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Diffstat (limited to 'library/alloc/src/collections/vec_deque/mod.rs')
| -rw-r--r-- | library/alloc/src/collections/vec_deque/mod.rs | 3137 |
1 files changed, 3137 insertions, 0 deletions
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs new file mode 100644 index 000000000..4d895d837 --- /dev/null +++ b/library/alloc/src/collections/vec_deque/mod.rs @@ -0,0 +1,3137 @@ +//! A double-ended queue (deque) implemented with a growable ring buffer. +//! +//! This queue has *O*(1) amortized inserts and removals from both ends of the +//! container. It also has *O*(1) indexing like a vector. The contained elements +//! are not required to be copyable, and the queue will be sendable if the +//! contained type is sendable. + +#![stable(feature = "rust1", since = "1.0.0")] + +use core::cmp::{self, Ordering}; +use core::fmt; +use core::hash::{Hash, Hasher}; +use core::iter::{repeat_with, FromIterator}; +use core::marker::PhantomData; +use core::mem::{self, ManuallyDrop, MaybeUninit}; +use core::ops::{Index, IndexMut, Range, RangeBounds}; +use core::ptr::{self, NonNull}; +use core::slice; + +use crate::alloc::{Allocator, Global}; +use crate::collections::TryReserveError; +use crate::collections::TryReserveErrorKind; +use crate::raw_vec::RawVec; +use crate::vec::Vec; + +#[macro_use] +mod macros; + +#[stable(feature = "drain", since = "1.6.0")] +pub use self::drain::Drain; + +mod drain; + +#[stable(feature = "rust1", since = "1.0.0")] +pub use self::iter_mut::IterMut; + +mod iter_mut; + +#[stable(feature = "rust1", since = "1.0.0")] +pub use self::into_iter::IntoIter; + +mod into_iter; + +#[stable(feature = "rust1", since = "1.0.0")] +pub use self::iter::Iter; + +mod iter; + +use self::pair_slices::PairSlices; + +mod pair_slices; + +use self::ring_slices::RingSlices; + +mod ring_slices; + +use self::spec_extend::SpecExtend; + +mod spec_extend; + +#[cfg(test)] +mod tests; + +const INITIAL_CAPACITY: usize = 7; // 2^3 - 1 +const MINIMUM_CAPACITY: usize = 1; // 2 - 1 + +const MAXIMUM_ZST_CAPACITY: usize = 1 << (usize::BITS - 1); // Largest possible power of two + +/// A double-ended queue implemented with a growable ring buffer. +/// +/// The "default" usage of this type as a queue is to use [`push_back`] to add to +/// the queue, and [`pop_front`] to remove from the queue. [`extend`] and [`append`] +/// push onto the back in this manner, and iterating over `VecDeque` goes front +/// to back. +/// +/// A `VecDeque` with a known list of items can be initialized from an array: +/// +/// ``` +/// use std::collections::VecDeque; +/// +/// let deq = VecDeque::from([-1, 0, 1]); +/// ``` +/// +/// Since `VecDeque` is a ring buffer, its elements are not necessarily contiguous +/// in memory. If you want to access the elements as a single slice, such as for +/// efficient sorting, you can use [`make_contiguous`]. It rotates the `VecDeque` +/// so that its elements do not wrap, and returns a mutable slice to the +/// now-contiguous element sequence. +/// +/// [`push_back`]: VecDeque::push_back +/// [`pop_front`]: VecDeque::pop_front +/// [`extend`]: VecDeque::extend +/// [`append`]: VecDeque::append +/// [`make_contiguous`]: VecDeque::make_contiguous +#[cfg_attr(not(test), rustc_diagnostic_item = "VecDeque")] +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_insignificant_dtor] +pub struct VecDeque< + T, + #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global, +> { + // tail and head are pointers into the buffer. Tail always points + // to the first element that could be read, Head always points + // to where data should be written. + // If tail == head the buffer is empty. The length of the ringbuffer + // is defined as the distance between the two. + tail: usize, + head: usize, + buf: RawVec<T, A>, +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Clone, A: Allocator + Clone> Clone for VecDeque<T, A> { + fn clone(&self) -> Self { + let mut deq = Self::with_capacity_in(self.len(), self.allocator().clone()); + deq.extend(self.iter().cloned()); + deq + } + + fn clone_from(&mut self, other: &Self) { + self.truncate(other.len()); + + let mut iter = PairSlices::from(self, other); + while let Some((dst, src)) = iter.next() { + dst.clone_from_slice(&src); + } + + if iter.has_remainder() { + for remainder in iter.remainder() { + self.extend(remainder.iter().cloned()); + } + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<#[may_dangle] T, A: Allocator> Drop for VecDeque<T, A> { + fn drop(&mut self) { + /// Runs the destructor for all items in the slice when it gets dropped (normally or + /// during unwinding). + struct Dropper<'a, T>(&'a mut [T]); + + impl<'a, T> Drop for Dropper<'a, T> { + fn drop(&mut self) { + unsafe { + ptr::drop_in_place(self.0); + } + } + } + + let (front, back) = self.as_mut_slices(); + unsafe { + let _back_dropper = Dropper(back); + // use drop for [T] + ptr::drop_in_place(front); + } + // RawVec handles deallocation + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Default for VecDeque<T> { + /// Creates an empty deque. + #[inline] + fn default() -> VecDeque<T> { + VecDeque::new() + } +} + +impl<T, A: Allocator> VecDeque<T, A> { + /// Marginally more convenient + #[inline] + fn ptr(&self) -> *mut T { + self.buf.ptr() + } + + /// Marginally more convenient + #[inline] + fn cap(&self) -> usize { + if mem::size_of::<T>() == 0 { + // For zero sized types, we are always at maximum capacity + MAXIMUM_ZST_CAPACITY + } else { + self.buf.capacity() + } + } + + /// Turn ptr into a slice, since the elements of the backing buffer may be uninitialized, + /// we will return a slice of [`MaybeUninit<T>`]. + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and + /// incorrect usage of this method. + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[inline] + unsafe fn buffer_as_slice(&self) -> &[MaybeUninit<T>] { + unsafe { slice::from_raw_parts(self.ptr() as *mut MaybeUninit<T>, self.cap()) } + } + + /// Turn ptr into a mut slice, since the elements of the backing buffer may be uninitialized, + /// we will return a slice of [`MaybeUninit<T>`]. + /// + /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and + /// incorrect usage of this method. + /// + /// [zeroed]: mem::MaybeUninit::zeroed + #[inline] + unsafe fn buffer_as_mut_slice(&mut self) -> &mut [MaybeUninit<T>] { + unsafe { slice::from_raw_parts_mut(self.ptr() as *mut MaybeUninit<T>, self.cap()) } + } + + /// Moves an element out of the buffer + #[inline] + unsafe fn buffer_read(&mut self, off: usize) -> T { + unsafe { ptr::read(self.ptr().add(off)) } + } + + /// Writes an element into the buffer, moving it. + #[inline] + unsafe fn buffer_write(&mut self, off: usize, value: T) { + unsafe { + ptr::write(self.ptr().add(off), value); + } + } + + /// Returns `true` if the buffer is at full capacity. + #[inline] + fn is_full(&self) -> bool { + self.cap() - self.len() == 1 + } + + /// Returns the index in the underlying buffer for a given logical element + /// index. + #[inline] + fn wrap_index(&self, idx: usize) -> usize { + wrap_index(idx, self.cap()) + } + + /// Returns the index in the underlying buffer for a given logical element + /// index + addend. + #[inline] + fn wrap_add(&self, idx: usize, addend: usize) -> usize { + wrap_index(idx.wrapping_add(addend), self.cap()) + } + + /// Returns the index in the underlying buffer for a given logical element + /// index - subtrahend. + #[inline] + fn wrap_sub(&self, idx: usize, subtrahend: usize) -> usize { + wrap_index(idx.wrapping_sub(subtrahend), self.cap()) + } + + /// Copies a contiguous block of memory len long from src to dst + #[inline] + unsafe fn copy(&self, dst: usize, src: usize, len: usize) { + debug_assert!( + dst + len <= self.cap(), + "cpy dst={} src={} len={} cap={}", + dst, + src, + len, + self.cap() + ); + debug_assert!( + src + len <= self.cap(), + "cpy dst={} src={} len={} cap={}", + dst, + src, + len, + self.cap() + ); + unsafe { + ptr::copy(self.ptr().add(src), self.ptr().add(dst), len); + } + } + + /// Copies a contiguous block of memory len long from src to dst + #[inline] + unsafe fn copy_nonoverlapping(&self, dst: usize, src: usize, len: usize) { + debug_assert!( + dst + len <= self.cap(), + "cno dst={} src={} len={} cap={}", + dst, + src, + len, + self.cap() + ); + debug_assert!( + src + len <= self.cap(), + "cno dst={} src={} len={} cap={}", + dst, + src, + len, + self.cap() + ); + unsafe { + ptr::copy_nonoverlapping(self.ptr().add(src), self.ptr().add(dst), len); + } + } + + /// Copies a potentially wrapping block of memory len long from src to dest. + /// (abs(dst - src) + len) must be no larger than cap() (There must be at + /// most one continuous overlapping region between src and dest). + unsafe fn wrap_copy(&self, dst: usize, src: usize, len: usize) { + #[allow(dead_code)] + fn diff(a: usize, b: usize) -> usize { + if a <= b { b - a } else { a - b } + } + debug_assert!( + cmp::min(diff(dst, src), self.cap() - diff(dst, src)) + len <= self.cap(), + "wrc dst={} src={} len={} cap={}", + dst, + src, + len, + self.cap() + ); + + if src == dst || len == 0 { + return; + } + + let dst_after_src = self.wrap_sub(dst, src) < len; + + let src_pre_wrap_len = self.cap() - src; + let dst_pre_wrap_len = self.cap() - dst; + let src_wraps = src_pre_wrap_len < len; + let dst_wraps = dst_pre_wrap_len < len; + + match (dst_after_src, src_wraps, dst_wraps) { + (_, false, false) => { + // src doesn't wrap, dst doesn't wrap + // + // S . . . + // 1 [_ _ A A B B C C _] + // 2 [_ _ A A A A B B _] + // D . . . + // + unsafe { + self.copy(dst, src, len); + } + } + (false, false, true) => { + // dst before src, src doesn't wrap, dst wraps + // + // S . . . + // 1 [A A B B _ _ _ C C] + // 2 [A A B B _ _ _ A A] + // 3 [B B B B _ _ _ A A] + // . . D . + // + unsafe { + self.copy(dst, src, dst_pre_wrap_len); + self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len); + } + } + (true, false, true) => { + // src before dst, src doesn't wrap, dst wraps + // + // S . . . + // 1 [C C _ _ _ A A B B] + // 2 [B B _ _ _ A A B B] + // 3 [B B _ _ _ A A A A] + // . . D . + // + unsafe { + self.copy(0, src + dst_pre_wrap_len, len - dst_pre_wrap_len); + self.copy(dst, src, dst_pre_wrap_len); + } + } + (false, true, false) => { + // dst before src, src wraps, dst doesn't wrap + // + // . . S . + // 1 [C C _ _ _ A A B B] + // 2 [C C _ _ _ B B B B] + // 3 [C C _ _ _ B B C C] + // D . . . + // + unsafe { + self.copy(dst, src, src_pre_wrap_len); + self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len); + } + } + (true, true, false) => { + // src before dst, src wraps, dst doesn't wrap + // + // . . S . + // 1 [A A B B _ _ _ C C] + // 2 [A A A A _ _ _ C C] + // 3 [C C A A _ _ _ C C] + // D . . . + // + unsafe { + self.copy(dst + src_pre_wrap_len, 0, len - src_pre_wrap_len); + self.copy(dst, src, src_pre_wrap_len); + } + } + (false, true, true) => { + // dst before src, src wraps, dst wraps + // + // . . . S . + // 1 [A B C D _ E F G H] + // 2 [A B C D _ E G H H] + // 3 [A B C D _ E G H A] + // 4 [B C C D _ E G H A] + // . . D . . + // + debug_assert!