src/libcollections/btree/set.rs

   1 // Copyright 2014 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 // This is pretty much entirely stolen from TreeSet, since BTreeMap has an identical interface
  12 // to TreeMap
  13
  14 use core::cmp::Ordering::{self, Less, Greater, Equal};
  15 use core::cmp::{min, max};
  16 use core::fmt::Debug;
  17 use core::fmt;
  18 use core::iter::{Peekable, FromIterator, FusedIterator};
  19 use core::ops::{BitOr, BitAnd, BitXor, Sub};
  20
  21 use borrow::Borrow;
  22 use btree_map::{BTreeMap, Keys};
  23 use super::Recover;
  24 use range::RangeArgument;
  25
  26 // FIXME(conventions): implement bounded iterators
  27
  28 /// A set based on a B-Tree.
  29 ///
  30 /// See [`BTreeMap`]'s documentation for a detailed discussion of this collection's performance
  31 /// benefits and drawbacks.
  32 ///
  33 /// It is a logic error for an item to be modified in such a way that the item's ordering relative
  34 /// to any other item, as determined by the [`Ord`] trait, changes while it is in the set. This is
  35 /// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
  36 ///
  37 /// [`BTreeMap`]: struct.BTreeMap.html
  38 /// [`Ord`]: ../../std/cmp/trait.Ord.html
  39 /// [`Cell`]: ../../std/cell/struct.Cell.html
  40 /// [`RefCell`]: ../../std/cell/struct.RefCell.html
  41 ///
  42 /// # Examples
  43 ///
  44 /// ```
  45 /// use std::collections::BTreeSet;
  46 ///
  47 /// // Type inference lets us omit an explicit type signature (which
  48 /// // would be `BTreeSet<&str>` in this example).
  49 /// let mut books = BTreeSet::new();
  50 ///
  51 /// // Add some books.
  52 /// books.insert("A Dance With Dragons");
  53 /// books.insert("To Kill a Mockingbird");
  54 /// books.insert("The Odyssey");
  55 /// books.insert("The Great Gatsby");
  56 ///
  57 /// // Check for a specific one.
  58 /// if !books.contains("The Winds of Winter") {
  59 ///     println!("We have {} books, but The Winds of Winter ain't one.",
  60 ///              books.len());
  61 /// }
  62 ///
  63 /// // Remove a book.
  64 /// books.remove("The Odyssey");
  65 ///
  66 /// // Iterate over everything.
  67 /// for book in &books {
  68 ///     println!("{}", book);
  69 /// }
  70 /// ```
  71 #[derive(Clone, Hash, PartialEq, Eq, Ord, PartialOrd)]
  72 #[stable(feature = "rust1", since = "1.0.0")]
  73 pub struct BTreeSet<T> {
  74     map: BTreeMap<T, ()>,
  75 }
  76
  77 /// An iterator over a `BTreeSet`'s items.
  78 ///
  79 /// This structure is created by the [`iter`] method on [`BTreeSet`].
  80 ///
  81 /// [`BTreeSet`]: struct.BTreeSet.html
  82 /// [`iter`]: struct.BTreeSet.html#method.iter
  83 #[stable(feature = "rust1", since = "1.0.0")]
  84 pub struct Iter<'a, T: 'a> {
  85     iter: Keys<'a, T, ()>,
  86 }
  87
  88 #[stable(feature = "collection_debug", since = "1.17.0")]
  89 impl<'a, T: 'a + fmt::Debug> fmt::Debug for Iter<'a, T> {
  90     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  91         f.debug_tuple("Iter")
  92          .field(&self.iter.clone())
  93          .finish()
  94     }
  95 }
  96
  97 /// An owning iterator over a `BTreeSet`'s items.
  98 ///
  99 /// This structure is created by the `into_iter` method on [`BTreeSet`]
 100 /// [`BTreeSet`] (provided by the `IntoIterator` trait).
 101 ///
 102 /// [`BTreeSet`]: struct.BTreeSet.html
 103 #[stable(feature = "rust1", since = "1.0.0")]
 104 #[derive(Debug)]
 105 pub struct IntoIter<T> {
 106     iter: ::btree_map::IntoIter<T, ()>,
 107 }
 108
 109 /// An iterator over a sub-range of `BTreeSet`'s items.
 110 ///
 111 /// This structure is created by the [`range`] method on [`BTreeSet`].
 112 ///
 113 /// [`BTreeSet`]: struct.BTreeSet.html
 114 /// [`range`]: struct.BTreeSet.html#method.range
 115 #[derive(Debug)]
 116 #[stable(feature = "btree_range", since = "1.17.0")]
 117 pub struct Range<'a, T: 'a> {
 118     iter: ::btree_map::Range<'a, T, ()>,
 119 }
 120
 121 /// A lazy iterator producing elements in the set difference (in-order).
 122 ///
 123 /// This structure is created by the [`difference`] method on [`BTreeSet`].
 124 ///
 125 /// [`BTreeSet`]: struct.BTreeSet.html
 126 /// [`difference`]: struct.BTreeSet.html#method.difference
 127 #[stable(feature = "rust1", since = "1.0.0")]
 128 pub struct Difference<'a, T: 'a> {
 129     a: Peekable<Iter<'a, T>>,
 130     b: Peekable<Iter<'a, T>>,
 131 }
 132
 133 #[stable(feature = "collection_debug", since = "1.17.0")]
 134 impl<'a, T: 'a + fmt::Debug> fmt::Debug for Difference<'a, T> {
 135     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 136         f.debug_tuple("Difference")
 137          .field(&self.clone())
 138          .finish()
 139     }
 140 }
 141
 142 /// A lazy iterator producing elements in the set symmetric difference (in-order).
