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::default::Default;
  29 use core::fmt;
  30 use core::hash::{Hasher, Hash};
  31 #[cfg(stage0)]
  32 use core::hash::Writer;
  33 use core::iter::{self, FromIterator, IntoIterator};
  34 use core::mem;
  35 use core::ptr;
  36
  37 #[deprecated(since = "1.0.0", reason = "renamed to LinkedList")]
  38 #[unstable(feature = "collections")]
  39 pub use LinkedList as DList;
  40
  41 /// A doubly-linked list.
  42 #[stable(feature = "rust1", since = "1.0.0")]
  43 pub struct LinkedList<T> {
  44     length: usize,
  45     list_head: Link<T>,
  46     list_tail: Rawlink<Node<T>>,
  47 }
  48
  49 type Link<T> = Option<Box<Node<T>>>;
  50
  51 struct Rawlink<T> {
  52     p: *mut T,
  53 }
  54
  55 impl<T> Copy for Rawlink<T> {}
  56 unsafe impl<T:'static+Send> Send for Rawlink<T> {}
  57 unsafe impl<T:Send+Sync> Sync for Rawlink<T> {}
  58
  59 struct Node<T> {
  60     next: Link<T>,
  61     prev: Rawlink<Node<T>>,
  62     value: T,
  63 }
  64
  65 /// An iterator over references to the items of a `LinkedList`.
  66 #[stable(feature = "rust1", since = "1.0.0")]
  67 pub struct Iter<'a, T:'a> {
  68     head: &'a Link<T>,
  69     tail: Rawlink<Node<T>>,
  70     nelem: usize,
  71 }
  72
  73 // FIXME #19839: deriving is too aggressive on the bounds (T doesn't need to be Clone).
  74 #[stable(feature = "rust1", since = "1.0.0")]
  75 impl<'a, T> Clone for Iter<'a, T> {
  76     fn clone(&self) -> Iter<'a, T> {
  77         Iter {
  78             head: self.head.clone(),
  79             tail: self.tail,
  80             nelem: self.nelem,
  81         }
  82     }
  83 }
  84
  85 /// An iterator over mutable references to the items of a `LinkedList`.
  86 #[stable(feature = "rust1", since = "1.0.0")]
  87 pub struct IterMut<'a, T:'a> {
  88     list: &'a mut LinkedList<T>,
  89     head: Rawlink<Node<T>>,
  90     tail: Rawlink<Node<T>>,
  91     nelem: usize,
  92 }
  93
  94 /// An iterator over mutable references to the items of a `LinkedList`.
  95 #[derive(Clone)]
  96 #[stable(feature = "rust1", since = "1.0.0")]
  97 pub struct IntoIter<T> {
  98     list: LinkedList<T>
  99 }
 100
 101 /// Rawlink is a type like Option<T> but for holding a raw pointer
 102 impl<T> Rawlink<T> {
 103     /// Like Option::None for Rawlink
 104     fn none() -> Rawlink<T> {
 105         Rawlink{p: ptr::null_mut()}
 106     }
 107
 108     /// Like Option::Some for Rawlink
 109     fn some(n: &mut T) -> Rawlink<T> {
 110         Rawlink{p: n}
 111     }
 112
 113     /// Convert the `Rawlink` into an Option value
 114     fn resolve_immut<'a>(&self) -> Option<&'a T> {
 115         unsafe {
 116             mem::transmute(self.p.as_ref())
 117         }
 118     }
 119
 120     /// Convert the `Rawlink` into an Option value
 121     fn resolve<'a>(&mut self) -> Option<&'a mut T> {
 122         if self.p.is_null() {
 123             None
 124         } else {
 125             Some(unsafe { mem::transmute(self.p) })
 126         }
 127     }
 128
 129     /// Return the `Rawlink` and replace with `Rawlink::none()`
 130     fn take(&mut self) -> Rawlink<T> {
 131         mem::replace(self, Rawlink::none())
 132     }
 133 }
 134
 135 impl<T> Clone for Rawlink<T> {
 136     #[inline]
 137     fn clone(&self) -> Rawlink<T> {
 138         Rawlink{p: self.p}
 139     }
 140 }
 141
 142 impl<T> Node<T> {
 143     fn new(v: T) -> Node<T> {
 144         Node{value: v, next: None, prev: Rawlink::none()}
 145     }
 146 }
 147
 148 /// Set the .prev field on `next`, then return `Some(next)`
 149 fn link_with_prev<T>(mut next: Box<Node<T>>, prev: Rawlink<Node<T>>)
 150                   -> Link<T> {
 151     next.prev = prev;
 152     Some(next)
 153 }
 154
 155 // private methods
 156 impl<T> LinkedList<T> {
 157     /// Add a Node first in the list
 158     #[inline]
 159     fn push_front_node(&mut self, mut new_head: Box<Node<T>>) {
 160         match self.list_head {
 161             None => {
 162                 self.list_tail = Rawlink::some(&mut *new_head);
 163                 self.list_head = link_with_prev(new_head, Rawlink::none());
 164             }
 165             Some(ref mut head) => {
 166                 new_head.prev = Rawlink::none();
 167                 head.prev = Rawlink::some(&mut *new_head);
 168                 mem::swap(head, &mut new_head);
 169                 head.next = Some(new_head);
 170             }
 171         }
 172         self.length += 1;
 173     }
 174
 175     /// Remove the first Node and return it, or None if the list is empty
 176     #[inline]
 177     fn pop_front_node(&mut self) -> Option<Box<Node<T>>> {
 178         self.list_head.take().map(|mut front_node| {
 179             self.length -= 1;
 180             match front_node.next.take() {
 181                 Some(node) => self.list_head = link_with_prev(node, Rawlink::none()),
 182                 None => self.list_tail = Rawlink::none()
 183             }
 184             front_node
 185         })
 186     }
 187
 188     /// Add a Node last in the list
 189     #[inline]
 190     fn push_back_node(&mut self, mut new_tail: Box<Node<T>>) {
 191         match self.list_tail.resolve() {
 192             None => return self.push_front_node(new_tail),
 193             Some(tail) => {
 194                 self.list_tail = Rawlink::some(&mut *new_tail);
 195                 tail.next = link_with_prev(new_tail, Rawlink::some(tail));
 196             }
 197         }
 198         self.length += 1;
 199     }
 200
 201     /// Remove the last Node and return it, or None if the list is empty
 202     #[inline]
 203     fn pop_back_node(&mut self) -> Option<Box<Node<T>>> {
 204         self.list_tail.resolve().map_or(None, |tail| {
 205             self.length -= 1;
 206             self.list_tail = tail.prev;
 207             match tail.prev.resolve() {
 208                 None => self.list_head.take(),
 209                 Some(tail_prev) => tail_prev.next.take()
 210             }
 211         })
 212     }
 213 }
 214
 215 #[stable(feature = "rust1", since = "1.0.0")]
 216 impl<T> Default for LinkedList<T> {
 217     #[inline]
 218     #[stable(feature = "rust1", since = "1.0.0")]
 219     fn default() -> LinkedList<T> { LinkedList::new() }
 220 }
 221
 222 impl<T> LinkedList<T> {
 223     /// Creates an empty `LinkedList`.
