid <= self.len());
2389 let k = self.len() - mid;
2391 unsafe { self.rotate_left_inner(mid) }
2393 unsafe { self.rotate_right_inner(k) }
2397 /// Rotates the double-ended queue `k` places to the right.
2400 /// - Rotates the first item into position `k`.
2401 /// - Pops the last `k` items and pushes them to the front.
2402 /// - Rotates `len() - k` places to the left.
2406 /// If `k` is greater than `len()`. Note that `k == len()`
2407 /// does _not_ panic and is a no-op rotation.
2411 /// Takes `*O*(min(k, len() - k))` time and no extra space.
2416 /// use std::collections::VecDeque;
2418 /// let mut buf: VecDeque<_> = (0..10).collect();
2420 /// buf.rotate_right(3);
2421 /// assert_eq!(buf, [7, 8, 9, 0, 1, 2, 3, 4, 5, 6]);
2423 /// for i in 1..10 {
2424 /// assert_eq!(0, buf[i * 3 % 10]);
2425 /// buf.rotate_right(3);
2427 /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
2429 #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
2430 pub fn rotate_right(&mut self, k: usize) {
2431 assert!(k <= self.len());
2432 let mid = self.len() - k;
2434 unsafe { self.rotate_right_inner(k) }
2436 unsafe { self.rotate_left_inner(mid) }
2440 // SAFETY: the following two methods require that the rotation amount
2441 // be less than half the length of the deque.
2443 // `wrap_copy` requires that `min(x, cap() - x) + copy_len <= cap()`,
2444 // but than `min` is never more than half the capacity, regardless of x,
2445 // so it's sound to call here because we're calling with something
2446 // less than half the length, which is never above half the capacity.
2448 unsafe fn rotate_left_inner(&mut self, mid: usize) {
2449 debug_assert!(mid * 2 <= self.len());
2451 self.wrap_copy(self.head, self.tail, mid);
2453 self.head = self.wrap_add(self.head, mid);
2454 self.tail = self.wrap_add(self.tail, mid);
2457 unsafe fn rotate_right_inner(&mut self, k: usize) {
2458 debug_assert!(k * 2 <= self.len());
2459 self.head = self.wrap_sub(self.head, k);
2460 self.tail = self.wrap_sub(self.tail, k);
2462 self.wrap_copy(self.tail, self.head, k);
2466 /// Binary searches this sorted `VecDeque` for a given element.
2468 /// If the value is found then [`Result::Ok`] is returned, containing the
2469 /// index of the matching element. If there are multiple matches, then any
2470 /// one of the matches could be returned. If the value is not found then
2471 /// [`Result::Err`] is returned, containing the index where a matching
2472 /// element could be inserted while maintaining sorted order.
2474 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2476 /// [`binary_search_by`]: VecDeque::binary_search_by
2477 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2478 /// [`partition_point`]: VecDeque::partition_point
2482 /// Looks up a series of four elements. The first is found, with a
2483 /// uniquely determined position; the second and third are not
2484 /// found; the fourth could match any position in `[1, 4]`.
2487 /// use std::collections::VecDeque;
2489 /// let deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2491 /// assert_eq!(deque.binary_search(&13), Ok(9));
2492 /// assert_eq!(deque.binary_search(&4), Err(7));
2493 /// assert_eq!(deque.binary_search(&100), Err(13));
2494 /// let r = deque.binary_search(&1);
2495 /// assert!(matches!(r, Ok(1..=4)));
2498 /// If you want to insert an item to a sorted `VecDeque`, while maintaining
2502 /// use std::collections::VecDeque;
2504 /// let mut deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2506 /// let idx = deque.binary_search(&num).unwrap_or_else(|x| x);
2507 /// deque.insert(idx, num);
2508 /// assert_eq!(deque, &[0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2510 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2512 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2516 self.binary_search_by(|e| e.cmp(x))
2519 /// Binary searches this sorted `VecDeque` with a comparator function.
2521 /// The comparator function should implement an order consistent
2522 /// with the sort order of the underlying `VecDeque`, returning an
2523 /// order code that indicates whether its argument is `Less`,
2524 /// `Equal` or `Greater` than the desired target.
