library/alloc/src/collections/btree/set.rs

   1 // This is pretty much entirely stolen from TreeSet, since BTreeMap has an identical interface
   2 // to TreeMap
   3
   4 use core::borrow::Borrow;
   5 use core::cmp::Ordering::{Equal, Greater, Less};
   6 use core::cmp::{max, min};
   7 use core::fmt::{self, Debug};
   8 use core::iter::{FromIterator, FusedIterator, Peekable};
   9 use core::ops::{BitAnd, BitOr, BitXor, RangeBounds, Sub};
  10
  11 use super::map::{BTreeMap, Keys};
  12 use super::merge_iter::MergeIterInner;
  13 use super::Recover;
  14
  15 // FIXME(conventions): implement bounded iterators
  16
  17 /// A set based on a B-Tree.
  18 ///
  19 /// See [`BTreeMap`]'s documentation for a detailed discussion of this collection's performance
  20 /// benefits and drawbacks.
  21 ///
  22 /// It is a logic error for an item to be modified in such a way that the item's ordering relative
  23 /// to any other item, as determined by the [`Ord`] trait, changes while it is in the set. This is
  24 /// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
  25 ///
  26 /// [`Ord`]: core::cmp::Ord
  27 /// [`Cell`]: core::cell::Cell
  28 /// [`RefCell`]: core::cell::RefCell
  29 ///
  30 /// # Examples
  31 ///
  32 /// ```
  33 /// use std::collections::BTreeSet;
  34 ///
  35 /// // Type inference lets us omit an explicit type signature (which
  36 /// // would be `BTreeSet<&str>` in this example).
  37 /// let mut books = BTreeSet::new();
  38 ///
  39 /// // Add some books.
  40 /// books.insert("A Dance With Dragons");
  41 /// books.insert("To Kill a Mockingbird");
  42 /// books.insert("The Odyssey");
  43 /// books.insert("The Great Gatsby");
  44 ///
  45 /// // Check for a specific one.
  46 /// if !books.contains("The Winds of Winter") {
  47 ///     println!("We have {} books, but The Winds of Winter ain't one.",
  48 ///              books.len());
  49 /// }
  50 ///
  51 /// // Remove a book.
  52 /// books.remove("The Odyssey");
  53 ///
  54 /// // Iterate over everything.
  55 /// for book in &books {
  56 ///     println!("{}", book);
  57 /// }
  58 /// ```
  59 #[derive(Hash, PartialEq, Eq, Ord, PartialOrd)]
  60 #[stable(feature = "rust1", since = "1.0.0")]
  61 pub struct BTreeSet<T> {
  62     map: BTreeMap<T, ()>,
  63 }
  64
  65 #[stable(feature = "rust1", since = "1.0.0")]
  66 impl<T: Clone> Clone for BTreeSet<T> {
  67     fn clone(&self) -> Self {
  68         BTreeSet { map: self.map.clone() }
  69     }
  70
  71     fn clone_from(&mut self, other: &Self) {
  72         self.map.clone_from(&other.map);
  73     }
  74 }
  75
  76 /// An iterator over the items of a `BTreeSet`.
  77 ///
  78 /// This `struct` is created by the [`iter`] method on [`BTreeSet`].
  79 /// See its documentation for more.
  80 ///
  81 /// [`iter`]: BTreeSet::iter
  82 #[stable(feature = "rust1", since = "1.0.0")]
  83 pub struct Iter<'a, T: 'a> {
  84     iter: Keys<'a, T, ()>,
  85 }
  86
  87 #[stable(feature = "collection_debug", since = "1.17.0")]
  88 impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
  89     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  90         f.debug_tuple("Iter").field(&self.iter.clone()).finish()
  91     }
  92 }
  93
  94 /// An owning iterator over the items of a `BTreeSet`.
  95 ///
  96 /// This `struct` is created by the [`into_iter`] method on [`BTreeSet`]
  97 /// (provided by the `IntoIterator` trait). See its documentation for more.
  98 ///
  99 /// [`into_iter`]: BTreeSet#method.into_iter
 100 #[stable(feature = "rust1", since = "1.0.0")]
 101 #[derive(Debug)]
 102 pub struct IntoIter<T> {
 103     iter: super::map::IntoIter<T, ()>,
 104 }
 105
 106 /// An iterator over a sub-range of items in a `BTreeSet`.
