1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! VecDeque is a double-ended queue, which is implemented with the help of a
12 //! growing ring buffer.
14 //! This queue has `O(1)` amortized inserts and removals from both ends of the
15 //! container. It also has `O(1)` indexing like a vector. The contained elements
16 //! are not required to be copyable, and the queue will be sendable if the
17 //! contained type is sendable.
19 #![stable(feature = "rust1", since = "1.0.0")]
21 use core::cmp::Ordering;
23 use core::iter::{repeat, FromIterator, FusedIterator};
25 use core::ops::{Index, IndexMut};
27 use core::ptr::Shared;
30 use core::hash::{Hash, Hasher};
33 use alloc::raw_vec::RawVec;
35 use super::range::RangeArgument;
38 const INITIAL_CAPACITY: usize = 7; // 2^3 - 1
39 const MINIMUM_CAPACITY: usize = 1; // 2 - 1
40 #[cfg(target_pointer_width = "32")]
41 const MAXIMUM_ZST_CAPACITY: usize = 1 << (32 - 1); // Largest possible power of two
42 #[cfg(target_pointer_width = "64")]
43 const MAXIMUM_ZST_CAPACITY: usize = 1 << (64 - 1); // Largest possible power of two
45 /// `VecDeque` is a growable ring buffer, which can be used as a double-ended
46 /// queue efficiently.
48 /// The "default" usage of this type as a queue is to use `push_back` to add to
49 /// the queue, and `pop_front` to remove from the queue. `extend` and `append`
50 /// push onto the back in this manner, and iterating over `VecDeque` goes front
52 #[stable(feature = "rust1", since = "1.0.0")]
53 pub struct VecDeque<T> {
54 // tail and head are pointers into the buffer. Tail always points
55 // to the first element that could be read, Head always points
56 // to where data should be written.
57 // If tail == head the buffer is empty. The length of the ringbuffer
58 // is defined as the distance between the two.
64 #[stable(feature = "rust1", since = "1.0.0")]
65 impl<T: Clone> Clone for VecDeque<T> {
66 fn clone(&self) -> VecDeque<T> {
67 self.iter().cloned().collect()
71 #[stable(feature = "rust1", since = "1.0.0")]
72 unsafe impl<#[may_dangle] T> Drop for VecDeque<T> {
74 let (front, back) = self.as_mut_slices();
77 ptr::drop_in_place(front);
78 ptr::drop_in_place(back);
80 // RawVec handles deallocation
84 #[stable(feature = "rust1", since = "1.0.0")]
85 impl<T> Default for VecDeque<T> {
86 /// Creates an empty `VecDeque<T>`.
88 fn default() -> VecDeque<T> {
94 /// Marginally more convenient
96 fn ptr(&self) -> *mut T {
100 /// Marginally more convenient
102 fn cap(&self) -> usize {
103 if mem::size_of::<T>() == 0 {
104 // For zero sized types, we are always at maximum capacity
111 /// Turn ptr into a slice
113 unsafe fn buffer_as_slice(&self) -> &[T] {
114 slice::from_raw_parts(self.ptr(), self.cap())
117 /// Turn ptr into a mut slice
119 unsafe fn buffer_as_mut_slice(&mut self) -> &mut [T] {
120 slice::from_raw_parts_mut(self.ptr(), self.cap())
123 /// Moves an element out of the buffer
125 unsafe fn buffer_read(&mut self, off: usize) -> T {
126 ptr::read(self.ptr().offset(off as isize))
129 /// Writes an element into the buffer, moving it.
131 unsafe fn buffer_write(&mut self, off: usize, value: T) {
132 ptr::write(self.ptr().offset(off as isize), value);
135 /// Returns true if and only if the buffer is at capacity
137 fn is_full(&self) -> bool {
138 self.cap() - self.len() == 1
141 /// Returns the index in the underlying buffer for a given logical element
144 fn wrap_index(&self, idx: usize) -> usize {
145 wrap_index(idx, self.cap())
148 /// Returns the index in the underlying buffer for a given logical element
151 fn wrap_add(&self, idx: usize, addend: usize) -> usize {
152 wrap_index(idx.wrapping_add(addend), self.cap())
155 /// Returns the index in the underlying buffer for a given logical element
156 /// index - subtrahend.
158 fn wrap_sub(&self, idx: usize, subtrahend: usize) -> usize {
159 wrap_index(idx.wrapping_sub(subtrahend), self.cap())
162 /// Copies a contiguous block of memory len long from src to dst
164 unsafe fn copy(&self, dst: usize, src: usize, len: usize) {
165 debug_assert!(dst + len <= self.cap(),
166 "cpy dst={} src={} len={} cap={}",
171 debug_assert!(src + len <= self.cap(),
172 "cpy dst={} src={} len={} cap={}",
177 ptr::copy(self.ptr().offset(src as isize),
178 self.ptr().offset(dst as isize),
182 /// Copies a contiguous block of memory len long from src to dst
184 unsafe fn copy_nonoverlapping(&self, dst: usize, src: usize, len: usize) {
185 debug_assert!(dst + len <= self.cap(),
186 "cno dst={} src={} len={} cap={}",
191 debug_assert!(src + len <= self.cap(),
192 "cno dst={} src={} len={} cap={}",
197 ptr::copy_nonoverlapping(self.ptr().offset(src as isize),
198 self.ptr().offset(dst as isize),
202 /// Copies a potentially wrapping block of memory len long from src to dest.
203 /// (abs(dst - src) + len) must be no larger than cap() (There must be at
204 /// most one continuous overlapping region between src and dest).
205 unsafe fn wrap_copy(&self, dst: usize, src: usize, len: usize) {
207 fn diff(a: usize, b: usize) -> usize {
208 if a <= b { b - a } else { a - b }
210 debug_assert!(cmp::min(diff(dst, src), self.cap() - diff(dst, src)) + len <= self.cap(),
211 "wrc dst={} src={} len={} cap={}",
217 if src == dst || len == 0 {
221 let dst_after_src = self.wrap_sub(dst, src) < len;
223 let src_pre_wrap_len = self.cap() - src;
224 let dst_pre_wrap_len = self.cap() - dst;
225 let src_wraps = src_pre_wrap_len < len;
226 let dst_wraps = dst_pre_wrap_len < len;
228 match (dst_after_src, src_wraps, dst_wraps) {
229 (_, false, false) => {
230 // src doesn't wrap, dst doesn't wrap
233 // 1 [_ _ A A B B C C _]
234 // 2 [_ _ A A A A B B _]
237 self.copy(dst, src, len);
239 (false, false, true) => {
240 // dst before src, src doesn't wrap, dst wraps
243 // 1 [A A B B _ _ _ C C]
244 // 2 [A A B B _ _ _ A A]
245 // 3 [B B B B _ _ _ A A]
248 self.copy(dst, src, dst_pre_wrap_len);
249 self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len);
251 (true, false, true) => {
252 // src before dst, src doesn't wrap, dst wraps
255 // 1 [C C _ _ _ A A B B]
256 // 2 [B B _ _ _ A A B B]
257 // 3 [B B _ _ _ A A A A]
260 self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len);
261 self.copy(dst, src, dst_pre_wrap_len);
263 (false, true, false) => {
264 // dst before src, src wraps, dst doesn't wrap
267 // 1 [C C _ _ _ A A B B]
268 // 2 [C C _ _ _ B B B B]
269 // 3 [C C _ _ _ B B C C]
272 self.copy(dst, src, src_pre_wrap_len);
273 self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len);
275 (true, true, false) => {
276 // src before dst, src wraps, dst doesn't wrap
279 // 1 [A A B B _ _ _ C C]
280 // 2 [A A A A _ _ _ C C]
281 // 3 [C C A A _ _ _ C C]
284 self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len);
285 self.copy(dst, src, src_pre_wrap_len);
287 (false, true, true) => {
288 // dst before src, src wraps, dst wraps
291 // 1 [A B C D _ E F G H]
292 // 2 [A B C D _ E G H H]
293 // 3 [A B C D _ E G H A]
294 // 4 [B C C D _ E G H A]
297 debug_assert!(dst_pre_wrap_len > src_pre_wrap_len);
298 let delta = dst_pre_wrap_len - src_pre_wrap_len;
299 self.copy(dst, src, src_pre_wrap_len);
300 self.copy(dst + src_pre_wrap_len, 0, delta);
301 self.copy(0, delta, len - dst_pre_wrap_len);
303 (true, true, true) => {
304 // src before dst, src wraps, dst wraps
307 // 1 [A B C D _ E F G H]
308 // 2 [A A B D _ E F G H]
309 // 3 [H A B D _ E F G H]
310 // 4 [H A B D _ E F F G]
313 debug_assert!(src_pre_wrap_len > dst_pre_wrap_len);
314 let delta = src_pre_wrap_len - dst_pre_wrap_len;
315 self.copy(delta, 0, len - src_pre_wrap_len);
316 self.copy(0, self.cap() - delta, delta);
317 self.copy(dst, src, dst_pre_wrap_len);
322 /// Frobs the head and tail sections around to handle the fact that we
323 /// just reallocated. Unsafe because it trusts old_cap.