2526 /// If the value is found then [`Result::Ok`] is returned, containing the
2527 /// index of the matching element. If there are multiple matches, then any
2528 /// one of the matches could be returned. If the value is not found then
2529 /// [`Result::Err`] is returned, containing the index where a matching
2530 /// element could be inserted while maintaining sorted order.
2532 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2534 /// [`binary_search`]: VecDeque::binary_search
2535 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2536 /// [`partition_point`]: VecDeque::partition_point
2540 /// Looks up a series of four elements. The first is found, with a
2541 /// uniquely determined position; the second and third are not
2542 /// found; the fourth could match any position in `[1, 4]`.
2545 /// use std::collections::VecDeque;
2547 /// let deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2549 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&13)), Ok(9));
2550 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&4)), Err(7));
2551 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&100)), Err(13));
2552 /// let r = deque.binary_search_by(|x| x.cmp(&1));
2553 /// assert!(matches!(r, Ok(1..=4)));
2555 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2556 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2558 F: FnMut(&'a T) -> Ordering,
2560 let (front, back) = self.as_slices();
2561 let cmp_back = back.first().map(|elem| f(elem));
2563 if let Some(Ordering::Equal) = cmp_back {
2565 } else if let Some(Ordering::Less) = cmp_back {
2566 back.binary_search_by(f).map(|idx| idx + front.len()).map_err(|idx| idx + front.len())
2568 front.binary_search_by(f)
2572 /// Binary searches this sorted `VecDeque` with a key extraction function.
2574 /// Assumes that the `VecDeque` is sorted by the key, for instance with
2575 /// [`make_contiguous().sort_by_key()`] using the same key extraction function.
2577 /// If the value is found then [`Result::Ok`] is returned, containing the
2578 /// index of the matching element. If there are multiple matches, then any
2579 /// one of the matches could be returned. If the value is not found then
2580 /// [`Result::Err`] is returned, containing the index where a matching
2581 /// element could be inserted while maintaining sorted order.
2583 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2585 /// [`make_contiguous().sort_by_key()`]: VecDeque::make_contiguous
2586 /// [`binary_search`]: VecDeque::binary_search
2587 /// [`binary_search_by`]: VecDeque::binary_search_by
2588 /// [`partition_point`]: VecDeque::partition_point
2592 /// Looks up a series of four elements in a slice of pairs sorted by
2593 /// their second elements. The first is found, with a uniquely
2594 /// determined position; the second and third are not found; the
2595 /// fourth could match any position in `[1, 4]`.
2598 /// use std::collections::VecDeque;
2600 /// let deque: VecDeque<_> = vec![(0, 0), (2, 1), (4, 1), (5, 1),
2601 /// (3, 1), (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2602 /// (1, 21), (2, 34), (4, 55)].into();
2604 /// assert_eq!(deque.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2605 /// assert_eq!(deque.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2606 /// assert_eq!(deque.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2607 /// let r = deque.binary_search_by_key(&1, |&(a, b)| b);
2608 /// assert!(matches!(r, Ok(1..=4)));
2610 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2612 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2614 F: FnMut(&'a T) -> B,
2617 self.binary_search_by(|k| f(k).cmp(b))
2620 /// Returns the index of the partition point according to the given predicate
2621 /// (the index of the first element of the second partition).
2623 /// The deque is assumed to be partitioned according to the given predicate.
2624 /// This means that all elements for which the predicate returns true are at the start of the deque
2625 /// and all elements for which the predicate returns false are at the end.
2626 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
2627 /// (all odd numbers are at the start, all even at the end).
2629 /// If this deque is not partitioned, the returned result is unspecified and meaningless,
2630 /// as this method performs a kind of binary search.
