//! 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, } #[stable(feature = "rust1", since = "1.0.0")] impl Clone for VecDeque { 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 { 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 Default for VecDeque { /// Creates an empty deque. #[inline] fn default() -> VecDeque { VecDeque::new() } } impl VecDeque { /// Marginally more convenient #[inline] fn ptr(&self) -> *mut T { self.buf.ptr() } /// Marginally more convenient #[inline] fn cap(&self) -> usize { if mem::size_of::() == 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`]. /// /// 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] { unsafe { slice::from_raw_parts(self.ptr() as *mut MaybeUninit, 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`]. /// /// 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] { unsafe { slice::from_raw_parts_mut(self.ptr() as *mut MaybeUninit, 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, 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 VecDeque { /// Creates an empty deque. /// /// # Examples /// /// ``` /// use std::collections::VecDeque; /// /// let deque: VecDeque = VecDeque::new(); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] #[must_use] pub fn new() -> VecDeque { VecDeque::new_in(Global) } /// Creates an empty deque with space for at least `capacity` elements. /// /// # Examples /// /// ``` /// use std::collections::VecDeque; /// /// let deque: VecDeque = VecDeque::with_capacity(10); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] #[must_use] pub fn with_capacity(capacity: usize) -> VecDeque { Self::with_capacity_in(capacity, Global) } } impl VecDeque { /// Creates an empty deque. /// /// # Examples /// /// ``` /// use std::collections::VecDeque; /// /// let deque: VecDeque = VecDeque::new(); /// ``` #[inline] #[unstable(feature = "allocator_api", issue = "32838")] pub fn new_in(alloc: A) -> VecDeque { 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 = VecDeque::with_capacity(10); /// ``` #[unstable(feature = "allocator_api", issue = "32838")] pub fn with_capacity_in(capacity: usize, alloc: A) -> VecDeque { 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 = 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 = [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 = [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, 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. This method /// preserves the contents even if an error occurs. /// /// # 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, 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::>()[..], 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(&self, range: R) -> (usize, usize) where R: RangeBounds, { 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::>(); /// 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(&self, range: R) -> Iter<'_, T> where R: RangeBounds, { 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(&mut self, range: R) -> IterMut<'_, T> where R: RangeBounds, { 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::>(); /// 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(&mut self, range: R) -> Drain<'_, T, A> where R: RangeBounds, { // 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(); Drain::new(drain_head, head, ring, drain_tail, drain_head, 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 = 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, { 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 { 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 { 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 { 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 { 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 { 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(&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(&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 = right_edge + right_offset; ptr::swap(buf.add(i), buf.add(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 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 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 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

(&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 VecDeque { /// 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 PartialEq for VecDeque { 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 Eq for VecDeque {} __impl_slice_eq1! { [] VecDeque, Vec, } __impl_slice_eq1! { [] VecDeque, &[U], } __impl_slice_eq1! { [] VecDeque, &mut [U], } __impl_slice_eq1! { [const N: usize] VecDeque, [U; N], } __impl_slice_eq1! { [const N: usize] VecDeque, &[U; N], } __impl_slice_eq1! { [const N: usize] VecDeque, &mut [U; N], } #[stable(feature = "rust1", since = "1.0.0")] impl PartialOrd for VecDeque { fn partial_cmp(&self, other: &Self) -> Option { self.iter().partial_cmp(other.iter()) } } #[stable(feature = "rust1", since = "1.0.0")] impl Ord for VecDeque { #[inline] fn cmp(&self, other: &Self) -> Ordering { self.iter().cmp(other.iter()) } } #[stable(feature = "rust1", since = "1.0.0")] impl Hash for VecDeque { fn hash(&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 Index for VecDeque { 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 IndexMut for VecDeque { #[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 FromIterator for VecDeque { fn from_iter>(iter: I) -> VecDeque { 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 IntoIterator for VecDeque { type Item = T; type IntoIter = IntoIter; /// Consumes the deque into a front-to-back iterator yielding elements by /// value. fn into_iter(self) -> IntoIter { IntoIter::new(self) } } #[stable(feature = "rust1", since = "1.0.0")] impl<'a, T, A: Allocator> IntoIterator for &'a VecDeque { 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 { 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 Extend for VecDeque { fn extend>(&mut self, iter: I) { >::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 { fn extend>(&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 fmt::Debug for VecDeque { 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 From> for VecDeque { /// Turn a [`Vec`] into a [`VecDeque`]. /// /// [`Vec`]: crate::vec::Vec /// [`VecDeque`]: 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` came from `From>` and hasn't been reallocated. fn from(mut other: Vec) -> Self { let len = other.len(); if mem::size_of::() == 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 From> for Vec { /// Turn a [`VecDeque`] into a [`Vec`]. /// /// [`Vec`]: crate::vec::Vec /// [`VecDeque`]: 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) -> 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 From<[T; N]> for VecDeque { /// Converts a `[T; N]` into a `VecDeque`. /// /// ``` /// 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::() != 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 } }