325 unsafe fn handle_cap_increase(&mut self, old_cap: usize) {
326 let new_cap = self.cap();
328 // Move the shortest contiguous section of the ring buffer
330 // [o o o o o o o . ]
332 // A [o o o o o o o . . . . . . . . . ]
334 // [o o . o o o o o ]
336 // B [. . . o o o o o o o . . . . . . ]
338 // [o o o o o . o o ]
340 // C [o o o o o . . . . . . . . . o o ]
342 if self.tail <= self.head {
345 } else if self.head < old_cap - self.tail {
347 self.copy_nonoverlapping(old_cap, 0, self.head);
348 self.head += old_cap;
349 debug_assert!(self.head > self.tail);
352 let new_tail = new_cap - (old_cap - self.tail);
353 self.copy_nonoverlapping(new_tail, self.tail, old_cap - self.tail);
354 self.tail = new_tail;
355 debug_assert!(self.head < self.tail);
357 debug_assert!(self.head < self.cap());
358 debug_assert!(self.tail < self.cap());
359 debug_assert!(self.cap().count_ones() == 1);
363 impl<T> VecDeque<T> {
364 /// Creates an empty `VecDeque`.
369 /// use std::collections::VecDeque;
371 /// let vector: VecDeque<u32> = VecDeque::new();
373 #[stable(feature = "rust1", since = "1.0.0")]
374 pub fn new() -> VecDeque<T> {
375 VecDeque::with_capacity(INITIAL_CAPACITY)
378 /// Creates an empty `VecDeque` with space for at least `n` elements.
383 /// use std::collections::VecDeque;
385 /// let vector: VecDeque<u32> = VecDeque::with_capacity(10);
387 #[stable(feature = "rust1", since = "1.0.0")]
388 pub fn with_capacity(n: usize) -> VecDeque<T> {
389 // +1 since the ringbuffer always leaves one space empty
390 let cap = cmp::max(n + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
391 assert!(cap > n, "capacity overflow");
396 buf: RawVec::with_capacity(cap),
400 /// Retrieves an element in the `VecDeque` by index.
402 /// Element at index 0 is the front of the queue.
407 /// use std::collections::VecDeque;
409 /// let mut buf = VecDeque::new();
410 /// buf.push_back(3);
411 /// buf.push_back(4);
412 /// buf.push_back(5);
413 /// assert_eq!(buf.get(1), Some(&4));
415 #[stable(feature = "rust1", since = "1.0.0")]
416 pub fn get(&self, index: usize) -> Option<&T> {
417 if index < self.len() {
418 let idx = self.wrap_add(self.tail, index);
419 unsafe { Some(&*self.ptr().offset(idx as isize)) }
425 /// Retrieves an element in the `VecDeque` mutably by index.
427 /// Element at index 0 is the front of the queue.
432 /// use std::collections::VecDeque;
434 /// let mut buf = VecDeque::new();
435 /// buf.push_back(3);
436 /// buf.push_back(4);
437 /// buf.push_back(5);
438 /// if let Some(elem) = buf.get_mut(1) {
442 /// assert_eq!(buf[1], 7);
444 #[stable(feature = "rust1", since = "1.0.0")]
445 pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
446 if index < self.len() {
447 let idx = self.wrap_add(self.tail, index);
448 unsafe { Some(&mut *self.ptr().offset(idx as isize)) }
454 /// Swaps elements at indices `i` and `j`.
456 /// `i` and `j` may be equal.
458 /// Fails if there is no element with either index.
460 /// Element at index 0 is the front of the queue.
465 /// use std::collections::VecDeque;
467 /// let mut buf = VecDeque::new();
468 /// buf.push_back(3);
469 /// buf.push_back(4);
470 /// buf.push_back(5);
472 /// assert_eq!(buf[0], 5);
473 /// assert_eq!(buf[2], 3);
475 #[stable(feature = "rust1", since = "1.0.0")]
476 pub fn swap(&mut self, i: usize, j: usize) {
477 assert!(i < self.len());
478 assert!(j < self.len());
479 let ri = self.wrap_add(self.tail, i);
480 let rj = self.wrap_add(self.tail, j);
482 ptr::swap(self.ptr().offset(ri as isize),
483 self.ptr().offset(rj as isize))
487 /// Returns the number of elements the `VecDeque` can hold without
493 /// use std::collections::VecDeque;
495 /// let buf: VecDeque<i32> = VecDeque::with_capacity(10);
496 /// assert!(buf.capacity() >= 10);
499 #[stable(feature = "rust1", since = "1.0.0")]
500 pub fn capacity(&self) -> usize {
504 /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
505 /// given `VecDeque`. Does nothing if the capacity is already sufficient.
507 /// Note that the allocator may give the collection more space than it requests. Therefore
508 /// capacity can not be relied upon to be precisely minimal. Prefer `reserve` if future
509 /// insertions are expected.
513 /// Panics if the new capacity overflows `usize`.
518 /// use std::collections::VecDeque;
520 /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
521 /// buf.reserve_exact(10);
522 /// assert!(buf.capacity() >= 11);
524 #[stable(feature = "rust1", since = "1.0.0")]
525 pub fn reserve_exact(&mut self, additional: usize) {
526 self.reserve(additional);
529 /// Reserves capacity for at least `additional` more elements to be inserted in the given
530 /// `VecDeque`. The collection may reserve more space to avoid frequent reallocations.
534 /// Panics if the new capacity overflows `usize`.
539 /// use std::collections::VecDeque;
541 /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
543 /// assert!(buf.capacity() >= 11);
545 #[stable(feature = "rust1", since = "1.0.0")]
546 pub fn reserve(&mut self, additional: usize) {
547 let old_cap = self.cap();
548 let used_cap = self.len() + 1;
549 let new_cap = used_cap.checked_add(additional)
550 .and_then(|needed_cap| needed_cap.checked_next_power_of_two())
551 .expect("capacity overflow");
553 if new_cap > self.capacity() {
554 self.buf.reserve_exact(used_cap, new_cap - used_cap);
556 self.handle_cap_increase(old_cap);
561 /// Shrinks the capacity of the `VecDeque` as much as possible.
563 /// It will drop down as close as possible to the length but the allocator may still inform the
564 /// `VecDeque` that there is space for a few more elements.
569 /// use std::collections::VecDeque;
571 /// let mut buf = VecDeque::with_capacity(15);
572 /// buf.extend(0..4);
573 /// assert_eq!(buf.capacity(), 15);
574 /// buf.shrink_to_fit();
575 /// assert!(buf.capacity() >= 4);
577 #[stable(feature = "deque_extras_15", since = "1.5.0")]
578 pub fn shrink_to_fit(&mut self) {
579 // +1 since the ringbuffer always leaves one space empty
580 // len + 1 can't overflow for an existing, well-formed ringbuffer.
581 let target_cap = cmp::max(self.len() + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
582 if target_cap < self.cap() {
583 // There are three cases of interest:
584 // All elements are out of desired bounds
585 // Elements are contiguous, and head is out of desired bounds
586 // Elements are discontiguous, and tail is out of desired bounds
588 // At all other times, element positions are unaffected.
590 // Indicates that elements at the head should be moved.
591 let head_outside = self.head == 0 || self.head >= target_cap;
592 // Move elements from out of desired bounds (positions after target_cap)
593 if self.tail >= target_cap && head_outside {
595 // [. . . . . . . . o o o o o o o . ]
597 // [o o o o o o o . ]
599 self.copy_nonoverlapping(0, self.tail, self.len());
601 self.head = self.len();
603 } else if self.tail != 0 && self.tail < target_cap && head_outside {
605 // [. . . o o o o o o o . . . . . . ]
607 // [o o . o o o o o ]
608 let len = self.wrap_sub(self.head, target_cap);
610 self.copy_nonoverlapping(0, target_cap, len);
613 debug_assert!(self.head < self.tail);
614 } else if self.tail >= target_cap {
616 // [o o o o o . . . . . . . . . o o ]
618 // [o o o o o . o o ]
619 debug_assert!(self.wrap_sub(self.head, 1) < target_cap);
620 let len = self.cap() - self.tail;
621 let new_tail = target_cap - len;
623 self.copy_nonoverlapping(new_tail, self.tail, len);
625 self.tail = new_tail;
626 debug_assert!(self.head < self.tail);
629 self.buf.shrink_to_fit(target_cap);
631 debug_assert!(self.head < self.cap());
632 debug_assert!(self.tail < self.cap());
633 debug_assert!(self.cap().count_ones() == 1);
637 /// Shortens a `VecDeque`, dropping excess elements from the back.
639 /// If `len` is greater than the `VecDeque`'s current length, this has no
645 /// #![feature(deque_extras)]
647 /// use std::collections::VecDeque;
649 /// let mut buf = VecDeque::new();
650 /// buf.push_back(5);
651 /// buf.push_back(10);
652 /// buf.push_back(15);
654 /// assert_eq!(buf.len(), 1);
655 /// assert_eq!(Some(&5), buf.get(0));
657 #[unstable(feature = "deque_extras",
658 reason = "matches collection reform specification; waiting on panic semantics",
660 pub fn truncate(&mut self, len: usize) {
661 for _ in len..self.len() {
666 /// Returns a front-to-back iterator.
