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Diffstat (limited to 'library/alloc/src/collections/linked_list.rs')
| -rw-r--r-- | library/alloc/src/collections/linked_list.rs | 2012 |
1 files changed, 2012 insertions, 0 deletions
diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs new file mode 100644 index 000000000..e21c8aa3b --- /dev/null +++ b/library/alloc/src/collections/linked_list.rs @@ -0,0 +1,2012 @@ +//! A doubly-linked list with owned nodes. +//! +//! The `LinkedList` allows pushing and popping elements at either end +//! in constant time. +//! +//! NOTE: It is almost always better to use [`Vec`] or [`VecDeque`] because +//! array-based containers are generally faster, +//! more memory efficient, and make better use of CPU cache. +//! +//! [`Vec`]: crate::vec::Vec +//! [`VecDeque`]: super::vec_deque::VecDeque + +#![stable(feature = "rust1", since = "1.0.0")] + +use core::cmp::Ordering; +use core::fmt; +use core::hash::{Hash, Hasher}; +use core::iter::{FromIterator, FusedIterator}; +use core::marker::PhantomData; +use core::mem; +use core::ptr::NonNull; + +use super::SpecExtend; +use crate::boxed::Box; + +#[cfg(test)] +mod tests; + +/// A doubly-linked list with owned nodes. +/// +/// The `LinkedList` allows pushing and popping elements at either end +/// in constant time. +/// +/// A `LinkedList` with a known list of items can be initialized from an array: +/// ``` +/// use std::collections::LinkedList; +/// +/// let list = LinkedList::from([1, 2, 3]); +/// ``` +/// +/// NOTE: It is almost always better to use [`Vec`] or [`VecDeque`] because +/// array-based containers are generally faster, +/// more memory efficient, and make better use of CPU cache. +/// +/// [`Vec`]: crate::vec::Vec +/// [`VecDeque`]: super::vec_deque::VecDeque +#[stable(feature = "rust1", since = "1.0.0")] +#[cfg_attr(not(test), rustc_diagnostic_item = "LinkedList")] +#[rustc_insignificant_dtor] +pub struct LinkedList<T> { + head: Option<NonNull<Node<T>>>, + tail: Option<NonNull<Node<T>>>, + len: usize, + marker: PhantomData<Box<Node<T>>>, +} + +struct Node<T> { + next: Option<NonNull<Node<T>>>, + prev: Option<NonNull<Node<T>>>, + element: T, +} + +/// An iterator over the elements of a `LinkedList`. +/// +/// This `struct` is created by [`LinkedList::iter()`]. See its +/// documentation for more. +#[must_use = "iterators are lazy and do nothing unless consumed"] +#[stable(feature = "rust1", since = "1.0.0")] +pub struct Iter<'a, T: 'a> { + head: Option<NonNull<Node<T>>>, + tail: Option<NonNull<Node<T>>>, + len: usize, + marker: PhantomData<&'a Node<T>>, +} + +#[stable(feature = "collection_debug", since = "1.17.0")] +impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("Iter") + .field(&*mem::ManuallyDrop::new(LinkedList { + head: self.head, + tail: self.tail, + len: self.len, + marker: PhantomData, + })) + .field(&self.len) + .finish() + } +} + +// FIXME(#26925) Remove in favor of `#[derive(Clone)]` +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Clone for Iter<'_, T> { + fn clone(&self) -> Self { + Iter { ..*self } + } +} + +/// A mutable iterator over the elements of a `LinkedList`. +/// +/// This `struct` is created by [`LinkedList::iter_mut()`]. See its +/// documentation for more. +#[must_use = "iterators are lazy and do nothing unless consumed"] +#[stable(feature = "rust1", since = "1.0.0")] +pub struct IterMut<'a, T: 'a> { + head: Option<NonNull<Node<T>>>, + tail: Option<NonNull<Node<T>>>, + len: usize, + marker: PhantomData<&'a mut Node<T>>, +} + +#[stable(feature = "collection_debug", since = "1.17.0")] +impl<T: fmt::Debug> fmt::Debug for IterMut<'_, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("IterMut") + .field(&*mem::ManuallyDrop::new(LinkedList { + head: self.head, + tail: self.tail, + len: self.len, + marker: PhantomData, + })) + .field(&self.len) + .finish() + } +} + +/// An owning iterator over the elements of a `LinkedList`. +/// +/// This `struct` is created by the [`into_iter`] method on [`LinkedList`] +/// (provided by the [`IntoIterator`] trait). See its documentation for more. +/// +/// [`into_iter`]: LinkedList::into_iter +/// [`IntoIterator`]: core::iter::IntoIterator +#[derive(Clone)] +#[stable(feature = "rust1", since = "1.0.0")] +pub struct IntoIter<T> { + list: LinkedList<T>, +} + +#[stable(feature = "collection_debug", since = "1.17.0")] +impl<T: fmt::Debug> fmt::Debug for IntoIter<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("IntoIter").field(&self.list).finish() + } +} + +impl<T> Node<T> { + fn new(element: T) -> Self { + Node { next: None, prev: None, element } + } + + fn into_element(self: Box<Self>) -> T { + self.element + } +} + +// private methods +impl<T> LinkedList<T> { + /// Adds the given node to the front of the list. + #[inline] + fn push_front_node(&mut self, mut node: Box<Node<T>>) { + // This method takes care not to create mutable references to whole nodes, + // to maintain validity of aliasing pointers into `element`. + unsafe { + node.next = self.head; + node.prev = None; + let node = Some(Box::leak(node).into()); + + match self.head { + None => self.tail = node, + // Not creating new mutable (unique!) references overlapping `element`. + Some(head) => (*head.as_ptr()).prev = node, + } + + self.head = node; + self.len += 1; + } + } + + /// Removes and returns the node at the front of the list. + #[inline] + fn pop_front_node(&mut self) -> Option<Box<Node<T>>> { + // This method takes care not to create mutable references to whole nodes, + // to maintain validity of aliasing pointers into `element`. + self.head.map(|node| unsafe { + let node = Box::from_raw(node.as_ptr()); + self.head = node.next; + + match self.head { + None => self.tail = None, + // Not creating new mutable (unique!) references overlapping `element`. + Some(head) => (*head.as_ptr()).prev = None, + } + + self.len -= 1; + node + }) + } + + /// Adds the given node to the back of the list. + #[inline] + fn push_back_node(&mut self, mut node: Box<Node<T>>) { + // This method takes care not to create mutable references to whole nodes, + // to maintain validity of aliasing pointers into `element`. + unsafe { + node.next = None; + node.prev = self.tail; + let node = Some(Box::leak(node).into()); + + match self.tail { + None => self.head = node, + // Not creating new mutable (unique!) references overlapping `element`. + Some(tail) => (*tail.as_ptr()).next = node, + } + + self.tail = node; + self.len += 1; + } + } + + /// Removes and returns the node at the back of the list. + #[inline] + fn pop_back_node(&mut self) -> Option<Box<Node<T>>> { + // This method takes care not to create mutable references to whole nodes, + // to maintain validity of aliasing pointers into `element`. + self.tail.map(|node| unsafe { + let node = Box::from_raw(node.as_ptr()); + self.tail = node.prev; + + match self.tail { + None => self.head = None, + // Not