src/libcollections/linked_list.rs

   1 // Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! A doubly-linked list with owned nodes.
  12 //!
  13 //! The `LinkedList` allows pushing and popping elements at either end and is thus
  14 //! efficiently usable as a double-ended queue.
  15
  16 // LinkedList is constructed like a singly-linked list over the field `next`.
  17 // including the last link being None; each Node owns its `next` field.
  18 //
  19 // Backlinks over LinkedList::prev are raw pointers that form a full chain in
  20 // the reverse direction.
  21
  22 #![stable(feature = "rust1", since = "1.0.0")]
  23
  24 use core::prelude::*;
  25
  26 use alloc::boxed::Box;
  27 use core::cmp::Ordering;
  28 use core::fmt;
  29 use core::hash::{Hasher, Hash};
  30 use core::iter::{self, FromIterator};
  31 use core::mem;
  32 use core::ptr;
  33
  34 /// A doubly-linked list.
  35 #[stable(feature = "rust1", since = "1.0.0")]
  36 pub struct LinkedList<T> {
  37     length: usize,
  38     list_head: Link<T>,
  39     list_tail: Rawlink<Node<T>>,
  40 }
  41
  42 type Link<T> = Option<Box<Node<T>>>;
  43
  44 struct Rawlink<T> {
  45     p: *mut T,
  46 }
  47
  48 impl<T> Copy for Rawlink<T> {}
  49 unsafe impl<T:Send> Send for Rawlink<T> {}
  50 unsafe impl<T:Sync> Sync for Rawlink<T> {}
  51
  52 struct Node<T> {
  53     next: Link<T>,
  54     prev: Rawlink<Node<T>>,
  55     value: T,
  56 }
  57
  58 /// An iterator over references to the items of a `LinkedList`.
  59 #[stable(feature = "rust1", since = "1.0.0")]
  60 pub struct Iter<'a, T:'a> {
  61     head: &'a Link<T>,
  62     tail: Rawlink<Node<T>>,
  63     nelem: usize,
  64 }
  65
  66 // FIXME #19839: deriving is too aggressive on the bounds (T doesn't need to be Clone).
  67 #[stable(feature = "rust1", since = "1.0.0")]
  68 impl<'a, T> Clone for Iter<'a, T> {
  69     fn clone(&self) -> Iter<'a, T> {
  70         Iter {
  71             head: self.head.clone(),
  72             tail: self.tail,
  73             nelem: self.nelem,
  74         }
  75     }
  76 }
  77
  78 /// An iterator over mutable references to the items of a `LinkedList`.
  79 #[stable(feature = "rust1", since = "1.0.0")]
  80 pub struct IterMut<'a, T:'a> {
  81     list: &'a mut LinkedList<T>,
  82     head: Rawlink<Node<T>>,
  83     tail: Rawlink<Node<T>>,
  84     nelem: usize,
  85 }
  86
  87 /// An iterator over mutable references to the items of a `LinkedList`.
  88 #[derive(Clone)]
  89 #[stable(feature = "rust1", since = "1.0.0")]
  90 pub struct IntoIter<T> {
  91     list: LinkedList<T>
  92 }
  93
  94 /// Rawlink is a type like Option<T> but for holding a raw pointer
  95 impl<T> Rawlink<T> {
  96     /// Like Option::None for Rawlink
  97     fn none() -> Rawlink<T> {
  98         Rawlink{p: ptr::null_mut()}
  99     }
 100
 101     /// Like Option::Some for Rawlink
 102     fn some(n: &mut T) -> Rawlink<T> {
 103         Rawlink{p: n}
 104     }
 105
 106     /// Convert the `Rawlink` into an Option value
 107     fn resolve_immut<'a>(&self) -> Option<&'a T> {
 108         unsafe {
 109             mem::transmute(self.p.as_ref())
 110         }
 111     }
 112
 113     /// Convert the `Rawlink` into an Option value
 114     fn resolve<'a>(&mut self) -> Option<&'a mut T> {
 115         if self.p.is_null() {
 116             None
 117         } else {
 118             Some(unsafe { mem::transmute(self.p) })
 119         }
 120     }
 121
 122     /// Return the `Rawlink` and replace with `Rawlink::none()`
 123     fn take(&mut self) -> Rawlink<T> {
 124         mem::replace(self, Rawlink::none())
 125     }
 126 }
 127
 128 impl<T> Clone for Rawlink<T> {
 129     #[inline]
 130     fn clone(&self) -> Rawlink<T> {
 131         Rawlink{p: self.p}
 132     }
 133 }
 134
 135 impl<T> Node<T> {
 136     fn new(v: T) -> Node<T> {
 137         Node{value: v, next: None, prev: Rawlink::none()}
 138     }
 139 }
 140
 141 /// Set the .prev field on `next`, then return `Some(next)`
 142 fn link_with_prev<T>(mut next: Box<Node<T>>, prev: Rawlink<Node<T>>)
 143                   -> Link<T> {
 144     next.prev = prev;
 145     Some(next)
 146 }
 147
 148 // private methods
 149 impl<T> LinkedList<T> {
 150     /// Add a Node first in the list
 151     #[inline]
 152     fn push_front_node(&mut self, mut new_head: Box<Node<T>>) {
 153         match self.list_head {
 154             None => {
 155                 self.list_tail = Rawlink::some(&mut *new_head);
 156                 self.list_head = link_with_prev(new_head, Rawlink::none());
 157             }
 158             Some(ref mut head) => {