671 /// use std::collections::VecDeque;
673 /// let mut buf = VecDeque::new();
674 /// buf.push_back(5);
675 /// buf.push_back(3);
676 /// buf.push_back(4);
677 /// let b: &[_] = &[&5, &3, &4];
678 /// let c: Vec<&i32> = buf.iter().collect();
679 /// assert_eq!(&c[..], b);
681 #[stable(feature = "rust1", since = "1.0.0")]
682 pub fn iter(&self) -> Iter<T> {
686 ring: unsafe { self.buffer_as_slice() },
690 /// Returns a front-to-back iterator that returns mutable references.
695 /// use std::collections::VecDeque;
697 /// let mut buf = VecDeque::new();
698 /// buf.push_back(5);
699 /// buf.push_back(3);
700 /// buf.push_back(4);
701 /// for num in buf.iter_mut() {
704 /// let b: &[_] = &[&mut 3, &mut 1, &mut 2];
705 /// assert_eq!(&buf.iter_mut().collect::<Vec<&mut i32>>()[..], b);
707 #[stable(feature = "rust1", since = "1.0.0")]
708 pub fn iter_mut(&mut self) -> IterMut<T> {
712 ring: unsafe { self.buffer_as_mut_slice() },
716 /// Returns a pair of slices which contain, in order, the contents of the
722 /// use std::collections::VecDeque;
724 /// let mut vector = VecDeque::new();
726 /// vector.push_back(0);
727 /// vector.push_back(1);
728 /// vector.push_back(2);
730 /// assert_eq!(vector.as_slices(), (&[0, 1, 2][..], &[][..]));
732 /// vector.push_front(10);
733 /// vector.push_front(9);
735 /// assert_eq!(vector.as_slices(), (&[9, 10][..], &[0, 1, 2][..]));
738 #[stable(feature = "deque_extras_15", since = "1.5.0")]
739 pub fn as_slices(&self) -> (&[T], &[T]) {
741 let buf = self.buffer_as_slice();
742 RingSlices::ring_slices(buf, self.head, self.tail)
746 /// Returns a pair of slices which contain, in order, the contents of the
752 /// use std::collections::VecDeque;
754 /// let mut vector = VecDeque::new();
756 /// vector.push_back(0);
757 /// vector.push_back(1);
759 /// vector.push_front(10);
760 /// vector.push_front(9);
762 /// vector.as_mut_slices().0[0] = 42;
763 /// vector.as_mut_slices().1[0] = 24;
764 /// assert_eq!(vector.as_slices(), (&[42, 10][..], &[24, 1][..]));
767 #[stable(feature = "deque_extras_15", since = "1.5.0")]
768 pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) {
770 let head = self.head;
771 let tail = self.tail;
772 let buf = self.buffer_as_mut_slice();
773 RingSlices::ring_slices(buf, head, tail)
777 /// Returns the number of elements in the `VecDeque`.
782 /// use std::collections::VecDeque;
784 /// let mut v = VecDeque::new();
785 /// assert_eq!(v.len(), 0);
787 /// assert_eq!(v.len(), 1);
789 #[stable(feature = "rust1", since = "1.0.0")]
790 pub fn len(&self) -> usize {
791 count(self.tail, self.head, self.cap())
794 /// Returns true if the buffer contains no elements
799 /// use std::collections::VecDeque;
801 /// let mut v = VecDeque::new();
802 /// assert!(v.is_empty());
804 /// assert!(!v.is_empty());
806 #[stable(feature = "rust1", since = "1.0.0")]
807 pub fn is_empty(&self) -> bool {
808 self.tail == self.head
811 /// Create a draining iterator that removes the specified range in the
812 /// `VecDeque` and yields the removed items.
814 /// Note 1: The element range is removed even if the iterator is not
815 /// consumed until the end.
817 /// Note 2: It is unspecified how many elements are removed from the deque,
818 /// if the `Drain` value is not dropped, but the borrow it holds expires
819 /// (eg. due to mem::forget).
823 /// Panics if the starting point is greater than the end point or if
824 /// the end point is greater than the length of the vector.
829 /// use std::collections::VecDeque;
831 /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
832 /// assert_eq!(vec![3].into_iter().collect::<VecDeque<_>>(), v.drain(2..).collect());
833 /// assert_eq!(vec![1, 2].into_iter().collect::<VecDeque<_>>(), v);
835 /// // A full range clears all contents
837 /// assert!(v.is_empty());
840 #[stable(feature = "drain", since = "1.6.0")]
841 pub fn drain<R>(&mut self, range: R) -> Drain<T>
842 where R: RangeArgument<usize>
846 // When the Drain is first created, the source deque is shortened to
847 // make sure no uninitialized or moved-from elements are accessible at
848 // all if the Drain's destructor never gets to run.
850 // Drain will ptr::read out the values to remove.
851 // When finished, the remaining data will be copied back to cover the hole,
852 // and the head/tail values will be restored correctly.
854 let len = self.len();
855 let start = *range.start().unwrap_or(&0);
856 let end = *range.end().unwrap_or(&len);
857 assert!(start <= end, "drain lower bound was too large");
858 assert!(end <= len, "drain upper bound was too large");
860 // The deque's elements are parted into three segments:
861 // * self.tail -> drain_tail
862 // * drain_tail -> drain_head
863 // * drain_head -> self.head
865 // T = self.tail; H = self.head; t = drain_tail; h = drain_head
867 // We store drain_tail as self.head, and drain_head and self.head as
868 // after_tail and after_head respectively on the Drain. This also
869 // truncates the effective array such that if the Drain is leaked, we
870 // have forgotten about the potentially moved values after the start of
874 // [. . . o o x x o o . . .]
876 let drain_tail = self.wrap_add(self.tail, start);
877 let drain_head = self.wrap_add(self.tail, end);
878 let head = self.head;
880 // "forget" about the values after the start of the drain until after
881 // the drain is complete and the Drain destructor is run.
882 self.head = drain_tail;
885 deque: unsafe { Shared::new(self as *mut _) },
886 after_tail: drain_head,
891 ring: unsafe { self.buffer_as_mut_slice() },
896 /// Clears the buffer, removing all values.
901 /// use std::collections::VecDeque;
903 /// let mut v = VecDeque::new();
906 /// assert!(v.is_empty());
908 #[stable(feature = "rust1", since = "1.0.0")]
910 pub fn clear(&mut self) {
914 /// Returns `true` if the `VecDeque` contains an element equal to the
920 /// use std::collections::VecDeque;
922 /// let mut vector: VecDeque<u32> = VecDeque::new();
924 /// vector.push_back(0);
925 /// vector.push_back(1);
927 /// assert_eq!(vector.contains(&1), true);
928 /// assert_eq!(vector.contains(&10), false);
930 #[stable(feature = "vec_deque_contains", since = "1.12.0")]
931 pub fn contains(&self, x: &T) -> bool
932 where T: PartialEq<T>
934 let (a, b) = self.as_slices();
935 a.contains(x) || b.contains(x)
938 /// Provides a reference to the front element, or `None` if the sequence is
944 /// use std::collections::VecDeque;
946 /// let mut d = VecDeque::new();
947 /// assert_eq!(d.front(), None);
951 /// assert_eq!(d.front(), Some(&1));
953 #[stable(feature = "rust1", since = "1.0.0")]
954 pub fn front(&self) -> Option<&T> {
955 if !self.is_empty() {
962 /// Provides a mutable reference to the front element, or `None` if the
963 /// sequence is empty.
968 /// use std::collections::VecDeque;
970 /// let mut d = VecDeque::new();
971 /// assert_eq!(d.front_mut(), None);
975 /// match d.front_mut() {
976 /// Some(x) => *x = 9,
979 /// assert_eq!(d.front(), Some(&9));
981 #[stable(feature = "rust1", since = "1.0.0")]
982 pub fn front_mut(&mut self) -> Option<&mut T> {
983 if !self.is_empty() {
990 /// Provides a reference to the back element, or `None` if the sequence is
996 /// use std::collections::VecDeque;
998 /// let mut d = VecDeque::new();
999 /// assert_eq!(d.back(), None);
1003 /// assert_eq!(d.back(), Some(&2));
1005 #[stable(feature = "rust1", since = "1.0.0")]
1006 pub fn back(&self) -> Option<&T> {
1007 if !self.is_empty() {
1008 Some(&self[self.len() - 1])
1014 /// Provides a mutable reference to the back element, or `None` if the
1015 /// sequence is empty.