 224     #[inline]
 225     #[stable(feature = "rust1", since = "1.0.0")]
 226     pub fn new() -> LinkedList<T> {
 227         LinkedList{list_head: None, list_tail: Rawlink::none(), length: 0}
 228     }
 229
 230     /// Moves all elements from `other` to the end of the list.
 231     ///
 232     /// This reuses all the nodes from `other` and moves them into `self`. After
 233     /// this operation, `other` becomes empty.
 234     ///
 235     /// This operation should compute in O(1) time and O(1) memory.
 236     ///
 237     /// # Examples
 238     ///
 239     /// ```
 240     /// use std::collections::LinkedList;
 241     ///
 242     /// let mut a = LinkedList::new();
 243     /// let mut b = LinkedList::new();
 244     /// a.push_back(1);
 245     /// a.push_back(2);
 246     /// b.push_back(3);
 247     /// b.push_back(4);
 248     ///
 249     /// a.append(&mut b);
 250     ///
 251     /// for e in a.iter() {
 252     ///     println!("{}", e); // prints 1, then 2, then 3, then 4
 253     /// }
 254     /// println!("{}", b.len()); // prints 0
 255     /// ```
 256     pub fn append(&mut self, other: &mut LinkedList<T>) {
 257         match self.list_tail.resolve() {
 258             None => {
 259                 self.length = other.length;
 260                 self.list_head = other.list_head.take();
 261                 self.list_tail = other.list_tail.take();
 262             },
 263             Some(tail) => {
 264                 // Carefully empty `other`.
 265                 let o_tail = other.list_tail.take();
 266                 let o_length = other.length;
 267                 match other.list_head.take() {
 268                     None => return,
 269                     Some(node) => {
 270                         tail.next = link_with_prev(node, self.list_tail);
 271                         self.list_tail = o_tail;
 272                         self.length += o_length;
 273                     }
 274                 }
 275             }
 276         }
 277         other.length = 0;
 278     }
 279
 280     /// Provides a forward iterator.
 281     #[inline]
 282     #[stable(feature = "rust1", since = "1.0.0")]
 283     pub fn iter(&self) -> Iter<T> {
 284         Iter{nelem: self.len(), head: &self.list_head, tail: self.list_tail}
 285     }
 286
 287     /// Provides a forward iterator with mutable references.
 288     #[inline]
 289     #[stable(feature = "rust1", since = "1.0.0")]
 290     pub fn iter_mut(&mut self) -> IterMut<T> {
 291         let head_raw = match self.list_head {
 292             Some(ref mut h) => Rawlink::some(&mut **h),
 293             None => Rawlink::none(),
 294         };
 295         IterMut{
 296             nelem: self.len(),
 297             head: head_raw,
 298             tail: self.list_tail,
 299             list: self
 300         }
 301     }
 302
 303     /// Consumes the list into an iterator yielding elements by value.
 304     #[inline]
 305     #[stable(feature = "rust1", since = "1.0.0")]
 306     pub fn into_iter(self) -> IntoIter<T> {
 307         IntoIter{list: self}
 308     }
 309
 310     /// Returns `true` if the `LinkedList` is empty.
 311     ///
 312     /// This operation should compute in O(1) time.
 313     ///
 314     /// # Examples
 315     ///
 316     /// ```
 317     /// use std::collections::LinkedList;
 318     ///
 319     /// let mut dl = LinkedList::new();
 320     /// assert!(dl.is_empty());
 321     ///
 322     /// dl.push_front("foo");
 323     /// assert!(!dl.is_empty());
 324     /// ```
 325     #[inline]
 326     #[stable(feature = "rust1", since = "1.0.0")]
 327     pub fn is_empty(&self) -> bool {
 328         self.list_head.is_none()
 329     }
 330
 331     /// Returns the length of the `LinkedList`.
 332     ///
 333     /// This operation should compute in O(1) time.
 334     ///
 335     /// # Examples
 336     ///
 337     /// ```
 338     /// use std::collections::LinkedList;
 339     ///
 340     /// let mut dl = LinkedList::new();
 341     ///
 342     /// dl.push_front(2);
 343     /// assert_eq!(dl.len(), 1);
 344     ///
 345     /// dl.push_front(1);
 346     /// assert_eq!(dl.len(), 2);
 347     ///
 348     /// dl.push_back(3);
 349     /// assert_eq!(dl.len(), 3);
 350     ///
 351     /// ```
 352     #[inline]
 353     #[stable(feature = "rust1", since = "1.0.0")]
 354     pub fn len(&self) -> usize {
 355         self.length
 356     }
 357
 358     /// Removes all elements from the `LinkedList`.
 359     ///
 360     /// This operation should compute in O(n) time.
 361     ///
 362     /// # Examples
 363     ///
 364     /// ```
 365     /// use std::collections::LinkedList;
 366     ///
 367     /// let mut dl = LinkedList::new();
 368     ///
 369     /// dl.push_front(2);
 370     /// dl.push_front(1);
 371     /// assert_eq!(dl.len(), 2);
 372     /// assert_eq!(dl.front(), Some(&1));
 373     ///
 374     /// dl.clear();
 375     /// assert_eq!(dl.len(), 0);
 376     /// assert_eq!(dl.front(), None);
 377     ///
 378     /// ```
 379     #[inline]
 380     #[stable(feature = "rust1", since = "1.0.0")]
 381     pub fn clear(&mut self) {
 382         *self = LinkedList::new()
 383     }
 384
 385     /// Provides a reference to the front element, or `None` if the list is
 386     /// empty.
 387     ///
 388     /// # Examples
 389     ///
 390     /// ```
 391     /// use std::collections::LinkedList;
 392     ///
 393     /// let mut dl = LinkedList::new();
 394     /// assert_eq!(dl.front(), None);
 395     ///
 396     /// dl.push_front(1);
 397     /// assert_eq!(dl.front(), Some(&1));
 398     ///
 399     /// ```
 400     #[inline]
 401     #[stable(feature = "rust1", since = "1.0.0")]
 402     pub fn front(&self) -> Option<&T> {
 403         self.list_head.as_ref().map(|head| &head.value)
 404     }
 405
 406     /// Provides a mutable reference to the front element, or `None` if the list
 407     /// is empty.