 159                 new_head.prev = Rawlink::none();
 160                 head.prev = Rawlink::some(&mut *new_head);
 161                 mem::swap(head, &mut new_head);
 162                 head.next = Some(new_head);
 163             }
 164         }
 165         self.length += 1;
 166     }
 167
 168     /// Remove the first Node and return it, or None if the list is empty
 169     #[inline]
 170     fn pop_front_node(&mut self) -> Option<Box<Node<T>>> {
 171         self.list_head.take().map(|mut front_node| {
 172             self.length -= 1;
 173             match front_node.next.take() {
 174                 Some(node) => self.list_head = link_with_prev(node, Rawlink::none()),
 175                 None => self.list_tail = Rawlink::none()
 176             }
 177             front_node
 178         })
 179     }
 180
 181     /// Add a Node last in the list
 182     #[inline]
 183     fn push_back_node(&mut self, mut new_tail: Box<Node<T>>) {
 184         match self.list_tail.resolve() {
 185             None => return self.push_front_node(new_tail),
 186             Some(tail) => {
 187                 self.list_tail = Rawlink::some(&mut *new_tail);
 188                 tail.next = link_with_prev(new_tail, Rawlink::some(tail));
 189             }
 190         }
 191         self.length += 1;
 192     }
 193
 194     /// Remove the last Node and return it, or None if the list is empty
 195     #[inline]
 196     fn pop_back_node(&mut self) -> Option<Box<Node<T>>> {
 197         self.list_tail.resolve().map_or(None, |tail| {
 198             self.length -= 1;
 199             self.list_tail = tail.prev;
 200             match tail.prev.resolve() {
 201                 None => self.list_head.take(),
 202                 Some(tail_prev) => tail_prev.next.take()
 203             }
 204         })
 205     }
 206 }
 207
 208 #[stable(feature = "rust1", since = "1.0.0")]
 209 impl<T> Default for LinkedList<T> {
 210     #[inline]
 211     #[stable(feature = "rust1", since = "1.0.0")]
 212     fn default() -> LinkedList<T> { LinkedList::new() }
 213 }
 214
 215 impl<T> LinkedList<T> {
 216     /// Creates an empty `LinkedList`.
 217     #[inline]
 218     #[stable(feature = "rust1", since = "1.0.0")]
 219     pub fn new() -> LinkedList<T> {
 220         LinkedList{list_head: None, list_tail: Rawlink::none(), length: 0}
 221     }
 222
 223     /// Moves all elements from `other` to the end of the list.
 224     ///
 225     /// This reuses all the nodes from `other` and moves them into `self`. After
 226     /// this operation, `other` becomes empty.
 227     ///
 228     /// This operation should compute in O(1) time and O(1) memory.
 229     ///
 230     /// # Examples
 231     ///
 232     /// ```
 233     /// # #![feature(collections)]
 234     /// use std::collections::LinkedList;
 235     ///
 236     /// let mut a = LinkedList::new();
 237     /// let mut b = LinkedList::new();
 238     /// a.push_back(1);
 239     /// a.push_back(2);
 240     /// b.push_back(3);
 241     /// b.push_back(4);
 242     ///
 243     /// a.append(&mut b);
 244     ///
 245     /// for e in a.iter() {
 246     ///     println!("{}", e); // prints 1, then 2, then 3, then 4
 247     /// }
 248     /// println!("{}", b.len()); // prints 0
 249     /// ```
 250     #[stable(feature = "rust1", since = "1.0.0")]
 251     pub fn append(&mut self, other: &mut LinkedList<T>) {
 252         match self.list_tail.resolve() {
 253             None => {
 254                 self.length = other.length;
 255                 self.list_head = other.list_head.take();
 256                 self.list_tail = other.list_tail.take();
 257             },
 258             Some(tail) => {
 259                 // Carefully empty `other`.
 260                 let o_tail = other.list_tail.take();
 261                 let o_length = other.length;
 262                 match other.list_head.take() {
 263                     None => return,
 264                     Some(node) => {
 265                         tail.next = link_with_prev(node, self.list_tail);
 266                         self.list_tail = o_tail;
 267                         self.length += o_length;
 268                     }
 269                 }
 270             }
 271         }
 272         other.length = 0;
 273     }
 274
 275     /// Provides a forward iterator.
 276     #[inline]
 277     #[stable(feature = "rust1", since = "1.0.0")]
 278     pub fn iter(&self) -> Iter<T> {
 279         Iter{nelem: self.len(), head: &self.list_head, tail: self.list_tail}
 280     }
 281
 282     /// Provides a forward iterator with mutable references.