1020 /// use std::collections::VecDeque;
1022 /// let mut d = VecDeque::new();
1023 /// assert_eq!(d.back(), None);
1027 /// match d.back_mut() {
1028 /// Some(x) => *x = 9,
1031 /// assert_eq!(d.back(), Some(&9));
1033 #[stable(feature = "rust1", since = "1.0.0")]
1034 pub fn back_mut(&mut self) -> Option<&mut T> {
1035 let len = self.len();
1036 if !self.is_empty() {
1037 Some(&mut self[len - 1])
1043 /// Removes the first element and returns it, or `None` if the sequence is
1049 /// use std::collections::VecDeque;
1051 /// let mut d = VecDeque::new();
1055 /// assert_eq!(d.pop_front(), Some(1));
1056 /// assert_eq!(d.pop_front(), Some(2));
1057 /// assert_eq!(d.pop_front(), None);
1059 #[stable(feature = "rust1", since = "1.0.0")]
1060 pub fn pop_front(&mut self) -> Option<T> {
1061 if self.is_empty() {
1064 let tail = self.tail;
1065 self.tail = self.wrap_add(self.tail, 1);
1066 unsafe { Some(self.buffer_read(tail)) }
1070 /// Inserts an element first in the sequence.
1075 /// use std::collections::VecDeque;
1077 /// let mut d = VecDeque::new();
1078 /// d.push_front(1);
1079 /// d.push_front(2);
1080 /// assert_eq!(d.front(), Some(&2));
1082 #[stable(feature = "rust1", since = "1.0.0")]
1083 pub fn push_front(&mut self, value: T) {
1085 let old_cap = self.cap();
1088 self.handle_cap_increase(old_cap);
1090 debug_assert!(!self.is_full());
1093 self.tail = self.wrap_sub(self.tail, 1);
1094 let tail = self.tail;
1096 self.buffer_write(tail, value);
1100 /// Appends an element to the back of a buffer
1105 /// use std::collections::VecDeque;
1107 /// let mut buf = VecDeque::new();
1108 /// buf.push_back(1);
1109 /// buf.push_back(3);
1110 /// assert_eq!(3, *buf.back().unwrap());
1112 #[stable(feature = "rust1", since = "1.0.0")]
1113 pub fn push_back(&mut self, value: T) {
1115 let old_cap = self.cap();
1118 self.handle_cap_increase(old_cap);
1120 debug_assert!(!self.is_full());
1123 let head = self.head;
1124 self.head = self.wrap_add(self.head, 1);
1125 unsafe { self.buffer_write(head, value) }
1128 /// Removes the last element from a buffer and returns it, or `None` if
1134 /// use std::collections::VecDeque;
1136 /// let mut buf = VecDeque::new();
1137 /// assert_eq!(buf.pop_back(), None);
1138 /// buf.push_back(1);
1139 /// buf.push_back(3);
1140 /// assert_eq!(buf.pop_back(), Some(3));
1142 #[stable(feature = "rust1", since = "1.0.0")]
1143 pub fn pop_back(&mut self) -> Option<T> {
1144 if self.is_empty() {
1147 self.head = self.wrap_sub(self.head, 1);
1148 let head = self.head;
1149 unsafe { Some(self.buffer_read(head)) }
1154 fn is_contiguous(&self) -> bool {
1155 self.tail <= self.head
1158 /// Removes an element from anywhere in the `VecDeque` and returns it, replacing it with the
1161 /// This does not preserve ordering, but is O(1).
1163 /// Returns `None` if `index` is out of bounds.
1165 /// Element at index 0 is the front of the queue.
1170 /// use std::collections::VecDeque;
1172 /// let mut buf = VecDeque::new();
1173 /// assert_eq!(buf.swap_remove_back(0), None);
1174 /// buf.push_back(1);
1175 /// buf.push_back(2);
1176 /// buf.push_back(3);
1178 /// assert_eq!(buf.swap_remove_back(0), Some(1));
1179 /// assert_eq!(buf.len(), 2);
1180 /// assert_eq!(buf[0], 3);
1181 /// assert_eq!(buf[1], 2);
1183 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1184 pub fn swap_remove_back(&mut self, index: usize) -> Option<T> {
1185 let length = self.len();
1186 if length > 0 && index < length - 1 {
1187 self.swap(index, length - 1);
1188 } else if index >= length {
1194 /// Removes an element from anywhere in the `VecDeque` and returns it,
1195 /// replacing it with the first element.
1197 /// This does not preserve ordering, but is O(1).
1199 /// Returns `None` if `index` is out of bounds.
1201 /// Element at index 0 is the front of the queue.
1206 /// use std::collections::VecDeque;
1208 /// let mut buf = VecDeque::new();
1209 /// assert_eq!(buf.swap_remove_front(0), None);
1210 /// buf.push_back(1);
1211 /// buf.push_back(2);
1212 /// buf.push_back(3);
1214 /// assert_eq!(buf.swap_remove_front(2), Some(3));
1215 /// assert_eq!(buf.len(), 2);
1216 /// assert_eq!(buf[0], 2);
1217 /// assert_eq!(buf[1], 1);
1219 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1220 pub fn swap_remove_front(&mut self, index: usize) -> Option<T> {
1221 let length = self.len();
1222 if length > 0 && index < length && index != 0 {
1223 self.swap(index, 0);
1224 } else if index >= length {
1230 /// Inserts an element at `index` within the `VecDeque`, shifting all elements with indices
1231 /// greater than or equal to `index` towards the back.
1233 /// Element at index 0 is the front of the queue.
1237 /// Panics if `index` is greater than `VecDeque`'s length
1242 /// use std::collections::VecDeque;
1244 /// let mut vec_deque = VecDeque::new();
1245 /// vec_deque.push_back('a');
1246 /// vec_deque.push_back('b');
1247 /// vec_deque.push_back('c');
1249 /// vec_deque.insert(1, 'd');
1251 /// let vec = vec_deque.into_iter().collect::<Vec<_>>();
1252 /// assert_eq!(vec, ['a', 'd', 'b', 'c']);
1254 #[stable(feature = "deque_extras_15", since = "1.5.0")]
1255 pub fn insert(&mut self, index: usize, value: T) {
1256 assert!(index <= self.len(), "index out of bounds");
1258 let old_cap = self.cap();
1261 self.handle_cap_increase(old_cap);
1263 debug_assert!(!self.is_full());
1266 // Move the least number of elements in the ring buffer and insert
1269 // At most len/2 - 1 elements will be moved. O(min(n, n-i))
1271 // There are three main cases:
1272 // Elements are contiguous
1273 // - special case when tail is 0
1274 // Elements are discontiguous and the insert is in the tail section
1275 // Elements are discontiguous and the insert is in the head section
1277 // For each of those there are two more cases:
1278 // Insert is closer to tail
1279 // Insert is closer to head
1281 // Key: H - self.head
1283 // o - Valid element
1284 // I - Insertion element
1285 // A - The element that should be after the insertion point
1286 // M - Indicates element was moved
1288 let idx = self.wrap_add(self.tail, index);
1290 let distance_to_tail = index;
1291 let distance_to_head = self.len() - index;
1293 let contiguous = self.is_contiguous();
1295 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1296 (true, true, _) if index == 0 => {
1301 // [A o o o o o o . . . . . . . . .]
1304 // [A o o o o o o o . . . . . I]
1307 self.tail = self.wrap_sub(self.tail, 1);
1309 (true, true, _) => {
1311 // contiguous, insert closer to tail:
1314 // [. . . o o A o o o o . . . . . .]
1317 // [. . o o I A o o o o . . . . . .]
1320 // contiguous, insert closer to tail and tail is 0:
1324 // [o o A o o o o . . . . . . . . .]
1327 // [o I A o o o o o . . . . . . . o]
1330 let new_tail = self.wrap_sub(self.tail, 1);
1332 self.copy(new_tail, self.tail, 1);
1333 // Already moved the tail, so we only copy `index - 1` elements.
1334 self.copy(self.tail, self.tail + 1, index - 1);
1336 self.tail = new_tail;
1339 (true, false, _) => {
1341 // contiguous, insert closer to head:
1344 // [. . . o o o o A o o . . . . . .]
1347 // [. . . o o o o I A o o . . . . .]
1350 self.copy(idx + 1, idx, self.head - idx);
1351 self.head = self.wrap_add(self.head, 1);
1354 (false, true, true) => {
1356 // discontiguous, insert closer to tail, tail section:
1359 // [o o o o o o . . . . . o o A o o]
1362 // [o o o o o o . . . . o o I A o o]
1365 self.copy(self.tail - 1, self.tail, index);
1369 (false, false, true) => {
1371 // discontiguous, insert closer to head, tail section:
1374 // [o o . . . . . . . o o o o o A o]
1377 // [o o o . . . . . . o o o o o I A]
1380 // copy elements up to new head
1381 self.copy(1, 0, self.head);
1383 // copy last element into empty spot at bottom of buffer
1384 self.copy(0, self.cap() - 1, 1);
1386 // move elements from idx to end forward not including ^ element
1387 self.copy(idx + 1, idx, self.cap() - 1 - idx);
1392 (false, true, false) if idx == 0 => {
1394 // discontiguous, insert is closer to tail, head section,
1395 // and is at index zero in the internal buffer:
1398 // [A o o o o o o o o o . . . o o o]
1401 // [A o o o o o o o o o . . o o o I]
1404 // copy elements up to new tail
1405 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1407 // copy last element into empty spot at bottom of buffer
1408 self.copy(self.cap() - 1, 0, 1);
1413 (false, true, false) => {
1415 // discontiguous, insert closer to tail, head section:
1418 // [o o o A o o o o o o . . . o o o]
1421 // [o o I A o o o o o o . . o o o o]
1424 // copy elements up to new tail
1425 self.copy(self.tail - 1, self.tail, self.cap() - self.tail);
1427 // copy last element into empty spot at bottom of buffer
1428 self.copy(self.cap() - 1, 0, 1);
1430 // move elements from idx-1 to end forward not including ^ element
1431 self.copy(0, 1, idx - 1);
1436 (false, false, false) => {
1438 // discontiguous, insert closer to head, head section:
1441 // [o o o o A o o . . . . . . o o o]
1444 // [o o o o I A o o . . . . . o o o]
1447 self.copy(idx + 1, idx, self.head - idx);
1453 // tail might've been changed so we need to recalculate
1454 let new_idx = self.wrap_add(self.tail, index);
1456 self.buffer_write(new_idx, value);
1460 /// Removes and returns the element at `index` from the `VecDeque`.