creating new mutable (unique!) references overlapping `element`. + Some(tail) => (*tail.as_ptr()).next = None, + } + + self.len -= 1; + node + }) + } + + /// Unlinks the specified node from the current list. + /// + /// Warning: this will not check that the provided node belongs to the current list. + /// + /// This method takes care not to create mutable references to `element`, to + /// maintain validity of aliasing pointers. + #[inline] + unsafe fn unlink_node(&mut self, mut node: NonNull<Node<T>>) { + let node = unsafe { node.as_mut() }; // this one is ours now, we can create an &mut. + + // Not creating new mutable (unique!) references overlapping `element`. + match node.prev { + Some(prev) => unsafe { (*prev.as_ptr()).next = node.next }, + // this node is the head node + None => self.head = node.next, + }; + + match node.next { + Some(next) => unsafe { (*next.as_ptr()).prev = node.prev }, + // this node is the tail node + None => self.tail = node.prev, + }; + + self.len -= 1; + } + + /// Splices a series of nodes between two existing nodes. + /// + /// Warning: this will not check that the provided node belongs to the two existing lists. + #[inline] + unsafe fn splice_nodes( + &mut self, + existing_prev: Option<NonNull<Node<T>>>, + existing_next: Option<NonNull<Node<T>>>, + mut splice_start: NonNull<Node<T>>, + mut splice_end: NonNull<Node<T>>, + splice_length: usize, + ) { + // This method takes care not to create multiple mutable references to whole nodes at the same time, + // to maintain validity of aliasing pointers into `element`. + if let Some(mut existing_prev) = existing_prev { + unsafe { + existing_prev.as_mut().next = Some(splice_start); + } + } else { + self.head = Some(splice_start); + } + if let Some(mut existing_next) = existing_next { + unsafe { + existing_next.as_mut().prev = Some(splice_end); + } + } else { + self.tail = Some(splice_end); + } + unsafe { + splice_start.as_mut().prev = existing_prev; + splice_end.as_mut().next = existing_next; + } + + self.len += splice_length; + } + + /// Detaches all nodes from a linked list as a series of nodes. + #[inline] + fn detach_all_nodes(mut self) -> Option<(NonNull<Node<T>>, NonNull<Node<T>>, usize)> { + let head = self.head.take(); + let tail = self.tail.take(); + let len = mem::replace(&mut self.len, 0); + if let Some(head) = head { + // SAFETY: In a LinkedList, either both the head and tail are None because + // the list is empty, or both head and tail are Some because the list is populated. + // Since we have verified the head is Some, we are sure the tail is Some too. + let tail = unsafe { tail.unwrap_unchecked() }; + Some((head, tail, len)) + } else { + None + } + } + + #[inline] + unsafe fn split_off_before_node( + &mut self, + split_node: Option<NonNull<Node<T>>>, + at: usize, + ) -> Self { + // The split node is the new head node of the second part + if let Some(mut split_node) = split_node { + let first_part_head; + let first_part_tail; + unsafe { + first_part_tail = split_node.as_mut().prev.take(); + } + if let Some(mut tail) = first_part_tail { + unsafe { + tail.as_mut().next = None; + } + first_part_head = self.head; + } else { + first_part_head = None; + } + + let first_part = LinkedList { + head: first_part_head, + tail: first_part_tail, + len: at, + marker: PhantomData, + }; + + // Fix the head ptr of the second part + self.head = Some(split_node); + self.len = self.len - at; + + first_part + } else { + mem::replace(self, LinkedList::new()) + } + } + + #[inline] + unsafe fn split_off_after_node( + &mut self, + split_node: Option<NonNull<Node<T>>>, + at: usize, + ) -> Self { + // The split node is the new tail node of the first part and owns + // the head of the second part. + if let Some(mut split_node) = split_node { + let second_part_head; + let second_part_tail; + unsafe { + second_part_head = split_node.as_mut().next.take(); + } + if let Some(mut head) = second_part_head { + unsafe { + head.as_mut().prev = None; + } + second_part_tail = self.tail; + } else { + second_part_tail = None; + } + + let second_part = LinkedList { + head: second_part_head, + tail: second_part_tail, + len: self.len - at, + marker: PhantomData, + }; + + // Fix the tail ptr of the first part + self.tail = Some(split_node); + self.len = at; + + second_part + } else { + mem::replace(self, LinkedList::new()) + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Default for LinkedList<T> { + /// Creates an empty `LinkedList<T>`. + #[inline] + fn default() -> Self { + Self::new() + } +} + +impl<T> LinkedList<T> { + /// Creates an empty `LinkedList`. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let list: LinkedList<u32> = LinkedList::new(); + /// ``` + #[inline] + #[rustc_const_stable(feature = "const_linked_list_new", since = "1.39.0")] + #[stable(feature = "rust1", since = "1.0.0")] + #[must_use] + pub const fn new() -> Self { + LinkedList { head: None, tail: None, len: 0, marker: PhantomData } + } + + /// Moves all elements from `other` to the end of the list. + /// + /// This reuses all the nodes from `other` and moves them into `self`. After + /// this operation, `other` becomes empty. + /// + /// This operation should compute in *O*(1) time and *O*(1) memory. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut list1 = LinkedList::new(); + /// list1.push_back('a'); + /// + /// let mut list2 = LinkedList::new(); + /// list2.push_back('b'); + /// list2.push_back('c'); + /// + /// list1.append(&mut list2); + /// + /// let mut iter = list1.iter(); + /// assert_eq!(iter.next(), Some(&'a')); + /// assert_eq!(iter.next(), Some(&'b')); + /// assert_eq!(iter.next(), Some(&'c')); + /// assert!(iter.next().is_none()); + /// + /// assert!(list2.is_empty()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn append(&mut self, other: &mut Self) { + match self.tail { + None => mem::swap(self, other), + Some(mut tail) => { + // `as_mut` is okay here because we have exclusive access to the entirety + // of both lists. + if let Some(mut other_head) = other.head.take() { + unsafe { + tail.as_mut().next = Some(other_head); + other_head.as_mut().prev = Some(tail); + } + + self.tail = other.tail.take(); + self.len += mem::replace(&mut other.len, 0); + } + } + } + } + + /// Provides a forward iterator. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut list: LinkedList<u32> = LinkedList::new(); + /// + /// list.push_back(0); + /// list.push_back(1); + /// list.push_back(2); + /// + /// let mut iter = list.iter(); + /// assert_eq!(iter.next(), Some(&0)); + /// assert_eq!(iter.next(), Some(&1)); + /// assert_eq!(iter.next(), Some(&2)); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn iter(&self) -> Iter<'_, T> { + Iter { head: self.head, tail: self.tail, len: self.len, marker: PhantomData } + } + + /// Provides a forward iterator with mutable references. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut list: LinkedList<u32> = LinkedList::new(); + /// + /// list.push_back(0); + /// list.push_back(1); + /// list.push_back(2); + /// + /// for element in list.iter_mut() { + /// *element += 10; + /// } + /// + /// let mut iter = list.iter(); + /// assert_eq!(iter.next(), Some(&10)); + /// assert_eq!(iter.next(), Some(&11)); + /// assert_eq!(iter.next(), Some(&12)); + /// assert_eq!(iter.next(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn iter_mut(&mut self) -> IterMut<'_, T> { + IterMut { head: self.head, tail: self.tail, len: self.len, marker: PhantomData } + } + + /// Provides a cursor at the front element. + /// + /// The cursor is pointing to the "ghost" non-element if the list is empty. + #[inline] + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn cursor_front(&self) -> Cursor<'_, T> { + Cursor { index: 0, current: self.head, list: self } + } + + /// Provides a cursor with editing operations at the front element. + /// + /// The cursor is pointing to the "ghost" non-element if the list is empty. + #[inline] + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn cursor_front_mut(&mut self) -> CursorMut<'_, T> { + CursorMut { index: 0, current: self.head, list: self } + } + + /// Provides a cursor at the back element. + /// + /// The cursor is pointing to the "ghost" non-element if the list is empty. + #[inline] + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn cursor_back(&self) -> Cursor<'_, T> { + Cursor { index: self.len.checked_sub(1).unwrap_or(0), current: self.tail, list: self } + } + + /// Provides a cursor with editing operations at the back element. + /// + /// The cursor is pointing to the "ghost" non-element if the list is empty. + #[inline] + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn cursor_back_mut(&mut self) -> CursorMut<'_, T> { + CursorMut { index: self.len.checked_sub(1).unwrap_or(0), current: self.tail, list: self } + } + + /// Returns `true` if the `LinkedList` is empty. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut dl = LinkedList::new(); + /// assert!(dl.is_empty()); + /// + /// dl.push_front("foo"); + /// assert!(!dl.is_empty()); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn is_empty(&self) -> bool { + self.head.is_none() + } + + /// Returns the length of the `LinkedList`. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut dl = LinkedList::new(); + /// + /// dl.push_front(2); + /// assert_eq!(dl.len(), 1); + /// + /// dl.push_front(1); + /// assert_eq!(dl.len(), 2); + /// + /// dl.push_back(3); + /// assert_eq!(dl.len(), 3); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn len(&self) -> usize { + self.len + } + + /// Removes all elements from the `LinkedList`. + /// + /// This operation should compute in *O*(*n*) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut dl = LinkedList::new(); + /// + /// dl.push_front(2); + /// dl.push_front(1); + /// assert_eq!(dl.len(), 2); + /// assert_eq!(dl.front(), Some(&1)); + /// + /// dl.clear(); + /// assert_eq!(dl.len(), 0); + /// assert_eq!(dl.front(), None); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn clear(&mut self) { + *self = Self::new(); + } + + /// Returns `true` if the `LinkedList` contains an element equal to the + /// given value. + /// + /// This operation should compute linearly in *O*(*n*) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut list: LinkedList<u32> = LinkedList::new(); + /// + /// list.push_back(0); + /// list.push_back(1); + /// list.push_back(2); + /// + /// assert_eq!(list.contains(&0), true); + /// assert_eq!(list.contains(&10), false); + /// ``` + #[stable(feature = "linked_list_contains", since = "1.12.0")] + pub fn contains(&self, x: &T) -> bool + where + T: PartialEq<T>, + { + self.iter().any(|e| e == x) + } + + /// Provides a reference to the front element, or `None` if the list is + /// empty. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut dl = LinkedList::new(); + /// assert_eq!(dl.front(), None); + /// + /// dl.push_front(1); + /// assert_eq!(dl.front(), Some(&1)); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn front(&self) -> Option<&T> { + unsafe { self.head.as_ref().map(|node| &node.as_ref().element) } + } + + /// Provides a mutable reference to the front element, or `None` if the list + /// is empty. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut dl = LinkedList::new(); + /// assert_eq!(dl.front(), None); + /// + /// dl.push_front(1); + /// assert_eq!(dl.front(), Some(&1)); + /// + /// match dl.front_mut() { + /// None => {}, + /// Some(x) => *x = 5, + /// } + /// assert_eq!(dl.front(), Some(&5)); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn front_mut(&mut self) -> Option<&mut T> { + unsafe { self.head.as_mut().map(|node| &mut node.as_mut().element) } + } + + /// Provides a reference to the back element, or `None` if the list is + /// empty. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut dl = LinkedList::new(); + /// assert_eq!(dl.back(), None); + /// + /// dl.push_back(1); + /// assert_eq!(dl.back(), Some(&1)); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn back(&self) -> Option<&T> { + unsafe { self.tail.as_ref().map(|node| &node.as_ref().element) } + } + + /// Provides a mutable reference to the back element, or `None` if the list + /// is empty. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut dl = LinkedList::new(); + /// assert_eq!(dl.back(), None); + /// + /// dl.push_back(1); + /// assert_eq!(dl.back(), Some(&1)); + /// + /// match dl.back_mut() { + /// None => {}, + /// Some(x) => *x = 5, + /// } + /// assert_eq!(dl.back(), Some(&5)); + /// ``` + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn back_mut(&mut self) -> Option<&mut T> { + unsafe { self.tail.as_mut().map(|node| &mut node.as_mut().element) } + } + + /// Adds an element first in the list. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut dl = LinkedList::new(); + /// + /// dl.push_front(2); + /// assert_eq!(dl.front().unwrap(), &2); + /// + /// dl.push_front(1); + /// assert_eq!(dl.front().unwrap(), &1); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn push_front(&mut self, elt: T) { + self.push_front_node(Box::new(Node::new(elt))); + } + + /// Removes the first element and returns it, or `None` if the list is + /// empty. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut d = LinkedList::new(); + /// assert_eq!(d.pop_front(), None); + /// + /// d.push_front(1); + /// d.push_front(3); + /// assert_eq!(d.pop_front(), Some(3)); + /// assert_eq!(d.pop_front(), Some(1)); + /// assert_eq!(d.pop_front(), None); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn pop_front(&mut self) -> Option<T> { + self.pop_front_node().map(Node::into_element) + } + + /// Appends an element to the back of a list. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut d = LinkedList::new(); + /// d.push_back(1); + /// d.push_back(3); + /// assert_eq!