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 /// use std::collections::TryReserveError;
715 /// use std::collections::VecDeque;
717 /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> {
718 /// let mut output = VecDeque::new();
720 /// // Pre-reserve the memory, exiting if we can't
721 /// output.try_reserve_exact(data.len())?;
723 /// // Now we know this can't OOM(Out-Of-Memory) in the middle of our complex work
724 /// output.extend(data.iter().map(|&val| {
725 /// val * 2 + 5 // very complicated
730 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
732 #[stable(feature = "try_reserve", since = "1.57.0")]
733 pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
734 self.try_reserve(additional)
737 /// Tries to reserve capacity for at least `additional` more elements to be inserted
738 /// in the given `VecDeque<T>`. The collection may reserve more space to avoid
739 /// frequent reallocations. After calling `try_reserve`, capacity will be
740 /// greater than or equal to `self.len() + additional`. Does nothing if
741 /// capacity is already sufficient.
745 /// If the capacity overflows `usize`, or the allocator reports a failure, then an error
751 /// use std::collections::TryReserveError;
752 /// use std::collections::VecDeque;
754 /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> {
755 /// let mut output = VecDeque::new();
757 /// // Pre-reserve the memory, exiting if we can't
758 /// output.try_reserve(data.len())?;
760 /// // Now we know this can't OOM in the middle of our complex work
761 /// output.extend(data.iter().map(|&val| {
762 /// val * 2 + 5 // very complicated
767 /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
769 #[stable(feature = "try_reserve", since = "1.57.0")]
770 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
771 let old_cap = self.cap();
772 let used_cap = self.len() + 1;
773 let new_cap = used_cap
774 .checked_add(additional)
775 .and_then(|needed_cap| needed_cap.checked_next_power_of_two())
776 .ok_or(TryReserveErrorKind::CapacityOverflow)?;
778 if new_cap > old_cap {
779 self.buf.try_reserve_exact(used_cap, new_cap - used_cap)?;
781 self.handle_capacity_increase(old_cap);
787 /// Shrinks the capacity of the `VecDeque` as much as possible.
789 /// It will drop down as close as possible to the length but the allocator may still inform the
790 /// `VecDeque` that there is space for a few more elements.
795 /// use std::collections::VecDeque;
797 /// let mut buf = VecDeque::with_capacity(15);
798 /// buf.extend(0..4);
799 /// assert_eq!(buf.capacity(), 15);
800 /// buf.shrink_to_fit();
801 /// assert!(buf.capacity() >= 4);
803 #[stable(feature = "deque_extras_15", since = "1.5.0")]
804 pub fn shrink_to_fit(&mut self) {
808 /// Shrinks the capacity of the `VecDeque` with a lower bound.
810 /// The capacity will remain at least as large as both the length
811 /// and the supplied value.
813 /// If the current capacity is less than the lower limit, this is a no-op.
818 /// use std::collections::VecDeque;
820 /// let mut buf = VecDeque::with_capacity(15);
821 /// buf.extend(0..4);
822 /// assert_eq!(buf.capacity(), 15);
823 /// buf.shrink_to(6);
824 /// assert!(buf.capacity() >= 6);
825 /// buf.shrink_to(0);
826 /// assert!(buf.capacity() >= 4);
828 #[stable(feature = "shrink_to", since = "1.56.0")]
829 pub fn shrink_to(&mut self, min_capacity: usize) {
830 let min_capacity = cmp::min(min_capacity, self.capacity());
831 // We don't have to worry about an overflow as neither `self.len()` nor `self.capacity()`
832 // can ever be `usize::MAX`. +1 as the ringbuffer always leaves one space empty.
833 let target_cap = cmp::max(cmp::max(min_capacity, self.len()) + 1, MINIMUM_CAPACITY + 1)
834 .next_power_of_two();
836 if target_cap < self.cap() {
837 // There are three cases of interest:
838 // All elements are out of desired bounds
839 // Elements are contiguous, and head is out of desired bounds
840 // Elements are discontiguous, and tail is out of desired bounds
842 // At all other times, element positions are unaffected.
844 // Indicates that elements at the head should be moved.
845 let head_outside = self.head == 0 || self.head >= target_cap;
846 // Move elements from out of desired bounds (positions after target_cap)
847 if self.tail >= target_cap && head_outside {
849 // [. . . . . . . . o o o o o o o . ]
851 // [o o o o o o o . ]
853 self.copy_nonoverlapping(0, self.tail, self.len());
855 self.head = self.len();
857 } else if self.tail != 0 && self.tail < target_cap && head_outside {
859 // [. . . o o o o o o o . . . . . . ]
861 // [o o . o o o o o ]
862 let len = self.wrap_sub(self.head, target_cap);
864 self.copy_nonoverlapping(0, target_cap, len);
867 debug_assert!(self.head < self.tail);
868 } else if self.tail >= target_cap {
870 // [o o o o o . . . . . . . . . o o ]
872 // [o o o o o . o o ]
873 debug_assert!(self.wrap_sub(self.head, 1) < target_cap);
874 let len = self.cap() - self.tail;
875 let new_tail = target_cap - len;
877 self.copy_nonoverlapping(new_tail, self.tail, len);
879 self.tail = new_tail;
880 debug_assert!(self.head < self.tail);
883 self.buf.shrink_to_fit(target_cap);
885 debug_assert!(self.head < self.cap());
886 debug_assert!(self.tail < self.cap());
887 debug_assert!(self.cap().count_ones() == 1);
891 /// Shortens the `VecDeque`, keeping the first `len` elements and dropping
894 /// If `len` is greater than the `VecDeque`'s current length, this has no
900 /// use std::collections::VecDeque;
902 /// let mut buf = VecDeque::new();
903 /// buf.push_back(5);
904 /// buf.push_back(10);
905 /// buf.push_back(15);
906 /// assert_eq!(buf, [5, 10, 15]);
908 /// assert_eq!(buf, [5]);
910 #[stable(feature = "deque_extras", since = "1.16.0")]
911 pub fn truncate(&mut self, len: usize) {
912 /// Runs the destructor for all items in the slice when it gets dropped (normally or
913 /// during unwinding).
914 struct Dropper<'a, T>(&'a mut [T]);
916 impl<'a, T> Drop for Dropper<'a, T> {
919 ptr::drop_in_place(self.0);
926 // * Any slice passed to `drop_in_place` is valid; the second case has
927 // `len <= front.len()` and returning on `len > self.len()` ensures
928 // `begin <= back.len()` in the first case
929 // * The head of the VecDeque is moved before calling `drop_in_place`,
930 // so no value is dropped twice if `drop_in_place` panics
932 if len > self.len() {
935 let num_dropped = self.len() - len;
936 let (front, back) = self.as_mut_slices();
937 if len > front.len() {
938 let begin = len - front.len();
939 let drop_back = back.get_unchecked_mut(begin..) as *mut _;
940 self.head = self.wrap_sub(self.head, num_dropped);
941 ptr::drop_in_place(drop_back);
943 let drop_back = back as *mut _;
944 let drop_front = front.get_unchecked_mut(len..) as *mut _;
945 self.head = self.wrap_sub(self.head, num_dropped);
947 // Make sure the second half is dropped even when a destructor
948 // in the first one panics.
949 let _back_dropper = Dropper(&mut *drop_back);
950 ptr::drop_in_place(drop_front);
955 /// Returns a reference to the underlying allocator.
956 #[unstable(feature = "allocator_api", issue = "32838")]
958 pub fn allocator(&self) -> &A {
962 /// Returns a front-to-back iterator.
967 /// use std::collections::VecDeque;
969 /// let mut buf = VecDeque::new();
970 /// buf.push_back(5);
971 /// buf.push_back(3);
972 /// buf.push_back(4);
973 /// let b: &[_] = &[&5, &3, &4];
974 /// let c: Vec<&i32> = buf.iter().collect();
975 /// assert_eq!(&c[..], b);
977 #[stable(feature = "rust1", since = "1.0.0")]
978 pub fn iter(&self) -> Iter<'_, T> {
979 Iter { tail: self.tail, head: self.head, ring: unsafe { self.buffer_as_slice() } }
982 /// Returns a front-to-back iterator that returns mutable references.