1461 /// Whichever end is closer to the removal point will be moved to make
1462 /// room, and all the affected elements will be moved to new positions.
1463 /// Returns `None` if `index` is out of bounds.
1465 /// Element at index 0 is the front of the queue.
1470 /// use std::collections::VecDeque;
1472 /// let mut buf = VecDeque::new();
1473 /// buf.push_back(1);
1474 /// buf.push_back(2);
1475 /// buf.push_back(3);
1477 /// assert_eq!(buf.remove(1), Some(2));
1478 /// assert_eq!(buf.get(1), Some(&3));
1480 #[stable(feature = "rust1", since = "1.0.0")]
1481 pub fn remove(&mut self, index: usize) -> Option<T> {
1482 if self.is_empty() || self.len() <= index {
1486 // There are three main cases:
1487 // Elements are contiguous
1488 // Elements are discontiguous and the removal is in the tail section
1489 // Elements are discontiguous and the removal is in the head section
1490 // - special case when elements are technically contiguous,
1491 // but self.head = 0
1493 // For each of those there are two more cases:
1494 // Insert is closer to tail
1495 // Insert is closer to head
1497 // Key: H - self.head
1499 // o - Valid element
1500 // x - Element marked for removal
1501 // R - Indicates element that is being removed
1502 // M - Indicates element was moved
1504 let idx = self.wrap_add(self.tail, index);
1506 let elem = unsafe { Some(self.buffer_read(idx)) };
1508 let distance_to_tail = index;
1509 let distance_to_head = self.len() - index;
1511 let contiguous = self.is_contiguous();
1513 match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) {
1514 (true, true, _) => {
1516 // contiguous, remove closer to tail:
1519 // [. . . o o x o o o o . . . . . .]
1522 // [. . . . o o o o o o . . . . . .]
1525 self.copy(self.tail + 1, self.tail, index);
1529 (true, false, _) => {
1531 // contiguous, remove closer to head:
1534 // [. . . o o o o x o o . . . . . .]
1537 // [. . . o o o o o o . . . . . . .]
1540 self.copy(idx, idx + 1, self.head - idx - 1);
1544 (false, true, true) => {
1546 // discontiguous, remove closer to tail, tail section:
1549 // [o o o o o o . . . . . o o x o o]
1552 // [o o o o o o . . . . . . o o o o]
1555 self.copy(self.tail + 1, self.tail, index);
1556 self.tail = self.wrap_add(self.tail, 1);
1559 (false, false, false) => {
1561 // discontiguous, remove closer to head, head section:
1564 // [o o o o x o o . . . . . . o o o]
1567 // [o o o o o o . . . . . . . o o o]
1570 self.copy(idx, idx + 1, self.head - idx - 1);
1574 (false, false, true) => {
1576 // discontiguous, remove closer to head, tail section:
1579 // [o o o . . . . . . o o o o o x o]
1582 // [o o . . . . . . . o o o o o o o]
1585 // or quasi-discontiguous, remove next to head, tail section:
1588 // [. . . . . . . . . o o o o o x o]
1591 // [. . . . . . . . . o o o o o o .]
1594 // draw in elements in the tail section
1595 self.copy(idx, idx + 1, self.cap() - idx - 1);
1597 // Prevents underflow.
1599 // copy first element into empty spot
1600 self.copy(self.cap() - 1, 0, 1);
1602 // move elements in the head section backwards
1603 self.copy(0, 1, self.head - 1);
1606 self.head = self.wrap_sub(self.head, 1);
1609 (false, true, false) => {
1611 // discontiguous, remove closer to tail, head section:
1614 // [o o x o o o o o o o . . . o o o]
1617 // [o o o o o o o o o o . . . . o o]
1620 // draw in elements up to idx
1621 self.copy(1, 0, idx);
1623 // copy last element into empty spot
1624 self.copy(0, self.cap() - 1, 1);
1626 // move elements from tail to end forward, excluding the last one
1627 self.copy(self.tail + 1, self.tail, self.cap() - self.tail - 1);
1629 self.tail = self.wrap_add(self.tail, 1);
1637 /// Splits the collection into two at the given index.
1639 /// Returns a newly allocated `Self`. `self` contains elements `[0, at)`,
1640 /// and the returned `Self` contains elements `[at, len)`.
1642 /// Note that the capacity of `self` does not change.
1644 /// Element at index 0 is the front of the queue.
1648 /// Panics if `at > len`
1653 /// use std::collections::VecDeque;
1655 /// let mut buf: VecDeque<_> = vec![1,2,3].into_iter().collect();
1656 /// let buf2 = buf.split_off(1);
1657 /// // buf = [1], buf2 = [2, 3]
1658 /// assert_eq!(buf.len(), 1);
1659 /// assert_eq!(buf2.len(), 2);
1662 #[stable(feature = "split_off", since = "1.4.0")]
1663 pub fn split_off(&mut self, at: usize) -> Self {
1664 let len = self.len();
1665 assert!(at <= len, "`at` out of bounds");
1667 let other_len = len - at;
1668 let mut other = VecDeque::with_capacity(other_len);
1671 let (first_half, second_half) = self.as_slices();
1673 let first_len = first_half.len();
1674 let second_len = second_half.len();
1676 // `at` lies in the first half.
1677 let amount_in_first = first_len - at;
1679 ptr::copy_nonoverlapping(first_half.as_ptr().offset(at as isize),
1683 // just take all of the second half.
1684 ptr::copy_nonoverlapping(second_half.as_ptr(),
1685 other.ptr().offset(amount_in_first as isize),
1688 // `at` lies in the second half, need to factor in the elements we skipped
1689 // in the first half.
1690 let offset = at - first_len;
1691 let amount_in_second = second_len - offset;
1692 ptr::copy_nonoverlapping(second_half.as_ptr().offset(offset as isize),
1698 // Cleanup where the ends of the buffers are
1699 self.head = self.wrap_sub(self.head, other_len);
1700 other.head = other.wrap_index(other_len);
1705 /// Moves all the elements of `other` into `Self`, leaving `other` empty.
1709 /// Panics if the new number of elements in self overflows a `usize`.
1714 /// use std::collections::VecDeque;
1716 /// let mut buf: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
1717 /// let mut buf2: VecDeque<_> = vec![4, 5, 6].into_iter().collect();
1718 /// buf.append(&mut buf2);
1719 /// assert_eq!(buf.len(), 6);
1720 /// assert_eq!(buf2.len(), 0);
1723 #[stable(feature = "append", since = "1.4.0")]
1724 pub fn append(&mut self, other: &mut Self) {
1726 self.extend(other.drain(..));
1729 /// Retains only the elements specified by the predicate.
1731 /// In other words, remove all elements `e` such that `f(&e)` returns false.
1732 /// This method operates in place and preserves the order of the retained
1738 /// use std::collections::VecDeque;
1740 /// let mut buf = VecDeque::new();
1741 /// buf.extend(1..5);
1742 /// buf.retain(|&x| x%2 == 0);
1744 /// let v: Vec<_> = buf.into_iter().collect();
1745 /// assert_eq!(&v[..], &[2, 4]);
1747 #[stable(feature = "vec_deque_retain", since = "1.4.0")]
1748 pub fn retain<F>(&mut self, mut f: F)
1749 where F: FnMut(&T) -> bool
1751 let len = self.len();
1757 self.swap(i - del, i);
1761 self.truncate(len - del);
1766 impl<T: Clone> VecDeque<T> {
1767 /// Modifies the `VecDeque` in-place so that `len()` is equal to new_len,
1768 /// either by removing excess elements or by appending copies of a value to the back.
1773 /// #![feature(deque_extras)]
1775 /// use std::collections::VecDeque;
1777 /// let mut buf = VecDeque::new();
1778 /// buf.push_back(5);
1779 /// buf.push_back(10);
1780 /// buf.push_back(15);
1781 /// buf.resize(2, 0);
1782 /// buf.resize(6, 20);
1783 /// for (a, b) in [5, 10, 20, 20, 20, 20].iter().zip(&buf) {
1784 /// assert_eq!(a, b);
1787 #[unstable(feature = "deque_extras",
1788 reason = "matches collection reform specification; waiting on panic semantics",
1790 pub fn resize(&mut self, new_len: usize, value: T) {
1791 let len = self.len();
1794 self.extend(repeat(value).take(new_len - len))
1796 self.truncate(new_len);
1801 /// Returns the index in the underlying buffer for a given logical element index.