 283     #[inline]
 284     #[stable(feature = "rust1", since = "1.0.0")]
 285     pub fn iter_mut(&mut self) -> IterMut<T> {
 286         let head_raw = match self.list_head {
 287             Some(ref mut h) => Rawlink::some(&mut **h),
 288             None => Rawlink::none(),
 289         };
 290         IterMut{
 291             nelem: self.len(),
 292             head: head_raw,
 293             tail: self.list_tail,
 294             list: self
 295         }
 296     }
 297
 298     /// Returns `true` if the `LinkedList` is empty.
 299     ///
 300     /// This operation should compute in O(1) time.
 301     ///
 302     /// # Examples
 303     ///
 304     /// ```
 305     /// use std::collections::LinkedList;
 306     ///
 307     /// let mut dl = LinkedList::new();
 308     /// assert!(dl.is_empty());
 309     ///
 310     /// dl.push_front("foo");
 311     /// assert!(!dl.is_empty());
 312     /// ```
 313     #[inline]
 314     #[stable(feature = "rust1", since = "1.0.0")]
 315     pub fn is_empty(&self) -> bool {
 316         self.list_head.is_none()
 317     }
 318
 319     /// Returns the length of the `LinkedList`.
 320     ///
 321     /// This operation should compute in O(1) time.
 322     ///
 323     /// # Examples
 324     ///
 325     /// ```
 326     /// use std::collections::LinkedList;
 327     ///
 328     /// let mut dl = LinkedList::new();
 329     ///
 330     /// dl.push_front(2);
 331     /// assert_eq!(dl.len(), 1);
 332     ///
 333     /// dl.push_front(1);
 334     /// assert_eq!(dl.len(), 2);
 335     ///
 336     /// dl.push_back(3);
 337     /// assert_eq!(dl.len(), 3);
 338     ///
 339     /// ```
 340     #[inline]
 341     #[stable(feature = "rust1", since = "1.0.0")]
 342     pub fn len(&self) -> usize {
 343         self.length
 344     }
 345
 346     /// Removes all elements from the `LinkedList`.
 347     ///
 348     /// This operation should compute in O(n) time.
 349     ///
 350     /// # Examples
 351     ///
 352     /// ```
 353     /// use std::collections::LinkedList;
 354     ///
 355     /// let mut dl = LinkedList::new();
 356     ///
 357     /// dl.push_front(2);
 358     /// dl.push_front(1);
 359     /// assert_eq!(dl.len(), 2);
 360     /// assert_eq!(dl.front(), Some(&1));
 361     ///
 362     /// dl.clear();
 363     /// assert_eq!(dl.len(), 0);
 364     /// assert_eq!(dl.front(), None);
 365     ///
 366     /// ```
 367     #[inline]
 368     #[stable(feature = "rust1", since = "1.0.0")]
 369     pub fn clear(&mut self) {
 370         *self = LinkedList::new()
 371     }
 372
 373     /// Provides a reference to the front element, or `None` if the list is
 374     /// empty.
 375     ///
 376     /// # Examples
 377     ///
 378     /// ```
 379     /// use std::collections::LinkedList;
 380     ///
 381     /// let mut dl = LinkedList::new();
 382     /// assert_eq!(dl.front(), None);
 383     ///
 384     /// dl.push_front(1);
 385     /// assert_eq!(dl.front(), Some(&1));
 386     ///
 387     /// ```
 388     #[inline]
 389     #[stable(feature = "rust1", since = "1.0.0")]
 390     pub fn front(&self) -> Option<&T> {
 391         self.list_head.as_ref().map(|head| &head.value)
 392     }
 393
 394     /// Provides a mutable reference to the front element, or `None` if the list
 395     /// is empty.
 396     ///
 397     /// # Examples
 398     ///
 399     /// ```
 400     /// use std::collections::LinkedList;
 401     ///
 402     /// let mut dl = LinkedList::new();
 403     /// assert_eq!(dl.front(), None);
 404     ///
 405     /// dl.push_front(1);
 406     /// assert_eq!(dl.front(), Some(&1));
 407     ///
 408     /// match dl.front_mut() {
 409     ///     None => {},
 410     ///     Some(x) => *x = 5,
 411     /// }
 412     /// assert_eq!(dl.front(), Some(&5));
 413     ///
 414     /// ```
 415     #[inline]
 416     #[stable(feature = "rust1", since = "1.0.0")]
 417     pub fn front_mut(&mut self) -> Option<&mut T> {
 418         self.list_head.as_mut().map(|head| &mut head.value)
 419     }
 420
 421     /// Provides a reference to the back element, or `None` if the list is
 422     /// empty.
 423     ///
 424     /// # Examples
 425     ///
 426     /// ```
 427     /// use std::collections::LinkedList;
 428     ///
 429     /// let mut dl = LinkedList::new();
 430     /// assert_eq!(dl.back(), None);
 431     ///
 432     /// dl.push_back(1);
 433     /// assert_eq!(dl.back(), Some(&1));
 434     ///
 435     /// ```
 436     #[inline]
 437     #[stable(feature = "rust1", since = "1.0.0")]
 438     pub fn back(&self) -> Option<&T> {
 439         self.list_tail.resolve_immut().as_ref().map(|tail| &tail.value)
 440     }
 441
 442     /// Provides a mutable reference to the back element, or `None` if the list
 443     /// is empty.