 408     ///
 409     /// # Examples
 410     ///
 411     /// ```
 412     /// use std::collections::LinkedList;
 413     ///
 414     /// let mut dl = LinkedList::new();
 415     /// assert_eq!(dl.front(), None);
 416     ///
 417     /// dl.push_front(1);
 418     /// assert_eq!(dl.front(), Some(&1));
 419     ///
 420     /// match dl.front_mut() {
 421     ///     None => {},
 422     ///     Some(x) => *x = 5,
 423     /// }
 424     /// assert_eq!(dl.front(), Some(&5));
 425     ///
 426     /// ```
 427     #[inline]
 428     #[stable(feature = "rust1", since = "1.0.0")]
 429     pub fn front_mut(&mut self) -> Option<&mut T> {
 430         self.list_head.as_mut().map(|head| &mut head.value)
 431     }
 432
 433     /// Provides a reference to the back element, or `None` if the list is
 434     /// empty.
 435     ///
 436     /// # Examples
 437     ///
 438     /// ```
 439     /// use std::collections::LinkedList;
 440     ///
 441     /// let mut dl = LinkedList::new();
 442     /// assert_eq!(dl.back(), None);
 443     ///
 444     /// dl.push_back(1);
 445     /// assert_eq!(dl.back(), Some(&1));
 446     ///
 447     /// ```
 448     #[inline]
 449     #[stable(feature = "rust1", since = "1.0.0")]
 450     pub fn back(&self) -> Option<&T> {
 451         self.list_tail.resolve_immut().as_ref().map(|tail| &tail.value)
 452     }
 453
 454     /// Provides a mutable reference to the back element, or `None` if the list
 455     /// is empty.
 456     ///
 457     /// # Examples
 458     ///
 459     /// ```
 460     /// use std::collections::LinkedList;
 461     ///
 462     /// let mut dl = LinkedList::new();
 463     /// assert_eq!(dl.back(), None);
 464     ///
 465     /// dl.push_back(1);
 466     /// assert_eq!(dl.back(), Some(&1));
 467     ///
 468     /// match dl.back_mut() {
 469     ///     None => {},
 470     ///     Some(x) => *x = 5,
 471     /// }
 472     /// assert_eq!(dl.back(), Some(&5));
 473     ///
 474     /// ```
 475     #[inline]
 476     #[stable(feature = "rust1", since = "1.0.0")]
 477     pub fn back_mut(&mut self) -> Option<&mut T> {
 478         self.list_tail.resolve().map(|tail| &mut tail.value)
 479     }
 480
 481     /// Adds an element first in the list.
 482     ///
 483     /// This operation should compute in O(1) time.
 484     ///
 485     /// # Examples
 486     ///
 487     /// ```
 488     /// use std::collections::LinkedList;
 489     ///
 490     /// let mut dl = LinkedList::new();
 491     ///
 492     /// dl.push_front(2);
 493     /// assert_eq!(dl.front().unwrap(), &2);
 494     ///
 495     /// dl.push_front(1);
 496     /// assert_eq!(dl.front().unwrap(), &1);
 497     ///
 498     /// ```
 499     #[stable(feature = "rust1", since = "1.0.0")]
 500     pub fn push_front(&mut self, elt: T) {
 501         self.push_front_node(box Node::new(elt))
 502     }
 503
 504     /// Removes the first element and returns it, or `None` if the list is
 505     /// empty.
 506     ///
 507     /// This operation should compute in O(1) time.
 508     ///
 509     /// # Examples
 510     ///
 511     /// ```
 512     /// use std::collections::LinkedList;
 513     ///
 514     /// let mut d = LinkedList::new();
 515     /// assert_eq!(d.pop_front(), None);
 516     ///
 517     /// d.push_front(1);
 518     /// d.push_front(3);
 519     /// assert_eq!(d.pop_front(), Some(3));
 520     /// assert_eq!(d.pop_front(), Some(1));
 521     /// assert_eq!(d.pop_front(), None);
 522     ///
 523     /// ```
 524     ///
 525     #[stable(feature = "rust1", since = "1.0.0")]
 526     pub fn pop_front(&mut self) -> Option<T> {
 527         self.pop_front_node().map(|box Node{value, ..}| value)
 528     }
 529
 530     /// Appends an element to the back of a list
 531     ///
 532     /// # Examples
 533     ///
 534     /// ```
 535     /// use std::collections::LinkedList;
 536     ///
 537     /// let mut d = LinkedList::new();
 538     /// d.push_back(1);
 539     /// d.push_back(3);
 540     /// assert_eq!(3, *d.back().unwrap());
 541     /// ```
 542     #[stable(feature = "rust1", since = "1.0.0")]
 543     pub fn push_back(&mut self, elt: T) {
 544         self.push_back_node(box Node::new(elt))
 545     }
 546
 547     /// Removes the last element from a list and returns it, or `None` if
 548     /// it is empty.
 549     ///
 550     /// # Examples
 551     ///
 552     /// ```
 553     /// use std::collections::LinkedList;
 554     ///
 555     /// let mut d = LinkedList::new();
 556     /// assert_eq!(d.pop_back(), None);
 557     /// d.push_back(1);
 558     /// d.push_back(3);
 559     /// assert_eq!(d.pop_back(), Some(3));
 560     /// ```
 561     #[stable(feature = "rust1", since = "1.0.0")]
 562     pub fn pop_back(&mut self) -> Option<T> {
 563         self.pop_back_node().map(|box Node{value, ..}| value)
 564     }
 565
 566     /// Splits the list into two at the given index. Returns everything after the given index,
 567     /// including the index.
 568     ///
 569     /// # Panics
 570     ///
 571     /// Panics if `at > len`.
 572     ///
 573     /// This operation should compute in O(n) time.
 574     ///
 575     /// # Examples
 576     ///
 577     /// ```
 578     /// use std::collections::LinkedList;
 579     ///
 580     /// let mut d = LinkedList::new();
 581     ///
 582     /// d.push_front(1);
 583     /// d.push_front(2);
 584     /// d.push_front(3);
 585     ///
 586     /// let mut splitted = d.split_off(2);
 587     ///
 588     /// assert_eq!(splitted.pop_front(), Some(1));
 589     /// assert_eq!(splitted.pop_front(), None);
 590     /// ```
 591     #[stable(feature = "rust1", since = "1.0.0")]
 592     pub fn split_off(&mut self, at: usize) -> LinkedList<T> {
 593         let len = self.len();
 594         assert!(at <= len, "Cannot split off at a nonexistent index");
 595         if at == 0 {
 596             return mem::replace(self, LinkedList::new());
 597         } else if at == len {
 598             return LinkedList::new();
 599         }
 600
 601         // Below, we iterate towards the `i-1`th node, either from the start or the end,
 602         // depending on which would be faster.