 143 ///
 144 /// This structure is created by the [`symmetric_difference`] method on
 145 /// [`BTreeSet`].
 146 ///
 147 /// [`BTreeSet`]: struct.BTreeSet.html
 148 /// [`symmetric_difference`]: struct.BTreeSet.html#method.symmetric_difference
 149 #[stable(feature = "rust1", since = "1.0.0")]
 150 pub struct SymmetricDifference<'a, T: 'a> {
 151     a: Peekable<Iter<'a, T>>,
 152     b: Peekable<Iter<'a, T>>,
 153 }
 154
 155 #[stable(feature = "collection_debug", since = "1.17.0")]
 156 impl<'a, T: 'a + fmt::Debug> fmt::Debug for SymmetricDifference<'a, T> {
 157     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 158         f.debug_tuple("SymmetricDifference")
 159          .field(&self.clone())
 160          .finish()
 161     }
 162 }
 163
 164 /// A lazy iterator producing elements in the set intersection (in-order).
 165 ///
 166 /// This structure is created by the [`intersection`] method on [`BTreeSet`].
 167 ///
 168 /// [`BTreeSet`]: struct.BTreeSet.html
 169 /// [`intersection`]: struct.BTreeSet.html#method.intersection
 170 #[stable(feature = "rust1", since = "1.0.0")]
 171 pub struct Intersection<'a, T: 'a> {
 172     a: Peekable<Iter<'a, T>>,
 173     b: Peekable<Iter<'a, T>>,
 174 }
 175
 176 #[stable(feature = "collection_debug", since = "1.17.0")]
 177 impl<'a, T: 'a + fmt::Debug> fmt::Debug for Intersection<'a, T> {
 178     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 179         f.debug_tuple("Intersection")
 180          .field(&self.clone())
 181          .finish()
 182     }
 183 }
 184
 185 /// A lazy iterator producing elements in the set union (in-order).
 186 ///
 187 /// This structure is created by the [`union`] method on [`BTreeSet`].
 188 ///
 189 /// [`BTreeSet`]: struct.BTreeSet.html
 190 /// [`union`]: struct.BTreeSet.html#method.union
 191 #[stable(feature = "rust1", since = "1.0.0")]
 192 pub struct Union<'a, T: 'a> {
 193     a: Peekable<Iter<'a, T>>,
 194     b: Peekable<Iter<'a, T>>,
 195 }
 196
 197 #[stable(feature = "collection_debug", since = "1.17.0")]
 198 impl<'a, T: 'a + fmt::Debug> fmt::Debug for Union<'a, T> {
 199     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 200         f.debug_tuple("Union")
 201          .field(&self.clone())
 202          .finish()
 203     }
 204 }
 205
 206 impl<T: Ord> BTreeSet<T> {
 207     /// Makes a new `BTreeSet` with a reasonable choice of B.
 208     ///
 209     /// # Examples
 210     ///
 211     /// ```
 212     /// # #![allow(unused_mut)]
 213     /// use std::collections::BTreeSet;
 214     ///
 215     /// let mut set: BTreeSet<i32> = BTreeSet::new();
 216     /// ```
 217     #[stable(feature = "rust1", since = "1.0.0")]
 218     pub fn new() -> BTreeSet<T> {
 219         BTreeSet { map: BTreeMap::new() }
 220     }
 221 }
 222
 223 impl<T> BTreeSet<T> {
 224     /// Gets an iterator that visits the values in the `BTreeSet` in ascending order.
 225     ///
 226     /// # Examples
 227     ///
 228     /// ```
 229     /// use std::collections::BTreeSet;
 230     ///
 231     /// let set: BTreeSet<usize> = [1, 2, 3].iter().cloned().collect();
 232     /// let mut set_iter = set.iter();
 233     /// assert_eq!(set_iter.next(), Some(&1));
 234     /// assert_eq!(set_iter.next(), Some(&2));
 235     /// assert_eq!(set_iter.next(), Some(&3));
 236     /// assert_eq!(set_iter.next(), None);
 237     /// ```
 238     ///
 239     /// Values returned by the iterator are returned in ascending order:
 240     ///
 241     /// ```
 242     /// use std::collections::BTreeSet;
 243     ///
 244     /// let set: BTreeSet<usize> = [3, 1, 2].iter().cloned().collect();
 245     /// let mut set_iter = set.iter();
 246     /// assert_eq!(set_iter.next(), Some(&1));
 247     /// assert_eq!(set_iter.next(), Some(&2));
 248     /// assert_eq!(set_iter.next(), Some(&3));
 249     /// assert_eq!(set_iter.next(), None);
 250     /// ```
 251     #[stable(feature = "rust1", since = "1.0.0")]
 252     pub fn iter(&self) -> Iter<T> {
 253         Iter { iter: self.map.keys() }
 254     }
 255 }
 256
 257 impl<T: Ord> BTreeSet<T> {
 258     /// Constructs a double-ended iterator over a sub-range of elements in the set.
 259     /// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will
 260     /// yield elements from min (inclusive) to max (exclusive).