 444     ///
 445     /// # Examples
 446     ///
 447     /// ```
 448     /// use std::collections::LinkedList;
 449     ///
 450     /// let mut dl = LinkedList::new();
 451     /// assert_eq!(dl.back(), None);
 452     ///
 453     /// dl.push_back(1);
 454     /// assert_eq!(dl.back(), Some(&1));
 455     ///
 456     /// match dl.back_mut() {
 457     ///     None => {},
 458     ///     Some(x) => *x = 5,
 459     /// }
 460     /// assert_eq!(dl.back(), Some(&5));
 461     ///
 462     /// ```
 463     #[inline]
 464     #[stable(feature = "rust1", since = "1.0.0")]
 465     pub fn back_mut(&mut self) -> Option<&mut T> {
 466         self.list_tail.resolve().map(|tail| &mut tail.value)
 467     }
 468
 469     /// Adds an element first in the list.
 470     ///
 471     /// This operation should compute in O(1) time.
 472     ///
 473     /// # Examples
 474     ///
 475     /// ```
 476     /// # #![feature(collections)]
 477     /// use std::collections::LinkedList;
 478     ///
 479     /// let mut dl = LinkedList::new();
 480     ///
 481     /// dl.push_front(2);
 482     /// assert_eq!(dl.front().unwrap(), &2);
 483     ///
 484     /// dl.push_front(1);
 485     /// assert_eq!(dl.front().unwrap(), &1);
 486     ///
 487     /// ```
 488     #[stable(feature = "rust1", since = "1.0.0")]
 489     pub fn push_front(&mut self, elt: T) {
 490         self.push_front_node(box Node::new(elt))
 491     }
 492
 493     /// Removes the first element and returns it, or `None` if the list is
 494     /// empty.
 495     ///
 496     /// This operation should compute in O(1) time.
 497     ///
 498     /// # Examples
 499     ///
 500     /// ```
 501     /// use std::collections::LinkedList;
 502     ///
 503     /// let mut d = LinkedList::new();
 504     /// assert_eq!(d.pop_front(), None);
 505     ///
 506     /// d.push_front(1);
 507     /// d.push_front(3);
 508     /// assert_eq!(d.pop_front(), Some(3));
 509     /// assert_eq!(d.pop_front(), Some(1));
 510     /// assert_eq!(d.pop_front(), None);
 511     ///
 512     /// ```
 513     ///
 514     #[stable(feature = "rust1", since = "1.0.0")]
 515     pub fn pop_front(&mut self) -> Option<T> {
 516         self.pop_front_node().map(|box Node{value, ..}| value)
 517     }
 518
 519     /// Appends an element to the back of a list
 520     ///
 521     /// # Examples
 522     ///
 523     /// ```
 524     /// # #![feature(collections)]
 525     /// use std::collections::LinkedList;
 526     ///
 527     /// let mut d = LinkedList::new();
 528     /// d.push_back(1);
 529     /// d.push_back(3);
 530     /// assert_eq!(3, *d.back().unwrap());
 531     /// ```
 532     #[stable(feature = "rust1", since = "1.0.0")]
 533     pub fn push_back(&mut self, elt: T) {
 534         self.push_back_node(box Node::new(elt))
 535     }
 536
 537     /// Removes the last element from a list and returns it, or `None` if
 538     /// it is empty.
 539     ///
 540     /// # Examples
 541     ///
 542     /// ```
 543     /// # #![feature(collections)]
 544     /// use std::collections::LinkedList;
 545     ///
 546     /// let mut d = LinkedList::new();
 547     /// assert_eq!(d.pop_back(), None);
 548     /// d.push_back(1);
 549     /// d.push_back(3);
 550     /// assert_eq!(d.pop_back(), Some(3));
 551     /// ```
 552     #[stable(feature = "rust1", since = "1.0.0")]
 553     pub fn pop_back(&mut self) -> Option<T> {
 554         self.pop_back_node().map(|box Node{value, ..}| value)
 555     }
 556
 557     /// Splits the list into two at the given index. Returns everything after the given index,
 558     /// including the index.
 559     ///
 560     /// # Panics
 561     ///
 562     /// Panics if `at > len`.
 563     ///
 564     /// This operation should compute in O(n) time.
 565     ///
 566     /// # Examples
 567     ///
 568     /// ```
 569     /// # #![feature(collections)]
 570     /// use std::collections::LinkedList;
 571     ///
 572     /// let mut d = LinkedList::new();
 573     ///
 574     /// d.push_front(1);
 575     /// d.push_front(2);
 576     /// d.push_front(3);
 577     ///
 578     /// let mut splitted = d.split_off(2);
 579     ///
 580     /// assert_eq!(splitted.pop_front(), Some(1));
 581     /// assert_eq!(splitted.pop_front(), None);
 582     /// ```
 583     #[stable(feature = "rust1", since = "1.0.0")]
 584     pub fn split_off(&mut self, at: usize) -> LinkedList<T> {
 585         let len = self.len();
 586         assert!(at <= len, "Cannot split off at a nonexistent index");
 587         if at == 0 {
 588             return mem::replace(self, LinkedList::new());
 589         } else if at == len {
 590             return LinkedList::new();
 591         }
 592
 593         // Below, we iterate towards the `i-1`th node, either from the start or the end,
 594         // depending on which would be faster.
