//! 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_n, repeat_with, ByRefSized}; use core::mem::{ManuallyDrop, SizedTypeProperties}; use core::ops::{Index, IndexMut, Range, RangeBounds}; use core::ptr; use core::slice; // This is used in a bunch of intra-doc links. // FIXME: For some reason, `#[cfg(doc)]` wasn't sufficient, resulting in // failures in linkchecker even though rustdoc built the docs just fine. #[allow(unused_imports)] use core::mem; 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::spec_extend::SpecExtend; mod spec_extend; use self::spec_from_iter::SpecFromIter; mod spec_from_iter; #[cfg(test)] mod tests; /// 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, > { // `self[0]`, if it exists, is `buf[head]`. // `head < buf.capacity()`, unless `buf.capacity() == 0` when `head == 0`. head: usize, // the number of initialized elements, starting from the one at `head` and potentially wrapping around. // if `len == 0`, the exact value of `head` is unimportant. // if `T` is zero-Sized, then `self.len <= usize::MAX`, otherwise `self.len <= isize::MAX as usize`. len: 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.clear(); self.extend(other.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() } /// 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 a slice pointer into the buffer. /// `range` must lie inside `0..self.capacity()`. #[inline] unsafe fn buffer_range(&self, range: Range) -> *mut [T] { unsafe { ptr::slice_from_raw_parts_mut(self.ptr().add(range.start), range.end - range.start) } } /// Returns `true` if the buffer is at full capacity. #[inline] fn is_full(&self) -> bool { self.len == self.capacity() } /// 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.capacity()) } #[inline] fn to_physical_idx(&self, idx: usize) -> usize { self.wrap_add(self.head, idx) } /// 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).wrapping_add(self.capacity()), self.capacity()) } /// Copies a contiguous block of memory len long from src to dst #[inline] unsafe fn copy(&mut self, src: usize, dst: usize, len: usize) { debug_assert!( dst + len <= self.capacity(), "cpy dst={} src={} len={} cap={}", dst, src, len, self.capacity() ); debug_assert!( src + len <= self.capacity(), "cpy dst={} src={} len={} cap={}", dst, src, len, self.capacity() ); 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(&mut self, src: usize, dst: usize, len: usize) { debug_assert!( dst + len <= self.capacity(), "cno dst={} src={} len={} cap={}", dst, src, len, self.capacity() ); debug_assert!( src + len <= self.capacity(), "cno dst={} src={} len={} cap={}", dst, src, len, self.capacity() ); 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 capacity() (There must be at /// most one continuous overlapping region between src and dest). unsafe fn wrap_copy(&mut self, src: usize, dst: usize, len: usize) { debug_assert!( cmp::min(src.abs_diff(dst), self.capacity() - src.abs_diff(dst)) + len <= self.capacity(), "wrc dst={} src={} len={} cap={}", dst, src, len, self.capacity() ); // If T is a ZST, don't do any copying. if T::IS_ZST || src == dst || len == 0 { return; } let dst_after_src = self.wrap_sub(dst, src) < len; let src_pre_wrap_len = self.capacity() - src; let dst_pre_wrap_len = self.capacity() - 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(src, dst, 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(src, dst, dst_pre_wrap_len); self.copy(src + dst_pre_wrap_len, 0, 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(src + dst_pre_wrap_len, 0, len - dst_pre_wrap_len); self.copy(src, dst, 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(src, dst, src_pre_wrap_len); self.copy(0, dst + src_pre_wrap_len, 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(0, dst + src_pre_wrap_len, len - src_pre_wrap_len); self.copy(src, dst, 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(src, dst, src_pre_wrap_len); self.copy(0, dst + src_pre_wrap_len, delta); self.copy(delta, 0, 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(0, delta, len - src_pre_wrap_len); self.copy(self.capacity() - delta, 0, delta); self.copy(src, dst, 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.capacity()); let head_room = self.capacity() - 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; }); } /// Writes all values from `iter` to `dst`, wrapping /// at the end of the buffer and returns the number /// of written values. /// /// # Safety /// /// Assumes that `iter` yields at most `len` items. /// Assumes capacity is sufficient. unsafe fn write_iter_wrapping( &mut self, dst: usize, mut iter: impl Iterator, len: usize, ) -> usize { struct Guard<'a, T, A: Allocator> { deque: &'a mut VecDeque, written: usize, } impl<'a, T, A: Allocator> Drop for Guard<'a, T, A> { fn drop(&mut self) { self.deque.len += self.written; } } let head_room = self.capacity() - dst; let mut guard = Guard { deque: self, written: 0 }; if head_room >= len { unsafe { guard.deque.write_iter(dst, iter, &mut guard.written) }; } else { unsafe { guard.deque.write_iter( dst, ByRefSized(&mut iter).take(head_room), &mut guard.written, ); guard.deque.write_iter(0, iter, &mut guard.written) }; } guard.written } /// 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.capacity(); debug_assert!