 261     /// The range may also be entered as `(Bound<T>, Bound<T>)`, so for example
 262     /// `range((Excluded(4), Included(10)))` will yield a left-exclusive, right-inclusive
 263     /// range from 4 to 10.
 264     ///
 265     /// # Examples
 266     ///
 267     /// ```
 268     /// use std::collections::BTreeSet;
 269     /// use std::collections::Bound::Included;
 270     ///
 271     /// let mut set = BTreeSet::new();
 272     /// set.insert(3);
 273     /// set.insert(5);
 274     /// set.insert(8);
 275     /// for &elem in set.range((Included(&4), Included(&8))) {
 276     ///     println!("{}", elem);
 277     /// }
 278     /// assert_eq!(Some(&5), set.range(4..).next());
 279     /// ```
 280     #[stable(feature = "btree_range", since = "1.17.0")]
 281     pub fn range<K: ?Sized, R>(&self, range: R) -> Range<T>
 282         where K: Ord, T: Borrow<K>, R: RangeArgument<K>
 283     {
 284         Range { iter: self.map.range(range) }
 285     }
 286 }
 287
 288 impl<T: Ord> BTreeSet<T> {
 289     /// Visits the values representing the difference,
 290     /// i.e. the values that are in `self` but not in `other`,
 291     /// in ascending order.
 292     ///
 293     /// # Examples
 294     ///
 295     /// ```
 296     /// use std::collections::BTreeSet;
 297     ///
 298     /// let mut a = BTreeSet::new();
 299     /// a.insert(1);
 300     /// a.insert(2);
 301     ///
 302     /// let mut b = BTreeSet::new();
 303     /// b.insert(2);
 304     /// b.insert(3);
 305     ///
 306     /// let diff: Vec<_> = a.difference(&b).cloned().collect();
 307     /// assert_eq!(diff, [1]);
 308     /// ```
 309     #[stable(feature = "rust1", since = "1.0.0")]
 310     pub fn difference<'a>(&'a self, other: &'a BTreeSet<T>) -> Difference<'a, T> {
 311         Difference {
 312             a: self.iter().peekable(),
 313             b: other.iter().peekable(),
 314         }
 315     }
 316
 317     /// Visits the values representing the symmetric difference,
 318     /// i.e. the values that are in `self` or in `other` but not in both,
 319     /// in ascending order.
 320     ///
 321     /// # Examples
 322     ///
 323     /// ```
 324     /// use std::collections::BTreeSet;
 325     ///
 326     /// let mut a = BTreeSet::new();
 327     /// a.insert(1);
 328     /// a.insert(2);
 329     ///
 330     /// let mut b = BTreeSet::new();
 331     /// b.insert(2);
 332     /// b.insert(3);
 333     ///
 334     /// let sym_diff: Vec<_> = a.symmetric_difference(&b).cloned().collect();
 335     /// assert_eq!(sym_diff, [1, 3]);
 336     /// ```
 337     #[stable(feature = "rust1", since = "1.0.0")]
 338     pub fn symmetric_difference<'a>(&'a self,
 339                                     other: &'a BTreeSet<T>)
 340                                     -> SymmetricDifference<'a, T> {
 341         SymmetricDifference {
 342             a: self.iter().peekable(),
 343             b: other.iter().peekable(),
 344         }
 345     }
 346
 347     /// Visits the values representing the intersection,
 348     /// i.e. the values that are both in `self` and `other`,
 349     /// in ascending order.
 350     ///
 351     /// # Examples
 352     ///
 353     /// ```
 354     /// use std::collections::BTreeSet;
 355     ///
 356     /// let mut a = BTreeSet::new();
 357     /// a.insert(1);
 358     /// a.insert(2);
 359     ///
 360     /// let mut b = BTreeSet::new();
 361     /// b.insert(2);
 362     /// b.insert(3);
 363     ///
 364     /// let intersection: Vec<_> = a.intersection(&b).cloned().collect();
 365     /// assert_eq!(intersection, [2]);
 366     /// ```
 367     #[stable(feature = "rust1", since = "1.0.0")]
 368     pub fn intersection<'a>(&'a self, other: &'a BTreeSet<T>) -> Intersection<'a, T> {
 369         Intersection {
 370             a: self.iter().peekable(),
 371             b: other.iter().peekable(),
 372         }
 373     }
 374
 375     /// Visits the values representing the union,
 376     /// i.e. all the values in `self` or `other`, without duplicates,
 377     /// in ascending order.
 378     ///
 379     /// # Examples
 380     ///
 381     /// ```
 382     /// use std::collections::BTreeSet;
 383     ///
 384     /// let mut a = BTreeSet::new();
 385     /// a.insert(1);
 386     ///
 387     /// let mut b = BTreeSet::new();
 388     /// b.insert(2);
 389     ///
 390     /// let union: Vec<_> = a.union(&b).cloned().collect();
 391     /// assert_eq!(union, [1, 2]);
 392     /// ```
 393     #[stable(feature = "rust1", since = "1.0.0")]
 394     pub fn union<'a>(&'a self, other: &'a BTreeSet<T>) -> Union<'a, T> {
 395         Union {
 396             a: self.iter().peekable(),
 397             b: other.iter().peekable(),
 398         }
 399     }
 400
 401     /// Returns the number of elements in the set.