987 /// use std::collections::VecDeque;
989 /// let mut buf = VecDeque::new();
990 /// buf.push_back(5);
991 /// buf.push_back(3);
992 /// buf.push_back(4);
993 /// for num in buf.iter_mut() {
996 /// let b: &[_] = &[&mut 3, &mut 1, &mut 2];
997 /// assert_eq!(&buf.iter_mut().collect::<Vec<&mut i32>>()[..], b);
999 #[stable(feature = "rust1", since = "1.0.0")]
1000 pub fn iter_mut(&mut self) -> IterMut<'_, T> {
1001 // SAFETY: The internal `IterMut` safety invariant is established because the
1002 // `ring` we create is a dereferencable slice for lifetime '_.
1003 let ring = ptr::slice_from_raw_parts_mut(self.ptr(), self.cap());
1005 unsafe { IterMut::new(ring, self.tail, self.head, PhantomData) }
1008 /// Returns a pair of slices which contain, in order, the contents of the
1011 /// If [`make_contiguous`] was previously called, all elements of the
1012 /// `VecDeque` will be in the first slice and the second slice will be empty.
1014 /// [`make_contiguous`]: VecDeque::make_contiguous
1019 /// use std::collections::VecDeque;
1021 /// let mut vector = VecDeque::new();
1023 /// vector.push_back(0);
1024 /// vector.push_back(1);
1025 /// vector.push_back(2);
1027 /// assert_eq!(vector.as_slices(), (&[0, 1, 2][..], &[][..]));
1029 /// vector.push_front(10);
1030 /// vector.push_front(9);
1032 /// assert_eq!(vector.as_slices(), (&[9, 10][..], &[0, 1, 2][..]));
1035 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1036 pub fn as_slices(&self) -> (&[T], &[T]) {
1038 let buf = self.buffer_as_slice();
1039 RingSlices::ring_slices(buf, self.head, self.tail)
1043 /// Returns a pair of slices which contain, in order, the contents of the
1046 /// If [`make_contiguous`] was previously called, all elements of the
1047 /// `VecDeque` will be in the first slice and the second slice will be empty.
1049 /// [`make_contiguous`]: VecDeque::make_contiguous
1054 /// use std::collections::VecDeque;
1056 /// let mut vector = VecDeque::new();
1058 /// vector.push_back(0);
1059 /// vector.push_back(1);
1061 /// vector.push_front(10);
1062 /// vector.push_front(9);
1064 /// vector.as_mut_slices().0[0] = 42;
1065 /// vector.as_mut_slices().1[0] = 24;
1066 /// assert_eq!(vector.as_slices(), (&[42, 10][..], &[24, 1][..]));
1069 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1070 pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) {
1072 let head = self.head;
1073 let tail = self.tail;
1074 let buf = self.buffer_as_mut_slice();
1075 RingSlices::ring_slices(buf, head, tail)
1079 /// Returns the number of elements in the `VecDeque`.
1084 /// use std::collections::VecDeque;
1086 /// let mut v = VecDeque::new();
1087 /// assert_eq!(v.len(), 0);
1089 /// assert_eq!(v.len(), 1);
1091 #[stable(feature = "rust1", since = "1.0.0")]
1092 pub fn len(&self) -> usize {
1093 count(self.tail, self.head, self.cap())
1096 /// Returns `true` if the `VecDeque` is empty.
1101 /// use std::collections::VecDeque;
1103 /// let mut v = VecDeque::new();
1104 /// assert!(v.is_empty());
1105 /// v.push_front(1);
1106 /// assert!(!v.is_empty());
1108 #[stable(feature = "rust1", since = "1.0.0")]
1109 pub fn is_empty(&self) -> bool {
1110 self.tail == self.head
1113 fn range_tail_head<R>(&self, range: R) -> (usize, usize)
1115 R: RangeBounds<usize>,
1117 let Range { start, end } = slice::range(range, ..self.len());
1118 let tail = self.wrap_add(self.tail, start);
1119 let head = self.wrap_add(self.tail, end);
1123 /// Creates an iterator that covers the specified range in the `VecDeque`.
1127 /// Panics if the starting point is greater than the end point or if
1128 /// the end point is greater than the length of the vector.
1133 /// use std::collections::VecDeque;
1135 /// let v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1136 /// let range = v.range(2..).copied().collect::<VecDeque<_>>();
1137 /// assert_eq!(range, [3]);
1139 /// // A full range covers all contents
1140 /// let all = v.range(..);
1141 /// assert_eq!(all.len(), 3);
1144 #[stable(feature = "deque_range", since = "1.51.0")]
1145 pub fn range<R>(&self, range: R) -> Iter<'_, T>
1147 R: RangeBounds<usize>,
1149 let (tail, head) = self.range_tail_head(range);
1153 // The shared reference we have in &self is maintained in the '_ of Iter.
1154 ring: unsafe { self.buffer_as_slice() },
1158 /// Creates an iterator that covers the specified mutable range in the `VecDeque`.
1162 /// Panics if the starting point is greater than the end point or if
1163 /// the end point is greater than the length of the vector.
1168 /// use std::collections::VecDeque;
1170 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1171 /// for v in v.range_mut(2..) {
1174 /// assert_eq!(v, vec![1, 2, 6]);
1176 /// // A full range covers all contents
1177 /// for v in v.range_mut(..) {
1180 /// assert_eq!(v, vec![2, 4, 12]);
1183 #[stable(feature = "deque_range", since = "1.51.0")]
1184 pub fn range_mut<R>(&mut self, range: R) -> IterMut<'_, T>
1186 R: RangeBounds<usize>,
1188 let (tail, head) = self.range_tail_head(range);
1190 // SAFETY: The internal `IterMut` safety invariant is established because the
1191 // `ring` we create is a dereferencable slice for lifetime '_.
1192 let ring = ptr::slice_from_raw_parts_mut(self.ptr(), self.cap());
1194 unsafe { IterMut::new(ring, tail, head, PhantomData) }
1197 /// Creates a draining iterator that removes the specified range in the
1198 /// `VecDeque` and yields the removed items.
1200 /// Note 1: The element range is removed even if the iterator is not
1201 /// consumed until the end.
1203 /// Note 2: It is unspecified how many elements are removed from the deque,
1204 /// if the `Drain` value is not dropped, but the borrow it holds expires
1205 /// (e.g., due to `mem::forget`).
1209 /// Panics if the starting point is greater than the end point or if
1210 /// the end point is greater than the length of the vector.
1215 /// use std::collections::VecDeque;
1217 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1218 /// let drained = v.drain(2..).collect::<VecDeque<_>>();
1219 /// assert_eq!(drained, [3]);
1220 /// assert_eq!(v, [1, 2]);
1222 /// // A full range clears all contents
1224 /// assert!(v.is_empty());
1227 #[stable(feature = "drain", since = "1.6.0")]
1228 pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
1230 R: RangeBounds<usize>,
1234 // When the Drain is first created, the source deque is shortened to
1235 // make sure no uninitialized or moved-from elements are accessible at
1236 // all if the Drain's destructor never gets to run.
1238 // Drain will ptr::read out the values to remove.
1239 // When finished, the remaining data will be copied back to cover the hole,
1240 // and the head/tail values will be restored correctly.
1242 let (drain_tail, drain_head) = self.range_tail_head(range);
1244 // The deque's elements are parted into three segments:
1245 // * self.tail -> drain_tail
1246 // * drain_tail -> drain_head
1247 // * drain_head -> self.head
1249 // T = self.tail; H = self.head; t = drain_tail; h = drain_head
1251 // We store drain_tail as self.head, and drain_head and self.head as
1252 // after_tail and after_head respectively on the Drain. This also
1253 // truncates the effective array such that if the Drain is leaked, we
1254 // have forgotten about the potentially moved values after the start of
1258 // [. . . o o x x o o . . .]
1260 let head = self.head;
1262 // "forget" about the values after the start of the drain until after
1263 // the drain is complete and the Drain destructor is run.
1264 self.head = drain_tail;
1266 let deque = NonNull::from(&mut *self);
1270 // Crucially, we only create shared references from `self` here and read from
1271 // it. We do not write to `self` nor reborrow to a mutable reference.
1272 // Hence the raw pointer we created above, for `deque`, remains valid.