(new_capacity >= old_capacity); // Move the shortest contiguous section of the ring buffer // // H := head // L := last element (`self.to_physical_idx(self.len - 1)`) // // H L // [o o o o o o o . ] // H L // A [o o o o o o o . . . . . . . . . ] // L H // [o o o o o o o o ] // H L // B [. . . o o o o o o o . . . . . . ] // L H // [o o o o o o o o ] // L H // C [o o o o o . . . . . . . . . o o ] // can't use is_contiguous() because the capacity is already updated. if self.head <= old_capacity - self.len { // A // Nop } else { let head_len = old_capacity - self.head; let tail_len = self.len - head_len; if head_len > tail_len && new_capacity - old_capacity >= tail_len { // B unsafe { self.copy_nonoverlapping(0, old_capacity, tail_len); } } else { // C let new_head = new_capacity - head_len; unsafe { // can't use copy_nonoverlapping here, because if e.g. head_len = 2 // and new_capacity = old_capacity + 1, then the heads overlap. self.copy(self.head, new_head, head_len); } self.head = new_head; } } debug_assert!(self.head < self.capacity() || self.capacity() == 0); } } impl VecDeque { /// Creates an empty deque. /// /// # Examples /// /// ``` /// use std::collections::VecDeque; /// /// let deque: VecDeque = VecDeque::new(); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] #[rustc_const_stable(feature = "const_vec_deque_new", since = "1.68.0")] #[must_use] pub const fn new() -> VecDeque { // FIXME: This should just be `VecDeque::new_in(Global)` once that hits stable. VecDeque { head: 0, len: 0, buf: RawVec::NEW } } /// 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 const fn new_in(alloc: A) -> VecDeque { VecDeque { head: 0, len: 0, buf: RawVec::new_in(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 { VecDeque { head: 0, len: 0, buf: RawVec::with_capacity_in(capacity, alloc) } } /// Creates a `VecDeque` from a raw allocation, when the initialized /// part of that allocation forms a *contiguous* subslice thereof. /// /// For use by `vec::IntoIter::into_vecdeque` /// /// # Safety /// /// All the usual requirements on the allocated memory like in /// `Vec::from_raw_parts_in`, but takes a *range* of elements that are /// initialized rather than only supporting `0..len`. Requires that /// `initialized.start` ≤ `initialized.end` ≤ `capacity`. #[inline] pub(crate) unsafe fn from_contiguous_raw_parts_in( ptr: *mut T, initialized: Range, capacity: usize, alloc: A, ) -> Self { debug_assert!(initialized.start <= initialized.end); debug_assert!(initialized.end <= capacity); // SAFETY: Our safety precondition guarantees the range length won't wrap, // and that the allocation is valid for use in `RawVec`. unsafe { VecDeque { head: initialized.start, len: initialized.end.unchecked_sub(initialized.start), buf: RawVec::from_raw_parts_in(ptr, capacity, 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); /// buf.push_back(6); /// 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.to_physical_idx(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); /// buf.push_back(6); /// assert_eq!(buf[1], 4); /// 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.to_physical_idx(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.to_physical_idx(i); let rj = self.to_physical_idx(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 { if T::IS_ZST { usize::MAX } else { self.buf.capacity() } } /// 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) { let new_cap = self.len.checked_add(additional).expect("capacity overflow"); let old_cap = self.capacity(); if new_cap > old_cap { self.buf.reserve_exact(self.len, additional); unsafe { self.handle_capacity_increase(old_cap); } } } /// 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 new_cap = self.len.checked_add(additional).expect("capacity overflow"); let old_cap = self.capacity(); if new_cap > old_cap { // we don't need to reserve_exact(), as the size doesn't have // to be a power of 2. self.buf.reserve(self.len, additional); 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> { let