 402     ///
 403     /// # Examples
 404     ///
 405     /// ```
 406     /// use std::collections::BTreeSet;
 407     ///
 408     /// let mut v = BTreeSet::new();
 409     /// assert_eq!(v.len(), 0);
 410     /// v.insert(1);
 411     /// assert_eq!(v.len(), 1);
 412     /// ```
 413     #[stable(feature = "rust1", since = "1.0.0")]
 414     pub fn len(&self) -> usize {
 415         self.map.len()
 416     }
 417
 418     /// Returns true if the set contains no elements.
 419     ///
 420     /// # Examples
 421     ///
 422     /// ```
 423     /// use std::collections::BTreeSet;
 424     ///
 425     /// let mut v = BTreeSet::new();
 426     /// assert!(v.is_empty());
 427     /// v.insert(1);
 428     /// assert!(!v.is_empty());
 429     /// ```
 430     #[stable(feature = "rust1", since = "1.0.0")]
 431     pub fn is_empty(&self) -> bool {
 432         self.len() == 0
 433     }
 434
 435     /// Clears the set, removing all values.
 436     ///
 437     /// # Examples
 438     ///
 439     /// ```
 440     /// use std::collections::BTreeSet;
 441     ///
 442     /// let mut v = BTreeSet::new();
 443     /// v.insert(1);
 444     /// v.clear();
 445     /// assert!(v.is_empty());
 446     /// ```
 447     #[stable(feature = "rust1", since = "1.0.0")]
 448     pub fn clear(&mut self) {
 449         self.map.clear()
 450     }
 451
 452     /// Returns `true` if the set contains a value.
 453     ///
 454     /// The value may be any borrowed form of the set's value type,
 455     /// but the ordering on the borrowed form *must* match the
 456     /// ordering on the value type.
 457     ///
 458     /// # Examples
 459     ///
 460     /// ```
 461     /// use std::collections::BTreeSet;
 462     ///
 463     /// let set: BTreeSet<_> = [1, 2, 3].iter().cloned().collect();
 464     /// assert_eq!(set.contains(&1), true);
 465     /// assert_eq!(set.contains(&4), false);
 466     /// ```
 467     #[stable(feature = "rust1", since = "1.0.0")]
 468     pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool
 469         where T: Borrow<Q>,
 470               Q: Ord
 471     {
 472         self.map.contains_key(value)
 473     }
 474
 475     /// Returns a reference to the value in the set, if any, that is equal to the given value.
 476     ///
 477     /// The value may be any borrowed form of the set's value type,
 478     /// but the ordering on the borrowed form *must* match the
 479     /// ordering on the value type.
 480     #[stable(feature = "set_recovery", since = "1.9.0")]
 481     pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>
 482         where T: Borrow<Q>,
 483               Q: Ord
 484     {
 485         Recover::get(&self.map, value)
 486     }
 487
 488     /// Returns `true` if `self` has no elements in common with `other`.
 489     /// This is equivalent to checking for an empty intersection.
 490     ///
 491     /// # Examples
 492     ///
 493     /// ```
 494     /// use std::collections::BTreeSet;
 495     ///
 496     /// let a: BTreeSet<_> = [1, 2, 3].iter().cloned().collect();
 497     /// let mut b = BTreeSet::new();
 498     ///
 499     /// assert_eq!(a.is_disjoint(&b), true);
 500     /// b.insert(4);
 501     /// assert_eq!(a.is_disjoint(&b), true);
 502     /// b.insert(1);
 503     /// assert_eq!(a.is_disjoint(&b), false);
 504     /// ```
 505     #[stable(feature = "rust1", since = "1.0.0")]
 506     pub fn is_disjoint(&self, other: &BTreeSet<T>) -> bool {
 507         self.intersection(other).next().is_none()
 508     }
 509
 510     /// Returns `true` if the set is a subset of another,
 511     /// i.e. `other` contains at least all the values in `self`.
 512     ///
 513     /// # Examples
 514     ///
 515     /// ```
 516     /// use std::collections::BTreeSet;
 517     ///
 518     /// let sup: BTreeSet<_> = [1, 2, 3].iter().cloned().collect();
 519     /// let mut set = BTreeSet::new();
 520     ///
 521     /// assert_eq!(set.is_subset(&sup), true);
 522     /// set.insert(2);
 523     /// assert_eq!(set.is_subset(&sup), true);
 524     /// set.insert(4);
 525     /// assert_eq!(set.is_subset(&sup), false);
 526     /// ```
 527     #[stable(feature = "rust1", since = "1.0.0")]
 528     pub fn is_subset(&self, other: &BTreeSet<T>) -> bool {
 529         // Stolen from TreeMap
 530         let mut x = self.iter();
 531         let mut y = other.iter();
 532         let mut a = x.next();
 533         let mut b = y.next();
 534         while a.is_some() {
 535             if b.is_none() {
 536                 return false;
 537             }
 538
 539             let a1 = a.unwrap();
 540             let b1 = b.unwrap();
 541
 542             match b1.cmp(a1) {
 543                 Less => (),
 544                 Greater => return false,
 545                 Equal => a = x.next(),
 546             }
 547
 548             b = y.next();
 549         }
 550         true
 551     }
 552
 553     /// Returns `true` if the set is a superset of another,
 554     /// i.e. `self` contains at least all the values in `other`.