1273 ring: unsafe { self.buffer_as_slice() },
1276 unsafe { Drain::new(drain_head, head, iter, deque) }
1279 /// Clears the `VecDeque`, removing all values.
1284 /// use std::collections::VecDeque;
1286 /// let mut v = VecDeque::new();
1289 /// assert!(v.is_empty());
1291 #[stable(feature = "rust1", since = "1.0.0")]
1293 pub fn clear(&mut self) {
1297 /// Returns `true` if the `VecDeque` contains an element equal to the
1303 /// use std::collections::VecDeque;
1305 /// let mut vector: VecDeque<u32> = VecDeque::new();
1307 /// vector.push_back(0);
1308 /// vector.push_back(1);
1310 /// assert_eq!(vector.contains(&1), true);
1311 /// assert_eq!(vector.contains(&10), false);
1313 #[stable(feature = "vec_deque_contains", since = "1.12.0")]
1314 pub fn contains(&self, x: &T) -> bool
1318 let (a, b) = self.as_slices();
1319 a.contains(x) || b.contains(x)
1322 /// Provides a reference to the front element, or `None` if the `VecDeque` is
1328 /// use std::collections::VecDeque;
1330 /// let mut d = VecDeque::new();
1331 /// assert_eq!(d.front(), None);
1335 /// assert_eq!(d.front(), Some(&1));
1337 #[stable(feature = "rust1", since = "1.0.0")]
1338 pub fn front(&self) -> Option<&T> {
1342 /// Provides a mutable reference to the front element, or `None` if the
1343 /// `VecDeque` is empty.
1348 /// use std::collections::VecDeque;
1350 /// let mut d = VecDeque::new();
1351 /// assert_eq!(d.front_mut(), None);
1355 /// match d.front_mut() {
1356 /// Some(x) => *x = 9,
1359 /// assert_eq!(d.front(), Some(&9));
1361 #[stable(feature = "rust1", since = "1.0.0")]
1362 pub fn front_mut(&mut self) -> Option<&mut T> {
1366 /// Provides a reference to the back element, or `None` if the `VecDeque` is
1372 /// use std::collections::VecDeque;
1374 /// let mut d = VecDeque::new();
1375 /// assert_eq!(d.back(), None);
1379 /// assert_eq!(d.back(), Some(&2));
1381 #[stable(feature = "rust1", since = "1.0.0")]
1382 pub fn back(&self) -> Option<&T> {
1383 self.get(self.len().wrapping_sub(1))
1386 /// Provides a mutable reference to the back element, or `None` if the
1387 /// `VecDeque` is empty.
1392 /// use std::collections::VecDeque;
1394 /// let mut d = VecDeque::new();
1395 /// assert_eq!(d.back(), None);
1399 /// match d.back_mut() {
1400 /// Some(x) => *x = 9,
1403 /// assert_eq!(d.back(), Some(&9));
1405 #[stable(feature = "rust1", since = "1.0.0")]
1406 pub fn back_mut(&mut self) -> Option<&mut T> {
1407 self.get_mut(self.len().wrapping_sub(1))
1410 /// Removes the first element and returns it, or `None` if the `VecDeque` is
1416 /// use std::collections::VecDeque;
1418 /// let mut d = VecDeque::new();
1422 /// assert_eq!(d.pop_front(), Some(1));
1423 /// assert_eq!(d.pop_front(), Some(2));
1424 /// assert_eq!(d.pop_front(), None);
1426 #[stable(feature = "rust1", since = "1.0.0")]
1427 pub fn pop_front(&mut self) -> Option<T> {
1428 if self.is_empty() {
1431 let tail = self.tail;
1432 self.tail = self.wrap_add(self.tail, 1);
1433 unsafe { Some(self.buffer_read(tail)) }
1437 /// Removes the last element from the `VecDeque` and returns it, or `None` if
1443 /// use std::collections::VecDeque;
1445 /// let mut buf = VecDeque::new();
1446 /// assert_eq!(buf.pop_back(), None);
1447 /// buf.push_back(1);
1448 /// buf.push_back(3);
1449 /// assert_eq!(buf.pop_back(), Some(3));
1451 #[stable(feature = "rust1", since = "1.0.0")]
1452 pub fn pop_back(&mut self) -> Option<T> {
1453 if self.is_empty() {
1456 self.head = self.wrap_sub(self.head, 1);
1457 let head = self.head;
1458 unsafe { Some(self.buffer_read(head)) }
1462 /// Prepends an element to the `VecDeque`.
1467 /// use std::collections::VecDeque;
1469 /// let mut d = VecDeque::new();
1470 /// d.push_front(1);
1471 /// d.push_front(2);
1472 /// assert_eq!(d.front(), Some(&2));
1474 #[stable(feature = "rust1", since = "1.0.0")]
1475 pub fn push_front(&mut self, value: T) {
1480 self.tail = self.wrap_sub(self.tail, 1);
1481 let tail = self.tail;
1483 self.buffer_write(tail, value);
1487 /// Appends an element to the back of the `VecDeque`.
1492 /// use std::collections::VecDeque;
1494 /// let mut buf = VecDeque::new();
1495 /// buf.push_back(1);
1496 /// buf.push_back(3);
1497 /// assert_eq!(3, *buf.back().unwrap());
1499 #[stable(feature = "rust1", since = "1.0.0")]
1500 pub fn push_back(&mut self, value: T) {
1505 let head = self.head;
1506 self.head = self.wrap_add(self.head, 1);
1507 unsafe { self.buffer_write(head, value) }
1511 fn is_contiguous(&self) -> bool {
1512 // FIXME: Should we consider `head == 0` to mean
1513 // that `self` is contiguous?
1514 self.tail <= self.head
1517 /// Removes an element from anywhere in the `VecDeque` and returns it,
1518 /// replacing it with the first element.
1520 /// This does not preserve ordering, but is *O*(1).
1522 /// Returns `None` if `index` is out of bounds.
1524 /// Element at index 0 is the front of the queue.
1529 /// use std::collections::VecDeque;
1531 /// let mut buf = VecDeque::new();
1532 /// assert_eq!(buf.swap_remove_front(0), None);
1533 /// buf.push_back(1);
1534 /// buf.push_back(2);
1535 /// buf.push_back(3);
1536 /// assert_eq!(buf, [1, 2, 3]);
1538 /// assert_eq!(buf.swap_remove_front(2), Some(3));
1539 /// assert_eq!(buf, [2, 1]);
1541 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1542 pub fn swap_remove_front(&mut self, index: usize) -> Option<T> {
1543 let length = self.len();
1544 if length > 0 && index < length && index != 0 {
1545 self.swap(index, 0);
1546 } else if index >= length {
1552 /// Removes an element from anywhere in the `VecDeque` and returns it, replacing it with the
1555 /// This does not preserve ordering, but is *O*(1).
1557 /// Returns `None` if `index` is out of bounds.
1559 /// Element at index 0 is the front of the queue.
1564 /// use std::collections::VecDeque;
1566 /// let mut buf = VecDeque::new();
1567 /// assert_eq!(buf.swap_remove_back(0), None);
1568 /// buf.push_back(1);
1569 /// buf.push_back(2);
1570 /// buf.push_back(3);
1571 /// assert_eq!(buf, [1, 2, 3]);
1573 /// assert_eq!(buf.swap_remove_back(0), Some(1));
1574 /// assert_eq!(buf, [3, 2]);
1576 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1577 pub fn swap_remove_back(&mut self, index: usize) -> Option<T> {
1578 let length = self.len();
1579 if length > 0 && index < length - 1 {
1580 self.swap(index, length - 1);
1581 } else if index >= length {
1587 /// Inserts an element at `index` within the `VecDeque`, shifting all elements with indices
1588 /// greater than or equal to `index` towards the back.
1590 /// Element at index 0 is the front of the queue.