 603         let mut split_node = if at - 1 <= len - 1 - (at - 1) {
 604             let mut iter = self.iter_mut();
 605             // instead of skipping using .skip() (which creates a new struct),
 606             // we skip manually so we can access the head field without
 607             // depending on implementation details of Skip
 608             for _ in 0..at - 1 {
 609                 iter.next();
 610             }
 611             iter.head
 612         }  else {
 613             // better off starting from the end
 614             let mut iter = self.iter_mut();
 615             for _ in 0..len - 1 - (at - 1) {
 616                 iter.next_back();
 617             }
 618             iter.tail
 619         };
 620
 621         let mut splitted_list = LinkedList {
 622             list_head: None,
 623             list_tail: self.list_tail,
 624             length: len - at
 625         };
 626
 627         mem::swap(&mut split_node.resolve().unwrap().next, &mut splitted_list.list_head);
 628         self.list_tail = split_node;
 629         self.length = at;
 630
 631         splitted_list
 632     }
 633 }
 634
 635 #[unsafe_destructor]
 636 #[stable(feature = "rust1", since = "1.0.0")]
 637 impl<T> Drop for LinkedList<T> {
 638     fn drop(&mut self) {
 639         // Dissolve the linked_list in backwards direction
 640         // Just dropping the list_head can lead to stack exhaustion
 641         // when length is >> 1_000_000
 642         let mut tail = self.list_tail;
 643         loop {
 644             match tail.resolve() {
 645                 None => break,
 646                 Some(prev) => {
 647                     prev.next.take(); // release Box<Node<T>>
 648                     tail = prev.prev;
 649                 }
 650             }
 651         }
 652         self.length = 0;
 653         self.list_head = None;
 654         self.list_tail = Rawlink::none();
 655     }
 656 }
 657
 658 #[stable(feature = "rust1", since = "1.0.0")]
 659 impl<'a, A> Iterator for Iter<'a, A> {
 660     type Item = &'a A;
 661
 662     #[inline]
 663     fn next(&mut self) -> Option<&'a A> {
 664         if self.nelem == 0 {
 665             return None;
 666         }
 667         self.head.as_ref().map(|head| {
 668             self.nelem -= 1;
 669             self.head = &head.next;
 670             &head.value
 671         })
 672     }
 673
 674     #[inline]
 675     fn size_hint(&self) -> (usize, Option<usize>) {
 676         (self.nelem, Some(self.nelem))
 677     }
 678 }
 679
 680 #[stable(feature = "rust1", since = "1.0.0")]
 681 impl<'a, A> DoubleEndedIterator for Iter<'a, A> {
 682     #[inline]
 683     fn next_back(&mut self) -> Option<&'a A> {
 684         if self.nelem == 0 {
 685             return None;
 686         }
 687         self.tail.resolve_immut().as_ref().map(|prev| {
 688             self.nelem -= 1;
 689             self.tail = prev.prev;
 690             &prev.value
 691         })
 692     }
 693 }
 694
 695 #[stable(feature = "rust1", since = "1.0.0")]
 696 impl<'a, A> ExactSizeIterator for Iter<'a, A> {}
 697
 698 #[stable(feature = "rust1", since = "1.0.0")]
 699 impl<'a, A> Iterator for IterMut<'a, A> {
 700     type Item = &'a mut A;
 701     #[inline]
 702     fn next(&mut self) -> Option<&'a mut A> {
 703         if self.nelem == 0 {
 704             return None;
 705         }
 706         self.head.resolve().map(|next| {
 707             self.nelem -= 1;
 708             self.head = match next.next {
 709                 Some(ref mut node) => Rawlink::some(&mut **node),
 710                 None => Rawlink::none(),
 711             };
 712             &mut next.value
 713         })
 714     }
 715
 716     #[inline]
 717     fn size_hint(&self) -> (usize, Option<usize>) {
 718         (self.nelem, Some(self.nelem))
 719     }
 720 }
 721
 722 #[stable(feature = "rust1", since = "1.0.0")]
 723 impl<'a, A> DoubleEndedIterator for IterMut<'a, A> {
 724     #[inline]
 725     fn next_back(&mut self) -> Option<&'a mut A> {
 726         if self.nelem == 0 {
 727             return None;
 728         }
 729         self.tail.resolve().map(|prev| {
 730             self.nelem -= 1;
 731             self.tail = prev.prev;
 732             &mut prev.value
 733         })
 734     }
 735 }
 736
 737 #[stable(feature = "rust1", since = "1.0.0")]
 738 impl<'a, A> ExactSizeIterator for IterMut<'a, A> {}
 739
 740 // private methods for IterMut
 741 impl<'a, A> IterMut<'a, A> {
 742     fn insert_next_node(&mut self, mut ins_node: Box<Node<A>>) {
 743         // Insert before `self.head` so that it is between the
 744         // previously yielded element and self.head.
 745         //
 746         // The inserted node will not appear in further iteration.
 747         match self.head.resolve() {
 748             None => { self.list.push_back_node(ins_node); }
 749             Some(node) => {
 750                 let prev_node = match node.prev.resolve() {
 751                     None => return self.list.push_front_node(ins_node),
 752                     Some(prev) => prev,
 753                 };
 754                 let node_own = prev_node.next.take().unwrap();
 755                 ins_node.next = link_with_prev(node_own, Rawlink::some(&mut *ins_node));
 756                 prev_node.next = link_with_prev(ins_node, Rawlink::some(prev_node));
 757                 self.list.length += 1;
 758             }
 759         }
 760     }
 761 }
 762
 763 impl<'a, A> IterMut<'a, A> {
 764     /// Inserts `elt` just after the element most recently returned by `.next()`.
 765     /// The inserted element does not appear in the iteration.
 766     ///
 767     /// # Examples
 768     ///
 769     /// ```
 770     /// use std::collections::LinkedList;
 771     ///
 772     /// let mut list: LinkedList<_> = vec![1, 3, 4].into_iter().collect();
 773     ///
 774     /// {
 775     ///     let mut it = list.iter_mut();
 776     ///     assert_eq!(it.next().unwrap(), &1);
 777     ///     // insert `2` after `1`
 778     ///     it.insert_next(2);
 779     /// }
 780     /// {
 781     ///     let vec: Vec<_> = list.into_iter().collect();
 782     ///     assert_eq!(vec, vec![1, 2, 3, 4]);
 783     /// }
 784     /// ```
 785     #[inline]
 786     #[unstable(feature = "collections",
 787                reason = "this is probably better handled by a cursor type -- we'll see")]
 788     pub fn insert_next(&mut self, elt: A) {
 789         self.insert_next_node(box Node::new(elt))
 790     }
 791
 792     /// Provides a reference to the next element, without changing the iterator.