 555     ///
 556     /// # Examples
 557     ///
 558     /// ```
 559     /// use std::collections::BTreeSet;
 560     ///
 561     /// let sub: BTreeSet<_> = [1, 2].iter().cloned().collect();
 562     /// let mut set = BTreeSet::new();
 563     ///
 564     /// assert_eq!(set.is_superset(&sub), false);
 565     ///
 566     /// set.insert(0);
 567     /// set.insert(1);
 568     /// assert_eq!(set.is_superset(&sub), false);
 569     ///
 570     /// set.insert(2);
 571     /// assert_eq!(set.is_superset(&sub), true);
 572     /// ```
 573     #[stable(feature = "rust1", since = "1.0.0")]
 574     pub fn is_superset(&self, other: &BTreeSet<T>) -> bool {
 575         other.is_subset(self)
 576     }
 577
 578     /// Adds a value to the set.
 579     ///
 580     /// If the set did not have this value present, `true` is returned.
 581     ///
 582     /// If the set did have this value present, `false` is returned, and the
 583     /// entry is not updated. See the [module-level documentation] for more.
 584     ///
 585     /// [module-level documentation]: index.html#insert-and-complex-keys
 586     ///
 587     /// # Examples
 588     ///
 589     /// ```
 590     /// use std::collections::BTreeSet;
 591     ///
 592     /// let mut set = BTreeSet::new();
 593     ///
 594     /// assert_eq!(set.insert(2), true);
 595     /// assert_eq!(set.insert(2), false);
 596     /// assert_eq!(set.len(), 1);
 597     /// ```
 598     #[stable(feature = "rust1", since = "1.0.0")]
 599     pub fn insert(&mut self, value: T) -> bool {
 600         self.map.insert(value, ()).is_none()
 601     }
 602
 603     /// Adds a value to the set, replacing the existing value, if any, that is equal to the given
 604     /// one. Returns the replaced value.
 605     #[stable(feature = "set_recovery", since = "1.9.0")]
 606     pub fn replace(&mut self, value: T) -> Option<T> {
 607         Recover::replace(&mut self.map, value)
 608     }
 609
 610     /// Removes a value from the set. Returns `true` if the value was
 611     /// present in the set.
 612     ///
 613     /// The value may be any borrowed form of the set's value type,
 614     /// but the ordering on the borrowed form *must* match the
 615     /// ordering on the value type.
 616     ///
 617     /// # Examples
 618     ///
 619     /// ```
 620     /// use std::collections::BTreeSet;
 621     ///
 622     /// let mut set = BTreeSet::new();
 623     ///
 624     /// set.insert(2);
 625     /// assert_eq!(set.remove(&2), true);
 626     /// assert_eq!(set.remove(&2), false);
 627     /// ```
 628     #[stable(feature = "rust1", since = "1.0.0")]
 629     pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool
 630         where T: Borrow<Q>,
 631               Q: Ord
 632     {
 633         self.map.remove(value).is_some()
 634     }
 635
 636     /// Removes and returns the value in the set, if any, that is equal to the given one.
 637     ///
 638     /// The value may be any borrowed form of the set's value type,
 639     /// but the ordering on the borrowed form *must* match the
 640     /// ordering on the value type.
 641     #[stable(feature = "set_recovery", since = "1.9.0")]
 642     pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
 643         where T: Borrow<Q>,
 644               Q: Ord
 645     {
 646         Recover::take(&mut self.map, value)
 647     }
 648
 649     /// Moves all elements from `other` into `Self`, leaving `other` empty.
 650     ///
 651     /// # Examples
 652     ///
 653     /// ```
 654     /// use std::collections::BTreeSet;
 655     ///
 656     /// let mut a = BTreeSet::new();
 657     /// a.insert(1);
 658     /// a.insert(2);
 659     /// a.insert(3);
 660     ///
 661     /// let mut b = BTreeSet::new();
 662     /// b.insert(3);
 663     /// b.insert(4);
 664     /// b.insert(5);
 665     ///
 666     /// a.append(&mut b);
 667     ///
 668     /// assert_eq!(a.len(), 5);
 669     /// assert_eq!(b.len(), 0);
 670     ///
 671     /// assert!(a.contains(&1));
 672     /// assert!(a.contains(&2));
 673     /// assert!(a.contains(&3));
 674     /// assert!(a.contains(&4));
 675     /// assert!(a.contains(&5));
 676     /// ```
 677     #[stable(feature = "btree_append", since = "1.11.0")]
 678     pub fn append(&mut self, other: &mut Self) {
 679         self.map.append(&mut other.map);
 680     }
 681
 682     /// Splits the collection into two at the given key. Returns everything after the given key,
 683     /// including the key.