(3, *d.back().unwrap()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn push_back(&mut self, elt: T) { + self.push_back_node(Box::new(Node::new(elt))); + } + + /// Removes the last element from a list and returns it, or `None` if + /// it is empty. + /// + /// This operation should compute in *O*(1) time. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut d = LinkedList::new(); + /// assert_eq!(d.pop_back(), None); + /// d.push_back(1); + /// d.push_back(3); + /// assert_eq!(d.pop_back(), Some(3)); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn pop_back(&mut self) -> Option<T> { + self.pop_back_node().map(Node::into_element) + } + + /// Splits the list into two at the given index. Returns everything after the given index, + /// including the index. + /// + /// This operation should compute in *O*(*n*) time. + /// + /// # Panics + /// + /// Panics if `at > len`. + /// + /// # Examples + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let mut d = LinkedList::new(); + /// + /// d.push_front(1); + /// d.push_front(2); + /// d.push_front(3); + /// + /// let mut split = d.split_off(2); + /// + /// assert_eq!(split.pop_front(), Some(1)); + /// assert_eq!(split.pop_front(), None); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn split_off(&mut self, at: usize) -> LinkedList<T> { + let len = self.len(); + assert!(at <= len, "Cannot split off at a nonexistent index"); + if at == 0 { + return mem::take(self); + } else if at == len { + return Self::new(); + } + + // Below, we iterate towards the `i-1`th node, either from the start or the end, + // depending on which would be faster. + let split_node = if at - 1 <= len - 1 - (at - 1) { + let mut iter = self.iter_mut(); + // instead of skipping using .skip() (which creates a new struct), + // we skip manually so we can access the head field without + // depending on implementation details of Skip + for _ in 0..at - 1 { + iter.next(); + } + iter.head + } else { + // better off starting from the end + let mut iter = self.iter_mut(); + for _ in 0..len - 1 - (at - 1) { + iter.next_back(); + } + iter.tail + }; + unsafe { self.split_off_after_node(split_node, at) } + } + + /// Removes the element at the given index and returns it. + /// + /// This operation should compute in *O*(*n*) time. + /// + /// # Panics + /// Panics if at >= len + /// + /// # Examples + /// + /// ``` + /// #![feature(linked_list_remove)] + /// use std::collections::LinkedList; + /// + /// let mut d = LinkedList::new(); + /// + /// d.push_front(1); + /// d.push_front(2); + /// d.push_front(3); + /// + /// assert_eq!(d.remove(1), 2); + /// assert_eq!(d.remove(0), 3); + /// assert_eq!(d.remove(0), 1); + /// ``` + #[unstable(feature = "linked_list_remove", issue = "69210")] + pub fn remove(&mut self, at: usize) -> T { + let len = self.len(); + assert!(at < len, "Cannot remove at an index outside of the list bounds"); + + // Below, we iterate towards the node at the given index, either from + // the start or the end, depending on which would be faster. + let offset_from_end = len - at - 1; + if at <= offset_from_end { + let mut cursor = self.cursor_front_mut(); + for _ in 0..at { + cursor.move_next(); + } + cursor.remove_current().unwrap() + } else { + let mut cursor = self.cursor_back_mut(); + for _ in 0..offset_from_end { + cursor.move_prev(); + } + cursor.remove_current().unwrap() + } + } + + /// Creates an iterator which uses a closure to determine if an element should be removed. + /// + /// If the closure returns true, then the element is removed and yielded. + /// If the closure returns false, the element will remain in the list and will not be yielded + /// by the iterator. + /// + /// Note that `drain_filter` lets you mutate every element in the filter closure, regardless of + /// whether you choose to keep or remove it. + /// + /// # Examples + /// + /// Splitting a list into evens and odds, reusing the original list: + /// + /// ``` + /// #![feature(drain_filter)] + /// use std::collections::LinkedList; + /// + /// let mut numbers: LinkedList<u32> = LinkedList::new(); + /// numbers.extend(&[1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15]); + /// + /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<LinkedList<_>>(); + /// let odds = numbers; + /// + /// assert_eq!(evens.into_iter().collect::<Vec<_>>(), vec![2, 4, 6, 8, 14]); + /// assert_eq!(odds.into_iter().collect::<Vec<_>>(), vec![1, 3, 5, 9, 11, 13, 15]); + /// ``` + #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] + pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F> + where + F: FnMut(&mut T) -> bool, + { + // avoid borrow issues. + let it = self.head; + let old_len = self.len; + + DrainFilter { list: self, it, pred: filter, idx: 0, old_len } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<#[may_dangle] T> Drop for LinkedList<T> { + fn drop(&mut self) { + struct DropGuard<'a, T>(&'a mut LinkedList<T>); + + impl<'a, T> Drop for DropGuard<'a, T> { + fn drop(&mut self) { + // Continue the same loop we do below. This only runs when a destructor has + // panicked. If another one panics this will abort. + while self.0.pop_front_node().is_some() {} + } + } + + while let Some(node) = self.pop_front_node() { + let guard = DropGuard(self); + drop(node); + mem::forget(guard); + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> Iterator for Iter<'a, T> { + type Item = &'a T; + + #[inline] + fn next(&mut self) -> Option<&'a T> { + if self.len == 0 { + None + } else { + self.head.map(|node| unsafe { + // Need an unbound lifetime to get 'a + let node = &*node.as_ptr(); + self.len -= 1; + self.head = node.next; + &node.element + }) + } + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + (self.len, Some(self.len)) + } + + #[inline] + fn last(mut self) -> Option<&'a T> { + self.next_back() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> DoubleEndedIterator for Iter<'a, T> { + #[inline] + fn next_back(&mut self) -> Option<&'a T> { + if self.len == 0 { + None + } else { + self.tail.map(|node| unsafe { + // Need an unbound lifetime to get 'a + let node = &*node.as_ptr(); + self.len -= 1; + self.tail = node.prev; + &node.element + }) + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> ExactSizeIterator for Iter<'_, T> {} + +#[stable(feature = "fused", since = "1.26.0")] +impl<T> FusedIterator for Iter<'_, T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> Iterator for IterMut<'a, T> { + type Item = &'a mut T; + + #[inline] + fn next(&mut self) -> Option<&'a mut T> { + if self.len == 0 { + None + } else { + self.head.map(|node| unsafe { + // Need an unbound lifetime to get 'a + let node = &mut *node.as_ptr(); + self.len -= 1; + self.head = node.next; + &mut node.element + }) + } + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + (self.len, Some(self.len)) + } + + #[inline] + fn last(mut self) -> Option<&'a mut