(dst_pre_wrap_len > src_pre_wrap_len); + let delta = dst_pre_wrap_len - src_pre_wrap_len; + unsafe { + self.copy(dst, src, src_pre_wrap_len); + self.copy(dst + src_pre_wrap_len, 0, delta); + self.copy(0, delta, len - dst_pre_wrap_len); + } + } + (true, true, true) => { + // src before dst, src wraps, dst wraps + // + // . . S . . + // 1 [A B C D _ E F G H] + // 2 [A A B D _ E F G H] + // 3 [H A B D _ E F G H] + // 4 [H A B D _ E F F G] + // . . . D . + // + debug_assert!(src_pre_wrap_len > dst_pre_wrap_len); + let delta = src_pre_wrap_len - dst_pre_wrap_len; + unsafe { + self.copy(delta, 0, len - src_pre_wrap_len); + self.copy(0, self.cap() - delta, delta); + self.copy(dst, src, dst_pre_wrap_len); + } + } + } + } + + /// Copies all values from `src` to `dst`, wrapping around if needed. + /// Assumes capacity is sufficient. + #[inline] + unsafe fn copy_slice(&mut self, dst: usize, src: &[T]) { + debug_assert!(src.len() <= self.cap()); + let head_room = self.cap() - dst; + if src.len() <= head_room { + unsafe { + ptr::copy_nonoverlapping(src.as_ptr(), self.ptr().add(dst), src.len()); + } + } else { + let (left, right) = src.split_at(head_room); + unsafe { + ptr::copy_nonoverlapping(left.as_ptr(), self.ptr().add(dst), left.len()); + ptr::copy_nonoverlapping(right.as_ptr(), self.ptr(), right.len()); + } + } + } + + /// Writes all values from `iter` to `dst`. + /// + /// # Safety + /// + /// Assumes no wrapping around happens. + /// Assumes capacity is sufficient. + #[inline] + unsafe fn write_iter( + &mut self, + dst: usize, + iter: impl Iterator<Item = T>, + written: &mut usize, + ) { + iter.enumerate().for_each(|(i, element)| unsafe { + self.buffer_write(dst + i, element); + *written += 1; + }); + } + + /// Frobs the head and tail sections around to handle the fact that we + /// just reallocated. Unsafe because it trusts old_capacity. + #[inline] + unsafe fn handle_capacity_increase(&mut self, old_capacity: usize) { + let new_capacity = self.cap(); + + // Move the shortest contiguous section of the ring buffer + // T H + // [o o o o o o o . ] + // T H + // A [o o o o o o o . . . . . . . . . ] + // H T + // [o o . o o o o o ] + // T H + // B [. . . o o o o o o o . . . . . . ] + // H T + // [o o o o o . o o ] + // H T + // C [o o o o o . . . . . . . . . o o ] + + if self.tail <= self.head { + // A + // Nop + } else if self.head < old_capacity - self.tail { + // B + unsafe { + self.copy_nonoverlapping(old_capacity, 0, self.head); + } + self.head += old_capacity; + debug_assert!(self.head > self.tail); + } else { + // C + let new_tail = new_capacity - (old_capacity - self.tail); + unsafe { + self.copy_nonoverlapping(new_tail, self.tail, old_capacity - self.tail); + } + self.tail = new_tail; + debug_assert!(self.head < self.tail); + } + debug_assert!(self.head < self.cap()); + debug_assert!(self.tail < self.cap()); + debug_assert!(self.cap().count_ones() == 1); + } +} + +impl<T> VecDeque<T> { + /// Creates an empty deque. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<u32> = VecDeque::new(); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + #[must_use] + pub fn new() -> VecDeque<T> { + VecDeque::new_in(Global) + } + + /// Creates an empty deque with space for at least `capacity` elements. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<u32> = VecDeque::with_capacity(10); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + #[must_use] + pub fn with_capacity(capacity: usize) -> VecDeque<T> { + Self::with_capacity_in(capacity, Global) + } +} + +impl<T, A: Allocator> VecDeque<T, A> { + /// Creates an empty deque. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<u32> = VecDeque::new(); + /// ``` + #[inline] + #[unstable(feature = "allocator_api", issue = "32838")] + pub fn new_in(alloc: A) -> VecDeque<T, A> { + VecDeque::with_capacity_in(INITIAL_CAPACITY, alloc) + } + + /// Creates an empty deque with space for at least `capacity` elements. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<u32> = VecDeque::with_capacity(10); + /// ``` + #[unstable(feature = "allocator_api", issue = "32838")] + pub fn with_capacity_in(capacity: usize, alloc: A) -> VecDeque<T, A> { + assert!(capacity < 1_usize << usize::BITS - 1, "capacity overflow"); + // +1 since the ringbuffer always leaves one space empty + let cap = cmp::max(capacity + 1, MINIMUM_CAPACITY + 1).next_power_of_two(); + + VecDeque { tail: 0, head: 0, buf: RawVec::with_capacity_in(cap, alloc) } + } + + /// Provides a reference to the element at the given index. + /// + /// Element at index 0 is the front of the queue. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(3); + /// buf.push_back(4); + /// buf.push_back(5); + /// assert_eq!(buf.get(1), Some(&4)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn get(&self, index: usize) -> Option<&T> { + if index < self.len() { + let idx = self.wrap_add(self.tail, index); + unsafe { Some(&*self.ptr().add(idx)) } + } else { + None + } + } + + /// Provides a mutable reference to the element at the given index. + /// + /// Element at index 0 is the front of the queue. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(3); + /// buf.push_back(4); + /// buf.push_back(5); + /// if let Some(elem) = buf.get_mut(1) { + /// *elem = 7; + /// } + /// + /// assert_eq!(buf[1], 7); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn get_mut(&mut self, index: usize) -> Option<&mut T> { + if index < self.len() { + let idx = self.wrap_add(self.tail, index); + unsafe { Some(&mut *self.ptr().add(idx)) } + } else { + None + } + } + + /// Swaps elements at indices `i` and `j`. + /// + /// `i` and `j` may be equal. + /// + /// Element at index 0 is the front of the queue. + /// + /// # Panics + /// + /// Panics if either index is out of bounds. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(3); + /// buf.push_back(4); + /// buf.push_back(5); + /// assert_eq!(buf, [3, 4, 5]); + /// buf.swap(0, 2); + /// assert_eq!(buf, [5, 4, 3]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn swap(&mut self, i: usize, j: usize) { + assert!(i < self.len()); + assert!(j < self.len()); + let ri = self.wrap_add(self.tail, i); + let rj = self.wrap_add(self.tail, j); + unsafe { ptr::swap(self.ptr().add(ri), self.ptr().add(rj)) } + } + + /// Returns the number of elements the deque can hold without + /// reallocating. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let buf: VecDeque<i32> = VecDeque::with_capacity(10); + /// assert!(buf.capacity() >= 10); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn capacity(&self) -> usize { + self.cap() - 1 + } + + /// Reserves the minimum capacity for at least `additional` more elements to be inserted in the + /// given deque. Does nothing if the capacity is already sufficient. + /// + /// Note that the allocator may give the collection more space than it requests. Therefore + /// capacity can not be relied upon to be precisely minimal. Prefer [`reserve`] if future + /// insertions are expected. + /// + /// # Panics + /// + /// Panics if the new capacity overflows `usize`. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf: VecDeque<i32> = [1].into(); + /// buf.reserve_exact(10); + /// assert!(buf.capacity() >= 11); + /// ``` + /// + /// [`reserve`]: VecDeque::reserve + #[stable(feature = "rust1", since = "1.0.0")] + pub fn reserve_exact(&mut self, additional: usize) { + self.reserve(additional); + } + + /// Reserves capacity for at least `additional` more elements to be inserted in the given + /// deque. The collection may reserve more space to speculatively avoid frequent reallocations. + /// + /// # Panics + /// + /// Panics if the new capacity overflows `usize`. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf: VecDeque<i32> = [1].into(); + /// buf.reserve(10); + /// assert!(buf.capacity() >= 11); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn reserve(&mut self, additional: usize) { + let old_cap = self.cap(); + let used_cap = self.len() + 1; + let new_cap = used_cap + .checked_add(additional) + .and_then(|needed_cap| needed_cap.checked_next_power_of_two()) + .expect("capacity overflow"); + + if new_cap > old_cap { + self.buf.reserve_exact(used_cap, new_cap - used_cap); + unsafe { + self.handle_capacity_increase(old_cap); + } + } + } + + /// Tries to reserve the minimum capacity for at least `additional` more elements to + /// be inserted in the given deque. After calling `try_reserve_exact`, + /// capacity will be greater than or equal to `self.len() + additional` if + /// it returns `Ok(())`. Does nothing if the capacity is already sufficient. + /// + /// Note that the allocator may give the collection more space than it + /// requests. Therefore, capacity can not be relied upon to be precisely + /// minimal. Prefer [`try_reserve`] if future insertions are expected. + /// + /// [`try_reserve`]: VecDeque::try_reserve + /// + /// # Errors + /// + /// If the capacity overflows `usize`, or the allocator reports a failure, then an error + /// is returned. + /// + /// # Examples + /// + /// ``` + /// use std::collections::TryReserveError; + /// use std::collections::VecDeque; + /// + /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> { + /// let mut output = VecDeque::new(); + /// + /// // Pre-reserve the memory, exiting if we can't + /// output.try_reserve_exact(data.len())?; + /// + /// // Now we know this can't OOM(Out-Of-Memory) in the middle of our complex work + /// output.extend(data.iter().map(|&val| { + /// val * 2 + 5 // very complicated + /// })); + /// + /// Ok(output) + /// } + /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?"); + /// ``` + #[stable(feature = "try_reserve", since = "1.57.0")] + pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> { + self.try_reserve(additional) + } + + /// Tries to reserve capacity for at least `additional` more elements to be inserted + /// in the given deque. The collection may reserve more space to speculatively avoid + /// frequent reallocations. After calling `try_reserve`, capacity will be + /// greater than or equal to `self.len() + additional` if it returns + /// `Ok(())`. Does nothing if capacity is already sufficient. + /// + /// # Errors + /// + /// If the capacity overflows `usize`, or the allocator reports a failure, then an error + /// is returned. + /// + /// # Examples + /// + /// ``` + /// use std::collections::TryReserveError; + /// use std::collections::VecDeque; + /// + /// fn process_data(data: &[u32]) -> Result<VecDeque<u32>, TryReserveError> { + /// let mut output = VecDeque::new(); + /// + /// // Pre-reserve the memory, exiting if we can't + /// output.try_reserve(data.len())?; + /// + /// // Now we know this can't OOM in the middle of our complex work + /// output.extend(data.iter().map(|&val| { + /// val * 2 + 5 // very complicated + /// })); + /// + /// Ok(output) + /// } + /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?"); + /// ``` + #[stable(feature = "try_reserve", since = "1.57.0")] + pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> { + let old_cap = self.cap(); + let used_cap = self.len() + 1; + let new_cap = used_cap + .checked_add(additional) + .and_then(|needed_cap| needed_cap.checked_next_power_of_two()) + .ok_or(TryReserveErrorKind::CapacityOverflow)?; + + if new_cap > old_cap { + self.buf.try_reserve_exact(used_cap, new_cap - used_cap)?; + unsafe { + self.handle_capacity_increase(old_cap); + } + } + Ok(()) + } + + /// Shrinks the capacity of the deque as much as possible. + /// + /// It will drop down as close as possible to the length but the allocator may still inform the + /// deque that there is space for a few more elements. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::with_capacity(15); + /// buf.extend(0..4); + /// assert_eq!(buf.capacity(), 15); + /// buf.shrink_to_fit(); + /// assert!(buf.capacity() >= 4); + /// ``` + #[stable(feature = "deque_extras_15", since = "1.5.0")] + pub fn shrink_to_fit(&mut self) { + self.shrink_to(0); + } + + /// Shrinks the capacity of the deque with a lower bound. + /// + /// The capacity will remain at least as large as both the length + /// and the supplied value. + /// + /// If the current capacity is less than the lower limit, this is a no-op. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::with_capacity(15); + /// buf.extend(0..4); + /// assert_eq!(buf.capacity(), 15); + /// buf.shrink_to(6); + /// assert!(buf.capacity() >= 6); + /// buf.shrink_to(0); + /// assert!(buf.capacity() >= 4); + /// ``` + #[stable(feature = "shrink_to", since = "1.56.0")] + pub fn shrink_to(&mut self, min_capacity: usize) { + let min_capacity = cmp::min(min_capacity, self.capacity()); + // We don't have to worry about an overflow as neither `self.len()` nor `self.capacity()` + // can ever be `usize::MAX`. +1 as the ringbuffer always leaves one space empty. + let target_cap = cmp::max(cmp::max(min_capacity, self.len()) + 1, MINIMUM_CAPACITY + 1) + .next_power_of_two(); + + if target_cap < self.cap() { + // There are three cases of interest: + // All elements are out of desired bounds + // Elements are contiguous, and head is out of desired bounds + // Elements are discontiguous, and tail is out of desired bounds + // + // At all other times, element positions are unaffected. + // + // Indicates that elements at the head should be moved. + let head_outside = self.head == 0 || self.head >= target_cap; + // Move elements from out of desired bounds (positions after target_cap) + if self.tail >= target_cap && head_outside { + // T H + // [. . . . . . . . o o o o o o o . ] + // T H + // [o o o o o o o . ] + unsafe { + self.copy_nonoverlapping(0, self.tail, self.len()); + } + self.head = self.len(); + self.tail = 0; + } else if self.tail != 0 && self.tail < target_cap && head_outside { + // T H + // [. . . o o o o o o o . . . . . . ] + // H T + // [o o . o o o o o ] + let len = self.wrap_sub(self.head, target_cap); + unsafe { + self.copy_nonoverlapping(0, target_cap, len); + } + self.head = len; + debug_assert!(self.head < self.tail); + } else if self.tail >= target_cap { + // H T + // [o o o o o . . . . . . . . . o o ] + // H T + // [o o o o o . o o ] + debug_assert!(self.wrap_sub(self.head, 1) < target_cap); + let len = self.cap() - self.tail; + let new_tail = target_cap - len; + unsafe { + self.copy_nonoverlapping(new_tail, self.tail, len); + } + self.tail = new_tail; + debug_assert!(self.head < self.tail); + } + + self.buf.shrink_to_fit(target_cap); + + debug_assert!(self.head < self.cap()); + debug_assert!(self.tail < self.cap()); + debug_assert!(self.cap().count_ones() == 1); + } + } + + /// Shortens the deque, keeping the first `len` elements and dropping + /// the rest. + /// + /// If `len` is greater than the deque's current length, this has no + /// effect. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(5); + /// buf.push_back(10); + /// buf.push_back(15); + /// assert_eq!(buf, [5, 10, 15]); + /// buf.truncate(1); + /// assert_eq!(buf, [5]); + /// ``` + #[stable(feature = "deque_extras", since = "1.16.0")] + pub fn truncate(&mut self, len: usize) { + /// Runs the destructor for all items in the slice when it gets dropped (normally or + /// during unwinding). + struct Dropper<'a, T>(&'a mut [T]); + + impl<'a, T> Drop for Dropper<'a, T> { + fn drop(&mut self) { + unsafe { + ptr::drop_in_place(self.0); + } + } + } + + // Safe because: + // + // * Any slice passed to `drop_in_place` is valid; the second case has + // `len <= front.len()` and returning on `len > self.len()` ensures + // `begin <= back.len()` in the first case + // * The head of the VecDeque is moved before calling `drop_in_place`, + // so no value is dropped twice if `drop_in_place` panics + unsafe { + if len > self.len() { + return; + } + let num_dropped = self.len() - len; + let (front, back) = self.as_mut_slices(); + if len > front.len() { + let begin = len - front.len(); + let drop_back = back.get_unchecked_mut(begin..) as *mut _; + self.head = self.wrap_sub(self.head, num_dropped); + ptr::drop_in_place(drop_back); + } else { + let drop_back = back as *mut _; + let drop_front = front.get_unchecked_mut(len..) as *mut _; + self.head = self.wrap_sub(self.head, num_dropped); + + // Make sure the second half is dropped even when a destructor + // in the first one panics. + let _back_dropper = Dropper(&mut *drop_back); + ptr::drop_in_place(drop_front); + } + } + } + + /// Returns a reference to the underlying allocator. + #[unstable(feature = "allocator_api", issue = "32838")] + #[inline] + pub fn allocator(&self) -> &A { + self.buf.allocator() + } + + /// Returns a front-to-back iterator. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(5); + /// buf.push_back(3); + /// buf.push_back(4); + /// let b: &[_] = &[&5, &3, &4]; + /// let c: Vec<&i32> = buf.iter().collect(); + /// assert_eq!(&c[..], b); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn iter(&self) -> Iter<'_, T> { + Iter::new(unsafe { self.buffer_as_slice() }, self.tail, self.head) + } + + /// Returns a front-to-back iterator that returns mutable references. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(5); + /// buf.push_back(3); + /// buf.push_back(4); + /// for num in buf.iter_mut() { + /// *num = *num - 2; + /// } + /// let b: &[_] = &[&mut 3, &mut 1, &mut 2]; + /// assert_eq!(&buf.iter_mut().collect::<Vec<&mut i32>>()[..], b); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn iter_mut(&mut self) -> IterMut<'_, T> { + // SAFETY: The internal `IterMut` safety invariant is established because the + // `ring` we create is a dereferenceable slice for lifetime '_. + let ring = ptr::slice_from_raw_parts_mut(self.ptr(), self.cap()); + + unsafe { IterMut::new(ring, self.tail, self.head, PhantomData) } + } + + /// Returns a pair of slices which contain, in order, the contents of the + /// deque. + /// + /// If [`make_contiguous`] was previously called, all elements of the + /// deque will be in the first slice and the second slice will be empty. + /// + /// [`make_contiguous`]: VecDeque::make_contiguous + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque = VecDeque::new(); + /// + /// deque.push_back(0); + /// deque.push_back(1); + /// deque.push_back(2); + /// + /// assert_eq!(deque.as_slices(), (&[0, 1, 2][..], &[][..])); + /// + /// deque.push_front(10); + /// deque.push_front(9); + /// + /// assert_eq!(deque.as_slices(), (&[9, 10][..], &[0, 1, 2][..])); + /// ``` + #[inline] + #[stable(feature = "deque_extras_15", since = "1.5.0")] + pub fn as_slices(&self) -> (&[T], &[T]) { + // Safety: + // - `self.head` and `self.tail` in a ring buffer are always valid indices. + // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized. + unsafe { + let buf = self.buffer_as_slice(); + let (front, back) = RingSlices::ring_slices(buf, self.head, self.tail); + (MaybeUninit::slice_assume_init_ref(front), MaybeUninit::slice_assume_init_ref(back)) + } + } + + /// Returns a pair of slices which contain, in order, the contents of the + /// deque. + /// + /// If [`make_contiguous`] was previously called, all elements of the + /// deque will be in the first slice and the second slice will be empty. + /// + /// [`make_contiguous`]: VecDeque::make_contiguous + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque = VecDeque::new(); + /// + /// deque.push_back(0); + /// deque.push_back(1); + /// + /// deque.push_front(10); + /// deque.push_front(9); + /// + /// deque.as_mut_slices().0[0] = 42; + /// deque.as_mut_slices().1[0] = 24; + /// assert_eq!(deque.as_slices(), (&[42, 10][..], &[24, 1][..])); + /// ``` + #[inline] + #[stable(feature = "deque_extras_15", since = "1.5.0")] + pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) { + // Safety: + // - `self.head` and `self.tail` in a ring buffer are always valid indices. + // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized. + unsafe { + let head = self.head; + let tail = self.tail; + let buf = self.buffer_as_mut_slice(); + let (front, back) = RingSlices::ring_slices(buf, head, tail); + (MaybeUninit::slice_assume_init_mut(front), MaybeUninit::slice_assume_init_mut(back)) + } + } + + /// Returns the number of elements in the deque. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque = VecDeque::new(); + /// assert_eq!(deque.len(), 0); + /// deque.push_back(1); + /// assert_eq!(deque.len(), 1); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn len(&self) -> usize { + count(self.tail, self.head, self.cap()) + } + + /// Returns `true` if the deque is empty. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque = VecDeque::new(); + /// assert!(deque.is_empty()); + /// deque.push_front(1); + /// assert!(!deque.is_empty()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn is_empty(&self) -> bool { + self.tail == self.head + } + + fn range_tail_head<R>(&self, range: R) -> (usize, usize) + where + R: RangeBounds<usize>, + { + let Range { start, end } = slice::range(range, ..self.len()); + let tail = self.wrap_add(self.tail, start); + let head = self.wrap_add(self.tail, end); + (tail, head) + } + + /// Creates an iterator that covers the specified range in the deque. + /// + /// # Panics + /// + /// Panics if the starting point is greater than the end point or if + /// the end point is greater than the length of the deque. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<_> = [1, 2, 3].into(); + /// let range = deque.range(2..).copied().collect::<VecDeque<_>>(); + /// assert_eq!(range, [3]); + /// + /// // A full range covers all contents + /// let all = deque.range(..); + /// assert_eq!(all.len(), 3); + /// ``` + #[inline] + #[stable(feature = "deque_range", since = "1.51.0")] + pub fn range<R>(&self, range: R) -> Iter<'_, T> + where + R: RangeBounds<usize>, + { + let (tail, head) = self.range_tail_head(range); + // The shared reference we have in &self is maintained in the '_ of Iter. + Iter::new(unsafe { self.buffer_as_slice() }, tail, head) + } + + /// Creates an iterator that covers the specified mutable range in the deque. + /// + /// # Panics + /// + /// Panics if the starting point is greater than the end point or if + /// the end point is greater than the length of the deque. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque: VecDeque<_> = [1, 2, 3].into(); + /// for v in deque.range_mut(2..) { + /// *v *= 2; + /// } + /// assert_eq!(deque, [1, 2, 6]); + /// + /// // A full range covers all contents + /// for v in deque.range_mut(..) { + /// *v *= 2; + /// } + /// assert_eq!(deque, [2, 4, 12]); + /// ``` + #[inline] + #[stable(feature = "deque_range", since = "1.51.0")] + pub fn range_mut<R>(&mut self, range: R) -> IterMut<'_, T> + where + R: RangeBounds<usize>, + { + let (tail, head) = self.range_tail_head(range); + + // SAFETY: The internal `IterMut` safety invariant is established because the + // `ring` we create is a dereferenceable slice for lifetime '_. + let ring = ptr::slice_from_raw_parts_mut(self.ptr(), self.cap()); + + unsafe { IterMut::new(ring, tail, head, PhantomData) } + } + + /// Removes the specified range from the deque in bulk, returning all + /// removed elements as an iterator. If the iterator is dropped before + /// being fully consumed, it drops the remaining removed elements. + /// + /// The returned iterator keeps a mutable borrow on the queue to optimize + /// its implementation. + /// + /// + /// # Panics + /// + /// Panics if the starting point is greater than the end point or if + /// the end point is greater than the length of the deque. + /// + /// # Leaking + /// + /// If the returned iterator goes out of scope without being dropped (due to + /// [`mem::forget`], for example), the deque may have lost and leaked + /// elements arbitrarily, including elements outside the range. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque: VecDeque<_> = [1, 2, 3].into(); + /// let drained = deque.drain(2..).collect::<VecDeque<_>>(); + /// assert_eq!(drained, [3]); + /// assert_eq!(deque, [1, 2]); + /// + /// // A full range clears all contents, like `clear()` does + /// deque.drain(..); + /// assert!(deque.is_empty()); + /// ``` + #[inline] + #[stable(feature = "drain", since = "1.6.0")] + pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A> + where + R: RangeBounds<usize>, + { + // Memory safety + // + // When the Drain is first created, the source deque is shortened to + // make sure no uninitialized or moved-from elements are accessible at + // all if the Drain's destructor never gets to run. + // + // Drain will ptr::read out the values to remove. + // When finished, the remaining data will be copied back to cover the hole, + // and the head/tail values will be restored correctly. + // + let (drain_tail, drain_head) = self.range_tail_head(range); + + // The deque's elements are parted into three segments: + // * self.tail -> drain_tail + // * drain_tail -> drain_head + // * drain_head -> self.head + // + // T = self.tail; H = self.head; t = drain_tail; h = drain_head + // + // We store drain_tail as self.head, and drain_head and self.head as + // after_tail and after_head respectively on the Drain. This also + // truncates the effective array such that if the Drain is leaked, we + // have forgotten about the potentially moved values after the start of + // the drain. + // + // T t h H + // [. . . o o x x o o . . .] + // + let head = self.head; + + // "forget" about the values after the start of the drain until after + // the drain is complete and the Drain destructor is run. + self.head = drain_tail; + + let deque = NonNull::from(&mut *self); + unsafe { + // Crucially, we only create shared references from `self` here and read from + // it. We do not write to `self` nor reborrow to a mutable reference. + // Hence the raw pointer we created above, for `deque`, remains valid. + let ring = self.buffer_as_slice(); + let iter = Iter::new(ring, drain_tail, drain_head); + + Drain::new(drain_head, head, iter, deque) + } + } + + /// Clears the deque, removing all values. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque = VecDeque::new(); + /// deque.push_back(1); + /// deque.clear(); + /// assert!(deque.is_empty()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn clear(&mut self) { + self.truncate(0); + } + + /// Returns `true` if the deque contains an element equal to the + /// given value. + /// + /// This operation is *O*(*n*). + /// + /// Note that if you have a sorted `VecDeque`, [`binary_search`] may be faster. + /// + /// [`binary_search`]: VecDeque::binary_search + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque: VecDeque<u32> = VecDeque::new(); + /// + /// deque.push_back(0); + /// deque.push_back(1); + /// + /// assert_eq!(deque.contains(&1), true); + /// assert_eq!(deque.contains(&10), false); + /// ``` + #[stable(feature = "vec_deque_contains", since = "1.12.0")] + pub fn contains(&self, x: &T) -> bool + where + T: PartialEq<T>, + { + let (a, b) = self.as_slices(); + a.contains(x) || b.contains(x) + } + + /// Provides a reference to the front element, or `None` if the deque is + /// empty. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut d = VecDeque::new(); + /// assert_eq!(d.front(), None); + /// + /// d.push_back(1); + /// d.push_back(2); + /// assert_eq!(d.front(), Some(&1)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn front(&self) -> Option<&T> { + self.get(0) + } + + /// Provides a mutable reference to the front element, or `None` if the + /// deque is empty. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut d = VecDeque::new(); + /// assert_eq!(d.front_mut(), None); + /// + /// d.push_back(1); + /// d.push_back(2); + /// match d.front_mut() { + /// Some(x) => *x = 9, + /// None => (), + /// } + /// assert_eq!(d.front(), Some(&9)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn front_mut(&mut self) -> Option<&mut T> { + self.get_mut(0) + } + + /// Provides a reference to the back element, or `None` if the deque is + /// empty. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut d = VecDeque::new(); + /// assert_eq!(d.back(), None); + /// + /// d.push_back(1); + /// d.push_back(2); + /// assert_eq!(d.back(), Some(&2)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn back(&self) -> Option<&T> { + self.get(self.len().wrapping_sub(1)) + } + + /// Provides a mutable reference to the back element, or `None` if the + /// deque is empty. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut d = VecDeque::new(); + /// assert_eq!(d.back(), None); + /// + /// d.push_back(1); + /// d.push_back(2); + /// match d.back_mut() { + /// Some(x) => *x = 9, + /// None => (), + /// } + /// assert_eq!(d.back(), Some(&9)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn back_mut(&mut self) -> Option<&mut T> { + self.get_mut(self.len().wrapping_sub(1)) + } + + /// Removes the first element and returns it, or `None` if the deque is + /// empty. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut d = VecDeque::new(); + /// d.push_back(1); + /// d.push_back(2); + /// + /// assert_eq!(d.pop_front(), Some(1)); + /// assert_eq!(d.pop_front(), Some(2)); + /// assert_eq!(d.pop_front(), None); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn pop_front(&mut self) -> Option<T> { + if self.is_empty() { + None + } else { + let tail = self.tail; + self.tail = self.wrap_add(self.tail, 1); + unsafe { Some(self.buffer_read(tail)) } + } + } + + /// Removes the last element from the deque and returns it, or `None` if + /// it is empty. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// assert_eq!(buf.pop_back(), None); + /// buf.push_back(1); + /// buf.push_back(3); + /// assert_eq!(buf.pop_back(), Some(3)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn pop_back(&mut self) -> Option<T> { + if self.is_empty() { + None + } else { + self.head = self.wrap_sub(self.head, 1); + let head = self.head; + unsafe { Some(self.buffer_read(head)) } + } + } + + /// Prepends an element to the deque. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut d = VecDeque::new(); + /// d.push_front(1); + /// d.push_front(2); + /// assert_eq!(d.front(), Some(&2)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn push_front(&mut self, value: T) { + if self.is_full() { + self.grow(); + } + + self.tail = self.wrap_sub(self.tail, 1); + let tail = self.tail; + unsafe { + self.buffer_write(tail, value); + } + } + + /// Appends an element to the back of the deque. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(1); + /// buf.push_back(3); + /// assert_eq!(3, *buf.back().unwrap()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn push_back(&mut self, value: T) { + if self.is_full() { + self.grow(); + } + + let head = self.head; + self.head = self.wrap_add(self.head, 1); + unsafe { self.buffer_write(head, value) } + } + + #[inline] + fn is_contiguous(&self) -> bool { + // FIXME: Should we consider `head == 0` to mean + // that `self` is contiguous? + self.tail <= self.head + } + + /// Removes an element from anywhere in the deque and returns it, + /// replacing it with the first element. + /// + /// This does not preserve ordering, but is *O*(1). + /// + /// Returns `None` if `index` is out of bounds. + /// + /// Element at index 0 is the front of the queue. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// assert_eq!(buf.swap_remove_front(0), None); + /// buf.push_back(1); + /// buf.push_back(2); + /// buf.push_back(3); + /// assert_eq!(buf, [1, 2, 3]); + /// + /// assert_eq!(buf.swap_remove_front(2), Some(3)); + /// assert_eq!(buf, [2, 1]); + /// ``` + #[stable(feature = "deque_extras_15", since = "1.5.0")] + pub fn swap_remove_front(&mut self, index: usize) -> Option<T> { + let length = self.len(); + if length > 0 && index < length && index != 0 { + self.swap(index, 0); + } else if index >= length { + return None; + } + self.pop_front() + } + + /// Removes an element from anywhere in the deque and returns it, + /// replacing it with the last element. + /// + /// This does not preserve ordering, but is *O*(1). + /// + /// Returns `None` if `index` is out of bounds. + /// + /// Element at index 0 is the front of the queue. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// assert_eq!(buf.swap_remove_back(0), None); + /// buf.push_back(1); + /// buf.push_back(2); + /// buf.push_back(3); + /// assert_eq!(buf, [1, 2, 3]); + /// + /// assert_eq!(buf.swap_remove_back(0), Some(1)); + /// assert_eq!(buf, [3, 2]); + /// ``` + #[stable(feature = "deque_extras_15", since = "1.5.0")] + pub fn swap_remove_back(&mut self, index: usize) -> Option<T> { + let length = self.len(); + if length > 0 && index < length - 1 { + self.swap(index, length - 1); + } else if index >= length { + return None; + } + self.pop_back() + } + + /// Inserts an element at `index` within the deque, shifting all elements + /// with indices greater than or equal to `index` towards the back. + /// + /// Element at index 0 is the front of the queue. + /// + /// # Panics + /// + /// Panics if `index` is greater than deque's length + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut vec_deque = VecDeque::new(); + /// vec_deque.push_back('a'); + /// vec_deque.push_back('b'); + /// vec_deque.push_back('c'); + /// assert_eq!(vec_deque, &['a', 'b', 'c']); + /// + /// vec_deque.insert(1, 'd'); + /// assert_eq!(vec_deque, &['a', 'd', 'b', 'c']); + /// ``` + #[stable(feature = "deque_extras_15", since = "1.5.0")] + pub fn insert(&mut self, index: usize, value: T) { + assert!(index <= self.len(), "index out of bounds"); + if self.is_full() { + self.grow(); + } + + // Move the least number of elements in the ring buffer and insert + // the given object + // + // At most len/2 - 1 elements will be moved. O(min(n, n-i)) + // + // There are three main cases: + // Elements are contiguous + // - special case when tail is 0 + // Elements are discontiguous and the insert is in the tail section + // Elements are discontiguous and the insert is in the head section + // + // For each of those there are two more cases: + // Insert is closer to tail + // Insert is closer to head + // + // Key: H - self.head + // T - self.tail + // o - Valid element + // I - Insertion element + // A - The element that should be after the insertion point + // M - Indicates element was moved + + let idx = self.wrap_add(self.tail, index); + + let distance_to_tail = index; + let distance_to_head = self.len() - index; + + let contiguous = self.is_contiguous(); + + match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) { + (true, true, _) if index == 0 => { + // push_front + // + // T + // I H + // [A o o o o o o . . . . . . . . .] + // + // H T + // [A o o o o o o o . . . . . I] + // + + self.tail = self.wrap_sub(self.tail, 1); + } + (true, true, _) => { + unsafe { + // contiguous, insert closer to tail: + // + // T I H + // [. . . o o A o o o o . . . . . .] + // + // T H + // [. . o o I A o o o o . . . . . .] + // M M + // + // contiguous, insert closer to tail and tail is 0: + // + // + // T I H + // [o o A o o o o . . . . . . . . .] + // + // H T + // [o I A o o o o o . . . . . . . o] + // M M + + let new_tail = self.wrap_sub(self.tail, 1); + + self.copy(new_tail, self.tail, 1); + // Already moved the tail, so we only copy `index - 1` elements. + self.copy(self.tail, self.tail + 1, index - 1); + + self.tail = new_tail; + } + } + (true, false, _) => { + unsafe { + // contiguous, insert closer to head: + // + // T I H + // [. . . o o o o A o o . . . . . .] + // + // T H + // [. . . o o o o I A o o . . . . .] + // M M M + + self.copy(idx + 1, idx, self.head - idx); + self.head = self.wrap_add(self.head, 1); + } + } + (false, true, true) => { + unsafe { + // discontiguous, insert closer to tail, tail section: + // + // H T I + // [o o o o o o . . . . . o o A o o] + // + // H T + // [o o o o o o . . . . o o I A o o] + // M M + + self.copy(self.tail - 1, self.tail, index); + self.tail -= 1; + } + } + (false, false, true) => { + unsafe { + // discontiguous, insert closer to head, tail section: + // + // H T I + // [o o . . . . . . . o o o o o A o] + // + // H T + // [o o o . . . . . . o o o o o I A] + // M M M M + + // copy elements up to new head + self.copy(1, 0, self.head); + + // copy last element into empty spot at bottom of buffer + self.copy(0, self.cap() - 1, 1); + + // move elements from idx to end forward not including ^ element + self.copy(idx + 1, idx, self.cap() - 1 - idx); + + self.head += 1; + } + } + (false, true, false) if idx == 0 => { + unsafe { + // discontiguous, insert is closer to tail, head section, + // and is at index zero in the internal buffer: + // + // I H T + // [A o o o o o o o o o . . . o o o] + // + // H T + // [A o o o o o o o o o . . o o o I] + // M M M + + // copy elements up to new tail + self.copy(self.tail - 1, self.tail, self.cap() - self.tail); + + // copy last element into empty spot at bottom of buffer + self.copy(self.cap() - 1, 0, 1); + + self.tail -= 1; + } + } + (false, true, false) => { + unsafe { + // discontiguous, insert closer to tail, head section: + // + // I H T + // [o o o A o o o o o o . . . o o o] + // + // H T + // [o o I A o o o o o o . . o o o o] + // M M M M M M + + // copy elements up to new tail + self.copy(self.tail - 1, self.tail, self.cap() - self.tail); + + // copy last element into empty spot at bottom of buffer + self.copy(self.cap() - 1, 0, 1); + + // move elements from idx-1 to end forward not including ^ element + self.copy(0, 1, idx - 1); + + self.tail -= 1; + } + } + (false, false, false) => { + unsafe { + // discontiguous, insert closer to head, head section: + // + // I H T + // [o o o o A o o . . . . . . o o o] + // + // H T + // [o o o o I A o o . . . . . o o o] + // M M M + + self.copy(idx + 1, idx, self.head - idx); + self.head += 1; + } + } + } + + // tail might've been changed so we need to recalculate + let new_idx = self.wrap_add(self.tail, index); + unsafe { + self.buffer_write(new_idx, value); + } + } + + /// Removes and returns the element at `index` from the deque. + /// Whichever end is closer to the removal point will be moved to make + /// room, and all the affected elements will be moved to new positions. + /// Returns `None` if `index` is out of bounds. + /// + /// Element at index 0 is the front of the queue. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(1); + /// buf.push_back(2); + /// buf.push_back(3); + /// assert_eq!(buf, [1, 2, 3]); + /// + /// assert_eq!(buf.remove(1), Some(2)); + /// assert_eq!(buf, [1, 3]); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn remove(&mut self, index: usize) -> Option<T> { + if self.is_empty() || self.len() <= index { + return None; + } + + // There are three main cases: + // Elements are contiguous + // Elements are discontiguous and the removal is in the tail section + // Elements are discontiguous and the removal is in the head section + // - special case when elements are technically contiguous, + // but self.head = 0 + // + // For each of those there are two more cases: + // Insert is closer to tail + // Insert is closer to head + // + // Key: H - self.head + // T - self.tail + // o - Valid element + // x - Element marked for removal + // R - Indicates element that is being removed + // M - Indicates element was moved + + let idx = self.wrap_add(self.tail, index); + + let elem = unsafe { Some(self.buffer_read(idx)) }; + + let distance_to_tail = index; + let distance_to_head = self.len() - index; + + let contiguous = self.is_contiguous(); + + match (contiguous, distance_to_tail <= distance_to_head, idx >= self.tail) { + (true, true, _) => { + unsafe { + // contiguous, remove closer to tail: + // + // T R H + // [. . . o o x o o o o . . . . . .] + // + // T H + // [. . . . o o o o o o . . . . . .] + // M M + + self.copy(self.tail + 1, self.tail, index); + self.tail += 1; + } + } + (true, false, _) => { + unsafe { + // contiguous, remove closer to head: + // + // T R H + // [. . . o o o o x o o . . . . . .] + // + // T H + // [. . . o o o o o o . . . . . . .] + // M M + + self.copy(idx, idx + 1, self.head - idx - 1); + self.head -= 1; + } + } + (false, true, true) => { + unsafe { + // discontiguous, remove closer to tail, tail section: + // + // H T R + // [o o o o o o . . . . . o o x o o] + // + // H T + // [o o o o o o . . . . . . o o o o] + // M M + + self.copy(self.tail + 1, self.tail, index); + self.tail = self.wrap_add(self.tail, 1); + } + } + (false, false, false) => { + unsafe { + // discontiguous, remove closer to head, head section: + // + // R H T + // [o o o o x o o . . . . . . o o o] + // + // H T + // [o o o o o o . . . . . . . o o o] + // M M + + self.copy(idx, idx + 1, self.head - idx - 1); + self.head -= 1; + } + } + (false, false, true) => { + unsafe { + // discontiguous, remove closer to head, tail section: + // + // H T R + // [o o o . . . . . . o o o o o x o] + // + // H T + // [o o . . . . . . . o o o o o o o] + // M M M M + // + // or quasi-discontiguous, remove next to head, tail section: + // + // H T R + // [. . . . . . . . . o o o o o x o] + // + // T H + // [. . . . . . . . . o o o o o o .] + // M + + // draw in elements in the tail section + self.copy(idx, idx + 1, self.cap() - idx - 1); + + // Prevents underflow. + if self.head != 0 { + // copy first element into empty spot + self.copy(self.cap() - 1, 0, 1); + + // move elements in the head section backwards + self.copy(0, 1, self.head - 1); + } + + self.head = self.wrap_sub(self.head, 1); + } + } + (false, true, false) => { + unsafe { + // discontiguous, remove closer to tail, head section: + // + // R H T + // [o o x o o o o o o o . . . o o o] + // + // H T + // [o o o o o o o o o o . . . . o o] + // M M M M M + + // draw in elements up to idx + self.copy(1, 0, idx); + + // copy last element into empty spot + self.copy(0, self.cap() - 1, 1); + + // move elements from tail to end forward, excluding the last one + self.copy(self.tail + 1, self.tail, self.cap() - self.tail - 1); + + self.tail = self.wrap_add(self.tail, 1); + } + } + } + + elem + } + + /// Splits the deque into two at the given index. + /// + /// Returns a newly allocated `VecDeque`. `self` contains elements `[0, at)`, + /// and the returned deque contains elements `[at, len)`. + /// + /// Note that the capacity of `self` does not change. + /// + /// Element at index 0 is the front of the queue. + /// + /// # Panics + /// + /// Panics if `at > len`. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf: VecDeque<_> = [1, 2, 3].into(); + /// let buf2 = buf.split_off(1); + /// assert_eq!(buf, [1]); + /// assert_eq!(buf2, [2, 3]); + /// ``` + #[inline] + #[must_use = "use `.truncate()` if you don't need the other half"] + #[stable(feature = "split_off", since = "1.4.0")] + pub fn split_off(&mut self, at: usize) -> Self + where + A: Clone, + { + let len = self.len(); + assert!