1803 fn wrap_index(index: usize, size: usize) -> usize {
1804 // size is always a power of 2
1805 debug_assert!(size.is_power_of_two());
1809 /// Returns the two slices that cover the VecDeque's valid range
1810 trait RingSlices: Sized {
1811 fn slice(self, from: usize, to: usize) -> Self;
1812 fn split_at(self, i: usize) -> (Self, Self);
1814 fn ring_slices(buf: Self, head: usize, tail: usize) -> (Self, Self) {
1815 let contiguous = tail <= head;
1817 let (empty, buf) = buf.split_at(0);
1818 (buf.slice(tail, head), empty)
1820 let (mid, right) = buf.split_at(tail);
1821 let (left, _) = mid.split_at(head);
1827 impl<'a, T> RingSlices for &'a [T] {
1828 fn slice(self, from: usize, to: usize) -> Self {
1831 fn split_at(self, i: usize) -> (Self, Self) {
1836 impl<'a, T> RingSlices for &'a mut [T] {
1837 fn slice(self, from: usize, to: usize) -> Self {
1840 fn split_at(self, i: usize) -> (Self, Self) {
1841 (*self).split_at_mut(i)
1845 /// Calculate the number of elements left to be read in the buffer
1847 fn count(tail: usize, head: usize, size: usize) -> usize {
1848 // size is always a power of 2
1849 (head.wrapping_sub(tail)) & (size - 1)
1852 /// `VecDeque` iterator.
1853 #[stable(feature = "rust1", since = "1.0.0")]
1854 pub struct Iter<'a, T: 'a> {
1860 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1861 #[stable(feature = "rust1", since = "1.0.0")]
1862 impl<'a, T> Clone for Iter<'a, T> {
1863 fn clone(&self) -> Iter<'a, T> {
1872 #[stable(feature = "rust1", since = "1.0.0")]
1873 impl<'a, T> Iterator for Iter<'a, T> {
1877 fn next(&mut self) -> Option<&'a T> {
1878 if self.tail == self.head {
1881 let tail = self.tail;
1882 self.tail = wrap_index(self.tail.wrapping_add(1), self.ring.len());
1883 unsafe { Some(self.ring.get_unchecked(tail)) }
1887 fn size_hint(&self) -> (usize, Option<usize>) {
1888 let len = count(self.tail, self.head, self.ring.len());
1892 fn fold<Acc, F>(self, mut accum: Acc, mut f: F) -> Acc
1893 where F: FnMut(Acc, Self::Item) -> Acc
1895 let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
1896 accum = front.iter().fold(accum, &mut f);
1897 back.iter().fold(accum, &mut f)
1901 #[stable(feature = "rust1", since = "1.0.0")]
1902 impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
1904 fn next_back(&mut self) -> Option<&'a T> {
1905 if self.tail == self.head {
1908 self.head = wrap_index(self.head.wrapping_sub(1), self.ring.len());
1909 unsafe { Some(self.ring.get_unchecked(self.head)) }
1913 #[stable(feature = "rust1", since = "1.0.0")]
1914 impl<'a, T> ExactSizeIterator for Iter<'a, T> {
1915 fn is_empty(&self) -> bool {
1916 self.head == self.tail
1920 #[unstable(feature = "fused", issue = "35602")]
1921 impl<'a, T> FusedIterator for Iter<'a, T> {}
1924 /// `VecDeque` mutable iterator.
1925 #[stable(feature = "rust1", since = "1.0.0")]
1926 pub struct IterMut<'a, T: 'a> {
1932 #[stable(feature = "rust1", since = "1.0.0")]
1933 impl<'a, T> Iterator for IterMut<'a, T> {
1934 type Item = &'a mut T;
1937 fn next(&mut self) -> Option<&'a mut T> {
1938 if self.tail == self.head {
1941 let tail = self.tail;
1942 self.tail = wrap_index(self.tail.wrapping_add(1), self.ring.len());
1945 let elem = self.ring.get_unchecked_mut(tail);
1946 Some(&mut *(elem as *mut _))
1951 fn size_hint(&self) -> (usize, Option<usize>) {
1952 let len = count(self.tail, self.head, self.ring.len());
1956 fn fold<Acc, F>(self, mut accum: Acc, mut f: F) -> Acc
1957 where F: FnMut(Acc, Self::Item) -> Acc
1959 let (front, back) = RingSlices::ring_slices(self.ring, self.head, self.tail);
1960 accum = front.iter_mut().fold(accum, &mut f);
1961 back.iter_mut().fold(accum, &mut f)
1965 #[stable(feature = "rust1", since = "1.0.0")]
1966 impl<'a, T> DoubleEndedIterator for IterMut<'a, T> {
1968 fn next_back(&mut self) -> Option<&'a mut T> {
1969 if self.tail == self.head {
1972 self.head = wrap_index(self.head.wrapping_sub(1), self.ring.len());
1975 let elem = self.ring.get_unchecked_mut(self.head);
1976 Some(&mut *(elem as *mut _))
1981 #[stable(feature = "rust1", since = "1.0.0")]
1982 impl<'a, T> ExactSizeIterator for IterMut<'a, T> {
1983 fn is_empty(&self) -> bool {
1984 self.head == self.tail
1988 #[unstable(feature = "fused", issue = "35602")]
1989 impl<'a, T> FusedIterator for IterMut<'a, T> {}
1991 /// A by-value VecDeque iterator
1993 #[stable(feature = "rust1", since = "1.0.0")]
1994 pub struct IntoIter<T> {
1998 #[stable(feature = "rust1", since = "1.0.0")]
1999 impl<T> Iterator for IntoIter<T> {
2003 fn next(&mut self) -> Option<T> {
2004 self.inner.pop_front()
2008 fn size_hint(&self) -> (usize, Option<usize>) {
2009 let len = self.inner.len();
2014 #[stable(feature = "rust1", since = "1.0.0")]
2015 impl<T> DoubleEndedIterator for IntoIter<T> {
2017 fn next_back(&mut self) -> Option<T> {
2018 self.inner.pop_back()
2022 #[stable(feature = "rust1", since = "1.0.0")]
2023 impl<T> ExactSizeIterator for IntoIter<T> {
2024 fn is_empty(&self) -> bool {
2025 self.inner.is_empty()
2029 #[unstable(feature = "fused", issue = "35602")]
2030 impl<T> FusedIterator for IntoIter<T> {}
2032 /// A draining VecDeque iterator
2033 #[stable(feature = "drain", since = "1.6.0")]
2034 pub struct Drain<'a, T: 'a> {
2038 deque: Shared<VecDeque<T>>,
2041 #[stable(feature = "drain", since = "1.6.0")]
2042 unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}
2043 #[stable(feature = "drain", since = "1.6.0")]
2044 unsafe impl<'a, T: Send> Send for Drain<'a, T> {}
2046 #[stable(feature = "drain", since = "1.6.0")]
2047 impl<'a, T: 'a> Drop for Drain<'a, T> {
2048 fn drop(&mut self) {
2049 for _ in self.by_ref() {}
2051 let source_deque = unsafe { &mut **self.deque };
2053 // T = source_deque_tail; H = source_deque_head; t = drain_tail; h = drain_head
2056 // [. . . o o x x o o . . .]