1594 /// Panics if `index` is greater than `VecDeque`'s length
1599 /// use std::collections::VecDeque;
1601 /// let mut vec_deque = VecDeque::new();
1602 /// vec_deque.push_back('a');
1603 /// vec_deque.push_back('b');
1604 /// vec_deque.push_back('c');
1605 /// assert_eq!(vec_deque, &['a', 'b', 'c']);
1607 /// vec_deque.insert(1, 'd');
1608 /// assert_eq!(vec_deque, &['a', 'd', 'b', 'c']);
1610 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1611 pub fn insert(&mut self, index: usize, value: T) {
1612 assert!(index <= self.len(), "index out of bounds");
1617 // Move the least number of elements in the ring buffer and insert
1620 // At most len/2 - 1 elements will be moved. O(min(n, n-i))
1622 // There are three main cases:
1623 // Elements are contiguous
1624 // - special case when tail is 0
1625 // Elements are discontiguous and the insert is in the tail section
1626 // Elements are discontiguous and the insert is in the head section
1628 // For each of those there are two more cases:
1629 // Insert is closer to tail
1630 // Insert is closer to head
1632 // Key: H - self.head
1634 // o - Valid element
1635 // I - Insertion element
1636 // A - The element that should be after the insertion point
1637 // M - Indicates element was moved
1639 let idx = self.wrap_add(self.tail, index);
1641 let distance_to_tail = index;
1642 let distance_to_head = self.len() - index;
1644 let contiguous = self.is_contiguous();
1646 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1647 (true, true, _) if index == 0 => {
1652 // [A o o o o o o . . . . . . . . .]
1655 // [A o o o o o o o . . . . . I]
1658 self.tail = self.wrap_sub(self.tail, 1);
1660 (true, true, _) => {
1662 // contiguous, insert closer to tail:
1665 // [. . . o o A o o o o . . . . . .]
1668 // [. . o o I A o o o o . . . . . .]
1671 // contiguous, insert closer to tail and tail is 0:
1675 // [o o A o o o o . . . . . . . . .]
1678 // [o I A o o o o o . . . . . . . o]
1681 let new_tail = self.wrap_sub(self.tail, 1);
1683 self.copy(new_tail, self.tail, 1);
1684 // Already moved the tail, so we only copy `index - 1` elements.
1685 self.copy(self.tail, self.tail + 1, index - 1);
1687 self.tail = new_tail;
1690 (true, false, _) => {
1692 // contiguous, insert closer to head:
1695 // [. . . o o o o A o o . . . . . .]
1698 // [. . . o o o o I A o o . . . . .]
1701 self.copy(idx + 1, idx, self.head - idx);
1702 self.head = self.wrap_add(self.head, 1);
1705 (false, true, true) => {
1707 // discontiguous, insert closer to tail, tail section:
1710 // [o o o o o o . . . . . o o A o o]
1713 // [o o o o o o . . . . o o I A o o]
1716 self.copy(self.tail - 1, self.tail, index);
1720 (false, false, true) => {
1722 // discontiguous, insert closer to head, tail section:
1725 // [o o . . . . . . . o o o o o A o]
1728 // [o o o . . . . . . o o o o o I A]
1731 // copy elements up to new head
1732 self.copy(1, 0, self.head);
1734 // copy last element into empty spot at bottom of buffer
1735 self.copy(0, self.cap() - 1, 1);
1737 // move elements from idx to end forward not including ^ element
1738 self.copy(idx + 1, idx, self.cap() - 1 - idx);
1743 (false, true, false) if idx == 0 => {
1745 // discontiguous, insert is closer to tail, head section,
1746 // and is at index zero in the internal buffer:
1749 // [A o o o o o o o o o . . . o o o]
1752 // [A o o o o o o o o o . . o o o I]
1755 // copy elements up to new tail
1756 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1758 // copy last element into empty spot at bottom of buffer
1759 self.copy(self.cap() - 1, 0, 1);
1764 (false, true, false) => {
1766 // discontiguous, insert closer to tail, head section:
1769 // [o o o A o o o o o o . . . o o o]
1772 // [o o I A o o o o o o . . o o o o]
1775 // copy elements up to new tail
1776 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1778 // copy last element into empty spot at bottom of buffer
1779 self.copy(self.cap() - 1, 0, 1);
1781 // move elements from idx-1 to end forward not including ^ element
1782 self.copy(0, 1, idx - 1);
1787 (false, false, false) => {
1789 // discontiguous, insert closer to head, head section:
1792 // [o o o o A o o . . . . . . o o o]
1795 // [o o o o I A o o . . . . . o o o]
1798 self.copy(idx + 1, idx, self.head - idx);
1804 // tail might've been changed so we need to recalculate
1805 let new_idx = self.wrap_add(self.tail, index);
1807 self.buffer_write(new_idx, value);
1811 /// Removes and returns the element at `index` from the `VecDeque`.
1812 /// Whichever end is closer to the removal point will be moved to make
1813 /// room, and all the affected elements will be moved to new positions.
1814 /// Returns `None` if `index` is out of bounds.
1816 /// Element at index 0 is the front of the queue.
1821 /// use std::collections::VecDeque;
1823 /// let mut buf = VecDeque::new();
1824 /// buf.push_back(1);
1825 /// buf.push_back(2);
1826 /// buf.push_back(3);
1827 /// assert_eq!(buf, [1, 2, 3]);
1829 /// assert_eq!(buf.remove(1), Some(2));
1830 /// assert_eq!(buf, [1, 3]);
1832 #[stable(feature = "rust1", since = "1.0.0")]
1833 pub fn remove(&mut self, index: usize) -> Option<T> {
1834 if self.is_empty() || self.len() <= index {
1838 // There are three main cases:
1839 // Elements are contiguous
1840 // Elements are discontiguous and the removal is in the tail section
1841 // Elements are discontiguous and the removal is in the head section
1842 // - special case when elements are technically contiguous,
1843 // but self.head = 0
1845 // For each of those there are two more cases:
1846 // Insert is closer to tail
1847 // Insert is closer to head
1849 // Key: H - self.head
1851 // o - Valid element
1852 // x - Element marked for removal
1853 // R - Indicates element that is being removed
1854 // M - Indicates element was moved
1856 let idx = self.wrap_add(self.tail, index);
1858 let elem = unsafe { Some(self.buffer_read(idx)) };
1860 let distance_to_tail = index;
1861 let distance_to_head = self.len() - index;
1863 let contiguous = self.is_contiguous();
1865 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1866 (true, true, _) => {
1868 // contiguous, remove closer to tail:
1871 // [. . . o o x o o o o . . . . . .]
1874 // [. . . . o o o o o o . . . . . .]
1877 self.copy(self.tail + 1, self.tail, index);
1881 (true, false, _) => {
1883 // contiguous, remove closer to head:
1886 // [. . . o o o o x o o . . . . . .]
1889 // [. . . o o o o o o . . . . . . .]
1892 self.copy(idx, idx + 1, self.head - idx - 1);
1896 (false, true, true) => {
1898 // discontiguous, remove closer to tail, tail section:
1901 // [o o o o o o . . . . . o o x o o]
1904 // [o o o o o o . . . . . . o o o o]
1907 self.copy(self.tail + 1, self.tail, index);
1908 self.tail = self.wrap_add(self.tail, 1);
1911 (false, false, false) => {
1913 // discontiguous, remove closer to head, head section:
1916 // [o o o o x o o . . . . . . o o o]
1919 // [o o o o o o . . . . . . . o o o]
1922 self.copy(idx, idx + 1, self.head - idx - 1);
1926 (false, false, true) => {
1928 // discontiguous, remove closer to head, tail section:
1931 // [o o o . . . . . . o o o o o x o]
1934 // [o o . . . . . . . o o o o o o o]
1937 // or quasi-discontiguous, remove next to head, tail section:
1940 // [. . . . . . . . . o o o o o x o]
1943 // [. . . . . . . . . o o o o o o .]
1946 // draw in elements in the tail section
1947 self.copy(idx, idx + 1, self.cap() - idx - 1);
1949 // Prevents underflow.
1951 // copy first element into empty spot
1952 self.copy(self.cap() - 1, 0, 1);
1954 // move elements in the head section backwards
1955 self.copy(0, 1, self.head - 1);
1958 self.head = self.wrap_sub(self.head, 1);
1961 (false, true, false) => {
1963 // discontiguous, remove closer to tail, head section:
1966 // [o o x o o o o o o o . . . o o o]
1969 // [o o o o o o o o o o . . . . o o]
1972 // draw in elements up to idx
1973 self.copy(1, 0, idx);
1975 // copy last element into empty spot
1976 self.copy(0, self.cap() - 1, 1);
1978 // move elements from tail to end forward, excluding the last one
1979 self.copy(self.tail + 1, self.tail, self.cap() - self.tail - 1);
1981 self.tail = self.wrap_add(self.tail, 1);
1989 /// Splits the `VecDeque` into two at the given index.