(at <= len, "`at` out of bounds"); + + let other_len = len - at; + let mut other = VecDeque::with_capacity_in(other_len, self.allocator().clone()); + + unsafe { + let (first_half, second_half) = self.as_slices(); + + let first_len = first_half.len(); + let second_len = second_half.len(); + if at < first_len { + // `at` lies in the first half. + let amount_in_first = first_len - at; + + ptr::copy_nonoverlapping(first_half.as_ptr().add(at), other.ptr(), amount_in_first); + + // just take all of the second half. + ptr::copy_nonoverlapping( + second_half.as_ptr(), + other.ptr().add(amount_in_first), + second_len, + ); + } else { + // `at` lies in the second half, need to factor in the elements we skipped + // in the first half. + let offset = at - first_len; + let amount_in_second = second_len - offset; + ptr::copy_nonoverlapping( + second_half.as_ptr().add(offset), + other.ptr(), + amount_in_second, + ); + } + } + + // Cleanup where the ends of the buffers are + self.head = self.wrap_sub(self.head, other_len); + other.head = other.wrap_index(other_len); + + other + } + + /// Moves all the elements of `other` into `self`, leaving `other` empty. + /// + /// # Panics + /// + /// Panics if the new number of elements in self overflows a `usize`. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf: VecDeque<_> = [1, 2].into(); + /// let mut buf2: VecDeque<_> = [3, 4].into(); + /// buf.append(&mut buf2); + /// assert_eq!(buf, [1, 2, 3, 4]); + /// assert_eq!(buf2, []); + /// ``` + #[inline] + #[stable(feature = "append", since = "1.4.0")] + pub fn append(&mut self, other: &mut Self) { + self.reserve(other.len()); + unsafe { + let (left, right) = other.as_slices(); + self.copy_slice(self.head, left); + self.copy_slice(self.wrap_add(self.head, left.len()), right); + } + // SAFETY: Update pointers after copying to avoid leaving doppelganger + // in case of panics. + self.head = self.wrap_add(self.head, other.len()); + // Silently drop values in `other`. + other.tail = other.head; + } + + /// Retains only the elements specified by the predicate. + /// + /// In other words, remove all elements `e` for which `f(&e)` returns false. + /// This method operates in place, visiting each element exactly once in the + /// original order, and preserves the order of the retained elements. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.extend(1..5); + /// buf.retain(|&x| x % 2 == 0); + /// assert_eq!(buf, [2, 4]); + /// ``` + /// + /// Because the elements are visited exactly once in the original order, + /// external state may be used to decide which elements to keep. + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.extend(1..6); + /// + /// let keep = [false, true, true, false, true]; + /// let mut iter = keep.iter(); + /// buf.retain(|_| *iter.next().unwrap()); + /// assert_eq!(buf, [2, 3, 5]); + /// ``` + #[stable(feature = "vec_deque_retain", since = "1.4.0")] + pub fn retain<F>(&mut self, mut f: F) + where + F: FnMut(&T) -> bool, + { + self.retain_mut(|elem| f(elem)); + } + + /// Retains only the elements specified by the predicate. + /// + /// In other words, remove all elements `e` for which `f(&e)` returns false. + /// This method operates in place, visiting each element exactly once in the + /// original order, and preserves the order of the retained elements. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.extend(1..5); + /// buf.retain_mut(|x| if *x % 2 == 0 { + /// *x += 1; + /// true + /// } else { + /// false + /// }); + /// assert_eq!(buf, [3, 5]); + /// ``` + #[stable(feature = "vec_retain_mut", since = "1.61.0")] + pub fn retain_mut<F>(&mut self, mut f: F) + where + F: FnMut(&mut T) -> bool, + { + let len = self.len(); + let mut idx = 0; + let mut cur = 0; + + // Stage 1: All values are retained. + while cur < len { + if !f(&mut self[cur]) { + cur += 1; + break; + } + cur += 1; + idx += 1; + } + // Stage 2: Swap retained value into current idx. + while cur < len { + if !f(&mut self[cur]) { + cur += 1; + continue; + } + + self.swap(idx, cur); + cur += 1; + idx += 1; + } + // Stage 3: Truncate all values after idx. + if cur != idx { + self.truncate(idx); + } + } + + // Double the buffer size. This method is inline(never), so we expect it to only + // be called in cold paths. + // This may panic or abort + #[inline(never)] + fn grow(&mut self) { + // Extend or possibly remove this assertion when valid use-cases for growing the + // buffer without it being full emerge + debug_assert!(self.is_full()); + let old_cap = self.cap(); + self.buf.reserve_exact(old_cap, old_cap); + assert!(self.cap() == old_cap * 2); + unsafe { + self.handle_capacity_increase(old_cap); + } + debug_assert!(!self.is_full()); + } + + /// Modifies the deque in-place so that `len()` is equal to `new_len`, + /// either by removing excess elements from the back or by appending + /// elements generated by calling `generator` to the back. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(5); + /// buf.push_back(10); + /// buf.push_back(15); + /// assert_eq!(buf, [5, 10, 15]); + /// + /// buf.resize_with(5, Default::default); + /// assert_eq!(buf, [5, 10, 15, 0, 0]); + /// + /// buf.resize_with(2, || unreachable!()); + /// assert_eq!(buf, [5, 10]); + /// + /// let mut state = 100; + /// buf.resize_with(5, || { state += 1; state }); + /// assert_eq!(buf, [5, 10, 101, 102, 103]); + /// ``` + #[stable(feature = "vec_resize_with", since = "1.33.0")] + pub fn resize_with(&mut self, new_len: usize, generator: impl FnMut() -> T) { + let len = self.len(); + + if new_len > len { + self.extend(repeat_with(generator).take(new_len - len)) + } else { + self.truncate(new_len); + } + } + + /// Rearranges the internal storage of this deque so it is one contiguous + /// slice, which is then returned. + /// + /// This method does not allocate and does not change the order of the + /// inserted elements. As it returns a mutable slice, this can be used to + /// sort a deque. + /// + /// Once the internal storage is contiguous, the [`as_slices`] and + /// [`as_mut_slices`] methods will return the entire contents of the + /// deque in a single slice. + /// + /// [`as_slices`]: VecDeque::as_slices + /// [`as_mut_slices`]: VecDeque::as_mut_slices + /// + /// # Examples + /// + /// Sorting the content of a deque. + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::with_capacity(15); + /// + /// buf.push_back(2); + /// buf.push_back(1); + /// buf.push_front(3); + /// + /// // sorting the deque + /// buf.make_contiguous().sort(); + /// assert_eq!(buf.as_slices(), (&[1, 2, 3] as &[_], &[] as &[_])); + /// + /// // sorting it in reverse order + /// buf.make_contiguous().sort_by(|a, b| b.cmp(a)); + /// assert_eq!(buf.as_slices(), (&[3, 2, 1] as &[_], &[] as &[_])); + /// ``` + /// + /// Getting immutable access to the contiguous slice. + /// + /// ```rust + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// + /// buf.push_back(2); + /// buf.push_back(1); + /// buf.push_front(3); + /// + /// buf.make_contiguous(); + /// if let (slice, &[]) = buf.as_slices() { + /// // we can now be sure that `slice` contains all elements of the deque, + /// // while still having immutable access to `buf`. + /// assert_eq!(buf.len(), slice.len()); + /// assert_eq!(slice, &[3, 2, 1] as &[_]); + /// } + /// ``` + #[stable(feature = "deque_make_contiguous", since = "1.48.0")] + pub fn make_contiguous(&mut self) -> &mut [T] { + if self.is_contiguous() { + let tail = self.tail; + let head = self.head; + // Safety: + // - `self.head` and `self.tail` in a ring buffer are always valid indices. + // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized. + return unsafe { + MaybeUninit::slice_assume_init_mut( + RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0, + ) + }; + } + + let buf = self.buf.ptr(); + let cap = self.cap(); + let len = self.len(); + + let free = self.tail - self.head; + let tail_len = cap - self.tail; + + if free >= tail_len { + // there is enough free space to copy the tail in one go, + // this means that we first shift the head backwards, and then + // copy the tail to the correct position. + // + // from: DEFGH....ABC + // to: ABCDEFGH.... + unsafe { + ptr::copy(buf, buf.add(tail_len), self.head); + // ...DEFGH.ABC + ptr::copy_nonoverlapping(buf.add(self.tail), buf, tail_len); + // ABCDEFGH.... + + self.tail = 0; + self.head = len; + } + } else if free > self.head { + // FIXME: We currently do not consider ....ABCDEFGH + // to be contiguous because `head` would be `0` in this + // case. While we probably want to change this it + // isn't trivial as a few places expect `is_contiguous` + // to mean that we can just slice using `buf[tail..head]`. + + // there is enough free space to copy the head in one go, + // this means that we first shift the tail forwards, and then + // copy the head to the correct position. + // + // from: FGH....ABCDE + // to: ...ABCDEFGH. + unsafe { + ptr::copy(buf.add(self.tail), buf.add(self.head), tail_len); + // FGHABCDE.... + ptr::copy_nonoverlapping(buf, buf.add(self.head + tail_len), self.head); + // ...ABCDEFGH. + + self.tail = self.head; + self.head = self.wrap_add(self.tail, len); + } + } else { + // free is smaller than both head and tail, + // this means we have to slowly "swap" the tail and the head. + // + // from: EFGHI...ABCD or HIJK.ABCDEFG + // to: ABCDEFGHI... or ABCDEFGHIJK. + let mut left_edge: usize = 0; + let mut right_edge: usize = self.tail; + unsafe { + // The general problem looks like this + // GHIJKLM...ABCDEF - before any swaps + // ABCDEFM...GHIJKL - after 1 pass of swaps + // ABCDEFGHIJM...KL - swap until the left edge reaches the temp store + // - then restart the algorithm with a new (smaller) store + // Sometimes the temp store is reached when the right edge is at the end + // of the buffer - this means we've hit the right order with fewer swaps! + // E.g + // EF..ABCD + // ABCDEF.. - after four only swaps we've finished + while left_edge < len && right_edge != cap { + let mut right_offset = 0; + for i in left_edge..right_edge { + right_offset = (i - left_edge) % (cap - right_edge); + let src: isize = (right_edge + right_offset) as isize; + ptr::swap(buf.add(i), buf.offset(src)); + } + let n_ops = right_edge - left_edge; + left_edge += n_ops; + right_edge += right_offset + 1; + } + + self.tail = 0; + self.head = len; + } + } + + let tail = self.tail; + let head = self.head; + // Safety: + // - `self.head` and `self.tail` in a ring buffer are always valid indices. + // - `RingSlices::ring_slices` guarantees that the slices split according to `self.head` and `self.tail` are initialized. + unsafe { + MaybeUninit::slice_assume_init_mut( + RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0, + ) + } + } + + /// Rotates the double-ended queue `mid` places to the left. + /// + /// Equivalently, + /// - Rotates item `mid` into the first position. + /// - Pops the first `mid` items and pushes them to the end. + /// - Rotates `len() - mid` places to the right. + /// + /// # Panics + /// + /// If `mid` is greater than `len()`. Note that `mid == len()` + /// does _not_ panic and is a no-op rotation. + /// + /// # Complexity + /// + /// Takes `*O*(min(mid, len() - mid))` time and no extra space. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf: VecDeque<_> = (0..10).collect(); + /// + /// buf.rotate_left(3); + /// assert_eq!(buf, [3, 4, 5, 6, 7, 8, 9, 0, 1, 2]); + /// + /// for i in 1..10 { + /// assert_eq!(i * 3 % 10, buf[0]); + /// buf.rotate_left(3); + /// } + /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]); + /// ``` + #[stable(feature = "vecdeque_rotate", since = "1.36.0")] + pub fn rotate_left(&mut self, mid: usize) { + assert!(mid <= self.len()); + let k = self.len() - mid; + if mid <= k { + unsafe { self.rotate_left_inner(mid) } + } else { + unsafe { self.rotate_right_inner(k) } + } + } + + /// Rotates the double-ended queue `k` places to the right. + /// + /// Equivalently, + /// - Rotates the first item into position `k`. + /// - Pops the last `k` items and pushes them to the front. + /// - Rotates `len() - k` places to the left. + /// + /// # Panics + /// + /// If `k` is greater than `len()`. Note that `k == len()` + /// does _not_ panic and is a no-op rotation. + /// + /// # Complexity + /// + /// Takes `*O*(min(k, len() - k))` time and no extra space. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf: VecDeque<_> = (0..10).collect(); + /// + /// buf.rotate_right(3); + /// assert_eq!(buf, [7, 8, 9, 0, 1, 2, 3, 4, 5, 6]); + /// + /// for i in 1..10 { + /// assert_eq!(0, buf[i * 3 % 10]); + /// buf.rotate_right(3); + /// } + /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]); + /// ``` + #[stable(feature = "vecdeque_rotate", since = "1.36.0")] + pub fn rotate_right(&mut self, k: usize) { + assert!(k <= self.len()); + let mid = self.len() - k; + if k <= mid { + unsafe { self.rotate_right_inner(k) } + } else { + unsafe { self.rotate_left_inner(mid) } + } + } + + // SAFETY: the following two methods require that the rotation amount + // be less than half the length of the deque. + // + // `wrap_copy` requires that `min(x, cap() - x) + copy_len <= cap()`, + // but than `min` is never more than half the capacity, regardless of x, + // so it's sound to call here because we're calling with something + // less than half the length, which is never above half the capacity. + + unsafe fn rotate_left_inner(&mut self, mid: usize) { + debug_assert!(mid * 2 <= self.len()); + unsafe { + self.wrap_copy(self.head, self.tail, mid); + } + self.head = self.wrap_add(self.head, mid); + self.tail = self.wrap_add(self.tail, mid); + } + + unsafe fn rotate_right_inner(&mut self, k: usize) { + debug_assert!(k * 2 <= self.len()); + self.head = self.wrap_sub(self.head, k); + self.tail = self.wrap_sub(self.tail, k); + unsafe { + self.wrap_copy(self.tail, self.head, k); + } + } + + /// Binary searches this `VecDeque` for a given element. + /// This behaves similarly to [`contains`] if this `VecDeque` is sorted. + /// + /// If the value is found then [`Result::Ok`] is returned, containing the + /// index of the matching element. If there are multiple matches, then any + /// one of the matches could be returned. If the value is not found then + /// [`Result::Err`] is returned, containing the index where a matching + /// element could be inserted while maintaining sorted order. + /// + /// See also [`binary_search_by`], [`binary_search_by_key`], and [`partition_point`]. + /// + /// [`contains`]: VecDeque::contains + /// [`binary_search_by`]: VecDeque::binary_search_by + /// [`binary_search_by_key`]: VecDeque::binary_search_by_key + /// [`partition_point`]: VecDeque::partition_point + /// + /// # Examples + /// + /// Looks up a series of four elements. The first is found, with a + /// uniquely determined position; the second and third are not + /// found; the fourth could match any position in `[1, 4]`. + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<_> = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into(); + /// + /// assert_eq!(deque.binary_search(&13), Ok(9)); + /// assert_eq!(deque.binary_search(&4), Err(7)); + /// assert_eq!(deque.binary_search(&100), Err(13)); + /// let r = deque.binary_search(&1); + /// assert!(matches!(r, Ok(1..=4))); + /// ``` + /// + /// If you want to insert an item to a sorted deque, while maintaining + /// sort order, consider using [`partition_point`]: + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque: VecDeque<_> = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into(); + /// let num = 42; + /// let idx = deque.partition_point(|&x| x < num); + /// // The above is equivalent to `let idx = deque.binary_search(&num).unwrap_or_else(|x| x);` + /// deque.insert(idx, num); + /// assert_eq!(deque, &[0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]); + /// ``` + #[stable(feature = "vecdeque_binary_search", since = "1.54.0")] + #[inline] + pub fn binary_search(&self, x: &T) -> Result<usize, usize> + where + T: Ord, + { + self.binary_search_by(|e| e.cmp(x)) + } + + /// Binary searches this `VecDeque` with a comparator function. + /// This behaves similarly to [`contains`] if this `VecDeque` is sorted. + /// + /// The comparator function should implement an order consistent + /// with the sort order of the deque, returning an order code that + /// indicates whether its argument is `Less`, `Equal` or `Greater` + /// than the desired target. + /// + /// If the value is found then [`Result::Ok`] is returned, containing the + /// index of the matching element. If there are multiple matches, then any + /// one of the matches could be returned. If the value is not found then + /// [`Result::Err`] is returned, containing the index where a matching + /// element could be inserted while maintaining sorted order. + /// + /// See also [`binary_search`], [`binary_search_by_key`], and [`partition_point`]. + /// + /// [`contains`]: VecDeque::contains + /// [`binary_search`]: VecDeque::binary_search + /// [`binary_search_by_key`]: VecDeque::binary_search_by_key + /// [`partition_point`]: VecDeque::partition_point + /// + /// # Examples + /// + /// Looks up a series of four elements. The first is found, with a + /// uniquely determined position; the second and third are not + /// found; the fourth could match any position in `[1, 4]`. + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<_> = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into(); + /// + /// assert_eq!(deque.binary_search_by(|x| x.cmp(&13)), Ok(9)); + /// assert_eq!(deque.binary_search_by(|x| x.cmp(&4)), Err(7)); + /// assert_eq!(deque.binary_search_by(|x| x.cmp(&100)), Err(13)); + /// let r = deque.binary_search_by(|x| x.cmp(&1)); + /// assert!(matches!(r, Ok(1..=4))); + /// ``` + #[stable(feature = "vecdeque_binary_search", since = "1.54.0")] + pub fn binary_search_by<'a, F>(&'a self, mut f: F) -> Result<usize, usize> + where + F: FnMut(&'a T) -> Ordering, + { + let (front, back) = self.as_slices(); + let cmp_back = back.first().map(|elem| f(elem)); + + if let Some(Ordering::Equal) = cmp_back { + Ok(front.len()) + } else if let Some(Ordering::Less) = cmp_back { + back.binary_search_by(f).map(|idx| idx + front.len()).map_err(|idx| idx + front.len()) + } else { + front.binary_search_by(f) + } + } + + /// Binary searches this `VecDeque` with a key extraction function. + /// This behaves similarly to [`contains`] if this `VecDeque` is sorted. + /// + /// Assumes that the deque is sorted by the key, for instance with + /// [`make_contiguous().sort_by_key()`] using the same key extraction function. + /// + /// If the value is found then [`Result::Ok`] is returned, containing the + /// index of the matching element. If there are multiple matches, then any + /// one of the matches could be returned. If the value is not found then + /// [`Result::Err`] is returned, containing the index where a matching + /// element could be inserted while maintaining sorted order. + /// + /// See also [`binary_search`], [`binary_search_by`], and [`partition_point`]. + /// + /// [`contains`]: VecDeque::contains + /// [`make_contiguous().sort_by_key()`]: VecDeque::make_contiguous + /// [`binary_search`]: VecDeque::binary_search + /// [`binary_search_by`]: VecDeque::binary_search_by + /// [`partition_point`]: VecDeque::partition_point + /// + /// # Examples + /// + /// Looks up a series of four elements in a slice of pairs sorted by + /// their second elements. The first is found, with a uniquely + /// determined position; the second and third are not found; the + /// fourth could match any position in `[1, 4]`. + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<_> = [(0, 0), (2, 1), (4, 1), (5, 1), + /// (3, 1), (1, 2), (2, 3), (4, 5), (5, 8), (3, 13), + /// (1, 21), (2, 34), (4, 55)].into(); + /// + /// assert_eq!(deque.binary_search_by_key(&13, |&(a, b)| b), Ok(9)); + /// assert_eq!(deque.binary_search_by_key(&4, |&(a, b)| b), Err(7)); + /// assert_eq!(deque.binary_search_by_key(&100, |&(a, b)| b), Err(13)); + /// let r = deque.binary_search_by_key(&1, |&(a, b)| b); + /// assert!(matches!(r, Ok(1..=4))); + /// ``` + #[stable(feature = "vecdeque_binary_search", since = "1.54.0")] + #[inline] + pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize> + where + F: FnMut(&'a T) -> B, + B: Ord, + { + self.binary_search_by(|k| f(k).cmp(b)) + } + + /// Returns the index of the partition point according to the given predicate + /// (the index of the first element of the second partition). + /// + /// The deque is assumed to be partitioned according to the given predicate. + /// This means that all elements for which the predicate returns true are at the start of the deque + /// and all elements for which the predicate returns false are at the end. + /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0 + /// (all odd numbers are at the start, all even at the end). + /// + /// If the deque is not partitioned, the returned result is unspecified and meaningless, + /// as this method performs a kind of binary search. + /// + /// See also [`binary_search`], [`binary_search_by`], and [`binary_search_by_key`]. + /// + /// [`binary_search`]: VecDeque::binary_search + /// [`binary_search_by`]: VecDeque::binary_search_by + /// [`binary_search_by_key`]: VecDeque::binary_search_by_key + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deque: VecDeque<_> = [1, 2, 3, 3, 5, 6, 7].into(); + /// let i = deque.partition_point(|&x| x < 5); + /// + /// assert_eq!