 107 ///
 108 /// This `struct` is created by the [`range`] method on [`BTreeSet`].
 109 /// See its documentation for more.
 110 ///
 111 /// [`range`]: BTreeSet::range
 112 #[derive(Debug)]
 113 #[stable(feature = "btree_range", since = "1.17.0")]
 114 pub struct Range<'a, T: 'a> {
 115     iter: super::map::Range<'a, T, ()>,
 116 }
 117
 118 /// A lazy iterator producing elements in the difference of `BTreeSet`s.
 119 ///
 120 /// This `struct` is created by the [`difference`] method on [`BTreeSet`].
 121 /// See its documentation for more.
 122 ///
 123 /// [`difference`]: BTreeSet::difference
 124 #[stable(feature = "rust1", since = "1.0.0")]
 125 pub struct Difference<'a, T: 'a> {
 126     inner: DifferenceInner<'a, T>,
 127 }
 128 #[derive(Debug)]
 129 enum DifferenceInner<'a, T: 'a> {
 130     Stitch {
 131         // iterate all of `self` and some of `other`, spotting matches along the way
 132         self_iter: Iter<'a, T>,
 133         other_iter: Peekable<Iter<'a, T>>,
 134     },
 135     Search {
 136         // iterate `self`, look up in `other`
 137         self_iter: Iter<'a, T>,
 138         other_set: &'a BTreeSet<T>,
 139     },
 140     Iterate(Iter<'a, T>), // simply produce all values in `self`
 141 }
 142
 143 #[stable(feature = "collection_debug", since = "1.17.0")]
 144 impl<T: fmt::Debug> fmt::Debug for Difference<'_, T> {
 145     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 146         f.debug_tuple("Difference").field(&self.inner).finish()
 147     }
 148 }
 149
 150 /// A lazy iterator producing elements in the symmetric difference of `BTreeSet`s.
 151 ///
 152 /// This `struct` is created by the [`symmetric_difference`] method on
 153 /// [`BTreeSet`]. See its documentation for more.
 154 ///
 155 /// [`symmetric_difference`]: BTreeSet::symmetric_difference
 156 #[stable(feature = "rust1", since = "1.0.0")]
 157 pub struct SymmetricDifference<'a, T: 'a>(MergeIterInner<Iter<'a, T>>);
 158
 159 #[stable(feature = "collection_debug", since = "1.17.0")]
 160 impl<T: fmt::Debug> fmt::Debug for SymmetricDifference<'_, T> {
 161     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 162         f.debug_tuple("SymmetricDifference").field(&self.0).finish()
 163     }
 164 }
 165
 166 /// A lazy iterator producing elements in the intersection of `BTreeSet`s.
 167 ///
 168 /// This `struct` is created by the [`intersection`] method on [`BTreeSet`].
 169 /// See its documentation for more.
 170 ///
 171 /// [`intersection`]: BTreeSet::intersection
 172 #[stable(feature = "rust1", since = "1.0.0")]
 173 pub struct Intersection<'a, T: 'a> {
 174     inner: IntersectionInner<'a, T>,
 175 }
 176 #[derive(Debug)]
 177 enum IntersectionInner<'a, T: 'a> {
 178     Stitch {
 179         // iterate similarly sized sets jointly, spotting matches along the way
 180         a: Iter<'a, T>,
 181         b: Iter<'a, T>,
 182     },
 183     Search {
 184         // iterate a small set, look up in the large set
 185         small_iter: Iter<'a, T>,
 186         large_set: &'a BTreeSet<T>,
 187     },
 188     Answer(Option<&'a T>), // return a specific value or emptiness
 189 }
 190
 191 #[stable(feature = "collection_debug", since = "1.17.0")]
 192 impl<T: fmt::Debug> fmt::Debug for Intersection<'_, T> {
 193     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 194         f.debug_tuple("Intersection").field(&self.inner).finish()
 195     }
 196 }
 197
 198 /// A lazy iterator producing elements in the union of `BTreeSet`s.