1991 /// Returns a newly allocated `VecDeque`. `self` contains elements `[0, at)`,
1992 /// and the returned `VecDeque` contains elements `[at, len)`.
1994 /// Note that the capacity of `self` does not change.
1996 /// Element at index 0 is the front of the queue.
2000 /// Panics if `at > len`.
2005 /// use std::collections::VecDeque;
2007 /// let mut buf: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
2008 /// let buf2 = buf.split_off(1);
2009 /// assert_eq!(buf, [1]);
2010 /// assert_eq!(buf2, [2, 3]);
2013 #[must_use = "use `.truncate()` if you don't need the other half"]
2014 #[stable(feature = "split_off", since = "1.4.0")]
2015 pub fn split_off(&mut self, at: usize) -> Self
2019 let len = self.len();
2020 assert!(at <= len, "`at` out of bounds");
2022 let other_len = len - at;
2023 let mut other = VecDeque::with_capacity_in(other_len, self.allocator().clone());
2026 let (first_half, second_half) = self.as_slices();
2028 let first_len = first_half.len();
2029 let second_len = second_half.len();
2031 // `at` lies in the first half.
2032 let amount_in_first = first_len - at;
2034 ptr::copy_nonoverlapping(first_half.as_ptr().add(at), other.ptr(), amount_in_first);
2036 // just take all of the second half.
2037 ptr::copy_nonoverlapping(
2038 second_half.as_ptr(),
2039 other.ptr().add(amount_in_first),
2043 // `at` lies in the second half, need to factor in the elements we skipped
2044 // in the first half.
2045 let offset = at - first_len;
2046 let amount_in_second = second_len - offset;
2047 ptr::copy_nonoverlapping(
2048 second_half.as_ptr().add(offset),
2055 // Cleanup where the ends of the buffers are
2056 self.head = self.wrap_sub(self.head, other_len);
2057 other.head = other.wrap_index(other_len);
2062 /// Moves all the elements of `other` into `self`, leaving `other` empty.
2066 /// Panics if the new number of elements in self overflows a `usize`.
2071 /// use std::collections::VecDeque;
2073 /// let mut buf: VecDeque<_> = vec![1, 2].into_iter().collect();
2074 /// let mut buf2: VecDeque<_> = vec![3, 4].into_iter().collect();
2075 /// buf.append(&mut buf2);
2076 /// assert_eq!(buf, [1, 2, 3, 4]);
2077 /// assert_eq!(buf2, []);
2080 #[stable(feature = "append", since = "1.4.0")]
2081 pub fn append(&mut self, other: &mut Self) {
2083 self.extend(other.drain(..));
2086 /// Retains only the elements specified by the predicate.
2088 /// In other words, remove all elements `e` such that `f(&e)` returns false.
2089 /// This method operates in place, visiting each element exactly once in the
2090 /// original order, and preserves the order of the retained elements.
2095 /// use std::collections::VecDeque;
2097 /// let mut buf = VecDeque::new();
2098 /// buf.extend(1..5);
2099 /// buf.retain(|&x| x % 2 == 0);
2100 /// assert_eq!(buf, [2, 4]);
2103 /// Because the elements are visited exactly once in the original order,
2104 /// external state may be used to decide which elements to keep.
2107 /// use std::collections::VecDeque;
2109 /// let mut buf = VecDeque::new();
2110 /// buf.extend(1..6);
2112 /// let keep = [false, true, true, false, true];
2113 /// let mut iter = keep.iter();
2114 /// buf.retain(|_| *iter.next().unwrap());
2115 /// assert_eq!(buf, [2, 3, 5]);
2117 #[stable(feature = "vec_deque_retain", since = "1.4.0")]
2118 pub fn retain<F>(&mut self, mut f: F)
2120 F: FnMut(&T) -> bool,
2122 let len = self.len();
2126 // Stage 1: All values are retained.
2135 // Stage 2: Swap retained value into current idx.
2142 self.swap(idx, cur);
2146 // Stage 3: Trancate all values after idx.
2152 // This may panic or abort
2154 fn grow(&mut self) {
2156 let old_cap = self.cap();
2157 // Double the buffer size.
2158 self.buf.reserve_exact(old_cap, old_cap);
2159 assert!(self.cap() == old_cap * 2);
2161 self.handle_capacity_increase(old_cap);
2163 debug_assert!(!self.is_full());
2167 /// Modifies the `VecDeque` in-place so that `len()` is equal to `new_len`,
2168 /// either by removing excess elements from the back or by appending
2169 /// elements generated by calling `generator` to the back.
2174 /// use std::collections::VecDeque;
2176 /// let mut buf = VecDeque::new();
2177 /// buf.push_back(5);
2178 /// buf.push_back(10);
2179 /// buf.push_back(15);
2180 /// assert_eq!(buf, [5, 10, 15]);
2182 /// buf.resize_with(5, Default::default);
2183 /// assert_eq!(buf, [5, 10, 15, 0, 0]);
2185 /// buf.resize_with(2, || unreachable!());
2186 /// assert_eq!(buf, [5, 10]);
2188 /// let mut state = 100;
2189 /// buf.resize_with(5, || { state += 1; state });
2190 /// assert_eq!(buf, [5, 10, 101, 102, 103]);
2192 #[stable(feature = "vec_resize_with", since = "1.33.0")]
2193 pub fn resize_with(&mut self, new_len: usize, generator: impl FnMut() -> T) {
2194 let len = self.len();
2197 self.extend(repeat_with(generator).take(new_len - len))
2199 self.truncate(new_len);
2203 /// Rearranges the internal storage of this deque so it is one contiguous
2204 /// slice, which is then returned.
2206 /// This method does not allocate and does not change the order of the
2207 /// inserted elements. As it returns a mutable slice, this can be used to
2210 /// Once the internal storage is contiguous, the [`as_slices`] and
2211 /// [`as_mut_slices`] methods will return the entire contents of the
2212 /// `VecDeque` in a single slice.
2214 /// [`as_slices`]: VecDeque::as_slices
2215 /// [`as_mut_slices`]: VecDeque::as_mut_slices
2219 /// Sorting the content of a deque.
2222 /// use std::collections::VecDeque;
2224 /// let mut buf = VecDeque::with_capacity(15);
2226 /// buf.push_back(2);
2227 /// buf.push_back(1);
2228 /// buf.push_front(3);
2230 /// // sorting the deque
2231 /// buf.make_contiguous().sort();
2232 /// assert_eq!(buf.as_slices(), (&[1, 2, 3] as &[_], &[] as &[_]));
2234 /// // sorting it in reverse order
2235 /// buf.make_contiguous().sort_by(|a, b| b.cmp(a));
2236 /// assert_eq!(buf.as_slices(), (&[3, 2, 1] as &[_], &[] as &[_]));
2239 /// Getting immutable access to the contiguous slice.
2242 /// use std::collections::VecDeque;
2244 /// let mut buf = VecDeque::new();
2246 /// buf.push_back(2);
2247 /// buf.push_back(1);
2248 /// buf.push_front(3);
2250 /// buf.make_contiguous();
2251 /// if let (slice, &[]) = buf.as_slices() {
2252 /// // we can now be sure that `slice` contains all elements of the deque,
2253 /// // while still having immutable access to `buf`.
2254 /// assert_eq!(buf.len(), slice.len());
2255 /// assert_eq!(slice, &[3, 2, 1] as &[_]);
2258 #[stable(feature = "deque_make_contiguous", since = "1.48.0")]
2259 pub fn make_contiguous(&mut self) -> &mut [T] {
2260 if self.is_contiguous() {
2261 let tail = self.tail;
2262 let head = self.head;
2263 return unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 };
2266 let buf = self.buf.ptr();
2267 let cap = self.cap();
2268 let len = self.len();
2270 let free = self.tail - self.head;
2271 let tail_len = cap - self.tail;
2273 if free >= tail_len {
2274 // there is enough free space to copy the tail in one go,
2275 // this means that we first shift the head backwards, and then
2276 // copy the tail to the correct position.