2632 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
2634 /// [`binary_search`]: VecDeque::binary_search
2635 /// [`binary_search_by`]: VecDeque::binary_search_by
2636 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2641 /// use std::collections::VecDeque;
2643 /// let deque: VecDeque<_> = vec![1, 2, 3, 3, 5, 6, 7].into();
2644 /// let i = deque.partition_point(|&x| x < 5);
2646 /// assert_eq!(i, 4);
2647 /// assert!(deque.iter().take(i).all(|&x| x < 5));
2648 /// assert!(deque.iter().skip(i).all(|&x| !(x < 5)));
2650 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2651 pub fn partition_point<P>(&self, mut pred: P) -> usize
2653 P: FnMut(&T) -> bool,
2655 let (front, back) = self.as_slices();
2657 if let Some(true) = back.first().map(|v| pred(v)) {
2658 back.partition_point(pred) + front.len()
2660 front.partition_point(pred)
2665 impl<T: Clone, A: Allocator> VecDeque<T, A> {
2666 /// Modifies the `VecDeque` in-place so that `len()` is equal to new_len,
2667 /// either by removing excess elements from the back or by appending clones of `value`
2673 /// use std::collections::VecDeque;
2675 /// let mut buf = VecDeque::new();
2676 /// buf.push_back(5);
2677 /// buf.push_back(10);
2678 /// buf.push_back(15);
2679 /// assert_eq!(buf, [5, 10, 15]);
2681 /// buf.resize(2, 0);
2682 /// assert_eq!(buf, [5, 10]);
2684 /// buf.resize(5, 20);
2685 /// assert_eq!(buf, [5, 10, 20, 20, 20]);
2687 #[stable(feature = "deque_extras", since = "1.16.0")]
2688 pub fn resize(&mut self, new_len: usize, value: T) {
2689 self.resize_with(new_len, || value.clone());
2693 /// Returns the index in the underlying buffer for a given logical element index.
2695 fn wrap_index(index: usize, size: usize) -> usize {
2696 // size is always a power of 2
2697 debug_assert!(size.is_power_of_two());
2701 /// Calculate the number of elements left to be read in the buffer
2703 fn count(tail: usize, head: usize, size: usize) -> usize {
2704 // size is always a power of 2
2705 (head.wrapping_sub(tail)) & (size - 1)
2708 #[stable(feature = "rust1", since = "1.0.0")]
2709 impl<T: PartialEq, A: Allocator> PartialEq for VecDeque<T, A> {
2710 fn eq(&self, other: &Self) -> bool {
2711 if self.len() != other.len() {
2714 let (sa, sb) = self.as_slices();
2715 let (oa, ob) = other.as_slices();
2716 if sa.len() == oa.len() {
2717 sa == oa && sb == ob
2718 } else if sa.len() < oa.len() {
2719 // Always divisible in three sections, for example:
2720 // self: [a b c|d e f]
2721 // other: [0 1 2 3|4 5]
2722 // front = 3, mid = 1,
2723 // [a b c] == [0 1 2] && [d] == [3] && [e f] == [4 5]
2724 let front = sa.len();
2725 let mid = oa.len() - front;
2727 let (oa_front, oa_mid) = oa.split_at(front);
2728 let (sb_mid, sb_back) = sb.split_at(mid);
2729 debug_assert_eq!(sa.len(), oa_front.len());
2730 debug_assert_eq!(sb_mid.len(), oa_mid.len());
2731 debug_assert_eq!(sb_back.len(), ob.len());
2732 sa == oa_front && sb_mid == oa_mid && sb_back == ob
2734 let front = oa.len();
2735 let mid = sa.len() - front;
2737 let (sa_front, sa_mid) = sa.split_at(front);
2738 let (ob_mid, ob_back) = ob.split_at(mid);
2739 debug_assert_eq!(sa_front.len(), oa.len());
2740 debug_assert_eq!(sa_mid.len(), ob_mid.len());
2741 debug_assert_eq!(sb.len(), ob_back.len());
2742 sa_front == oa && sa_mid == ob_mid && sb == ob_back
2747 #[stable(feature = "rust1", since = "1.0.0")]
2748 impl<T: Eq, A: Allocator> Eq for VecDeque<T, A> {}
2750 __impl_slice_eq1! { [] VecDeque<T, A>, Vec<U, A>, }
2751 __impl_slice_eq1! { [] VecDeque<T, A>, &[U], }
2752 __impl_slice_eq1! { [] VecDeque<T, A>, &mut [U], }
2753 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, [U; N], }
2754 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &[U; N], }
2755 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &mut [U; N], }
2757 #[stable(feature = "rust1", since = "1.0.0")]
2758 impl<T: PartialOrd, A: Allocator> PartialOrd for VecDeque<T, A> {
2759 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2760 self.iter().partial_cmp(other.iter())
2764 #[stable(feature = "rust1", since = "1.0.0")]
2765 impl<T: Ord, A: Allocator> Ord for VecDeque<T, A> {
2767 fn cmp(&self, other: &Self) -> Ordering {
2768 self.iter().cmp(other.iter())
2772 #[stable(feature = "rust1", since = "1.0.0")]
2773 impl<T: Hash, A: Allocator> Hash for VecDeque<T, A> {
2774 fn hash<H: Hasher>(&self, state: &mut H) {
2775 self.len().hash(state);
2776 // It's not possible to use Hash::hash_slice on slices
2777 // returned by as_slices method as their length can vary
2778 // in otherwise identical deques.