(i, 4); + /// assert!(deque.iter().take(i).all(|&x| x < 5)); + /// assert!(deque.iter().skip(i).all(|&x| !(x < 5))); + /// ``` + /// + /// If you want to insert an item to a sorted deque, while maintaining + /// sort order: + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut deque: VecDeque<_> = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55].into(); + /// let num = 42; + /// let idx = deque.partition_point(|&x| x < num); + /// deque.insert(idx, num); + /// assert_eq!(deque, &[0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]); + /// ``` + #[stable(feature = "vecdeque_binary_search", since = "1.54.0")] + pub fn partition_point<P>(&self, mut pred: P) -> usize + where + P: FnMut(&T) -> bool, + { + let (front, back) = self.as_slices(); + + if let Some(true) = back.first().map(|v| pred(v)) { + back.partition_point(pred) + front.len() + } else { + front.partition_point(pred) + } + } +} + +impl<T: Clone, A: Allocator> VecDeque<T, A> { + /// Modifies the deque in-place so that `len()` is equal to new_len, + /// either by removing excess elements from the back or by appending clones of `value` + /// to the back. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(5); + /// buf.push_back(10); + /// buf.push_back(15); + /// assert_eq!(buf, [5, 10, 15]); + /// + /// buf.resize(2, 0); + /// assert_eq!(buf, [5, 10]); + /// + /// buf.resize(5, 20); + /// assert_eq!(buf, [5, 10, 20, 20, 20]); + /// ``` + #[stable(feature = "deque_extras", since = "1.16.0")] + pub fn resize(&mut self, new_len: usize, value: T) { + self.resize_with(new_len, || value.clone()); + } +} + +/// Returns the index in the underlying buffer for a given logical element index. +#[inline] +fn wrap_index(index: usize, size: usize) -> usize { + // size is always a power of 2 + debug_assert!(size.is_power_of_two()); + index & (size - 1) +} + +/// Calculate the number of elements left to be read in the buffer +#[inline] +fn count(tail: usize, head: usize, size: usize) -> usize { + // size is always a power of 2 + (head.wrapping_sub(tail)) & (size - 1) +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: PartialEq, A: Allocator> PartialEq for VecDeque<T, A> { + fn eq(&self, other: &Self) -> bool { + if self.len() != other.len() { + return false; + } + let (sa, sb) = self.as_slices(); + let (oa, ob) = other.as_slices(); + if sa.len() == oa.len() { + sa == oa && sb == ob + } else if sa.len() < oa.len() { + // Always divisible in three sections, for example: + // self: [a b c|d e f] + // other: [0 1 2 3|4 5] + // front = 3, mid = 1, + // [a b c] == [0 1 2] && [d] == [3] && [e f] == [4 5] + let front = sa.len(); + let mid = oa.len() - front; + + let (oa_front, oa_mid) = oa.split_at(front); + let (sb_mid, sb_back) = sb.split_at(mid); + debug_assert_eq!(sa.len(), oa_front.len()); + debug_assert_eq!(sb_mid.len(), oa_mid.len()); + debug_assert_eq!(sb_back.len(), ob.len()); + sa == oa_front && sb_mid == oa_mid && sb_back == ob + } else { + let front = oa.len(); + let mid = sa.len() - front; + + let (sa_front, sa_mid) = sa.split_at(front); + let (ob_mid, ob_back) = ob.split_at(mid); + debug_assert_eq!(sa_front.len(), oa.len()); + debug_assert_eq!(sa_mid.len(), ob_mid.len()); + debug_assert_eq!(sb.len(), ob_back.len()); + sa_front == oa && sa_mid == ob_mid && sb == ob_back + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Eq, A: Allocator> Eq for VecDeque<T, A> {} + +__impl_slice_eq1! { [] VecDeque<T, A>, Vec<U, A>, } +__impl_slice_eq1! { [] VecDeque<T, A>, &[U], } +__impl_slice_eq1! { [] VecDeque<T, A>, &mut [U], } +__impl_slice_eq1! { [const N: usize] VecDeque<T, A>, [U; N], } +__impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &[U; N], } +__impl_slice_eq1! { [const N: usize] VecDeque<T, A>, &mut [U; N], } + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: PartialOrd, A: Allocator> PartialOrd for VecDeque<T, A> { + fn partial_cmp(&self, other: &Self) -> Option<Ordering> { + self.iter().partial_cmp(other.iter()) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Ord, A: Allocator> Ord for VecDeque<T, A> { + #[inline] + fn cmp(&self, other: &Self) -> Ordering { + self.iter().cmp(other.iter()) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Hash, A: Allocator> Hash for VecDeque<T, A> { + fn hash<H: Hasher>(&self, state: &mut H) { + state.write_length_prefix(self.len()); + // It's not possible to use Hash::hash_slice on slices + // returned by as_slices method as their length can vary + // in otherwise identical deques. + // + // Hasher only guarantees equivalence for the exact same + // set of calls to its methods. + self.iter().for_each(|elem| elem.hash(state)); + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T, A: Allocator> Index<usize> for VecDeque<T, A> { + type Output = T; + + #[inline] + fn index(&self, index: usize) -> &T { + self.get(index).expect("Out of bounds access") + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T, A: Allocator> IndexMut<usize> for VecDeque<T, A> { + #[inline] + fn index_mut(&mut self, index: usize) -> &mut T { + self.get_mut(index).expect("Out of bounds access") + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> FromIterator<T> for VecDeque<T> { + fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> VecDeque<T> { + let iterator = iter.into_iter(); + let (lower, _) = iterator.size_hint(); + let mut deq = VecDeque::with_capacity(lower); + deq.extend(iterator); + deq + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T, A: Allocator> IntoIterator for VecDeque<T, A> { + type Item = T; + type IntoIter = IntoIter<T, A>; + + /// Consumes the deque into a front-to-back iterator yielding elements by + /// value. + fn into_iter(self) -> IntoIter<T, A> { + IntoIter::new(self) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T, A: Allocator> IntoIterator for &'a VecDeque<T, A> { + type Item = &'a T; + type IntoIter = Iter<'a, T>; + + fn into_iter(self) -> Iter<'a, T> { + self.iter() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T, A: Allocator> IntoIterator for &'a mut VecDeque<T, A> { + type Item = &'a mut T; + type IntoIter = IterMut<'a, T>; + + fn into_iter(self) -> IterMut<'a, T> { + self.iter_mut() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T, A: Allocator> Extend<T> for VecDeque<T, A> { + fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) { + <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter()); + } + + #[inline] + fn extend_one(&mut self, elem: T) { + self.push_back(elem); + } + + #[inline] + fn extend_reserve(&mut self, additional: usize) { + self.reserve(additional); + } +} + +#[stable(feature = "extend_ref", since = "1.2.0")] +impl<'a, T: 'a + Copy, A: Allocator> Extend<&'a T> for VecDeque<T, A> { + fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) { + self.spec_extend(iter.into_iter()); + } + + #[inline] + fn extend_one(&mut self, &elem: &T) { + self.push_back(elem); + } + + #[inline] + fn extend_reserve(&mut self, additional: usize) { + self.reserve(additional); + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: fmt::Debug, A: Allocator> fmt::Debug for VecDeque<T, A> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_list().entries(self).finish() + } +} + +#[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")] +impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A> { + /// Turn a [`Vec<T>`] into a [`VecDeque<T>`]. + /// + /// [`Vec<T>`]: crate::vec::Vec + /// [`VecDeque<T>`]: crate::collections::VecDeque + /// + /// This avoids reallocating where possible, but the conditions for that are + /// strict, and subject to change, and so shouldn't be relied upon unless the + /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated. + fn from(mut other: Vec<T, A>) -> Self { + let len = other.len(); + if mem::size_of::<T>() == 0 { + // There's no actual allocation for ZSTs to worry about capacity, + // but `VecDeque` can't handle as much length as `Vec`. + assert!(len < MAXIMUM_ZST_CAPACITY, "capacity overflow"); + } else { + // We need to resize if the capacity is not a power of two, too small or + // doesn't have at least one free space. We do this while it's still in + // the `Vec` so the items will drop on panic. + let min_cap = cmp::max(MINIMUM_CAPACITY, len) + 1; + let cap = cmp::max(min_cap, other.capacity()).next_power_of_two(); + if other.capacity() != cap { + other.reserve_exact(cap - len); + } + } + + unsafe { + let (other_buf, len, capacity, alloc) = other.into_raw_parts_with_alloc(); + let buf = RawVec::from_raw_parts_in(other_buf, capacity, alloc); + VecDeque { tail: 0, head: len, buf } + } + } +} + +#[stable(feature = "vecdeque_vec_conversions", since = "1.10.0")] +impl<T, A: Allocator> From<VecDeque<T, A>> for Vec<T, A> { + /// Turn a [`VecDeque<T>`] into a [`Vec<T>`]. + /// + /// [`Vec<T>`]: crate::vec::Vec + /// [`VecDeque<T>`]: crate::collections::VecDeque + /// + /// This never needs to re-allocate, but does need to do *O*(*n*) data movement if + /// the circular buffer doesn't happen to be at the beginning of the allocation. + /// + /// # Examples + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// // This one is *O*(1). + /// let deque: VecDeque<_> = (1..5).collect(); + /// let ptr = deque.as_slices().0.as_ptr(); + /// let vec = Vec::from(deque); + /// assert_eq!(vec, [1, 2, 3, 4]); + /// assert_eq!(vec.as_ptr(), ptr); + /// + /// // This one needs data rearranging. + /// let mut deque: VecDeque<_> = (1..5).collect(); + /// deque.push_front(9); + /// deque.push_front(8); + /// let ptr = deque.as_slices().1.as_ptr(); + /// let vec = Vec::from(deque); + /// assert_eq!(vec, [8, 9, 1, 2, 3, 4]); + /// assert_eq!(vec.as_ptr(), ptr); + /// ``` + fn from(mut other: VecDeque<T, A>) -> Self { + other.make_contiguous(); + + unsafe { + let other = ManuallyDrop::new(other); + let buf = other.buf.ptr(); + let len = other.len(); + let cap = other.cap(); + let alloc = ptr::read(other.allocator()); + + if other.tail != 0 { + ptr::copy(buf.add(other.tail), buf, len); + } + Vec::from_raw_parts_in(buf, len, cap, alloc) + } + } +} + +#[stable(feature = "std_collections_from_array", since = "1.56.0")] +impl<T, const N: usize> From<[T; N]> for VecDeque<T> { + /// Converts a `[T; N]` into a `VecDeque<T>`. + /// + /// ``` + /// use std::collections::VecDeque; + /// + /// let deq1 = VecDeque::from([1, 2, 3, 4]); + /// let deq2: VecDeque<_> = [1, 2, 3, 4].into(); + /// assert_eq!(deq1, deq2); + /// ``` + fn from(arr: [T; N]) -> Self { + let mut deq = VecDeque::with_capacity(N); + let arr = ManuallyDrop::new(arr); + if mem::size_of::<T>() != 0 { + // SAFETY: VecDeque::with_capacity ensures that there is enough capacity. + unsafe { + ptr::copy_nonoverlapping(arr.as_ptr(), deq.ptr(), N); + } + } + deq.tail = 0; + deq.head = N; + deq + } +} |