 793     ///
 794     /// # Examples
 795     ///
 796     /// ```
 797     /// use std::collections::LinkedList;
 798     ///
 799     /// let mut list: LinkedList<_> = vec![1, 2, 3].into_iter().collect();
 800     ///
 801     /// let mut it = list.iter_mut();
 802     /// assert_eq!(it.next().unwrap(), &1);
 803     /// assert_eq!(it.peek_next().unwrap(), &2);
 804     /// // We just peeked at 2, so it was not consumed from the iterator.
 805     /// assert_eq!(it.next().unwrap(), &2);
 806     /// ```
 807     #[inline]
 808     #[unstable(feature = "collections",
 809                reason = "this is probably better handled by a cursor type -- we'll see")]
 810     pub fn peek_next(&mut self) -> Option<&mut A> {
 811         if self.nelem == 0 {
 812             return None
 813         }
 814         self.head.resolve().map(|head| &mut head.value)
 815     }
 816 }
 817
 818 #[stable(feature = "rust1", since = "1.0.0")]
 819 impl<A> Iterator for IntoIter<A> {
 820     type Item = A;
 821
 822     #[inline]
 823     fn next(&mut self) -> Option<A> { self.list.pop_front() }
 824
 825     #[inline]
 826     fn size_hint(&self) -> (usize, Option<usize>) {
 827         (self.list.length, Some(self.list.length))
 828     }
 829 }
 830
 831 #[stable(feature = "rust1", since = "1.0.0")]
 832 impl<A> DoubleEndedIterator for IntoIter<A> {
 833     #[inline]
 834     fn next_back(&mut self) -> Option<A> { self.list.pop_back() }
 835 }
 836
 837 #[stable(feature = "rust1", since = "1.0.0")]
 838 impl<A> FromIterator<A> for LinkedList<A> {
 839     fn from_iter<T: IntoIterator<Item=A>>(iter: T) -> LinkedList<A> {
 840         let mut ret = DList::new();
 841         ret.extend(iter);
 842         ret
 843     }
 844 }
 845
 846 #[stable(feature = "rust1", since = "1.0.0")]
 847 impl<T> IntoIterator for LinkedList<T> {
 848     type Item = T;
 849     type IntoIter = IntoIter<T>;
 850
 851     fn into_iter(self) -> IntoIter<T> {
 852         self.into_iter()
 853     }
 854 }
 855
 856 #[stable(feature = "rust1", since = "1.0.0")]
 857 impl<'a, T> IntoIterator for &'a LinkedList<T> {
 858     type Item = &'a T;
 859     type IntoIter = Iter<'a, T>;
 860
 861     fn into_iter(self) -> Iter<'a, T> {
 862         self.iter()
 863     }
 864 }
 865
 866 impl<'a, T> IntoIterator for &'a mut LinkedList<T> {
 867     type Item = &'a mut T;
 868     type IntoIter = IterMut<'a, T>;
 869
 870     fn into_iter(mut self) -> IterMut<'a, T> {
 871         self.iter_mut()
 872     }
 873 }
 874
 875 #[stable(feature = "rust1", since = "1.0.0")]
 876 impl<A> Extend<A> for LinkedList<A> {
 877     fn extend<T: IntoIterator<Item=A>>(&mut self, iter: T) {
 878         for elt in iter { self.push_back(elt); }
 879     }
 880 }
 881
 882 #[stable(feature = "rust1", since = "1.0.0")]
 883 impl<A: PartialEq> PartialEq for LinkedList<A> {
 884     fn eq(&self, other: &LinkedList<A>) -> bool {
 885         self.len() == other.len() &&
 886             iter::order::eq(self.iter(), other.iter())
 887     }
 888
 889     fn ne(&self, other: &LinkedList<A>) -> bool {
 890         self.len() != other.len() ||
 891             iter::order::ne(self.iter(), other.iter())
 892     }
 893 }
 894
 895 #[stable(feature = "rust1", since = "1.0.0")]
 896 impl<A: Eq> Eq for LinkedList<A> {}
 897
 898 #[stable(feature = "rust1", since = "1.0.0")]
 899 impl<A: PartialOrd> PartialOrd for LinkedList<A> {
 900     fn partial_cmp(&self, other: &LinkedList<A>) -> Option<Ordering> {
 901         iter::order::partial_cmp(self.iter(), other.iter())
 902     }
 903 }
 904
 905 #[stable(feature = "rust1", since = "1.0.0")]
 906 impl<A: Ord> Ord for LinkedList<A> {
 907     #[inline]
 908     fn cmp(&self, other: &LinkedList<A>) -> Ordering {
 909         iter::order::cmp(self.iter(), other.iter())
 910     }
 911 }
 912
 913 #[stable(feature = "rust1", since = "1.0.0")]
 914 impl<A: Clone> Clone for LinkedList<A> {
 915     fn clone(&self) -> LinkedList<A> {
 916         self.iter().cloned().collect()
 917     }
 918 }
 919
 920 #[stable(feature = "rust1", since = "1.0.0")]
 921 impl<A: fmt::Debug> fmt::Debug for LinkedList<A> {
 922     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 923         try!(write!(f, "LinkedList ["));
 924
 925         for (i, e) in self.iter().enumerate() {
 926             if i != 0 { try!(write!(f, ", ")); }
 927             try!(write!(f, "{:?}", *e));
 928         }
 929
 930         write!(f, "]")
 931     }
 932 }
 933
 934 #[stable(feature = "rust1", since = "1.0.0")]
 935 #[cfg(stage0)]
 936 impl<S: Writer + Hasher, A: Hash<S>> Hash<S> for LinkedList<A> {
 937     fn hash(&self, state: &mut S) {
 938         self.len().hash(state);
 939         for elt in self {
 940             elt.hash(state);
 941         }
 942     }
 943 }
 944 #[stable(feature = "rust1", since = "1.0.0")]
 945 #[cfg(not(stage0))]
 946 impl<A: Hash> Hash for LinkedList<A> {
 947     fn hash<H: Hasher>(&self, state: &mut H) {
 948         self.len().hash(state);
 949         for elt in self {
 950             elt.hash(state);
 951         }
 952     }
 953 }
 954
 955 #[cfg(test)]
 956 mod tests {
 957     use prelude::*;
 958     use std::rand;
 959     use std::hash::{self, SipHasher};
 960     use std::thread;
 961     use test::Bencher;
 962     use test;
 963
 964     use super::{LinkedList, Node};
 965
 966     pub fn check_links<T>(list: &LinkedList<T>) {
 967         let mut len = 0;
 968         let mut last_ptr: Option<&Node<T>> = None;
 969         let mut node_ptr: &Node<T>;
 970         match list.list_head {
 971             None => { assert_eq!(0, list.length); return }
 972             Some(ref node) => node_ptr = &**node,
 973         }
 974         loop {
 975             match (last_ptr, node_ptr.prev.resolve_immut()) {
 976                 (None   , None      ) => {}
 977                 (None   , _         ) => panic!("prev link for list_head"),
 978                 (Some(p), Some(pptr)) => {