2780 // Hasher only guarantees equivalence for the exact same
2781 // set of calls to its methods.
2782 self.iter().for_each(|elem| elem.hash(state));
2786 #[stable(feature = "rust1", since = "1.0.0")]
2787 impl<T, A: Allocator> Index<usize> for VecDeque<T, A> {
2791 fn index(&self, index: usize) -> &T {
2792 self.get(index).expect("Out of bounds access")
2796 #[stable(feature = "rust1", since = "1.0.0")]
2797 impl<T, A: Allocator> IndexMut<usize> for VecDeque<T, A> {
2799 fn index_mut(&mut self, index: usize) -> &mut T {
2800 self.get_mut(index).expect("Out of bounds access")
2804 #[stable(feature = "rust1", since = "1.0.0")]
2805 impl<T> FromIterator<T> for VecDeque<T> {
2806 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> VecDeque<T> {
2807 let iterator = iter.into_iter();
2808 let (lower, _) = iterator.size_hint();
2809 let mut deq = VecDeque::with_capacity(lower);
2810 deq.extend(iterator);
2815 #[stable(feature = "rust1", since = "1.0.0")]
2816 impl<T, A: Allocator> IntoIterator for VecDeque<T, A> {
2818 type IntoIter = IntoIter<T, A>;
2820 /// Consumes the `VecDeque` into a front-to-back iterator yielding elements by
2822 fn into_iter(self) -> IntoIter<T, A> {
2827 #[stable(feature = "rust1", since = "1.0.0")]
2828 impl<'a, T, A: Allocator> IntoIterator for &'a VecDeque<T, A> {
2830 type IntoIter = Iter<'a, T>;
2832 fn into_iter(self) -> Iter<'a, T> {
2837 #[stable(feature = "rust1", since = "1.0.0")]
2838 impl<'a, T, A: Allocator> IntoIterator for &'a mut VecDeque<T, A> {
2839 type Item = &'a mut T;
2840 type IntoIter = IterMut<'a, T>;
2842 fn into_iter(self) -> IterMut<'a, T> {
2847 #[stable(feature = "rust1", since = "1.0.0")]
2848 impl<T, A: Allocator> Extend<T> for VecDeque<T, A> {
2849 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2850 // This function should be the moral equivalent of:
2852 // for item in iter.into_iter() {
2853 // self.push_back(item);
2855 let mut iter = iter.into_iter();
2856 while let Some(element) = iter.next() {
2857 if self.len() == self.capacity() {
2858 let (lower, _) = iter.size_hint();
2859 self.reserve(lower.saturating_add(1));
2862 let head = self.head;
2863 self.head = self.wrap_add(self.head, 1);
2865 self.buffer_write(head, element);
2871 fn extend_one(&mut self, elem: T) {
2872 self.push_back(elem);
2876 fn extend_reserve(&mut self, additional: usize) {
2877 self.reserve(additional);
2881 #[stable(feature = "extend_ref", since = "1.2.0")]
2882 impl<'a, T: 'a + Copy, A: Allocator> Extend<&'a T> for VecDeque<T, A> {
2883 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2884 self.extend(iter.into_iter().cloned());
2888 fn extend_one(&mut self, &elem: &T) {
2889 self.push_back(elem);
2893 fn extend_reserve(&mut self, additional: usize) {
2894 self.reserve(additional);
2898 #[stable(feature = "rust1", since = "1.0.0")]
2899 impl<T: fmt::Debug, A: Allocator> fmt::Debug for VecDeque<T, A> {
2900 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2901 f.debug_list().entries(self).finish()
2905 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2906 impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A> {
2907 /// Turn a [`Vec<T>`] into a [`VecDeque<T>`].