2278 // from: DEFGH....ABC
2281 ptr::copy(buf, buf.add(tail_len), self.head);
2283 ptr::copy_nonoverlapping(buf.add(self.tail), buf, tail_len);
2289 } else if free > self.head {
2290 // FIXME: We currently do not consider ....ABCDEFGH
2291 // to be contiguous because `head` would be `0` in this
2292 // case. While we probably want to change this it
2293 // isn't trivial as a few places expect `is_contiguous`
2294 // to mean that we can just slice using `buf[tail..head]`.
2296 // there is enough free space to copy the head in one go,
2297 // this means that we first shift the tail forwards, and then
2298 // copy the head to the correct position.
2300 // from: FGH....ABCDE
2303 ptr::copy(buf.add(self.tail), buf.add(self.head), tail_len);
2305 ptr::copy_nonoverlapping(buf, buf.add(self.head + tail_len), self.head);
2308 self.tail = self.head;
2309 self.head = self.wrap_add(self.tail, len);
2312 // free is smaller than both head and tail,
2313 // this means we have to slowly "swap" the tail and the head.
2315 // from: EFGHI...ABCD or HIJK.ABCDEFG
2316 // to: ABCDEFGHI... or ABCDEFGHIJK.
2317 let mut left_edge: usize = 0;
2318 let mut right_edge: usize = self.tail;
2320 // The general problem looks like this
2321 // GHIJKLM...ABCDEF - before any swaps
2322 // ABCDEFM...GHIJKL - after 1 pass of swaps
2323 // ABCDEFGHIJM...KL - swap until the left edge reaches the temp store
2324 // - then restart the algorithm with a new (smaller) store
2325 // Sometimes the temp store is reached when the right edge is at the end
2326 // of the buffer - this means we've hit the right order with fewer swaps!
2329 // ABCDEF.. - after four only swaps we've finished
2330 while left_edge < len && right_edge != cap {
2331 let mut right_offset = 0;
2332 for i in left_edge..right_edge {
2333 right_offset = (i - left_edge) % (cap - right_edge);
2334 let src: isize = (right_edge + right_offset) as isize;
2335 ptr::swap(buf.add(i), buf.offset(src));
2337 let n_ops = right_edge - left_edge;
2339 right_edge += right_offset + 1;
2347 let tail = self.tail;
2348 let head = self.head;
2349 unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 }
2352 /// Rotates the double-ended queue `mid` places to the left.
2355 /// - Rotates item `mid` into the first position.
2356 /// - Pops the first `mid` items and pushes them to the end.
2357 /// - Rotates `len() - mid` places to the right.
2361 /// If `mid` is greater than `len()`. Note that `mid == len()`
2362 /// does _not_ panic and is a no-op rotation.
2366 /// Takes `*O*(min(mid, len() - mid))` time and no extra space.
2371 /// use std::collections::VecDeque;
2373 /// let mut buf: VecDeque<_> = (0..10).collect();
2375 /// buf.rotate_left(3);
2376 /// assert_eq!(buf, [3, 4, 5, 6, 7, 8, 9, 0, 1, 2]);
2378 /// for i in 1..10 {
2379 /// assert_eq!(i * 3 % 10, buf[0]);
2380 /// buf.rotate_left(3);
2382 /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
2384 #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
2385 pub fn rotate_left(&mut self, mid: usize) {
2386 assert!(mid <= self.len());
2387 let k = self.len() - mid;
2389 unsafe { self.rotate_left_inner(mid) }
2391 unsafe { self.rotate_right_inner(k) }
2395 /// Rotates the double-ended queue `k` places to the right.
2398 /// - Rotates the first item into position `k`.
2399 /// - Pops the last `k` items and pushes them to the front.
2400 /// - Rotates `len() - k` places to the left.
2404 /// If `k` is greater than `len()`. Note that `k == len()`
2405 /// does _not_ panic and is a no-op rotation.
2409 /// Takes `*O*(min(k, len() - k))` time and no extra space.
2414 /// use std::collections::VecDeque;
2416 /// let mut buf: VecDeque<_> = (0..10).collect();
2418 /// buf.rotate_right(3);
2419 /// assert_eq!(buf, [7, 8, 9, 0, 1, 2, 3, 4, 5, 6]);
2421 /// for i in 1..10 {
2422 /// assert_eq!(0, buf[i * 3 % 10]);
2423 /// buf.rotate_right(3);
2425 /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
2427 #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
2428 pub fn rotate_right(&mut self, k: usize) {
2429 assert!(k <= self.len());
2430 let mid = self.len() - k;
2432 unsafe { self.rotate_right_inner(k) }
2434 unsafe { self.rotate_left_inner(mid) }
2438 // SAFETY: the following two methods require that the rotation amount
2439 // be less than half the length of the deque.
2441 // `wrap_copy` requires that `min(x, cap() - x) + copy_len <= cap()`,
2442 // but than `min` is never more than half the capacity, regardless of x,
2443 // so it's sound to call here because we're calling with something
2444 // less than half the length, which is never above half the capacity.
2446 unsafe fn rotate_left_inner(&mut self, mid: usize) {
2447 debug_assert!(mid * 2 <= self.len());
2449 self.wrap_copy(self.head, self.tail, mid);
2451 self.head = self.wrap_add(self.head, mid);
2452 self.tail = self.wrap_add(self.tail, mid);
2455 unsafe fn rotate_right_inner(&mut self, k: usize) {
2456 debug_assert!(k * 2 <= self.len());
2457 self.head = self.wrap_sub(self.head, k);
2458 self.tail = self.wrap_sub(self.tail, k);
2460 self.wrap_copy(self.tail, self.head, k);
2464 /// Binary searches this sorted `VecDeque` for a given element.
2466 /// If the value is found then [`Result::Ok`] is returned, containing the
2467 /// index of the matching element. If there are multiple matches, then any
2468 /// one of the matches could be returned. If the value is not found then
2469 /// [`Result::Err`] is returned, containing the index where a matching
2470 /// element could be inserted while maintaining sorted order.
2472 /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`].
2474 /// [`binary_search_by`]: VecDeque::binary_search_by
2475 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2476 /// [`partition_point`]: VecDeque::partition_point
2480 /// Looks up a series of four elements. The first is found, with a
2481 /// uniquely determined position; the second and third are not
2482 /// found; the fourth could match any position in `[1, 4]`.
2485 /// use std::collections::VecDeque;
2487 /// let deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2489 /// assert_eq!(deque.binary_search(&13), Ok(9));
2490 /// assert_eq!(deque.binary_search(&4), Err(7));
2491 /// assert_eq!(deque.binary_search(&100), Err(13));
2492 /// let r = deque.binary_search(&1);
2493 /// assert!(matches!(r, Ok(1..=4)));
2496 /// If you want to insert an item to a sorted `VecDeque`, while maintaining
2500 /// use std::collections::VecDeque;
2502 /// let mut deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2504 /// let idx = deque.binary_search(&num).unwrap_or_else(|x| x);
2505 /// deque.insert(idx, num);
2506 /// assert_eq!(deque, &[0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
2508 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2510 pub fn binary_search(&self, x: &T) -> Result<usize, usize>
2514 self.binary_search_by(|e| e.cmp(x))
2517 /// Binary searches this sorted `VecDeque` with a comparator function.
2519 /// The comparator function should implement an order consistent
2520 /// with the sort order of the underlying `VecDeque`, returning an
2521 /// order code that indicates whether its argument is `Less`,
2522 /// `Equal` or `Greater` than the desired target.
2524 /// If the value is found then [`Result::Ok`] is returned, containing the
2525 /// index of the matching element. If there are multiple matches, then any
2526 /// one of the matches could be returned. If the value is not found then
2527 /// [`Result::Err`] is returned, containing the index where a matching
2528 /// element could be inserted while maintaining sorted order.
2530 /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`].
2532 /// [`binary_search`]: VecDeque::binary_search
2533 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2534 /// [`partition_point`]: VecDeque::partition_point
2538 /// Looks up a series of four elements. The first is found, with a
2539 /// uniquely determined position; the second and third are not
2540 /// found; the fourth could match any position in `[1, 4]`.