 684     ///
 685     /// # Examples
 686     ///
 687     /// Basic usage:
 688     ///
 689     /// ```
 690     /// use std::collections::BTreeMap;
 691     ///
 692     /// let mut a = BTreeMap::new();
 693     /// a.insert(1, "a");
 694     /// a.insert(2, "b");
 695     /// a.insert(3, "c");
 696     /// a.insert(17, "d");
 697     /// a.insert(41, "e");
 698     ///
 699     /// let b = a.split_off(&3);
 700     ///
 701     /// assert_eq!(a.len(), 2);
 702     /// assert_eq!(b.len(), 3);
 703     ///
 704     /// assert_eq!(a[&1], "a");
 705     /// assert_eq!(a[&2], "b");
 706     ///
 707     /// assert_eq!(b[&3], "c");
 708     /// assert_eq!(b[&17], "d");
 709     /// assert_eq!(b[&41], "e");
 710     /// ```
 711     #[stable(feature = "btree_split_off", since = "1.11.0")]
 712     pub fn split_off<Q: ?Sized + Ord>(&mut self, key: &Q) -> Self where T: Borrow<Q> {
 713         BTreeSet { map: self.map.split_off(key) }
 714     }
 715 }
 716
 717 #[stable(feature = "rust1", since = "1.0.0")]
 718 impl<T: Ord> FromIterator<T> for BTreeSet<T> {
 719     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> BTreeSet<T> {
 720         let mut set = BTreeSet::new();
 721         set.extend(iter);
 722         set
 723     }
 724 }
 725
 726 #[stable(feature = "rust1", since = "1.0.0")]
 727 impl<T> IntoIterator for BTreeSet<T> {
 728     type Item = T;
 729     type IntoIter = IntoIter<T>;
 730
 731     /// Gets an iterator for moving out the BtreeSet's contents.
 732     ///
 733     /// # Examples
 734     ///
 735     /// ```
 736     /// use std::collections::BTreeSet;
 737     ///
 738     /// let set: BTreeSet<usize> = [1, 2, 3, 4].iter().cloned().collect();
 739     ///
 740     /// let v: Vec<_> = set.into_iter().collect();
 741     /// assert_eq!(v, [1, 2, 3, 4]);
 742     /// ```
 743     fn into_iter(self) -> IntoIter<T> {
 744         IntoIter { iter: self.map.into_iter() }
 745     }
 746 }
 747
 748 #[stable(feature = "rust1", since = "1.0.0")]
 749 impl<'a, T> IntoIterator for &'a BTreeSet<T> {
 750     type Item = &'a T;
 751     type IntoIter = Iter<'a, T>;
 752
 753     fn into_iter(self) -> Iter<'a, T> {
 754         self.iter()
 755     }
 756 }
 757
 758 #[stable(feature = "rust1", since = "1.0.0")]
 759 impl<T: Ord> Extend<T> for BTreeSet<T> {
 760     #[inline]
 761     fn extend<Iter: IntoIterator<Item = T>>(&mut self, iter: Iter) {
 762         for elem in iter {
 763             self.insert(elem);
 764         }
 765     }
 766 }
 767
 768 #[stable(feature = "extend_ref", since = "1.2.0")]
 769 impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BTreeSet<T> {
 770     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
 771         self.extend(iter.into_iter().cloned());
 772     }
 773 }
 774
 775 #[stable(feature = "rust1", since = "1.0.0")]
 776 impl<T: Ord> Default for BTreeSet<T> {
 777     /// Makes an empty `BTreeSet<T>` with a reasonable choice of B.
 778     fn default() -> BTreeSet<T> {
 779         BTreeSet::new()
 780     }
 781 }
 782
 783 #[stable(feature = "rust1", since = "1.0.0")]
 784 impl<'a, 'b, T: Ord + Clone> Sub<&'b BTreeSet<T>> for &'a BTreeSet<T> {
 785     type Output = BTreeSet<T>;
 786
 787     /// Returns the difference of `self` and `rhs` as a new `BTreeSet<T>`.
 788     ///
 789     /// # Examples
 790     ///
 791     /// ```
 792     /// use std::collections::BTreeSet;
 793     ///
 794     /// let a: BTreeSet<_> = vec![1, 2, 3].into_iter().collect();
 795     /// let b: BTreeSet<_> = vec![3, 4, 5].into_iter().collect();
 796     ///
 797     /// let result = &a - &b;
 798     /// let result_vec: Vec<_> = result.into_iter().collect();
 799     /// assert_eq!(result_vec, [1, 2]);
 800     /// ```
 801     fn sub(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
 802         self.difference(rhs).cloned().collect()
 803     }
 804 }
 805
 806 #[stable(feature = "rust1", since = "1.0.0")]
 807 impl<'a, 'b, T: Ord + Clone> BitXor<&'b BTreeSet<T>> for &'a BTreeSet<T> {
 808     type Output = BTreeSet<T>;
 809
 810     /// Returns the symmetric difference of `self` and `rhs` as a new `BTreeSet<T>`.
 811     ///
 812     /// # Examples
 813     ///
 814     /// ```
 815     /// use std::collections::BTreeSet;
 816     ///
 817     /// let a: BTreeSet<_> = vec![1, 2, 3].into_iter().collect();
 818     /// let b: BTreeSet<_> = vec![2, 3, 4].into_iter().collect();
 819     ///
 820     /// let result = &a ^ &b;
 821     /// let result_vec: Vec<_> = result.into_iter().collect();
 822     /// assert_eq!(result_vec, [1, 4]);
 823     /// ```
 824     fn bitxor(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
 825         self.symmetric_difference(rhs).cloned().collect()
 826     }
 827 }
 828
 829 #[stable(feature = "rust1", since = "1.0.0")]
 830 impl<'a, 'b, T: Ord + Clone> BitAnd<&'b BTreeSet<T>> for &'a BTreeSet<T> {
 831     type Output = BTreeSet<T>;
 832
 833     /// Returns the intersection of `self` and `rhs` as a new `BTreeSet<T>`.