 595         let mut split_node = if at - 1 <= len - 1 - (at - 1) {
 596             let mut iter = self.iter_mut();
 597             // instead of skipping using .skip() (which creates a new struct),
 598             // we skip manually so we can access the head field without
 599             // depending on implementation details of Skip
 600             for _ in 0..at - 1 {
 601                 iter.next();
 602             }
 603             iter.head
 604         }  else {
 605             // better off starting from the end
 606             let mut iter = self.iter_mut();
 607             for _ in 0..len - 1 - (at - 1) {
 608                 iter.next_back();
 609             }
 610             iter.tail
 611         };
 612
 613         let mut splitted_list = LinkedList {
 614             list_head: None,
 615             list_tail: self.list_tail,
 616             length: len - at
 617         };
 618
 619         // Swap split_node.next with list_head (which is None), nulling out split_node.next,
 620         // as it is the new tail.
 621         mem::swap(&mut split_node.resolve().unwrap().next, &mut splitted_list.list_head);
 622         // Null out list_head.prev. Note this `unwrap` won't fail because if at == len
 623         // we already branched out at the top of the fn to return the empty list.
 624         splitted_list.list_head.as_mut().unwrap().prev = Rawlink::none();
 625         // Fix the tail ptr
 626         self.list_tail = split_node;
 627         self.length = at;
 628
 629         splitted_list
 630     }
 631 }
 632
 633 #[stable(feature = "rust1", since = "1.0.0")]
 634 impl<T> Drop for LinkedList<T> {
 635     fn drop(&mut self) {
 636         // Dissolve the linked_list in backwards direction
 637         // Just dropping the list_head can lead to stack exhaustion
 638         // when length is >> 1_000_000
 639         let mut tail = self.list_tail;
 640         loop {
 641             match tail.resolve() {
 642                 None => break,
 643                 Some(prev) => {
 644                     prev.next.take(); // release Box<Node<T>>
 645                     tail = prev.prev;
 646                 }
 647             }
 648         }
 649         self.length = 0;
 650         self.list_head = None;
 651         self.list_tail = Rawlink::none();
 652     }
 653 }
 654
 655 #[stable(feature = "rust1", since = "1.0.0")]
 656 impl<'a, A> Iterator for Iter<'a, A> {
 657     type Item = &'a A;
 658
 659     #[inline]
 660     fn next(&mut self) -> Option<&'a A> {
 661         if self.nelem == 0 {
 662             return None;
 663         }
 664         self.head.as_ref().map(|head| {
 665             self.nelem -= 1;
 666             self.head = &head.next;
 667             &head.value
 668         })
 669     }
 670
 671     #[inline]
 672     fn size_hint(&self) -> (usize, Option<usize>) {
 673         (self.nelem, Some(self.nelem))
 674     }
 675 }
 676
 677 #[stable(feature = "rust1", since = "1.0.0")]
 678 impl<'a, A> DoubleEndedIterator for Iter<'a, A> {
 679     #[inline]
 680     fn next_back(&mut self) -> Option<&'a A> {
 681         if self.nelem == 0 {
 682             return None;
 683         }
 684         self.tail.resolve_immut().as_ref().map(|prev| {
 685             self.nelem -= 1;
 686             self.tail = prev.prev;
 687             &prev.value
 688         })
 689     }
 690 }
 691
 692 #[stable(feature = "rust1", since = "1.0.0")]
 693 impl<'a, A> ExactSizeIterator for Iter<'a, A> {}
 694
 695 #[stable(feature = "rust1", since = "1.0.0")]
 696 impl<'a, A> Iterator for IterMut<'a, A> {
 697     type Item = &'a mut A;
 698     #[inline]
 699     fn next(&mut self) -> Option<&'a mut A> {
 700         if self.nelem == 0 {
 701             return None;
 702         }
 703         self.head.resolve().map(|next| {
 704             self.nelem -= 1;
 705             self.head = match next.next {
 706                 Some(ref mut node) => Rawlink::some(&mut **node),
 707                 None => Rawlink::none(),
 708             };
 709             &mut next.value
 710         })
 711     }
 712
 713     #[inline]
 714     fn size_hint(&self) -> (usize, Option<usize>) {
 715         (self.nelem, Some(self.nelem))
 716     }
 717 }
 718
 719 #[stable(feature = "rust1", since = "1.0.0")]
 720 impl<'a, A> DoubleEndedIterator for IterMut<'a, A> {
 721     #[inline]
 722     fn next_back(&mut self) -> Option<&'a mut A> {
 723         if self.nelem == 0 {
 724             return None;
 725         }
 726         self.tail.resolve().map(|prev| {
 727             self.nelem -= 1;
 728             self.tail = prev.prev;
 729             &mut prev.value
 730         })
 731     }
 732 }
 733
 734 #[stable(feature = "rust1", since = "1.0.0")]
 735 impl<'a, A> ExactSizeIterator for IterMut<'a, A> {}
 736
 737 // private methods for IterMut
 738 impl<'a, A> IterMut<'a, A> {
 739     fn insert_next_node(&mut self, mut ins_node: Box<Node<A>>) {
 740         // Insert before `self.head` so that it is between the
 741         // previously yielded element and self.head.