2058 let orig_tail = source_deque.tail;
2059 let drain_tail = source_deque.head;
2060 let drain_head = self.after_tail;
2061 let orig_head = self.after_head;
2063 let tail_len = count(orig_tail, drain_tail, source_deque.cap());
2064 let head_len = count(drain_head, orig_head, source_deque.cap());
2066 // Restore the original head value
2067 source_deque.head = orig_head;
2069 match (tail_len, head_len) {
2071 source_deque.head = 0;
2072 source_deque.tail = 0;
2075 source_deque.tail = drain_head;
2078 source_deque.head = drain_tail;
2081 if tail_len <= head_len {
2082 source_deque.tail = source_deque.wrap_sub(drain_head, tail_len);
2083 source_deque.wrap_copy(source_deque.tail, orig_tail, tail_len);
2085 source_deque.head = source_deque.wrap_add(drain_tail, head_len);
2086 source_deque.wrap_copy(drain_tail, drain_head, head_len);
2093 #[stable(feature = "drain", since = "1.6.0")]
2094 impl<'a, T: 'a> Iterator for Drain<'a, T> {
2098 fn next(&mut self) -> Option<T> {
2099 self.iter.next().map(|elt| unsafe { ptr::read(elt) })
2103 fn size_hint(&self) -> (usize, Option<usize>) {
2104 self.iter.size_hint()
2108 #[stable(feature = "drain", since = "1.6.0")]
2109 impl<'a, T: 'a> DoubleEndedIterator for Drain<'a, T> {
2111 fn next_back(&mut self) -> Option<T> {
2112 self.iter.next_back().map(|elt| unsafe { ptr::read(elt) })
2116 #[stable(feature = "drain", since = "1.6.0")]
2117 impl<'a, T: 'a> ExactSizeIterator for Drain<'a, T> {}
2119 #[unstable(feature = "fused", issue = "35602")]
2120 impl<'a, T: 'a> FusedIterator for Drain<'a, T> {}
2122 #[stable(feature = "rust1", since = "1.0.0")]
2123 impl<A: PartialEq> PartialEq for VecDeque<A> {
2124 fn eq(&self, other: &VecDeque<A>) -> bool {
2125 if self.len() != other.len() {
2128 let (sa, sb) = self.as_slices();
2129 let (oa, ob) = other.as_slices();
2130 if sa.len() == oa.len() {
2131 sa == oa && sb == ob
2132 } else if sa.len() < oa.len() {
2133 // Always divisible in three sections, for example:
2134 // self: [a b c|d e f]
2135 // other: [0 1 2 3|4 5]
2136 // front = 3, mid = 1,
2137 // [a b c] == [0 1 2] && [d] == [3] && [e f] == [4 5]
2138 let front = sa.len();
2139 let mid = oa.len() - front;
2141 let (oa_front, oa_mid) = oa.split_at(front);
2142 let (sb_mid, sb_back) = sb.split_at(mid);
2143 debug_assert_eq!(sa.len(), oa_front.len());
2144 debug_assert_eq!(sb_mid.len(), oa_mid.len());
2145 debug_assert_eq!(sb_back.len(), ob.len());
2146 sa == oa_front && sb_mid == oa_mid && sb_back == ob
2148 let front = oa.len();
2149 let mid = sa.len() - front;
2151 let (sa_front, sa_mid) = sa.split_at(front);
2152 let (ob_mid, ob_back) = ob.split_at(mid);
2153 debug_assert_eq!(sa_front.len(), oa.len());
2154 debug_assert_eq!(sa_mid.len(), ob_mid.len());
2155 debug_assert_eq!(sb.len(), ob_back.len());
2156 sa_front == oa && sa_mid == ob_mid && sb == ob_back
2161 #[stable(feature = "rust1", since = "1.0.0")]
2162 impl<A: Eq> Eq for VecDeque<A> {}
2164 #[stable(feature = "rust1", since = "1.0.0")]
2165 impl<A: PartialOrd> PartialOrd for VecDeque<A> {
2166 fn partial_cmp(&self, other: &VecDeque<A>) -> Option<Ordering> {
2167 self.iter().partial_cmp(other.iter())
2171 #[stable(feature = "rust1", since = "1.0.0")]
2172 impl<A: Ord> Ord for VecDeque<A> {
2174 fn cmp(&self, other: &VecDeque<A>) -> Ordering {
2175 self.iter().cmp(other.iter())
2179 #[stable(feature = "rust1", since = "1.0.0")]
2180 impl<A: Hash> Hash for VecDeque<A> {
2181 fn hash<H: Hasher>(&self, state: &mut H) {
2182 self.len().hash(state);
2183 let (a, b) = self.as_slices();
2184 Hash::hash_slice(a, state);
2185 Hash::hash_slice(b, state);
2189 #[stable(feature = "rust1", since = "1.0.0")]
2190 impl<A> Index<usize> for VecDeque<A> {
2194 fn index(&self, index: usize) -> &A {
2195 self.get(index).expect("Out of bounds access")
2199 #[stable(feature = "rust1", since = "1.0.0")]
2200 impl<A> IndexMut<usize> for VecDeque<A> {
2202 fn index_mut(&mut self, index: usize) -> &mut A {
2203 self.get_mut(index).expect("Out of bounds access")
2207 #[stable(feature = "rust1", since = "1.0.0")]
2208 impl<A> FromIterator<A> for VecDeque<A> {
2209 fn from_iter<T: IntoIterator<Item = A>>(iter: T) -> VecDeque<A> {
2210 let iterator = iter.into_iter();
2211 let (lower, _) = iterator.size_hint();
2212 let mut deq = VecDeque::with_capacity(lower);
2213 deq.extend(iterator);
2218 #[stable(feature = "rust1", since = "1.0.0")]
2219 impl<T> IntoIterator for VecDeque<T> {
2221 type IntoIter = IntoIter<T>;
2223 /// Consumes the list into a front-to-back iterator yielding elements by
2225 fn into_iter(self) -> IntoIter<T> {
2226 IntoIter { inner: self }
2230 #[stable(feature = "rust1", since = "1.0.0")]
2231 impl<'a, T> IntoIterator for &'a VecDeque<T> {
2233 type IntoIter = Iter<'a, T>;
2235 fn into_iter(self) -> Iter<'a, T> {
2240 #[stable(feature = "rust1", since = "1.0.0")]
2241 impl<'a, T> IntoIterator for &'a mut VecDeque<T> {
2242 type Item = &'a mut T;
2243 type IntoIter = IterMut<'a, T>;
2245 fn into_iter(mut self) -> IterMut<'a, T> {
2250 #[stable(feature = "rust1", since = "1.0.0")]
2251 impl<A> Extend<A> for VecDeque<A> {
2252 fn extend<T: IntoIterator<Item = A>>(&mut self, iter: T) {
2254 self.push_back(elt);
2259 #[stable(feature = "extend_ref", since = "1.2.0")]
2260 impl<'a, T: 'a + Copy> Extend<&'a T> for VecDeque<T> {
2261 fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
2262 self.extend(iter.into_iter().cloned());
2266 #[stable(feature = "rust1", since = "1.0.0")]
2267 impl<T: fmt::Debug> fmt::Debug for VecDeque<T> {
2268 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2269 f.debug_list().entries(self).finish()
2273 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2274 impl<T> From<Vec<T>> for VecDeque<T> {
2275 fn from(mut other: Vec<T>) -> Self {
2277 let other_buf = other.as_mut_ptr();
2278 let mut buf = RawVec::from_raw_parts(other_buf, other.capacity());
2279 let len = other.len();
2282 // We need to extend the buf if it's not a power of two, too small
2283 // or doesn't have at least one free space
2284 if !buf.cap().is_power_of_two() || (buf.cap() < (MINIMUM_CAPACITY + 1)) ||
2285 (buf.cap() == len) {
2286 let cap = cmp::max(buf.cap() + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
2287 buf.reserve_exact(len, cap - len);
2299 #[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")]
2300 impl<T> From<VecDeque<T>> for Vec<T> {
2301 fn from(other: VecDeque<T>) -> Self {
2303 let buf = other.buf.ptr();
2304 let len = other.len();
2305 let tail = other.tail;
2306 let head = other.head;
2307 let cap = other.cap();
2309 // Need to move the ring to the front of the buffer, as vec will expect this.
2310 if other.is_contiguous() {
2311 ptr::copy(buf.offset(tail as isize), buf, len);
2313 if (tail - head) >= cmp::min((cap - tail), head) {
2314 // There is enough free space in the centre for the shortest block so we can
2315 // do this in at most three copy moves.
2316 if (cap - tail) > head {
2317 // right hand block is the long one; move that enough for the left
2318 ptr::copy(buf.offset(tail as isize),
2319 buf.offset((tail - head) as isize),
2321 // copy left in the end
2322 ptr::copy(buf, buf.offset((cap - head) as isize), head);
2323 // shift the new thing to the start
2324 ptr::copy(buf.offset((tail - head) as isize), buf, len);
2326 // left hand block is the long one, we can do it in two!
2327 ptr::copy(buf, buf.offset((cap - tail) as isize), head);
2328 ptr::copy(buf.offset(tail as isize), buf, cap - tail);
2331 // Need to use N swaps to move the ring
2332 // We can use the space at the end of the ring as a temp store
2334 let mut left_edge: usize = 0;
2335 let mut right_edge: usize = tail;
2337 // The general problem looks like this
2338 // GHIJKLM...ABCDEF - before any swaps
2339 // ABCDEFM...GHIJKL - after 1 pass of swaps
2340 // ABCDEFGHIJM...KL - swap until the left edge reaches the temp store
2341 // - then restart the algorithm with a new (smaller) store
2342 // Sometimes the temp store is reached when the right edge is at the end
2343 // of the buffer - this means we've hit the right order with fewer swaps!
2346 // ABCDEF.. - after four only swaps we've finished
2348 while left_edge < len && right_edge != cap {
2349 let mut right_offset = 0;
2350 for i in left_edge..right_edge {
2351 right_offset = (i - left_edge) % (cap - right_edge);
2352 let src: isize = (right_edge + right_offset) as isize;
2353 ptr::swap(buf.offset(i as isize), buf.offset(src));
2355 let n_ops = right_edge - left_edge;
2357 right_edge += right_offset + 1;
2363 let out = Vec::from_raw_parts(buf, len, cap);
2374 use super::VecDeque;
2377 fn bench_push_back_100(b: &mut test::Bencher) {
2378 let mut deq = VecDeque::with_capacity(101);
2389 fn bench_push_front_100(b: &mut test::Bencher) {
2390 let mut deq = VecDeque::with_capacity(101);
2401 fn bench_pop_back_100(b: &mut test::Bencher) {
2402 let mut deq = VecDeque::<i32>::with_capacity(101);
2407 while !deq.is_empty() {
2408 test::black_box(deq.pop_back());
2414 fn bench_pop_front_100(b: &mut test::Bencher) {
2415 let mut deq = VecDeque::<i32>::with_capacity(101);
2420 while !deq.is_empty() {
2421 test::black_box(deq.pop_front());
2427 fn test_swap_front_back_remove() {
2428 fn test(back: bool) {
2429 // This test checks that every single combination of tail position and length is tested.