 979                     assert_eq!(p as *const Node<T>, pptr as *const Node<T>);
 980                 }
 981                 _ => panic!("prev link is none, not good"),
 982             }
 983             match node_ptr.next {
 984                 Some(ref next) => {
 985                     last_ptr = Some(node_ptr);
 986                     node_ptr = &**next;
 987                     len += 1;
 988                 }
 989                 None => {
 990                     len += 1;
 991                     break;
 992                 }
 993             }
 994         }
 995         assert_eq!(len, list.length);
 996     }
 997
 998     #[test]
 999     fn test_basic() {
1000         let mut m = LinkedList::new();
1001         assert_eq!(m.pop_front(), None);
1002         assert_eq!(m.pop_back(), None);
1003         assert_eq!(m.pop_front(), None);
1004         m.push_front(box 1);
1005         assert_eq!(m.pop_front(), Some(box 1));
1006         m.push_back(box 2);
1007         m.push_back(box 3);
1008         assert_eq!(m.len(), 2);
1009         assert_eq!(m.pop_front(), Some(box 2));
1010         assert_eq!(m.pop_front(), Some(box 3));
1011         assert_eq!(m.len(), 0);
1012         assert_eq!(m.pop_front(), None);
1013         m.push_back(box 1);
1014         m.push_back(box 3);
1015         m.push_back(box 5);
1016         m.push_back(box 7);
1017         assert_eq!(m.pop_front(), Some(box 1));
1018
1019         let mut n = LinkedList::new();
1020         n.push_front(2);
1021         n.push_front(3);
1022         {
1023             assert_eq!(n.front().unwrap(), &3);
1024             let x = n.front_mut().unwrap();
1025             assert_eq!(*x, 3);
1026             *x = 0;
1027         }
1028         {
1029             assert_eq!(n.back().unwrap(), &2);
1030             let y = n.back_mut().unwrap();
1031             assert_eq!(*y, 2);
1032             *y = 1;
1033         }
1034         assert_eq!(n.pop_front(), Some(0));
1035         assert_eq!(n.pop_front(), Some(1));
1036     }
1037
1038     #[cfg(test)]
1039     fn generate_test() -> LinkedList<i32> {
1040         list_from(&[0,1,2,3,4,5,6])
1041     }
1042
1043     #[cfg(test)]
1044     fn list_from<T: Clone>(v: &[T]) -> LinkedList<T> {
1045         v.iter().cloned().collect()
1046     }
1047
1048     #[test]
1049     fn test_append() {
1050         // Empty to empty
1051         {
1052             let mut m = LinkedList::<i32>::new();
1053             let mut n = LinkedList::new();
1054             m.append(&mut n);
1055             check_links(&m);
1056             assert_eq!(m.len(), 0);
1057             assert_eq!(n.len(), 0);
1058         }
1059         // Non-empty to empty
1060         {
1061             let mut m = LinkedList::new();
1062             let mut n = LinkedList::new();
1063             n.push_back(2);
1064             m.append(&mut n);
1065             check_links(&m);
1066             assert_eq!(m.len(), 1);
1067             assert_eq!(m.pop_back(), Some(2));
1068             assert_eq!(n.len(), 0);
1069             check_links(&m);
1070         }
1071         // Empty to non-empty
1072         {
1073             let mut m = LinkedList::new();
1074             let mut n = LinkedList::new();
1075             m.push_back(2);
1076             m.append(&mut n);
1077             check_links(&m);
1078             assert_eq!(m.len(), 1);
1079             assert_eq!(m.pop_back(), Some(2));
1080             check_links(&m);
1081         }
1082
1083         // Non-empty to non-empty
1084         let v = vec![1,2,3,4,5];
1085         let u = vec![9,8,1,2,3,4,5];
1086         let mut m = list_from(&v);
1087         let mut n = list_from(&u);
1088         m.append(&mut n);
1089         check_links(&m);
1090         let mut sum = v;
1091         sum.push_all(&u);
1092         assert_eq!(sum.len(), m.len());
1093         for elt in sum {
1094             assert_eq!(m.pop_front(), Some(elt))
1095         }
1096         assert_eq!(n.len(), 0);
1097         // let's make sure it's working properly, since we
1098         // did some direct changes to private members
1099         n.push_back(3);
1100         assert_eq!(n.len(), 1);
1101         assert_eq!(n.pop_front(), Some(3));
1102         check_links(&n);
1103     }
1104
1105     #[test]
1106     fn test_split_off() {
1107         // singleton
1108         {
1109             let mut m = LinkedList::new();
1110             m.push_back(1);
1111
1112             let p = m.split_off(0);
1113             assert_eq!(m.len(), 0);
1114             assert_eq!(p.len(), 1);
1115             assert_eq!(p.back(), Some(&1));
1116             assert_eq!(p.front(), Some(&1));
1117         }
1118
1119         // not singleton, forwards
1120         {
1121             let u = vec![1,2,3,4,5];
1122             let mut m = list_from(&u);
1123             let mut n = m.split_off(2);
1124             assert_eq!(m.len(), 2);
1125             assert_eq!(n.len(), 3);
1126             for elt in 1..3 {
1127                 assert_eq!(m.pop_front(), Some(elt));
1128             }
1129             for elt in 3..6 {
1130                 assert_eq!(n.pop_front(), Some(elt));
1131             }
1132         }
1133         // not singleton, backwards
1134         {
1135             let u = vec![1,2,3,4,5];
1136             let mut m = list_from(&u);
1137             let mut n = m.split_off(4);
1138             assert_eq!(m.len(), 4);
1139             assert_eq!(n.len(), 1);
1140             for elt in 1..5 {
1141                 assert_eq!(m.pop_front(), Some(elt));
1142             }
1143             for elt in 5..6 {
1144                 assert_eq!(n.pop_front(), Some(elt));
1145             }
1146         }
1147
1148         // no-op on the last index
1149         {
1150             let mut m = LinkedList::new();
1151             m.push_back(1);
1152
1153             let p = m.split_off(1);
1154             assert_eq!(m.len(), 1);
1155             assert_eq!(p.len(), 0);
1156             assert_eq!(m.back(), Some(&1));