T> { + self.next_back() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> DoubleEndedIterator for IterMut<'a, T> { + #[inline] + fn next_back(&mut self) -> Option<&'a mut T> { + if self.len == 0 { + None + } else { + self.tail.map(|node| unsafe { + // Need an unbound lifetime to get 'a + let node = &mut *node.as_ptr(); + self.len -= 1; + self.tail = node.prev; + &mut node.element + }) + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> ExactSizeIterator for IterMut<'_, T> {} + +#[stable(feature = "fused", since = "1.26.0")] +impl<T> FusedIterator for IterMut<'_, T> {} + +/// A cursor over a `LinkedList`. +/// +/// A `Cursor` is like an iterator, except that it can freely seek back-and-forth. +/// +/// Cursors always rest between two elements in the list, and index in a logically circular way. +/// To accommodate this, there is a "ghost" non-element that yields `None` between the head and +/// tail of the list. +/// +/// When created, cursors start at the front of the list, or the "ghost" non-element if the list is empty. +#[unstable(feature = "linked_list_cursors", issue = "58533")] +pub struct Cursor<'a, T: 'a> { + index: usize, + current: Option<NonNull<Node<T>>>, + list: &'a LinkedList<T>, +} + +#[unstable(feature = "linked_list_cursors", issue = "58533")] +impl<T> Clone for Cursor<'_, T> { + fn clone(&self) -> Self { + let Cursor { index, current, list } = *self; + Cursor { index, current, list } + } +} + +#[unstable(feature = "linked_list_cursors", issue = "58533")] +impl<T: fmt::Debug> fmt::Debug for Cursor<'_, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("Cursor").field(&self.list).field(&self.index()).finish() + } +} + +/// A cursor over a `LinkedList` with editing operations. +/// +/// A `Cursor` is like an iterator, except that it can freely seek back-and-forth, and can +/// safely mutate the list during iteration. This is because the lifetime of its yielded +/// references is tied to its own lifetime, instead of just the underlying list. This means +/// cursors cannot yield multiple elements at once. +/// +/// Cursors always rest between two elements in the list, and index in a logically circular way. +/// To accommodate this, there is a "ghost" non-element that yields `None` between the head and +/// tail of the list. +#[unstable(feature = "linked_list_cursors", issue = "58533")] +pub struct CursorMut<'a, T: 'a> { + index: usize, + current: Option<NonNull<Node<T>>>, + list: &'a mut LinkedList<T>, +} + +#[unstable(feature = "linked_list_cursors", issue = "58533")] +impl<T: fmt::Debug> fmt::Debug for CursorMut<'_, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("CursorMut").field(&self.list).field(&self.index()).finish() + } +} + +impl<'a, T> Cursor<'a, T> { + /// Returns the cursor position index within the `LinkedList`. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn index(&self) -> Option<usize> { + let _ = self.current?; + Some(self.index) + } + + /// Moves the cursor to the next element of the `LinkedList`. + /// + /// If the cursor is pointing to the "ghost" non-element then this will move it to + /// the first element of the `LinkedList`. If it is pointing to the last + /// element of the `LinkedList` then this will move it to the "ghost" non-element. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn move_next(&mut self) { + match self.current.take() { + // We had no current element; the cursor was sitting at the start position + // Next element should be the head of the list + None => { + self.current = self.list.head; + self.index = 0; + } + // We had a previous element, so let's go to its next + Some(current) => unsafe { + self.current = current.as_ref().next; + self.index += 1; + }, + } + } + + /// Moves the cursor to the previous element of the `LinkedList`. + /// + /// If the cursor is pointing to the "ghost" non-element then this will move it to + /// the last element of the `LinkedList`. If it is pointing to the first + /// element of the `LinkedList` then this will move it to the "ghost" non-element. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn move_prev(&mut self) { + match self.current.take() { + // No current. We're at the start of the list. Yield None and jump to the end. + None => { + self.current = self.list.tail; + self.index = self.list.len().checked_sub(1).unwrap_or(0); + } + // Have a prev. Yield it and go to the previous element. + Some(current) => unsafe { + self.current = current.as_ref().prev; + self.index = self.index.checked_sub(1).unwrap_or_else(|| self.list.len()); + }, + } + } + + /// Returns a reference to the element that the cursor is currently + /// pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn current(&self) -> Option<&'a T> { + unsafe { self.current.map(|current| &(*current.as_ptr()).element) } + } + + /// Returns a reference to the next element. + /// + /// If the cursor is pointing to the "ghost" non-element then this returns + /// the first element of the `LinkedList`. If it is pointing to the last + /// element of the `LinkedList` then this returns `None`. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn peek_next(&self) -> Option<&'a T> { + unsafe { + let next = match self.current { + None => self.list.head, + Some(current) => current.as_ref().next, + }; + next.map(|next| &(*next.as_ptr()).element) + } + } + + /// Returns a reference to the previous element. + /// + /// If the cursor is pointing to the "ghost" non-element then this returns + /// the last element of the `LinkedList`. If it is pointing to the first + /// element of the `LinkedList` then this returns `None`. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn peek_prev(&self) -> Option<&'a T> { + unsafe { + let prev = match self.current { + None => self.list.tail, + Some(current) => current.as_ref().prev, + }; + prev.map(|prev| &(*prev.as_ptr()).element) + } + } + + /// Provides a reference to the front element of the cursor's parent list, + /// or None if the list is empty. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn front(&self) -> Option<&'a T> { + self.list.front() + } + + /// Provides a reference to the back element of the cursor's parent list, + /// or None if the list is empty. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn back(&self) -> Option<&'a T> { + self.list.back() + } +} + +impl<'a, T> CursorMut<'a, T> { + /// Returns the cursor position index within the `LinkedList`. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn index(&self) -> Option<usize> { + let _ = self.current?; + Some(self.index) + } + + /// Moves the cursor to the next element of the `LinkedList`. + /// + /// If the cursor is pointing to the "ghost" non-element then this will move it to + /// the first element of the `LinkedList`. If it is pointing to the last + /// element of the `LinkedList` then this will move it to the "ghost" non-element. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn move_next(&mut self) { + match self.current.take() { + // We had no current element; the cursor was sitting at the start position + // Next element should be the head of the list + None => { + self.current = self.list.head; + self.index = 0; + } + // We had a previous element, so let's go to its next + Some(current) => unsafe { + self.current = current.as_ref().next; + self.index += 1; + }, + } + } + + /// Moves the cursor to the previous element of the `LinkedList`. + /// + /// If the cursor is pointing to the "ghost" non-element then this will move it to + /// the last element of the `LinkedList`. If it is pointing to the first + /// element of the `LinkedList` then this will move it to the "ghost" non-element. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn move_prev(&mut self) { + match self.current.take() { + // No current. We're at the start of the list. Yield None and jump to the end. + None => { + self.current = self.list.tail; + self.index = self.list.len().checked_sub(1).unwrap_or(0); + } + // Have a prev. Yield it and go to the previous element. + Some(current) => unsafe { + self.current = current.as_ref().prev; + self.index = self.index.checked_sub(1).unwrap_or_else(|| self.list.len()); + }, + } + } + + /// Returns a reference to the element that the cursor is currently + /// pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn current(&mut self) -> Option<&mut T> { + unsafe { self.current.map(|current| &mut (*current.as_ptr()).element) } + } + + /// Returns a reference to the next element. + /// + /// If the cursor is pointing to the "ghost" non-element then this returns + /// the first element of the `LinkedList`. If it is pointing to the last + /// element of the `LinkedList` then this returns `None`. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn peek_next(&mut self) -> Option<&mut T> { + unsafe { + let next = match self.current { + None => self.list.head, + Some(current) => current.as_ref().next, + }; + next.map(|next| &mut (*next.as_ptr()).element) + } + } + + /// Returns a reference to the previous element. + /// + /// If the cursor is pointing to the "ghost" non-element then this returns + /// the last element of the `LinkedList`. If it is pointing to the first + /// element of the `LinkedList` then this returns `None`. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn peek_prev(&mut self) -> Option<&mut T> { + unsafe { + let prev = match self.current { + None => self.list.tail, + Some(current) => current.as_ref().prev, + }; + prev.map(|prev| &mut (*prev.as_ptr()).element) + } + } + + /// Returns a read-only cursor pointing to the current element. + /// + /// The lifetime of the returned `Cursor` is bound to that of the + /// `CursorMut`, which means it cannot outlive the `CursorMut` and that the + /// `CursorMut` is frozen for the lifetime of the `Cursor`. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn as_cursor(&self) -> Cursor<'_, T> { + Cursor { list: self.list, current: self.current, index: self.index } + } +} + +// Now the list editing operations + +impl<'a, T> CursorMut<'a, T> { + /// Inserts a new element into the `LinkedList` after the current one. + /// + /// If the cursor is pointing at the "ghost" non-element then the new element is + /// inserted at the front of the `LinkedList`. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn insert_after(&mut self, item: T) { + unsafe { + let spliced_node = Box::leak(Box::new(Node::new(item))).into(); + let node_next = match self.current { + None => self.list.head, + Some(node) => node.as_ref().next, + }; + self.list.splice_nodes(self.current, node_next, spliced_node, spliced_node, 1); + if self.current.is_none() { + // The "ghost" non-element's index has changed. + self.index = self.list.len; + } + } + } + + /// Inserts a new element into the `LinkedList` before the current one. + /// + /// If the cursor is pointing at the "ghost" non-element then the new element is + /// inserted at the end of the `LinkedList`. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn insert_before(&mut self, item: T) { + unsafe { + let spliced_node = Box::leak(Box::new(Node::new(item))).into(); + let node_prev = match self.current { + None => self.list.tail, + Some(node) => node.as_ref().prev, + }; + self.list.splice_nodes(node_prev, self.current, spliced_node, spliced_node, 1); + self.index += 1; + } + } + + /// Removes the current element from the `LinkedList`. + /// + /// The element that was removed is returned, and the cursor is + /// moved to point to the next element in the `LinkedList`. + /// + /// If the cursor is currently pointing to the "ghost" non-element then no element + /// is removed and `None` is returned. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn remove_current(&mut self) -> Option<T> { + let unlinked_node = self.current?; + unsafe { + self.current = unlinked_node.as_ref().next; + self.list.unlink_node(unlinked_node); + let unlinked_node = Box::from_raw(unlinked_node.as_ptr()); + Some(unlinked_node.element) + } + } + + /// Removes the current element from the `LinkedList` without deallocating the list node. + /// + /// The node that was removed is returned as a new `LinkedList` containing only this node. + /// The cursor is moved to point to the next element in the current `LinkedList`. + /// + /// If the cursor is currently pointing to the "ghost" non-element then no element + /// is removed and `None` is returned. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn remove_current_as_list(&mut self) -> Option<LinkedList<T>> { + let mut unlinked_node = self.current?; + unsafe { + self.current = unlinked_node.as_ref().next; + self.list.unlink_node(unlinked_node); + + unlinked_node.as_mut().prev = None; + unlinked_node.as_mut().next = None; + Some(LinkedList { + head: Some(unlinked_node), + tail: Some(unlinked_node), + len: 1, + marker: PhantomData, + }) + } + } + + /// Inserts the elements from the given `LinkedList` after the current one. + /// + /// If the cursor is pointing at the "ghost" non-element then the new elements are + /// inserted at the start of the `LinkedList`. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn splice_after(&mut self, list: LinkedList<T>) { + unsafe { + let (splice_head, splice_tail, splice_len) = match list.detach_all_nodes() { + Some(parts) => parts, + _ => return, + }; + let node_next = match self.current { + None => self.list.head, + Some(node) => node.as_ref().next, + }; + self.list.splice_nodes(self.current, node_next, splice_head, splice_tail, splice_len); + if self.current.is_none() { + // The "ghost" non-element's index has changed. + self.index = self.list.len; + } + } + } + + /// Inserts the elements from the given `LinkedList` before the current one. + /// + /// If the cursor is pointing at the "ghost" non-element then the new elements are + /// inserted at the end of the `LinkedList`. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn splice_before(&mut self, list: LinkedList<T>) { + unsafe { + let (splice_head, splice_tail, splice_len) = match list.detach_all_nodes() { + Some(parts) => parts, + _ => return, + }; + let node_prev = match self.current { + None => self.list.tail, + Some(node) => node.as_ref().prev, + }; + self.list.splice_nodes(node_prev, self.current, splice_head, splice_tail, splice_len); + self.index += splice_len; + } + } + + /// Splits the list into two after the current element. This will return a + /// new list consisting of everything after the cursor, with the original + /// list retaining everything before. + /// + /// If the cursor is pointing at the "ghost" non-element then the entire contents + /// of the `LinkedList` are moved. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn split_after(&mut self) -> LinkedList<T> { + let split_off_idx = if self.index == self.list.len { 0 } else { self.index + 1 }; + if self.index == self.list.len { + // The "ghost" non-element's index has changed to 0. + self.index = 0; + } + unsafe { self.list.split_off_after_node(self.current, split_off_idx) } + } + + /// Splits the list into two before the current element. This will return a + /// new list consisting of everything before the cursor, with the original + /// list retaining everything after. + /// + /// If the cursor is pointing at the "ghost" non-element then the entire contents + /// of the `LinkedList` are moved. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn split_before(&mut self) -> LinkedList<T> { + let split_off_idx = self.index; + self.index = 0; + unsafe { self.list.split_off_before_node(self.current, split_off_idx) } + } + + /// Appends an element to the front of the cursor's parent list. The node + /// that the cursor points to is unchanged, even if it is the "ghost" node. + /// + /// This operation should compute in *O*(1) time. + // `push_front` continues to point to "ghost" when it addes a node to mimic + // the behavior of `insert_before` on an empty list. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn push_front(&mut self, elt: T) { + // Safety: We know that `push_front` does not change the position in + // memory of other nodes. This ensures that `self.current` remains + // valid. + self.list.push_front(elt); + self.index += 1; + } + + /// Appends an element to the back of the cursor's parent list. The node + /// that the cursor points to is unchanged, even if it is the "ghost" node. + /// + /// This operation should compute in *O*(1) time. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn push_back(&mut self, elt: T) { + // Safety: We know that `push_back` does not change the position in + // memory of other nodes. This ensures that `self.current` remains + // valid. + self.list.push_back(elt); + if self.current().is_none() { + // The index of "ghost" is the length of the list, so we just need + // to increment self.index to reflect the new length of the list. + self.index += 1; + } + } + + /// Removes the first element from the cursor's parent list and returns it, + /// or None if the list is empty. The element the cursor points to remains + /// unchanged, unless it was pointing to the front element. In that case, it + /// points to the new front element. + /// + /// This operation should compute in *O*(1) time. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn pop_front(&mut self) -> Option<T> { + // We can't check if current is empty, we must check the list directly. + // It is possible for `self.current == None` and the list to be + // non-empty. + if self.list.is_empty() { + None + } else { + // We can't point to the node that we pop. Copying the behavior of + // `remove_current`, we move on the the next node in the sequence. + // If the list is of length 1 then we end pointing to the "ghost" + // node at index 0, which is expected. + if self.list.head == self.current { + self.move_next(); + } else { + self.index -= 1; + } + self.list.pop_front() + } + } + + /// Removes the last element from the cursor's parent list and returns it, + /// or None if the list is empty. The element the cursor points to remains + /// unchanged, unless it was pointing to the back element. In that case, it + /// points to the "ghost" element. + /// + /// This operation should compute in *O*(1) time. + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn pop_back(&mut self) -> Option<T> { + if self.list.is_empty() { + None + } else { + if self.list.tail == self.current { + // The index now reflects the length of the list. It was the + // length of the list minus 1, but now the list is 1 smaller. No + // change is needed for `index`. + self.current = None; + } else if self.current.is_none() { + self.index = self.list.len - 1; + } + self.list.pop_back() + } + } + + /// Provides a reference to the front element of the cursor's parent list, + /// or None if the list is empty. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn front(&self) -> Option<&T> { + self.list.front() + } + + /// Provides a mutable reference to the front element of the cursor's + /// parent list, or None if the list is empty. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn front_mut(&mut self) -> Option<&mut T> { + self.list.front_mut() + } + + /// Provides a reference to the back element of the cursor's parent list, + /// or None if the list is empty. + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn back(&self) -> Option<&T> { + self.list.back() + } + + /// Provides a mutable reference to back element of the cursor's parent + /// list, or `None` if the list is empty. + /// + /// # Examples + /// Building and mutating a list with a cursor, then getting the back element: + /// ``` + /// #![feature(linked_list_cursors)] + /// use std::collections::LinkedList; + /// let mut dl = LinkedList::new(); + /// dl.push_front(3); + /// dl.push_front(2); + /// dl.push_front(1); + /// let mut cursor = dl.cursor_front_mut(); + /// *cursor.current().unwrap() = 99; + /// *cursor.back_mut().unwrap() = 0; + /// let mut contents = dl.into_iter(); + /// assert_eq!(contents.next(), Some(99)); + /// assert_eq!(contents.next(), Some(2)); + /// assert_eq!(contents.next(), Some(0)); + /// assert_eq!