 742         //
 743         // The inserted node will not appear in further iteration.
 744         match self.head.resolve() {
 745             None => { self.list.push_back_node(ins_node); }
 746             Some(node) => {
 747                 let prev_node = match node.prev.resolve() {
 748                     None => return self.list.push_front_node(ins_node),
 749                     Some(prev) => prev,
 750                 };
 751                 let node_own = prev_node.next.take().unwrap();
 752                 ins_node.next = link_with_prev(node_own, Rawlink::some(&mut *ins_node));
 753                 prev_node.next = link_with_prev(ins_node, Rawlink::some(prev_node));
 754                 self.list.length += 1;
 755             }
 756         }
 757     }
 758 }
 759
 760 impl<'a, A> IterMut<'a, A> {
 761     /// Inserts `elt` just after the element most recently returned by `.next()`.
 762     /// The inserted element does not appear in the iteration.
 763     ///
 764     /// # Examples
 765     ///
 766     /// ```
 767     /// # #![feature(collections)]
 768     /// use std::collections::LinkedList;
 769     ///
 770     /// let mut list: LinkedList<_> = vec![1, 3, 4].into_iter().collect();
 771     ///
 772     /// {
 773     ///     let mut it = list.iter_mut();
 774     ///     assert_eq!(it.next().unwrap(), &1);
 775     ///     // insert `2` after `1`
 776     ///     it.insert_next(2);
 777     /// }
 778     /// {
 779     ///     let vec: Vec<_> = list.into_iter().collect();
 780     ///     assert_eq!(vec, [1, 2, 3, 4]);
 781     /// }
 782     /// ```
 783     #[inline]
 784     #[unstable(feature = "collections",
 785                reason = "this is probably better handled by a cursor type -- we'll see")]
 786     pub fn insert_next(&mut self, elt: A) {
 787         self.insert_next_node(box Node::new(elt))
 788     }
 789
 790     /// Provides a reference to the next element, without changing the iterator.
 791     ///
 792     /// # Examples
 793     ///
 794     /// ```
 795     /// # #![feature(collections)]
 796     /// use std::collections::LinkedList;
 797     ///
 798     /// let mut list: LinkedList<_> = vec![1, 2, 3].into_iter().collect();
 799     ///
 800     /// let mut it = list.iter_mut();
 801     /// assert_eq!(it.next().unwrap(), &1);
 802     /// assert_eq!(it.peek_next().unwrap(), &2);
 803     /// // We just peeked at 2, so it was not consumed from the iterator.
 804     /// assert_eq!(it.next().unwrap(), &2);
 805     /// ```
 806     #[inline]
 807     #[unstable(feature = "collections",
 808                reason = "this is probably better handled by a cursor type -- we'll see")]
 809     pub fn peek_next(&mut self) -> Option<&mut A> {
 810         if self.nelem == 0 {
 811             return None
 812         }
 813         self.head.resolve().map(|head| &mut head.value)
 814     }
 815 }
 816
 817 #[stable(feature = "rust1", since = "1.0.0")]
 818 impl<A> Iterator for IntoIter<A> {
 819     type Item = A;
 820
 821     #[inline]
 822     fn next(&mut self) -> Option<A> { self.list.pop_front() }
 823
 824     #[inline]
 825     fn size_hint(&self) -> (usize, Option<usize>) {
 826         (self.list.length, Some(self.list.length))
 827     }
 828 }
 829
 830 #[stable(feature = "rust1", since = "1.0.0")]
 831 impl<A> DoubleEndedIterator for IntoIter<A> {
 832     #[inline]
 833     fn next_back(&mut self) -> Option<A> { self.list.pop_back() }
 834 }
 835
 836 impl<A> ExactSizeIterator for IntoIter<A> {}
 837
 838 #[stable(feature = "rust1", since = "1.0.0")]
 839 impl<A> FromIterator<A> for LinkedList<A> {
 840     fn from_iter<T: IntoIterator<Item=A>>(iter: T) -> LinkedList<A> {
 841         let mut ret = LinkedList::new();
 842         ret.extend(iter);
 843         ret
 844     }
 845 }
 846
 847 #[stable(feature = "rust1", since = "1.0.0")]
 848 impl<T> IntoIterator for LinkedList<T> {
 849     type Item = T;
 850     type IntoIter = IntoIter<T>;
 851
 852     /// Consumes the list into an iterator yielding elements by value.