1157             assert_eq!(m.front(), Some(&1));
1158         }
1159
1160     }
1161
1162     #[test]
1163     fn test_iterator() {
1164         let m = generate_test();
1165         for (i, elt) in m.iter().enumerate() {
1166             assert_eq!(i as i32, *elt);
1167         }
1168         let mut n = LinkedList::new();
1169         assert_eq!(n.iter().next(), None);
1170         n.push_front(4);
1171         let mut it = n.iter();
1172         assert_eq!(it.size_hint(), (1, Some(1)));
1173         assert_eq!(it.next().unwrap(), &4);
1174         assert_eq!(it.size_hint(), (0, Some(0)));
1175         assert_eq!(it.next(), None);
1176     }
1177
1178     #[test]
1179     fn test_iterator_clone() {
1180         let mut n = LinkedList::new();
1181         n.push_back(2);
1182         n.push_back(3);
1183         n.push_back(4);
1184         let mut it = n.iter();
1185         it.next();
1186         let mut jt = it.clone();
1187         assert_eq!(it.next(), jt.next());
1188         assert_eq!(it.next_back(), jt.next_back());
1189         assert_eq!(it.next(), jt.next());
1190     }
1191
1192     #[test]
1193     fn test_iterator_double_end() {
1194         let mut n = LinkedList::new();
1195         assert_eq!(n.iter().next(), None);
1196         n.push_front(4);
1197         n.push_front(5);
1198         n.push_front(6);
1199         let mut it = n.iter();
1200         assert_eq!(it.size_hint(), (3, Some(3)));
1201         assert_eq!(it.next().unwrap(), &6);
1202         assert_eq!(it.size_hint(), (2, Some(2)));
1203         assert_eq!(it.next_back().unwrap(), &4);
1204         assert_eq!(it.size_hint(), (1, Some(1)));
1205         assert_eq!(it.next_back().unwrap(), &5);
1206         assert_eq!(it.next_back(), None);
1207         assert_eq!(it.next(), None);
1208     }
1209
1210     #[test]
1211     fn test_rev_iter() {
1212         let m = generate_test();
1213         for (i, elt) in m.iter().rev().enumerate() {
1214             assert_eq!((6 - i) as i32, *elt);
1215         }
1216         let mut n = LinkedList::new();
1217         assert_eq!(n.iter().rev().next(), None);
1218         n.push_front(4);
1219         let mut it = n.iter().rev();
1220         assert_eq!(it.size_hint(), (1, Some(1)));
1221         assert_eq!(it.next().unwrap(), &4);
1222         assert_eq!(it.size_hint(), (0, Some(0)));
1223         assert_eq!(it.next(), None);
1224     }
1225
1226     #[test]
1227     fn test_mut_iter() {
1228         let mut m = generate_test();
1229         let mut len = m.len();
1230         for (i, elt) in m.iter_mut().enumerate() {
1231             assert_eq!(i as i32, *elt);
1232             len -= 1;
1233         }
1234         assert_eq!(len, 0);
1235         let mut n = LinkedList::new();
1236         assert!(n.iter_mut().next().is_none());
1237         n.push_front(4);
1238         n.push_back(5);
1239         let mut it = n.iter_mut();
1240         assert_eq!(it.size_hint(), (2, Some(2)));
1241         assert!(it.next().is_some());
1242         assert!(it.next().is_some());
1243         assert_eq!(it.size_hint(), (0, Some(0)));
1244         assert!(it.next().is_none());
1245     }
1246
1247     #[test]
1248     fn test_iterator_mut_double_end() {
1249         let mut n = LinkedList::new();
1250         assert!(n.iter_mut().next_back().is_none());
1251         n.push_front(4);
1252         n.push_front(5);
1253         n.push_front(6);
1254         let mut it = n.iter_mut();
1255         assert_eq!(it.size_hint(), (3, Some(3)));
1256         assert_eq!(*it.next().unwrap(), 6);
1257         assert_eq!(it.size_hint(), (2, Some(2)));
1258         assert_eq!(*it.next_back().unwrap(), 4);
1259         assert_eq!(it.size_hint(), (1, Some(1)));
1260         assert_eq!(*it.next_back().unwrap(), 5);
1261         assert!(it.next_back().is_none());
1262         assert!(it.next().is_none());
1263     }
1264
1265     #[test]
1266     fn test_insert_prev() {
1267         let mut m = list_from(&[0,2,4,6,8]);
1268         let len = m.len();
1269         {
1270             let mut it = m.iter_mut();
1271             it.insert_next(-2);
1272             loop {
1273                 match it.next() {
1274                     None => break,
1275                     Some(elt) => {
1276                         it.insert_next(*elt + 1);
1277                         match it.peek_next() {
1278                             Some(x) => assert_eq!(*x, *elt + 2),
1279                             None => assert_eq!(8, *elt),
1280                         }
1281                     }
1282                 }
1283             }
1284             it.insert_next(0);
1285             it.insert_next(1);
1286         }
1287         check_links(&m);
1288         assert_eq!(m.len(), 3 + len * 2);
1289         assert_eq!(m.into_iter().collect::<Vec<_>>(), vec![-2,0,1,2,3,4,5,6,7,8,9,0,1]);
1290     }
1291
1292     #[test]
1293     fn test_mut_rev_iter() {
1294         let mut m = generate_test();
1295         for (i, elt) in m.iter_mut().rev().enumerate() {
1296             assert_eq!((6 - i) as i32, *elt);
1297         }
1298         let mut n = LinkedList::new();
1299         assert!(n.iter_mut().rev().next().is_none());
1300         n.push_front(4);
1301         let mut it = n.iter_mut().rev();
1302         assert!(it.next().is_some());
1303         assert!(it.next().is_none());
1304     }
1305
1306     #[test]
1307     fn test_send() {
1308         let n = list_from(&[1,2,3]);
1309         thread::spawn(move || {
1310             check_links(&n);
1311             let a: &[_] = &[&1,&2,&3];
1312             assert_eq!(a, n.iter().collect::<Vec<_>>());
1313         }).join().ok().unwrap();
1314     }
1315
1316     #[test]
1317     fn test_eq() {
1318         let mut n = list_from(&[]);
1319         let mut m = list_from(&[]);
1320         assert!(n == m);
1321         n.push_front(1);
1322         assert!(n != m);
1323         m.push_back(1);
1324         assert!(n == m);
1325
1326         let n = list_from(&[2,3,4]);