2909 /// [`Vec<T>`]: crate::vec::Vec
2910 /// [`VecDeque<T>`]: crate::collections::VecDeque
2912 /// This avoids reallocating where possible, but the conditions for that are
2913 /// strict, and subject to change, and so shouldn't be relied upon unless the
2914 /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated.
2915 fn from(mut other: Vec<T, A>) -> Self {
2916 let len = other.len();
2917 if mem::size_of::<T>() == 0 {
2918 // There's no actual allocation for ZSTs to worry about capacity,
2919 // but `VecDeque` can't handle as much length as `Vec`.
2920 assert!(len < MAXIMUM_ZST_CAPACITY, "capacity overflow");
2922 // We need to resize if the capacity is not a power of two, too small or
2923 // doesn't have at least one free space. We do this while it's still in
2924 // the `Vec` so the items will drop on panic.
2925 let min_cap = cmp::max(MINIMUM_CAPACITY, len) + 1;
2926 let cap = cmp::max(min_cap, other.capacity()).next_power_of_two();
2927 if other.capacity() != cap {
2928 other.reserve_exact(cap - len);
2933 let (other_buf, len, capacity, alloc) = other.into_raw_parts_with_alloc();
2934 let buf = RawVec::from_raw_parts_in(other_buf, capacity, alloc);
2935 VecDeque { tail: 0, head: len, buf }
2940 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2941 impl<T, A: Allocator> From<VecDeque<T, A>> for Vec<T, A> {
2942 /// Turn a [`VecDeque<T>`] into a [`Vec<T>`].
2944 /// [`Vec<T>`]: crate::vec::Vec
2945 /// [`VecDeque<T>`]: crate::collections::VecDeque
2947 /// This never needs to re-allocate, but does need to do *O*(*n*) data movement if
2948 /// the circular buffer doesn't happen to be at the beginning of the allocation.
2953 /// use std::collections::VecDeque;
2955 /// // This one is *O*(1).
2956 /// let deque: VecDeque<_> = (1..5).collect();
2957 /// let ptr = deque.as_slices().0.as_ptr();
2958 /// let vec = Vec::from(deque);
2959 /// assert_eq!(vec, [1, 2, 3, 4]);
2960 /// assert_eq!(vec.as_ptr(), ptr);
2962 /// // This one needs data rearranging.
2963 /// let mut deque: VecDeque<_> = (1..5).collect();
2964 /// deque.push_front(9);
2965 /// deque.push_front(8);
2966 /// let ptr = deque.as_slices().1.as_ptr();
2967 /// let vec = Vec::from(deque);
2968 /// assert_eq!(vec, [8, 9, 1, 2, 3, 4]);
2969 /// assert_eq!(vec.as_ptr(), ptr);
2971 fn from(mut other: VecDeque<T, A>) -> Self {
2972 other.make_contiguous();
2975 let other = ManuallyDrop::new(other);
2976 let buf = other.buf.ptr();
2977 let len = other.len();
2978 let cap = other.cap();
2979 let alloc = ptr::read(other.allocator());
2981 if other.tail != 0 {
2982 ptr::copy(buf.add(other.tail), buf, len);
2984 Vec::from_raw_parts_in(buf, len, cap, alloc)
2989 #[stable(feature = "std_collections_from_array", since = "1.56.0")]
2990 impl<T, const N: usize> From<[T; N]> for VecDeque<T> {
2992 /// use std::collections::VecDeque;
2994 /// let deq1 = VecDeque::from([1, 2, 3, 4]);
2995 /// let deq2: VecDeque<_> = [1, 2, 3, 4].into();
2996 /// assert_eq!(deq1, deq2);
2998 fn from(arr: [T; N]) -> Self {
2999 let mut deq = VecDeque::with_capacity(N);
3000 let arr = ManuallyDrop::new(arr);
3001 if mem::size_of::<T>() != 0 {
3002 // SAFETY: VecDeque::with_capacity ensures that there is enough capacity.
3004 ptr::copy_nonoverlapping(arr.as_ptr(), deq.ptr(), N);