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android / platform / prebuilts / rust / b13c2a93d1f3eb2e6bdcdce1ad4dd61c50bc36c6 / . / linux-musl-x86 / 1.63.0 / src / stdlibs / library / alloc / src / collections / vec_deque / mod.rs
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//! 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
}
}