1327         let m = list_from(&[1,2,3]);
1328         assert!(n != m);
1329     }
1330
1331     #[test]
1332     fn test_hash() {
1333       let mut x = LinkedList::new();
1334       let mut y = LinkedList::new();
1335
1336       assert!(hash::hash::<_, SipHasher>(&x) == hash::hash::<_, SipHasher>(&y));
1337
1338       x.push_back(1);
1339       x.push_back(2);
1340       x.push_back(3);
1341
1342       y.push_front(3);
1343       y.push_front(2);
1344       y.push_front(1);
1345
1346       assert!(hash::hash::<_, SipHasher>(&x) == hash::hash::<_, SipHasher>(&y));
1347     }
1348
1349     #[test]
1350     fn test_ord() {
1351         let n = list_from(&[]);
1352         let m = list_from(&[1,2,3]);
1353         assert!(n < m);
1354         assert!(m > n);
1355         assert!(n <= n);
1356         assert!(n >= n);
1357     }
1358
1359     #[test]
1360     fn test_ord_nan() {
1361         let nan = 0.0f64/0.0;
1362         let n = list_from(&[nan]);
1363         let m = list_from(&[nan]);
1364         assert!(!(n < m));
1365         assert!(!(n > m));
1366         assert!(!(n <= m));
1367         assert!(!(n >= m));
1368
1369         let n = list_from(&[nan]);
1370         let one = list_from(&[1.0f64]);
1371         assert!(!(n < one));
1372         assert!(!(n > one));
1373         assert!(!(n <= one));
1374         assert!(!(n >= one));
1375
1376         let u = list_from(&[1.0f64,2.0,nan]);
1377         let v = list_from(&[1.0f64,2.0,3.0]);
1378         assert!(!(u < v));
1379         assert!(!(u > v));
1380         assert!(!(u <= v));
1381         assert!(!(u >= v));
1382
1383         let s = list_from(&[1.0f64,2.0,4.0,2.0]);
1384         let t = list_from(&[1.0f64,2.0,3.0,2.0]);
1385         assert!(!(s < t));
1386         assert!(s > one);
1387         assert!(!(s <= one));
1388         assert!(s >= one);
1389     }
1390
1391     #[test]
1392     fn test_fuzz() {
1393         for _ in 0..25 {
1394             fuzz_test(3);
1395             fuzz_test(16);
1396             fuzz_test(189);
1397         }
1398     }
1399
1400     #[test]
1401     fn test_show() {
1402         let list: LinkedList<_> = (0..10).collect();
1403         assert_eq!(format!("{:?}", list), "LinkedList [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]");
1404
1405         let list: LinkedList<_> = vec!["just", "one", "test", "more"].iter().cloned().collect();
1406         assert_eq!(format!("{:?}", list), "LinkedList [\"just\", \"one\", \"test\", \"more\"]");
1407     }
1408
1409     #[cfg(test)]
1410     fn fuzz_test(sz: i32) {
1411         let mut m: LinkedList<_> = LinkedList::new();
1412         let mut v = vec![];
1413         for i in 0..sz {
1414             check_links(&m);
1415             let r: u8 = rand::random();
1416             match r % 6 {
1417                 0 => {
1418                     m.pop_back();
1419                     v.pop();
1420                 }
1421                 1 => {
1422                     if !v.is_empty() {
1423                         m.pop_front();
1424                         v.remove(0);
1425                     }
1426                 }
1427                 2 | 4 =>  {
1428                     m.push_front(-i);
1429                     v.insert(0, -i);
1430                 }
1431                 3 | 5 | _ => {
1432                     m.push_back(i);
1433                     v.push(i);
1434                 }
1435             }
1436         }
1437
1438         check_links(&m);
1439
1440         let mut i = 0;
1441         for (a, &b) in m.into_iter().zip(v.iter()) {
1442             i += 1;
1443             assert_eq!(a, b);
1444         }
1445         assert_eq!(i, v.len());
1446     }
1447
1448     #[bench]
1449     fn bench_collect_into(b: &mut test::Bencher) {
1450         let v = &[0; 64];
1451         b.iter(|| {
1452             let _: LinkedList<_> = v.iter().cloned().collect();
1453         })
1454     }
1455
1456     #[bench]
1457     fn bench_push_front(b: &mut test::Bencher) {
1458         let mut m: LinkedList<_> = LinkedList::new();
1459         b.iter(|| {
1460             m.push_front(0);
1461         })
1462     }
1463
1464     #[bench]
1465     fn bench_push_back(b: &mut test::Bencher) {
1466         let mut m: LinkedList<_> = LinkedList::new();
1467         b.iter(|| {
1468             m.push_back(0);
1469         })
1470     }
1471
1472     #[bench]
1473     fn bench_push_back_pop_back(b: &mut test::Bencher) {
1474         let mut m: LinkedList<_> = LinkedList::new();
1475         b.iter(|| {
1476             m.push_back(0);
1477             m.pop_back();
1478         })
1479     }
1480
1481     #[bench]
1482     fn bench_push_front_pop_front(b: &mut test::Bencher) {
1483         let mut m: LinkedList<_> = LinkedList::new();
1484         b.iter(|| {
1485             m.push_front(0);
1486             m.pop_front();
1487         })
1488     }
1489
1490     #[bench]
1491     fn bench_iter(b: &mut test::Bencher) {
1492         let v = &[0; 128];
1493         let m: LinkedList<_> = v.iter().cloned().collect();
1494         b.iter(|| {
1495             assert!(m.iter().count() == 128);
1496         })
1497     }
1498     #[bench]
1499     fn bench_iter_mut(b: &mut test::Bencher) {
1500         let v = &[0; 128];
1501         let mut m: LinkedList<_> = v.iter().cloned().collect();
1502         b.iter(|| {
1503             assert!(m.iter_mut().count() == 128);
1504         })
1505     }
1506     #[bench]
1507     fn bench_iter_rev(b: &mut test::Bencher) {
1508         let v = &[0; 128];
1509         let m: LinkedList<_> = v.iter().cloned().collect();
1510         b.iter(|| {
1511             assert!(m.iter().rev().count() == 128);
1512         })
1513     }
1514     #[bench]
1515     fn bench_iter_mut_rev(b: &mut test::Bencher) {
1516         let v = &[0; 128];
1517         let mut m: LinkedList<_> = v.iter().cloned().collect();
1518         b.iter(|| {
1519             assert!(m.iter_mut().rev().count() == 128);
1520         })
1521     }
1522 }