2430 // Capacity 15 should be large enough to cover every case.
2431 let mut tester = VecDeque::with_capacity(15);
2432 let usable_cap = tester.capacity();
2433 let final_len = usable_cap / 2;
2435 for len in 0..final_len {
2436 let expected = if back {
2439 (0..len).rev().collect()
2441 for tail_pos in 0..usable_cap {
2442 tester.tail = tail_pos;
2443 tester.head = tail_pos;
2445 for i in 0..len * 2 {
2446 tester.push_front(i);
2449 assert_eq!(tester.swap_remove_back(i), Some(len * 2 - 1 - i));
2452 for i in 0..len * 2 {
2453 tester.push_back(i);
2456 let idx = tester.len() - 1 - i;
2457 assert_eq!(tester.swap_remove_front(idx), Some(len * 2 - 1 - i));
2460 assert!(tester.tail < tester.cap());
2461 assert!(tester.head < tester.cap());
2462 assert_eq!(tester, expected);
2472 // This test checks that every single combination of tail position, length, and
2473 // insertion position is tested. Capacity 15 should be large enough to cover every case.
2475 let mut tester = VecDeque::with_capacity(15);
2476 // can't guarantee we got 15, so have to get what we got.
2477 // 15 would be great, but we will definitely get 2^k - 1, for k >= 4, or else
2478 // this test isn't covering what it wants to
2479 let cap = tester.capacity();
2482 // len is the length *after* insertion
2484 // 0, 1, 2, .., len - 1
2485 let expected = (0..).take(len).collect();
2486 for tail_pos in 0..cap {
2487 for to_insert in 0..len {
2488 tester.tail = tail_pos;
2489 tester.head = tail_pos;
2492 tester.push_back(i);
2495 tester.insert(to_insert, to_insert);
2496 assert!(tester.tail < tester.cap());
2497 assert!(tester.head < tester.cap());
2498 assert_eq!(tester, expected);
2506 // This test checks that every single combination of tail position, length, and
2507 // removal position is tested. Capacity 15 should be large enough to cover every case.
2509 let mut tester = VecDeque::with_capacity(15);
2510 // can't guarantee we got 15, so have to get what we got.
2511 // 15 would be great, but we will definitely get 2^k - 1, for k >= 4, or else
2512 // this test isn't covering what it wants to
2513 let cap = tester.capacity();
2515 // len is the length *after* removal
2516 for len in 0..cap - 1 {
2517 // 0, 1, 2, .., len - 1
2518 let expected = (0..).take(len).collect();
2519 for tail_pos in 0..cap {
2520 for to_remove in 0..len + 1 {
2521 tester.tail = tail_pos;
2522 tester.head = tail_pos;
2525 tester.push_back(1234);
2527 tester.push_back(i);
2529 if to_remove == len {
2530 tester.push_back(1234);
2532 tester.remove(to_remove);
2533 assert!(tester.tail < tester.cap());
2534 assert!(tester.head < tester.cap());
2535 assert_eq!(tester, expected);
2543 let mut tester: VecDeque<usize> = VecDeque::with_capacity(7);
2545 let cap = tester.capacity();
2546 for len in 0..cap + 1 {
2547 for tail in 0..cap + 1 {
2548 for drain_start in 0..len + 1 {
2549 for drain_end in drain_start..len + 1 {
2553 tester.push_back(i);
2556 // Check that we drain the correct values
2557 let drained: VecDeque<_> = tester.drain(drain_start..drain_end).collect();
2558 let drained_expected: VecDeque<_> = (drain_start..drain_end).collect();
2559 assert_eq!(drained, drained_expected);
2561 // We shouldn't have changed the capacity or made the
2562 // head or tail out of bounds
2563 assert_eq!(tester.capacity(), cap);
2564 assert!(tester.tail < tester.cap());
2565 assert!(tester.head < tester.cap());
2567 // We should see the correct values in the VecDeque
2568 let expected: VecDeque<_> = (0..drain_start)
2569 .chain(drain_end..len)
2571 assert_eq!(expected, tester);
2579 fn test_shrink_to_fit() {
2580 // This test checks that every single combination of head and tail position,
2581 // is tested. Capacity 15 should be large enough to cover every case.
2583 let mut tester = VecDeque::with_capacity(15);
2584 // can't guarantee we got 15, so have to get what we got.
2585 // 15 would be great, but we will definitely get 2^k - 1, for k >= 4, or else
2586 // this test isn't covering what it wants to
2587 let cap = tester.capacity();
2589 let max_cap = tester.capacity();
2591 for len in 0..cap + 1 {
2592 // 0, 1, 2, .., len - 1
2593 let expected = (0..).take(len).collect();
2594 for tail_pos in 0..max_cap + 1 {
2595 tester.tail = tail_pos;
2596 tester.head = tail_pos;
2599 tester.push_back(i);
2601 tester.shrink_to_fit();
2602 assert!(tester.capacity() <= cap);
2603 assert!(tester.tail < tester.cap());
2604 assert!(tester.head < tester.cap());
2605 assert_eq!(tester, expected);
2611 fn test_split_off() {
2612 // This test checks that every single combination of tail position, length, and
2613 // split position is tested. Capacity 15 should be large enough to cover every case.
2615 let mut tester = VecDeque::with_capacity(15);
2616 // can't guarantee we got 15, so have to get what we got.
2617 // 15 would be great, but we will definitely get 2^k - 1, for k >= 4, or else
2618 // this test isn't covering what it wants to
2619 let cap = tester.capacity();
2621 // len is the length *before* splitting
2623 // index to split at
2624 for at in 0..len + 1 {
2625 // 0, 1, 2, .., at - 1 (may be empty)
2626 let expected_self = (0..).take(at).collect();
2627 // at, at + 1, .., len - 1 (may be empty)
2628 let expected_other = (at..).take(len - at).collect();
2630 for tail_pos in 0..cap {
2631 tester.tail = tail_pos;
2632 tester.head = tail_pos;
2634 tester.push_back(i);
2636 let result = tester.split_off(at);
2637 assert!(tester.tail < tester.cap());
2638 assert!(tester.head < tester.cap());
2639 assert!(result.tail < result.cap());
2640 assert!(result.head < result.cap());
2641 assert_eq!(tester, expected_self);
2642 assert_eq!(result, expected_other);
2649 fn test_from_vec() {
2650 use super::super::vec::Vec;
2652 for len in 0..cap + 1 {
2653 let mut vec = Vec::with_capacity(cap);
2656 let vd = VecDeque::from(vec.clone());
2657 assert!(vd.cap().is_power_of_two());
2658 assert_eq!(vd.len(), vec.len());
2659 assert!(vd.into_iter().eq(vec));
2665 fn test_vec_from_vecdeque() {
2666 use super::super::vec::Vec;
2668 fn create_vec_and_test_convert(cap: usize, offset: usize, len: usize) {
2669 let mut vd = VecDeque::with_capacity(cap);
2670 for _ in 0..offset {
2676 let vec: Vec<_> = Vec::from(vd.clone());
2677 assert_eq!(vec.len(), vd.len());
2678 assert!(vec.into_iter().eq(vd));
2681 for cap_pwr in 0..7 {
2682 // Make capacity as a (2^x)-1, so that the ring size is 2^x
2683 let cap = (2i32.pow(cap_pwr) - 1) as usize;
2685 // In these cases there is enough free space to solve it with copies
2686 for len in 0..((cap + 1) / 2) {
2687 // Test contiguous cases
2688 for offset in 0..(cap - len) {
2689 create_vec_and_test_convert(cap, offset, len)
2692 // Test cases where block at end of buffer is bigger than block at start
2693 for offset in (cap - len)..(cap - (len / 2)) {
2694 create_vec_and_test_convert(cap, offset, len)
2697 // Test cases where block at start of buffer is bigger than block at end
2698 for offset in (cap - (len / 2))..cap {
2699 create_vec_and_test_convert(cap, offset, len)
2703 // Now there's not (necessarily) space to straighten the ring with simple copies,
2704 // the ring will use swapping when:
2705 // (cap + 1 - offset) > (cap + 1 - len) && (len - (cap + 1 - offset)) > (cap + 1 - len))
2706 // right block size > free space && left block size > free space
2707 for len in ((cap + 1) / 2)..cap {
2708 // Test contiguous cases
2709 for offset in 0..(cap - len) {
2710 create_vec_and_test_convert(cap, offset, len)
2713 // Test cases where block at end of buffer is bigger than block at start
2714 for offset in (cap - len)..(cap - (len / 2)) {
2715 create_vec_and_test_convert(cap, offset, len)
2718 // Test cases where block at start of buffer is bigger than block at end
2719 for offset in (cap - (len / 2))..cap {
2720 create_vec_and_test_convert(cap, offset, len)