new_cap = self.len.checked_add(additional).ok_or(TryReserveErrorKind::CapacityOverflow)?; let old_cap = self.capacity(); if new_cap > old_cap { self.buf.try_reserve_exact(self.len, additional)?; unsafe { self.handle_capacity_increase(old_cap); } } Ok(()) } /// 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 new_cap = self.len.checked_add(additional).ok_or(TryReserveErrorKind::CapacityOverflow)?; let old_cap = self.capacity(); if new_cap > old_cap { self.buf.try_reserve(self.len, additional)?; 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 target_cap = min_capacity.max(self.len); // never shrink ZSTs if T::IS_ZST || self.capacity() <= target_cap { return; } // There are three cases of interest: // All elements are out of desired bounds // Elements are contiguous, and tail is out of desired bounds // Elements are discontiguous // // At all other times, element positions are unaffected. // `head` and `len` are at most `isize::MAX` and `target_cap < self.capacity()`, so nothing can // overflow. let tail_outside = (target_cap + 1..=self.capacity()).contains(&(self.head + self.len)); if self.len == 0 { self.head = 0; } else if self.head >= target_cap && tail_outside { // Head and tail are both out of bounds, so copy all of them to the front. // // H := head // L := last element // H L // [. . . . . . . . o o o o o o o . ] // H L // [o o o o o o o . ] unsafe { // nonoverlapping because `self.head >= target_cap >= self.len`. self.copy_nonoverlapping(self.head, 0, self.len); } self.head = 0; } else if self.head < target_cap && tail_outside { // Head is in bounds, tail is out of bounds. // Copy the overflowing part to the beginning of the // buffer. This won't overlap because `target_cap >= self.len`. // // H := head // L := last element // H L // [. . . o o o o o o o . . . . . . ] // L H // [o o . o o o o o ] let len = self.head + self.len - target_cap; unsafe { self.copy_nonoverlapping(target_cap, 0, len); } } else if !self.is_contiguous() { // The head slice is at least partially out of bounds, tail is in bounds. // Copy the head backwards so it lines up with the target capacity. // This won't overlap because `target_cap >= self.len`. // // H := head // L := last element // L H // [o o o o o . . . . . . . . . o o ] // L H // [o o o o o . o o ] let head_len = self.capacity() - self.head; let new_head = target_cap - head_len; unsafe { // can't use `copy_nonoverlapping()` here because the new and old // regions for the head might overlap. self.copy(self.head, new_head, head_len); } self.head = new_head; } self.buf.shrink_to_fit(target_cap); debug_assert!(self.head < self.capacity() || self.capacity() == 0); debug_assert!(self.len <= self.capacity()); } /// Shortens the deque, keeping the first `len` elements and dropping /// the rest. /// /// If `len` is greater or equal to 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 (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.len = len; ptr::drop_in_place(drop_back); } else { let drop_back = back as *mut _; let drop_front = front.get_unchecked_mut(len..) as *mut _; self.len = len; // 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> { let (a, b) = self.as_slices(); Iter::new(a.iter(), b.iter()) } /// 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> { let (a, b) = self.as_mut_slices(); IterMut::new(a.iter_mut(), b.iter_mut()) } /// 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]) { let (a_range, b_range) = self.slice_ranges(.., self.len); // SAFETY: `slice_ranges` always returns valid ranges into // the physical buffer. unsafe { (&*self.buffer_range(a_range), &*self.buffer_range(b_range)) } } /// 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]) { let (a_range, b_range) = self.slice_ranges(.., self.len); // SAFETY: `slice_ranges` always returns valid ranges into // the physical buffer. unsafe { (&mut *self.buffer_range(a_range), &mut *self.buffer_range(b_range)) } } /// 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 { self.len } /// 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.len == 0 } /// Given a range into the logical buffer of the deque, this function /// return two ranges into the physical buffer that correspond to /// the given range. The `len` parameter should usually just be `self.len`; /// the reason it's passed explicitly is that if the deque is wrapped in /// a `Drain`, then `self.len` is not actually the length of the deque. /// /// # Safety /// /// This function is always safe to call. For the resulting ranges to be valid /// ranges into the physical buffer, the caller must ensure that the result of /// calling `slice::range(range, ..len)` represents a valid range into the /// logical buffer, and that all elements in that range are initialized. fn slice_ranges(&self, range: R, len: usize) -> (Range, Range) where R: RangeBounds, { let Range { start, end } = slice::range(range, ..len); let len = end - start; if len == 0 { (0..0, 0..0) } else { // `slice::range` guarantees that `start <= end <= len`. // because `len != 0`, we know that `start < end`, so `start < len` // and the indexing is valid. let wrapped_start = self.to_physical_idx(start); // this subtraction can never overflow because `wrapped_start` is // at most `self.capacity()` (and if `self.capacity != 0`, then `wrapped_start` is strictly less // than `self.capacity`). let head_len = self.capacity() - wrapped_start; if head_len >= len { // we know that `len + wrapped_start <= self.capacity <= usize::MAX`, so this addition can't overflow (wrapped_start..wrapped_start + len, 0..0) } else { // can't overflow because of the if condition let tail_len = len - head_len; (wrapped_start..self.capacity(), 0..tail_len) } } } /// 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 (a_range, b_range) = self.slice_ranges(range, self.len); // SAFETY: The ranges returned by `slice_ranges` // are valid ranges into the physical buffer, so // it's ok to pass them to `buffer_range` and // dereference the result. let a = unsafe { &*self.buffer_range(a_range) }; let b = unsafe { &*self.buffer_range(b_range) }; Iter::new(a.iter(), b.iter()) } /// 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 (a_range, b_range) = self.slice_ranges(range, self.len); // SAFETY: The ranges returned by `slice_ranges` // are valid ranges into the physical buffer, so // it's ok to pass them to `buffer_range` and // dereference the result. let a = unsafe { &mut *self.buffer_range(a_range) }; let b = unsafe { &mut *self.buffer_range(b_range) }; IterMut::new(a.iter_mut(), b.iter_mut()) } /// 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 Range { start, end } = slice::range(range, ..self.len); let drain_start = start; let drain_len = end - start; // The deque's elements are parted into three segments: // * 0 -> drain_start // * drain_start -> drain_start+drain_len // * drain_start+drain_len -> self.len // // H = self.head; T = self.head+self.len; t = drain_start+drain_len; h = drain_head // // We store drain_start as self.len, and drain_len and self.len as // drain_len and orig_len 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. // // H h t T // [. . . o o x x o o . . .] // // "forget" about the values after the start of the drain until after // the drain is complete and the Drain destructor is run. unsafe { Drain::new(self, drain_start, drain_len) } } /// 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); // Not strictly necessary, but leaves things in a more consistent/predictable state. self.head = 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 old_head = self.head; self.head = self.to_physical_idx(1); self.len -= 1; Some(unsafe { self.buffer_read(old_head) }) } } /// 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.len -= 1; Some(unsafe { self.buffer_read(self.to_physical_idx(self.len)) }) } } /// 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.head = self.wrap_sub(self.head, 1); self.len += 1; unsafe { self.buffer_write(self.head, 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(); } unsafe { self.buffer_write(self.to_physical_idx(self.len), value) } self.len += 1; } #[inline] fn is_contiguous(&self) -> bool { // Do the calculation like this to avoid overflowing if len + head > usize::MAX self.head <= self.capacity() - self.len } /// 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 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(); } let k = self.len - index; if k < index { // `index + 1` can't overflow, because if index was usize::MAX, then either the // assert would've failed, or the deque would've tried to grow past usize::MAX // and panicked. unsafe { // see `remove()` for explanation why this wrap_copy() call is safe. self.wrap_copy(self.to_physical_idx(index), self.to_physical_idx(index + 1), k); self.buffer_write(self.to_physical_idx(index), value); self.len += 1; } } else { let old_head = self.head; self.head = self.wrap_sub(self.head, 1); unsafe { self.wrap_copy(old_head, self.head, index); self.buffer_write(self.to_physical_idx(index), value); self.len += 1; } } } /// 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.len <= index { return None; } let wrapped_idx = self.to_physical_idx(index); let elem = unsafe { Some(self.buffer_read(wrapped_idx)) }; let k = self.len - index - 1; // safety: due to the nature of the if-condition, whichever wrap_copy gets called, // its length argument will be at most `self.len / 2`, so there can't be more than // one overlapping area. if k < index { unsafe { self.wrap_copy(self.wrap_add(wrapped_idx, 1), wrapped_idx, k) }; self.len -= 1; } else { let old_head = self.head; self.head = self.to_physical_idx(1); unsafe { self.wrap_copy(old_head, self.head, index) }; self.len -= 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.len = at; other.len = 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) { if T::IS_ZST { self.len = self.len.checked_add(other.len).expect("capacity overflow"); other.len = 0; other.head = 0; return; } self.reserve(other.len); unsafe { let (left, right) = other.as_slices(); self.copy_slice(self.to_physical_idx(self.len), left); // no overflow, because self.capacity() >= old_cap + left.len() >= self.len + left.len() self.copy_slice(self.to_physical_idx(self.len + left.len()), right); } // SAFETY: Update pointers after copying to avoid leaving doppelganger // in case of panics. self.len += other.len; // Now that we own its values, forget everything in `other`. other.len = 0; other.head = 0; } /// 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.capacity(); self.buf.reserve_for_push(old_cap); 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 T::IS_ZST { self.head = 0; } if self.is_contiguous() { unsafe { return slice::from_raw_parts_mut(self.ptr().add(self.head), self.len) } } let &mut Self { head, len, .. } = self; let ptr = self.ptr(); let cap = self.capacity(); let free = cap - len; let head_len = cap - head; let tail = len - head_len; let tail_len = tail; if free >= head_len { // there is enough free space to copy the head in one go, // this means that we first shift the tail backwards, and then // copy the head to the correct position. // // from: DEFGH....ABC // to: ABCDEFGH.... unsafe { self.copy(0, head_len, tail_len); // ...DEFGH.ABC self.copy_nonoverlapping(head, 0, head_len); // ABCDEFGH.... } self.head = 0; } else if free >= tail_len { // there is enough free space to copy the tail in one go, // this means that we first shift the head forwards, and then // copy the tail to the correct position. // // from: FGH....ABCDE // to: ...ABCDEFGH. unsafe { self.copy(head, tail, head_len); // FGHABCDE.... self.copy_nonoverlapping(0, tail + head_len, tail_len); // ...ABCDEFGH. } self.head = tail; } else { // `free` is smaller than both `head_len` and `tail_len`. // the general algorithm for this first moves the slices // right next to each other and then uses `slice::rotate` // to rotate them into place: // // initially: HIJK..ABCDEFG // step 1: ..HIJKABCDEFG // step 2: ..ABCDEFGHIJK // // or: // // initially: FGHIJK..ABCDE // step 1: FGHIJKABCDE.. // step 2: ABCDEFGHIJK.. // pick the shorter of the 2 slices to reduce the amount // of memory that needs to be moved around. if head_len > tail_len { // tail is shorter, so: // 1. copy tail forwards // 2. rotate used part of the buffer // 3. update head to point to the new beginning (which is just `free`) unsafe { // if there is no free space in the buffer, then the slices are already // right next to each other and we don't need to move any memory. if free != 0 { // because we only move the tail forward as much as there's free space // behind it, we don't overwrite any elements of the head slice, and // the slices end up right next to each other. self.copy(0, free, tail_len); } // We just copied the tail right next to the head slice, // so all of the elements in the range are initialized let slice = &mut *self.buffer_range(free..self.capacity()); // because the deque wasn't contiguous, we know that `tail_len < self.len == slice.len()`, // so this will never panic. slice.rotate_left(tail_len); // the used part of the buffer now is `free..self.capacity()`, so set // `head` to the beginning of that range. self.head = free; } } else { // head is shorter so: // 1. copy head backwards // 2. rotate used part of the buffer // 3. update head to point to the new beginning (which is the beginning of the buffer) unsafe { // if there is no free space in the buffer, then the slices are already // right next to each other and we don't need to move any memory. if free != 0 { // copy the head slice to lie right behind the tail slice. self.copy(self.head, tail_len, head_len); } // because we copied the head slice so that both slices lie right // next to each other, all the elements in the range are initialized. let slice = &mut *self.buffer_range(0..self.len); // because the deque wasn't contiguous, we know that `head_len < self.len == slice.len()` // so this will never panic. slice.rotate_right(head_len); // the used part of the buffer now is `0..self.len`, so set // `head` to the beginning of that range. self.head = 0; } } } unsafe { slice::from_raw_parts_mut(ptr.add(self.head), self.len) } } /// Rotates the double-ended queue `n` places to the left. /// /// Equivalently, /// - Rotates item `n` into the first position. /// - Pops the first `n` items and pushes them to the end. /// - Rotates `len() - n` places to the right. /// /// # Panics /// /// If `n` is greater than `len()`. Note that `n == len()` /// does _not_ panic and is a no-op rotation. /// /// # Complexity /// /// Takes `*O*(min(n, len() - n))` 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, n: usize) { assert!(n <= self.len()); let k = self.len - n; if n <= k { unsafe { self.rotate_left_inner(n) } } else { unsafe { self.rotate_right_inner(k) } } } /// Rotates the double-ended queue `n` places to the right. /// /// Equivalently, /// - Rotates the first item into position `n`. /// - Pops the last `n` items and pushes them to the front. /// - Rotates `len() - n` places to the left. /// /// # Panics /// /// If `n` is greater than `len()`. Note that `n == len()` /// does _not_ panic and is a no-op rotation. /// /// # Complexity /// /// Takes `*O*(min(n, len() - n))` 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, n: usize) { assert!(n <= self.len()); let k = self.len - n; if n <= k { unsafe { self.rotate_right_inner(n) } } else { unsafe { self.rotate_left_inner(k) } } } // 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, capacity() - x) + copy_len <= capacity()`, // but then `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.to_physical_idx(self.len), mid); } self.head = self.to_physical_idx(mid); } unsafe fn rotate_right_inner(&mut self, k: usize) { debug_assert!(k * 2 <= self.len()); self.head = self.wrap_sub(self.head, k); unsafe { self.wrap_copy(self.to_physical_idx(self.len), self.head, k); } } /// Binary searches this `VecDeque` for a given element. /// If the `VecDeque` is not sorted, the returned result is unspecified and /// meaningless. /// /// 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`]. /// /// [`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. /// /// The comparator function should return an order code that indicates /// whether its argument is `Less`, `Equal` or `Greater` the desired /// target. /// If the `VecDeque` is not sorted or if the comparator function does not /// implement an order consistent with the sort order of the underlying /// `VecDeque`, the returned result is unspecified and meaningless. /// /// 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`]. /// /// [`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. /// /// 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 deque is not sorted by the key, the returned result is /// unspecified and meaningless. /// /// 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`]. /// /// [`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 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) { if new_len > self.len() { let extra = new_len - self.len(); self.extend(repeat_n(value, extra)) } else { self.truncate(new_len); } } } /// Returns the index in the underlying buffer for a given logical element index. #[inline] fn wrap_index(logical_index: usize, capacity: usize) -> usize { debug_assert!( (logical_index == 0 && capacity == 0) || logical_index < capacity || (logical_index - capacity) < capacity ); if logical_index >= capacity { logical_index - capacity } else { logical_index } } #[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 { SpecFromIter::spec_from_iter(iter.into_iter()) } } #[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: &'a 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.iter()).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 conversion is guaranteed to run in *O*(1) time /// and to not re-allocate the `Vec`'s buffer or allocate /// any additional memory. #[inline] fn from(other: Vec) -> Self { let (ptr, len, cap, alloc) = other.into_raw_parts_with_alloc(); Self { head: 0, len, buf: unsafe { RawVec::from_raw_parts_in(ptr, cap, alloc) } } } } #[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.capacity(); let alloc = ptr::read(other.allocator()); if other.head != 0 { ptr::copy(buf.add(other.head), 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 !::IS_ZST { // SAFETY: VecDeque::with_capacity ensures that there is enough capacity. unsafe { ptr::copy_nonoverlapping(arr.as_ptr(), deq.ptr(), N); } } deq.head = 0; deq.len = N; deq } }