 834     ///
 835     /// # Examples
 836     ///
 837     /// ```
 838     /// use std::collections::BTreeSet;
 839     ///
 840     /// let a: BTreeSet<_> = vec![1, 2, 3].into_iter().collect();
 841     /// let b: BTreeSet<_> = vec![2, 3, 4].into_iter().collect();
 842     ///
 843     /// let result = &a & &b;
 844     /// let result_vec: Vec<_> = result.into_iter().collect();
 845     /// assert_eq!(result_vec, [2, 3]);
 846     /// ```
 847     fn bitand(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
 848         self.intersection(rhs).cloned().collect()
 849     }
 850 }
 851
 852 #[stable(feature = "rust1", since = "1.0.0")]
 853 impl<'a, 'b, T: Ord + Clone> BitOr<&'b BTreeSet<T>> for &'a BTreeSet<T> {
 854     type Output = BTreeSet<T>;
 855
 856     /// Returns the union of `self` and `rhs` as a new `BTreeSet<T>`.
 857     ///
 858     /// # Examples
 859     ///
 860     /// ```
 861     /// use std::collections::BTreeSet;
 862     ///
 863     /// let a: BTreeSet<_> = vec![1, 2, 3].into_iter().collect();
 864     /// let b: BTreeSet<_> = vec![3, 4, 5].into_iter().collect();
 865     ///
 866     /// let result = &a | &b;
 867     /// let result_vec: Vec<_> = result.into_iter().collect();
 868     /// assert_eq!(result_vec, [1, 2, 3, 4, 5]);
 869     /// ```
 870     fn bitor(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
 871         self.union(rhs).cloned().collect()
 872     }
 873 }
 874
 875 #[stable(feature = "rust1", since = "1.0.0")]
 876 impl<T: Debug> Debug for BTreeSet<T> {
 877     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 878         f.debug_set().entries(self.iter()).finish()
 879     }
 880 }
 881
 882 #[stable(feature = "rust1", since = "1.0.0")]
 883 impl<'a, T> Clone for Iter<'a, T> {
 884     fn clone(&self) -> Iter<'a, T> {
 885         Iter { iter: self.iter.clone() }
 886     }
 887 }
 888 #[stable(feature = "rust1", since = "1.0.0")]
 889 impl<'a, T> Iterator for Iter<'a, T> {
 890     type Item = &'a T;
 891
 892     fn next(&mut self) -> Option<&'a T> {
 893         self.iter.next()
 894     }
 895     fn size_hint(&self) -> (usize, Option<usize>) {
 896         self.iter.size_hint()
 897     }
 898 }
 899 #[stable(feature = "rust1", since = "1.0.0")]
 900 impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
 901     fn next_back(&mut self) -> Option<&'a T> {
 902         self.iter.next_back()
 903     }
 904 }
 905 #[stable(feature = "rust1", since = "1.0.0")]
 906 impl<'a, T> ExactSizeIterator for Iter<'a, T> {
 907     fn len(&self) -> usize { self.iter.len() }
 908 }
 909
 910 #[unstable(feature = "fused", issue = "35602")]
 911 impl<'a, T> FusedIterator for Iter<'a, T> {}
 912
 913 #[stable(feature = "rust1", since = "1.0.0")]
 914 impl<T> Iterator for IntoIter<T> {
 915     type Item = T;
 916
 917     fn next(&mut self) -> Option<T> {
 918         self.iter.next().map(|(k, _)| k)
 919     }
 920     fn size_hint(&self) -> (usize, Option<usize>) {
 921         self.iter.size_hint()
 922     }
 923 }
 924 #[stable(feature = "rust1", since = "1.0.0")]
 925 impl<T> DoubleEndedIterator for IntoIter<T> {
 926     fn next_back(&mut self) -> Option<T> {
 927         self.iter.next_back().map(|(k, _)| k)
 928     }
 929 }
 930 #[stable(feature = "rust1", since = "1.0.0")]
 931 impl<T> ExactSizeIterator for IntoIter<T> {
 932     fn len(&self) -> usize { self.iter.len() }
 933 }
 934
 935 #[unstable(feature = "fused", issue = "35602")]
 936 impl<T> FusedIterator for IntoIter<T> {}
 937
 938 impl<'a, T> Clone for Range<'a, T> {
 939     fn clone(&self) -> Range<'a, T> {
 940         Range { iter: self.iter.clone() }
 941     }
 942 }
 943 impl<'a, T> Iterator for Range<'a, T> {
 944     type Item = &'a T;
 945
 946     fn next(&mut self) -> Option<&'a T> {
 947         self.iter.next().map(|(k, _)| k)
 948     }
 949 }
 950 impl<'a, T> DoubleEndedIterator for Range<'a, T> {
 951     fn next_back(&mut self) -> Option<&'a T> {
 952         self.iter.next_back().map(|(k, _)| k)
 953     }
 954 }
 955
 956 #[unstable(feature = "fused", issue = "35602")]
 957 impl<'a, T> FusedIterator for Range<'a, T> {}
 958
 959 /// Compare `x` and `y`, but return `short` if x is None and `long` if y is None
 960 fn cmp_opt<T: Ord>(x: Option<&T>, y: Option<&T>, short: Ordering, long: Ordering) -> Ordering {
 961     match (x, y) {
 962         (None, _) => short,
 963         (_, None) => long,
 964         (Some(x1), Some(y1)) => x1.cmp(y1),
 965     }
 966 }
 967
 968 #[stable(feature = "rust1", since = "1.0.0")]
 969 impl<'a, T> Clone for Difference<'a, T> {
 970     fn clone(&self) -> Difference<'a, T> {
 971         Difference {
 972             a: self.a.clone(),
 973             b: self.b.clone(),