 853     #[inline]
 854     fn into_iter(self) -> IntoIter<T> {
 855         IntoIter{list: self}
 856     }
 857 }
 858
 859 #[stable(feature = "rust1", since = "1.0.0")]
 860 impl<'a, T> IntoIterator for &'a LinkedList<T> {
 861     type Item = &'a T;
 862     type IntoIter = Iter<'a, T>;
 863
 864     fn into_iter(self) -> Iter<'a, T> {
 865         self.iter()
 866     }
 867 }
 868
 869 impl<'a, T> IntoIterator for &'a mut LinkedList<T> {
 870     type Item = &'a mut T;
 871     type IntoIter = IterMut<'a, T>;
 872
 873     fn into_iter(mut self) -> IterMut<'a, T> {
 874         self.iter_mut()
 875     }
 876 }
 877
 878 #[stable(feature = "rust1", since = "1.0.0")]
 879 impl<A> Extend<A> for LinkedList<A> {
 880     fn extend<T: IntoIterator<Item=A>>(&mut self, iter: T) {
 881         for elt in iter { self.push_back(elt); }
 882     }
 883 }
 884
 885 #[stable(feature = "rust1", since = "1.0.0")]
 886 impl<A: PartialEq> PartialEq for LinkedList<A> {
 887     fn eq(&self, other: &LinkedList<A>) -> bool {
 888         self.len() == other.len() &&
 889             iter::order::eq(self.iter(), other.iter())
 890     }
 891
 892     fn ne(&self, other: &LinkedList<A>) -> bool {
 893         self.len() != other.len() ||
 894             iter::order::ne(self.iter(), other.iter())
 895     }
 896 }
 897
 898 #[stable(feature = "rust1", since = "1.0.0")]
 899 impl<A: Eq> Eq for LinkedList<A> {}
 900
 901 #[stable(feature = "rust1", since = "1.0.0")]
 902 impl<A: PartialOrd> PartialOrd for LinkedList<A> {
 903     fn partial_cmp(&self, other: &LinkedList<A>) -> Option<Ordering> {
 904         iter::order::partial_cmp(self.iter(), other.iter())
 905     }
 906 }
 907
 908 #[stable(feature = "rust1", since = "1.0.0")]
 909 impl<A: Ord> Ord for LinkedList<A> {
 910     #[inline]
 911     fn cmp(&self, other: &LinkedList<A>) -> Ordering {
 912         iter::order::cmp(self.iter(), other.iter())
 913     }
 914 }
 915
 916 #[stable(feature = "rust1", since = "1.0.0")]
 917 impl<A: Clone> Clone for LinkedList<A> {
 918     fn clone(&self) -> LinkedList<A> {
 919         self.iter().cloned().collect()
 920     }
 921 }
 922
 923 #[stable(feature = "rust1", since = "1.0.0")]
 924 impl<A: fmt::Debug> fmt::Debug for LinkedList<A> {
 925     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 926         self.iter().fold(f.debug_list(), |b, e| b.entry(e)).finish()
 927     }
 928 }
 929
 930 #[stable(feature = "rust1", since = "1.0.0")]
 931 impl<A: Hash> Hash for LinkedList<A> {
 932     fn hash<H: Hasher>(&self, state: &mut H) {
 933         self.len().hash(state);
 934         for elt in self {
 935             elt.hash(state);
 936         }
 937     }
 938 }
 939
 940 #[cfg(test)]
 941 mod tests {
 942     use std::clone::Clone;
 943     use std::iter::{Iterator, IntoIterator};
 944     use std::option::Option::{Some, None, self};
 945     use std::__rand::{thread_rng, Rng};
 946     use std::thread;
 947     use std::vec::Vec;
 948
 949     use super::{LinkedList, Node};
 950
 951     #[cfg(test)]
 952     fn list_from<T: Clone>(v: &[T]) -> LinkedList<T> {
 953         v.iter().cloned().collect()
 954     }
 955
 956     pub fn check_links<T>(list: &LinkedList<T>) {
 957         let mut len = 0;
 958         let mut last_ptr: Option<&Node<T>> = None;
 959         let mut node_ptr: &Node<T>;
 960         match list.list_head {
 961             None => { assert_eq!(0, list.length); return }
 962             Some(ref node) => node_ptr = &**node,
 963         }
 964         loop {
 965             match (last_ptr, node_ptr.prev.resolve_immut()) {
 966                 (None   , None      ) => {}
 967                 (None   , _         ) => panic!("prev link for list_head"),
 968                 (Some(p), Some(pptr)) => {
 969                     assert_eq!(p as *const Node<T>, pptr as *const Node<T>);
 970                 }
 971                 _ => panic!("prev link is none, not good"),
 972             }
 973             match node_ptr.next {
 974                 Some(ref next) => {
 975                     last_ptr = Some(node_ptr);
 976                     node_ptr = &**next;
 977                     len += 1;
 978                 }
 979                 None => {
 980                     len += 1;
 981                     break;
 982                 }
 983             }
 984         }
 985         assert_eq!(len, list.length);
 986     }
 987
 988     #[test]
 989     fn test_append() {
 990         // Empty to empty
 991         {
 992             let mut m = LinkedList::<i32>::new();
 993             let mut n = LinkedList::new();
 994             m.append(&mut n);
 995             check_links(&m);
 996             assert_eq!(m.len(), 0);
 997             assert_eq!(n.len(), 0);
 998         }
 999         // Non-empty to empty
1000         {
1001             let mut m = LinkedList::new();
1002             let mut n = LinkedList::new();
1003             n.push_back(2);