2543 /// use std::collections::VecDeque;
2545 /// let deque: VecDeque<_> = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into();
2547 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&13)), Ok(9));
2548 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&4)), Err(7));
2549 /// assert_eq!(deque.binary_search_by(|x| x.cmp(&100)), Err(13));
2550 /// let r = deque.binary_search_by(|x| x.cmp(&1));
2551 /// assert!(matches!(r, Ok(1..=4)));
2553 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2554 pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize>
2556 F: FnMut(&'a T) -> Ordering,
2558 let (front, back) = self.as_slices();
2559 let cmp_back = back.first().map(|elem| f(elem));
2561 if let Some(Ordering::Equal) = cmp_back {
2563 } else if let Some(Ordering::Less) = cmp_back {
2564 back.binary_search_by(f).map(|idx| idx + front.len()).map_err(|idx| idx + front.len())
2566 front.binary_search_by(f)
2570 /// Binary searches this sorted `VecDeque` with a key extraction function.
2572 /// Assumes that the `VecDeque` is sorted by the key, for instance with
2573 /// [`make_contiguous().sort_by_key()`] using the same key extraction function.
2575 /// If the value is found then [`Result::Ok`] is returned, containing the
2576 /// index of the matching element. If there are multiple matches, then any
2577 /// one of the matches could be returned. If the value is not found then
2578 /// [`Result::Err`] is returned, containing the index where a matching
2579 /// element could be inserted while maintaining sorted order.
2581 /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`].
2583 /// [`make_contiguous().sort_by_key()`]: VecDeque::make_contiguous
2584 /// [`binary_search`]: VecDeque::binary_search
2585 /// [`binary_search_by`]: VecDeque::binary_search_by
2586 /// [`partition_point`]: VecDeque::partition_point
2590 /// Looks up a series of four elements in a slice of pairs sorted by
2591 /// their second elements. The first is found, with a uniquely
2592 /// determined position; the second and third are not found; the
2593 /// fourth could match any position in `[1, 4]`.
2596 /// use std::collections::VecDeque;
2598 /// let deque: VecDeque<_> = vec![(0, 0), (2, 1), (4, 1), (5, 1),
2599 /// (3, 1), (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
2600 /// (1, 21), (2, 34), (4, 55)].into();
2602 /// assert_eq!(deque.binary_search_by_key(&13, |&(a, b)| b), Ok(9));
2603 /// assert_eq!(deque.binary_search_by_key(&4, |&(a, b)| b), Err(7));
2604 /// assert_eq!(deque.binary_search_by_key(&100, |&(a, b)| b), Err(13));
2605 /// let r = deque.binary_search_by_key(&1, |&(a, b)| b);
2606 /// assert!(matches!(r, Ok(1..=4)));
2608 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2610 pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
2612 F: FnMut(&'a T) -> B,
2615 self.binary_search_by(|k| f(k).cmp(b))
2618 /// Returns the index of the partition point according to the given predicate
2619 /// (the index of the first element of the second partition).
2621 /// The deque is assumed to be partitioned according to the given predicate.
2622 /// This means that all elements for which the predicate returns true are at the start of the deque
2623 /// and all elements for which the predicate returns false are at the end.
2624 /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
2625 /// (all odd numbers are at the start, all even at the end).
2627 /// If this deque is not partitioned, the returned result is unspecified and meaningless,
2628 /// as this method performs a kind of binary search.
2630 /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`].
2632 /// [`binary_search`]: VecDeque::binary_search
2633 /// [`binary_search_by`]: VecDeque::binary_search_by
2634 /// [`binary_search_by_key`]: VecDeque::binary_search_by_key
2639 /// use std::collections::VecDeque;
2641 /// let deque: VecDeque<_> = vec![1, 2, 3, 3, 5, 6, 7].into();
2642 /// let i = deque.partition_point(|&x| x < 5);
2644 /// assert_eq!(i, 4);
2645 /// assert!(deque.iter().take(i).all(|&x| x < 5));
2646 /// assert!(deque.iter().skip(i).all(|&x| !(x < 5)));
2648 #[stable(feature = "vecdeque_binary_search", since = "1.54.0")]
2649 pub fn partition_point<P>(&self, mut pred: P) -> usize
2651 P: FnMut(&T) -> bool,
2653 let (front, back) = self.as_slices();
2655 if let Some(true) = back.first().map(|v| pred(v)) {
2656 back.partition_point(pred) + front.len()
2658 front.partition_point(pred)
2663 impl<T: Clone, A: Allocator> VecDeque<T, A> {
2664 /// Modifies the `VecDeque` in-place so that `len()` is equal to new_len,
2665 /// either by removing excess elements from the back or by appending clones of `value`
2671 /// use std::collections::VecDeque;
2673 /// let mut buf = VecDeque::new();
2674 /// buf.push_back(5);
2675 /// buf.push_back(10);
2676 /// buf.push_back(15);
2677 /// assert_eq!(buf, [5, 10, 15]);
2679 /// buf.resize(2, 0);
2680 /// assert_eq!(buf, [5, 10]);
2682 /// buf.resize(5, 20);
2683 /// assert_eq!(buf, [5, 10, 20, 20, 20]);
2685 #[stable(feature = "deque_extras", since = "1.16.0")]
2686 pub fn resize(&mut self, new_len: usize, value: T) {
2687 self.resize_with(new_len, || value.clone());
2691 /// Returns the index in the underlying buffer for a given logical element index.
2693 fn wrap_index(index: usize, size: usize) -> usize {
2694 // size is always a power of 2
2695 debug_assert!(size.is_power_of_two());
2699 /// Calculate the number of elements left to be read in the buffer
2701 fn count(tail: usize, head: usize, size: usize) -> usize {
2702 // size is always a power of 2
2703 (head.wrapping_sub(tail)) & (size - 1)
2706 #[stable(feature = "rust1", since = "1.0.0")]
2707 impl<T: PartialEq, A: Allocator> PartialEq for VecDeque<T, A> {
2708 fn eq(&self, other: &Self) -> bool {
2709 if self.len() != other.len() {
2712 let (sa, sb) = self.as_slices();
2713 let (oa, ob) = other.as_slices();
2714 if sa.len() == oa.len() {
2715 sa == oa && sb == ob
2716 } else if sa.len() < oa.len() {
2717 // Always divisible in three sections, for example:
2718 // self: [a b c|d e f]
2719 // other: [0 1 2 3|4 5]
2720 // front = 3, mid = 1,
2721 // [a b c] == [0 1 2] && [d] == [3] && [e f] == [4 5]
2722 let front = sa.len();
2723 let mid = oa.len() - front;
2725 let (oa_front, oa_mid) = oa.split_at(front);
2726 let (sb_mid, sb_back) = sb.split_at(mid);
2727 debug_assert_eq!(sa.len(), oa_front.len());
2728 debug_assert_eq!(sb_mid.len(), oa_mid.len());
2729 debug_assert_eq!(sb_back.len(), ob.len());
2730 sa == oa_front && sb_mid == oa_mid && sb_back == ob
2732 let front = oa.len();
2733 let mid = sa.len() - front;
2735 let (sa_front, sa_mid) = sa.split_at(front);
2736 let (ob_mid, ob_back) = ob.split_at(mid);
2737 debug_assert_eq!(sa_front.len(), oa.len());
2738 debug_assert_eq!(sa_mid.len(), ob_mid.len());
2739 debug_assert_eq!(sb.len(), ob_back.len());
2740 sa_front == oa && sa_mid == ob_mid && sb == ob_back
2745 #[stable(feature = "rust1", since = "1.0.0")]
2746 impl<T: Eq, A: Allocator> Eq for VecDeque<T, A> {}
2748 __impl_slice_eq1! { [] VecDeque<T, A>, Vec<U, A>, }
2749 __impl_slice_eq1! { [] VecDeque<T, A>, &[U], }
2750 __impl_slice_eq1! { [] VecDeque<T, A>, &mut [U], }
2751 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, [U; N], }
2752 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &[U; N], }
2753 __impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &mut [U; N], }
2755 #[stable(feature = "rust1", since = "1.0.0")]
2756 impl<T: PartialOrd, A: Allocator> PartialOrd for VecDeque<T, A> {
2757 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2758 self.iter().partial_cmp(other.iter())
2762 #[stable(feature = "rust1", since = "1.0.0")]
2763 impl<T: Ord, A: Allocator> Ord for VecDeque<T, A> {
2765 fn cmp(&self, other: &Self) -> Ordering {
2766 self.iter().cmp(other.iter())
2770 #[stable(feature = "rust1", since = "1.0.0")]
2771 impl<T: Hash, A: Allocator> Hash for VecDeque<T, A> {
2772 fn hash<H: Hasher>(&self, state: &mut H) {
2773 self.len().hash(state);
2774 // It's not possible to use Hash::hash_slice on slices
2775 // returned by as_slices method as their length can vary
2776 // in otherwise identical deques.