(contents.next(), None); + /// ``` + #[must_use] + #[unstable(feature = "linked_list_cursors", issue = "58533")] + pub fn back_mut(&mut self) -> Option<&mut T> { + self.list.back_mut() + } +} + +/// An iterator produced by calling `drain_filter` on LinkedList. +#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] +pub struct DrainFilter<'a, T: 'a, F: 'a> +where + F: FnMut(&mut T) -> bool, +{ + list: &'a mut LinkedList<T>, + it: Option<NonNull<Node<T>>>, + pred: F, + idx: usize, + old_len: usize, +} + +#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] +impl<T, F> Iterator for DrainFilter<'_, T, F> +where + F: FnMut(&mut T) -> bool, +{ + type Item = T; + + fn next(&mut self) -> Option<T> { + while let Some(mut node) = self.it { + unsafe { + self.it = node.as_ref().next; + self.idx += 1; + + if (self.pred)(&mut node.as_mut().element) { + // `unlink_node` is okay with aliasing `element` references. + self.list.unlink_node(node); + return Some(Box::from_raw(node.as_ptr()).element); + } + } + } + + None + } + + fn size_hint(&self) -> (usize, Option<usize>) { + (0, Some(self.old_len - self.idx)) + } +} + +#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] +impl<T, F> Drop for DrainFilter<'_, T, F> +where + F: FnMut(&mut T) -> bool, +{ + fn drop(&mut self) { + struct DropGuard<'r, 'a, T, F>(&'r mut DrainFilter<'a, T, F>) + where + F: FnMut(&mut T) -> bool; + + impl<'r, 'a, T, F> Drop for DropGuard<'r, 'a, T, F> + where + F: FnMut(&mut T) -> bool, + { + fn drop(&mut self) { + self.0.for_each(drop); + } + } + + while let Some(item) = self.next() { + let guard = DropGuard(self); + drop(item); + mem::forget(guard); + } + } +} + +#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")] +impl<T: fmt::Debug, F> fmt::Debug for DrainFilter<'_, T, F> +where + F: FnMut(&mut T) -> bool, +{ + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("DrainFilter").field(&self.list).finish() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Iterator for IntoIter<T> { + type Item = T; + + #[inline] + fn next(&mut self) -> Option<T> { + self.list.pop_front() + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + (self.list.len, Some(self.list.len)) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> DoubleEndedIterator for IntoIter<T> { + #[inline] + fn next_back(&mut self) -> Option<T> { + self.list.pop_back() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> ExactSizeIterator for IntoIter<T> {} + +#[stable(feature = "fused", since = "1.26.0")] +impl<T> FusedIterator for IntoIter<T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> FromIterator<T> for LinkedList<T> { + fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self { + let mut list = Self::new(); + list.extend(iter); + list + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> IntoIterator for LinkedList<T> { + type Item = T; + type IntoIter = IntoIter<T>; + + /// Consumes the list into an iterator yielding elements by value. + #[inline] + fn into_iter(self) -> IntoIter<T> { + IntoIter { list: self } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> IntoIterator for &'a LinkedList<T> { + 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> IntoIterator for &'a mut LinkedList<T> { + type Item = &'a mut T; + type IntoIter = IterMut<'a, T>; + + fn into_iter(self) -> IterMut<'a, T> { + self.iter_mut() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Extend<T> for LinkedList<T> { + fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) { + <Self as SpecExtend<I>>::spec_extend(self, iter); + } + + #[inline] + fn extend_one(&mut self, elem: T) { + self.push_back(elem); + } +} + +impl<I: IntoIterator> SpecExtend<I> for LinkedList<I::Item> { + default fn spec_extend(&mut self, iter: I) { + iter.into_iter().for_each(move |elt| self.push_back(elt)); + } +} + +impl<T> SpecExtend<LinkedList<T>> for LinkedList<T> { + fn spec_extend(&mut self, ref mut other: LinkedList<T>) { + self.append(other); + } +} + +#[stable(feature = "extend_ref", since = "1.2.0")] +impl<'a, T: 'a + Copy> Extend<&'a T> for LinkedList<T> { + fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) { + self.extend(iter.into_iter().cloned()); + } + + #[inline] + fn extend_one(&mut self, &elem: &'a T) { + self.push_back(elem); + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: PartialEq> PartialEq for LinkedList<T> { + fn eq(&self, other: &Self) -> bool { + self.len() == other.len() && self.iter().eq(other) + } + + fn ne(&self, other: &Self) -> bool { + self.len() != other.len() || self.iter().ne(other) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Eq> Eq for LinkedList<T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: PartialOrd> PartialOrd for LinkedList<T> { + fn partial_cmp(&self, other: &Self) -> Option<Ordering> { + self.iter().partial_cmp(other) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Ord> Ord for LinkedList<T> { + #[inline] + fn cmp(&self, other: &Self) -> Ordering { + self.iter().cmp(other) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Clone> Clone for LinkedList<T> { + fn clone(&self) -> Self { + self.iter().cloned().collect() + } + + fn clone_from(&mut self, other: &Self) { + let mut iter_other = other.iter(); + if self.len() > other.len() { + self.split_off(other.len()); + } + for (elem, elem_other) in self.iter_mut().zip(&mut iter_other) { + elem.clone_from(elem_other); + } + if !iter_other.is_empty() { + self.extend(iter_other.cloned()); + } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: fmt::Debug> fmt::Debug for LinkedList<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_list().entries(self).finish() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Hash> Hash for LinkedList<T> { + fn hash<H: Hasher>(&self, state: &mut H) { + state.write_length_prefix(self.len()); + for elt in self { + elt.hash(state); + } + } +} + +#[stable(feature = "std_collections_from_array", since = "1.56.0")] +impl<T, const N: usize> From<[T; N]> for LinkedList<T> { + /// Converts a `[T; N]` into a `LinkedList<T>`. + /// + /// ``` + /// use std::collections::LinkedList; + /// + /// let list1 = LinkedList::from([1, 2, 3, 4]); + /// let list2: LinkedList<_> = [1, 2, 3, 4].into(); + /// assert_eq!(list1, list2); + /// ``` + fn from(arr: [T; N]) -> Self { + Self::from_iter(arr) + } +} + +// Ensure that `LinkedList` and its read-only iterators are covariant in their type parameters. +#[allow(dead_code)] +fn assert_covariance() { + fn a<'a>(x: LinkedList<&'static str>) -> LinkedList<&'a str> { + x + } + fn b<'i, 'a>(x: Iter<'i, &'static str>) -> Iter<'i, &'a str> { + x + } + fn c<'a>(x: IntoIter<&'static str>) -> IntoIter<&'a str> { + x + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<T: Send> Send for LinkedList<T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<T: Sync> Sync for LinkedList<T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<T: Sync> Send for Iter<'_, T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<T: Sync> Sync for Iter<'_, T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<T: Send> Send for IterMut<'_, T> {} + +#[stable(feature = "rust1", since = "1.0.0")] +unsafe impl<T: Sync> Sync for IterMut<'_, T> {} + +#[unstable(feature = "linked_list_cursors", issue = "58533")] +unsafe impl<T: Sync> Send for Cursor<'_, T> {} + +#[unstable(feature = "linked_list_cursors", issue = "58533")] +unsafe impl<T: Sync> Sync for Cursor<'_, T> {} + +#[unstable(feature = "linked_list_cursors", issue = "58533")] +unsafe impl<T: Send> Send for CursorMut<'_, T> {} + +#[unstable(feature = "linked_list_cursors", issue = "58533")] +unsafe impl<T: Sync> Sync for CursorMut<'_, T> {} |