1004             m.append(&mut n);
1005             check_links(&m);
1006             assert_eq!(m.len(), 1);
1007             assert_eq!(m.pop_back(), Some(2));
1008             assert_eq!(n.len(), 0);
1009             check_links(&m);
1010         }
1011         // Empty to non-empty
1012         {
1013             let mut m = LinkedList::new();
1014             let mut n = LinkedList::new();
1015             m.push_back(2);
1016             m.append(&mut n);
1017             check_links(&m);
1018             assert_eq!(m.len(), 1);
1019             assert_eq!(m.pop_back(), Some(2));
1020             check_links(&m);
1021         }
1022
1023         // Non-empty to non-empty
1024         let v = vec![1,2,3,4,5];
1025         let u = vec![9,8,1,2,3,4,5];
1026         let mut m = list_from(&v);
1027         let mut n = list_from(&u);
1028         m.append(&mut n);
1029         check_links(&m);
1030         let mut sum = v;
1031         sum.push_all(&u);
1032         assert_eq!(sum.len(), m.len());
1033         for elt in sum {
1034             assert_eq!(m.pop_front(), Some(elt))
1035         }
1036         assert_eq!(n.len(), 0);
1037         // let's make sure it's working properly, since we
1038         // did some direct changes to private members
1039         n.push_back(3);
1040         assert_eq!(n.len(), 1);
1041         assert_eq!(n.pop_front(), Some(3));
1042         check_links(&n);
1043     }
1044
1045     #[test]
1046     fn test_insert_prev() {
1047         let mut m = list_from(&[0,2,4,6,8]);
1048         let len = m.len();
1049         {
1050             let mut it = m.iter_mut();
1051             it.insert_next(-2);
1052             loop {
1053                 match it.next() {
1054                     None => break,
1055                     Some(elt) => {
1056                         it.insert_next(*elt + 1);
1057                         match it.peek_next() {
1058                             Some(x) => assert_eq!(*x, *elt + 2),
1059                             None => assert_eq!(8, *elt),
1060                         }
1061                     }
1062                 }
1063             }
1064             it.insert_next(0);
1065             it.insert_next(1);
1066         }
1067         check_links(&m);
1068         assert_eq!(m.len(), 3 + len * 2);
1069         assert_eq!(m.into_iter().collect::<Vec<_>>(), [-2,0,1,2,3,4,5,6,7,8,9,0,1]);
1070     }
1071
1072     #[test]
1073     fn test_send() {
1074         let n = list_from(&[1,2,3]);
1075         thread::spawn(move || {
1076             check_links(&n);
1077             let a: &[_] = &[&1,&2,&3];
1078             assert_eq!(a, &n.iter().collect::<Vec<_>>()[..]);
1079         }).join().ok().unwrap();
1080     }
1081
1082     #[test]
1083     fn test_fuzz() {
1084         for _ in 0..25 {
1085             fuzz_test(3);
1086             fuzz_test(16);
1087             fuzz_test(189);
1088         }
1089     }
1090
1091     #[test]
1092     fn test_26021() {
1093         use std::iter::ExactSizeIterator;
1094         // There was a bug in split_off that failed to null out the RHS's head's prev ptr.
1095         // This caused the RHS's dtor to walk up into the LHS at drop and delete all of
1096         // its nodes.
1097         //
1098         // https://github.com/rust-lang/rust/issues/26021
1099         let mut v1 = LinkedList::new();
1100         v1.push_front(1u8);
1101         v1.push_front(1u8);
1102         v1.push_front(1u8);
1103         v1.push_front(1u8);
1104         let _ = v1.split_off(3); // Dropping this now should not cause laundry consumption
1105         assert_eq!(v1.len(), 3);
1106
1107         assert_eq!(v1.iter().len(), 3);
1108         assert_eq!(v1.iter().collect::<Vec<_>>().len(), 3);
1109     }
1110
1111     #[cfg(test)]
1112     fn fuzz_test(sz: i32) {
1113         let mut m: LinkedList<_> = LinkedList::new();
1114         let mut v = vec![];
1115         for i in 0..sz {
1116             check_links(&m);
1117             let r: u8 = thread_rng().next_u32() as u8;
1118             match r % 6 {
1119                 0 => {
1120                     m.pop_back();
1121                     v.pop();
1122                 }
1123                 1 => {
1124                     if !v.is_empty() {
1125                         m.pop_front();
1126                         v.remove(0);
1127                     }
1128                 }
1129                 2 | 4 =>  {
1130                     m.push_front(-i);
1131                     v.insert(0, -i);
1132                 }
1133                 3 | 5 | _ => {
1134                     m.push_back(i);
1135                     v.push(i);
1136                 }
1137             }
1138         }
1139
1140         check_links(&m);
1141
1142         let mut i = 0;
1143         for (a, &b) in m.into_iter().zip(v.iter()) {
1144             i += 1;
1145             assert_eq!(a, b);
1146         }
1147         assert_eq!(i, v.len());
1148     }
1149 }