2778 // Hasher only guarantees equivalence for the exact same
2779 // set of calls to its methods.
2780 self.iter().for_each(|elem| elem.hash(state));
2784 #[stable(feature = "rust1", since = "1.0.0")]
2785 impl<T, A: Allocator> Index<usize> for VecDeque<T, A> {
2789 fn index(&self, index: usize) -> &T {
2790 self.get(index).expect("Out of bounds access")
2794 #[stable(feature = "rust1", since = "1.0.0")]
2795 impl<T, A: Allocator> IndexMut<usize> for VecDeque<T, A> {
2797 fn index_mut(&mut self, index: usize) -> &mut T {
2798 self.get_mut(index).expect("Out of bounds access")
2802 #[stable(feature = "rust1", since = "1.0.0")]
2803 impl<T> FromIterator<T> for VecDeque<T> {
2804 fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> VecDeque<T> {
2805 let iterator = iter.into_iter();
2806 let (lower, _) = iterator.size_hint();
2807 let mut deq = VecDeque::with_capacity(lower);
2808 deq.extend(iterator);
2813 #[stable(feature = "rust1", since = "1.0.0")]
2814 impl<T, A: Allocator> IntoIterator for VecDeque<T, A> {
2816 type IntoIter = IntoIter<T, A>;
2818 /// Consumes the `VecDeque` into a front-to-back iterator yielding elements by
2820 fn into_iter(self) -> IntoIter<T, A> {
2825 #[stable(feature = "rust1", since = "1.0.0")]
2826 impl<'a, T, A: Allocator> IntoIterator for &'a VecDeque<T, A> {
2828 type IntoIter = Iter<'a, T>;
2830 fn into_iter(self) -> Iter<'a, T> {
2835 #[stable(feature = "rust1", since = "1.0.0")]
2836 impl<'a, T, A: Allocator> IntoIterator for &'a mut VecDeque<T, A> {
2837 type Item = &'a mut T;
2838 type IntoIter = IterMut<'a, T>;
2840 fn into_iter(self) -> IterMut<'a, T> {
2845 #[stable(feature = "rust1", since = "1.0.0")]
2846 impl<T, A: Allocator> Extend<T> for VecDeque<T, A> {
2847 fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
2848 // This function should be the moral equivalent of:
2850 // for item in iter.into_iter() {
2851 // self.push_back(item);
2853 let mut iter = iter.into_iter();
2854 while let Some(element) = iter.next() {
2855 if self.len() == self.capacity() {
2856 let (lower, _) = iter.size_hint();
2857 self.reserve(lower.saturating_add(1));
2860 let head = self.head;
2861 self.head = self.wrap_add(self.head, 1);
2863 self.buffer_write(head, element);
2869 fn extend_one(&mut self, elem: T) {
2870 self.push_back(elem);
2874 fn extend_reserve(&mut self, additional: usize) {
2875 self.reserve(additional);
2879 #[stable(feature = "extend_ref", since = "1.2.0")]
2880 impl<'a, T: 'a + Copy, A: Allocator> Extend<&'a T> for VecDeque<T, A> {
2881 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2882 self.extend(iter.into_iter().cloned());
2886 fn extend_one(&mut self, &elem: &T) {
2887 self.push_back(elem);
2891 fn extend_reserve(&mut self, additional: usize) {
2892 self.reserve(additional);
2896 #[stable(feature = "rust1", since = "1.0.0")]
2897 impl<T: fmt::Debug, A: Allocator> fmt::Debug for VecDeque<T, A> {
2898 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2899 f.debug_list().entries(self).finish()
2903 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2904 impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A> {
2905 /// Turn a [`Vec<T>`] into a [`VecDeque<T>`].
2907 /// [`Vec<T>`]: crate::vec::Vec
2908 /// [`VecDeque<T>`]: crate::collections::VecDeque
2910 /// This avoids reallocating where possible, but the conditions for that are
2911 /// strict, and subject to change, and so shouldn't be relied upon unless the
2912 /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated.
2913 fn from(mut other: Vec<T, A>) -> Self {
2914 let len = other.len();
2915 if mem::size_of::<T>() == 0 {
2916 // There's no actual allocation for ZSTs to worry about capacity,
2917 // but `VecDeque` can't handle as much length as `Vec`.
2918 assert!(len < MAXIMUM_ZST_CAPACITY, "capacity overflow");
2920 // We need to resize if the capacity is not a power of two, too small or
2921 // doesn't have at least one free space. We do this while it's still in
2922 // the `Vec` so the items will drop on panic.
2923 let min_cap = cmp::max(MINIMUM_CAPACITY, len) + 1;
2924 let cap = cmp::max(min_cap, other.capacity()).next_power_of_two();
2925 if other.capacity() != cap {
2926 other.reserve_exact(cap - len);
2931 let (other_buf, len, capacity, alloc) = other.into_raw_parts_with_alloc();
2932 let buf = RawVec::from_raw_parts_in(other_buf, capacity, alloc);
2933 VecDeque { tail: 0, head: len, buf }
2938 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2939 impl<T, A: Allocator> From<VecDeque<T, A>> for Vec<T, A> {
2940 /// Turn a [`VecDeque<T>`] into a [`Vec<T>`].
2942 /// [`Vec<T>`]: crate::vec::Vec
2943 /// [`VecDeque<T>`]: crate::collections::VecDeque
2945 /// This never needs to re-allocate, but does need to do *O*(*n*) data movement if
2946 /// the circular buffer doesn't happen to be at the beginning of the allocation.
2951 /// use std::collections::VecDeque;
2953 /// // This one is *O*(1).
2954 /// let deque: VecDeque<_> = (1..5).collect();
2955 /// let ptr = deque.as_slices().0.as_ptr();
2956 /// let vec = Vec::from(deque);
2957 /// assert_eq!(vec, [1, 2, 3, 4]);
2958 /// assert_eq!(vec.as_ptr(), ptr);
2960 /// // This one needs data rearranging.
2961 /// let mut deque: VecDeque<_> = (1..5).collect();
2962 /// deque.push_front(9);
2963 /// deque.push_front(8);
2964 /// let ptr = deque.as_slices().1.as_ptr();
2965 /// let vec = Vec::from(deque);
2966 /// assert_eq!(vec, [8, 9, 1, 2, 3, 4]);
2967 /// assert_eq!(vec.as_ptr(), ptr);
2969 fn from(mut other: VecDeque<T, A>) -> Self {
2970 other.make_contiguous();
2973 let other = ManuallyDrop::new(other);
2974 let buf = other.buf.ptr();
2975 let len = other.len();
2976 let cap = other.cap();
2977 let alloc = ptr::read(other.allocator());
2979 if other.tail != 0 {
2980 ptr::copy(buf.add(other.tail), buf, len);
2982 Vec::from_raw_parts_in(buf, len, cap, alloc)
2987 #[stable(feature = "std_collections_from_array", since = "1.56.0")]
2988 impl<T, const N: usize> From<[T; N]> for VecDeque<T> {
2990 /// use std::collections::VecDeque;
2992 /// let deq1 = VecDeque::from([1, 2, 3, 4]);
2993 /// let deq2: VecDeque<_> = [1, 2, 3, 4].into();
2994 /// assert_eq!(deq1, deq2);
2996 fn from(arr: [T; N]) -> Self {
2997 let mut deq = VecDeque::with_capacity(N);
2998 let arr = ManuallyDrop::new(arr);
2999 if mem::size_of::<T>() != 0 {
3000 // SAFETY: VecDeque::with_capacity ensures that there is enough capacity.
3002 ptr::copy_nonoverlapping(arr.as_ptr(), deq.ptr(), N);