 974         }
 975     }
 976 }
 977 #[stable(feature = "rust1", since = "1.0.0")]
 978 impl<'a, T: Ord> Iterator for Difference<'a, T> {
 979     type Item = &'a T;
 980
 981     fn next(&mut self) -> Option<&'a T> {
 982         loop {
 983             match cmp_opt(self.a.peek(), self.b.peek(), Less, Less) {
 984                 Less => return self.a.next(),
 985                 Equal => {
 986                     self.a.next();
 987                     self.b.next();
 988                 }
 989                 Greater => {
 990                     self.b.next();
 991                 }
 992             }
 993         }
 994     }
 995
 996     fn size_hint(&self) -> (usize, Option<usize>) {
 997         let a_len = self.a.len();
 998         let b_len = self.b.len();
 999         (a_len.saturating_sub(b_len), Some(a_len))
1000     }
1001 }
1002
1003 #[unstable(feature = "fused", issue = "35602")]
1004 impl<'a, T: Ord> FusedIterator for Difference<'a, T> {}
1005
1006 #[stable(feature = "rust1", since = "1.0.0")]
1007 impl<'a, T> Clone for SymmetricDifference<'a, T> {
1008     fn clone(&self) -> SymmetricDifference<'a, T> {
1009         SymmetricDifference {
1010             a: self.a.clone(),
1011             b: self.b.clone(),
1012         }
1013     }
1014 }
1015 #[stable(feature = "rust1", since = "1.0.0")]
1016 impl<'a, T: Ord> Iterator for SymmetricDifference<'a, T> {
1017     type Item = &'a T;
1018
1019     fn next(&mut self) -> Option<&'a T> {
1020         loop {
1021             match cmp_opt(self.a.peek(), self.b.peek(), Greater, Less) {
1022                 Less => return self.a.next(),
1023                 Equal => {
1024                     self.a.next();
1025                     self.b.next();
1026                 }
1027                 Greater => return self.b.next(),
1028             }
1029         }
1030     }
1031
1032     fn size_hint(&self) -> (usize, Option<usize>) {
1033         (0, Some(self.a.len() + self.b.len()))
1034     }
1035 }
1036
1037 #[unstable(feature = "fused", issue = "35602")]
1038 impl<'a, T: Ord> FusedIterator for SymmetricDifference<'a, T> {}
1039
1040 #[stable(feature = "rust1", since = "1.0.0")]
1041 impl<'a, T> Clone for Intersection<'a, T> {
1042     fn clone(&self) -> Intersection<'a, T> {
1043         Intersection {
1044             a: self.a.clone(),
1045             b: self.b.clone(),
1046         }
1047     }
1048 }
1049 #[stable(feature = "rust1", since = "1.0.0")]
1050 impl<'a, T: Ord> Iterator for Intersection<'a, T> {
1051     type Item = &'a T;
1052
1053     fn next(&mut self) -> Option<&'a T> {
1054         loop {
1055             let o_cmp = match (self.a.peek(), self.b.peek()) {
1056                 (None, _) => None,
1057                 (_, None) => None,
1058                 (Some(a1), Some(b1)) => Some(a1.cmp(b1)),
1059             };
1060             match o_cmp {
1061                 None => return None,
1062                 Some(Less) => {
1063                     self.a.next();
1064                 }
1065                 Some(Equal) => {
1066                     self.b.next();
1067                     return self.a.next();
1068                 }
1069                 Some(Greater) => {
1070                     self.b.next();
1071                 }
1072             }
1073         }
1074     }
1075
1076     fn size_hint(&self) -> (usize, Option<usize>) {
1077         (0, Some(min(self.a.len(), self.b.len())))
1078     }
1079 }
1080
1081 #[unstable(feature = "fused", issue = "35602")]
1082 impl<'a, T: Ord> FusedIterator for Intersection<'a, T> {}
1083
1084 #[stable(feature = "rust1", since = "1.0.0")]
1085 impl<'a, T> Clone for Union<'a, T> {
1086     fn clone(&self) -> Union<'a, T> {
1087         Union {
1088             a: self.a.clone(),
1089             b: self.b.clone(),
1090         }
1091     }
1092 }
1093 #[stable(feature = "rust1", since = "1.0.0")]
1094 impl<'a, T: Ord> Iterator for Union<'a, T> {
1095     type Item = &'a T;
1096
1097     fn next(&mut self) -> Option<&'a T> {
1098         loop {
1099             match cmp_opt(self.a.peek(), self.b.peek(), Greater, Less) {
1100                 Less => return self.a.next(),
1101                 Equal => {
1102                     self.b.next();
1103                     return self.a.next();
1104                 }
1105                 Greater => return self.b.next(),
1106             }
1107         }
1108     }
1109
1110     fn size_hint(&self) -> (usize, Option<usize>) {
1111         let a_len = self.a.len();
1112         let b_len = self.b.len();
1113         (max(a_len, b_len), Some(a_len + b_len))
1114     }
1115 }
1116
1117 #[unstable(feature = "fused", issue = "35602")]
1118 impl<'a, T: Ord> FusedIterator for Union<'a, T> {}