 199 ///
 200 /// This `struct` is created by the [`union`] method on [`BTreeSet`].
 201 /// See its documentation for more.
 202 ///
 203 /// [`union`]: BTreeSet::union
 204 #[stable(feature = "rust1", since = "1.0.0")]
 205 pub struct Union<'a, T: 'a>(MergeIterInner<Iter<'a, T>>);
 206
 207 #[stable(feature = "collection_debug", since = "1.17.0")]
 208 impl<T: fmt::Debug> fmt::Debug for Union<'_, T> {
 209     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 210         f.debug_tuple("Union").field(&self.0).finish()
 211     }
 212 }
 213
 214 // This constant is used by functions that compare two sets.
 215 // It estimates the relative size at which searching performs better
 216 // than iterating, based on the benchmarks in
 217 // https://github.com/ssomers/rust_bench_btreeset_intersection.
 218 // It's used to divide rather than multiply sizes, to rule out overflow,
 219 // and it's a power of two to make that division cheap.
 220 const ITER_PERFORMANCE_TIPPING_SIZE_DIFF: usize = 16;
 221
 222 impl<T: Ord> BTreeSet<T> {
 223     /// Makes a new, empty `BTreeSet`.
 224     ///
 225     /// Does not allocate anything on its own.
 226     ///
 227     /// # Examples
 228     ///
 229     /// ```
 230     /// # #![allow(unused_mut)]
 231     /// use std::collections::BTreeSet;
 232     ///
 233     /// let mut set: BTreeSet<i32> = BTreeSet::new();
 234     /// ```
 235     #[stable(feature = "rust1", since = "1.0.0")]
 236     #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
 237     pub const fn new() -> BTreeSet<T> {
 238         BTreeSet { map: BTreeMap::new() }
 239     }
 240
 241     /// Constructs a double-ended iterator over a sub-range of elements in the set.
 242     /// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will
 243     /// yield elements from min (inclusive) to max (exclusive).
 244     /// The range may also be entered as `(Bound<T>, Bound<T>)`, so for example
 245     /// `range((Excluded(4), Included(10)))` will yield a left-exclusive, right-inclusive
 246     /// range from 4 to 10.
 247     ///
 248     /// # Examples
 249     ///
 250     /// ```
 251     /// use std::collections::BTreeSet;
 252     /// use std::ops::Bound::Included;
 253     ///
 254     /// let mut set = BTreeSet::new();
 255     /// set.insert(3);
 256     /// set.insert(5);
 257     /// set.insert(8);
 258     /// for &elem in set.range((Included(&4), Included(&8))) {
 259     ///     println!("{}", elem);
 260     /// }
 261     /// assert_eq!(Some(&5), set.range(4..).next());
 262     /// ```
 263     #[stable(feature = "btree_range", since = "1.17.0")]
 264     pub fn range<K: ?Sized, R>(&self, range: R) -> Range<'_, T>
 265     where
 266         K: Ord,
 267         T: Borrow<K>,
 268         R: RangeBounds<K>,
 269     {
 270         Range { iter: self.map.range(range) }
 271     }
 272
 273     /// Visits the values representing the difference,
 274     /// i.e., the values that are in `self` but not in `other`,
 275     /// in ascending order.
 276     ///
 277     /// # Examples
 278     ///
 279     /// ```
 280     /// use std::collections::BTreeSet;
 281     ///
 282     /// let mut a = BTreeSet::new();
 283     /// a.insert(1);
 284     /// a.insert(2);
 285     ///
 286     /// let mut b = BTreeSet::new();
 287     /// b.insert(2);
 288     /// b.insert(3);
 289     ///
 290     /// let diff: Vec<_> = a.difference(&b).cloned().collect();
 291     /// assert_eq!(diff, [1]);
 292     /// ```
 293     #[stable(feature = "rust1", since = "1.0.0")]
 294     pub fn difference<'a>(&'a self, other: &'a BTreeSet<T>) -> Difference<'a, T> {
 295         let (self_min, self_max) =
 296             if let (Some(self_min), Some(self_max)) = (self.first(), self.last()) {
 297                 (self_min, self_max)
 298             } else {
 299                 return Difference { inner: DifferenceInner::Iterate(self.iter()) };
 300             };
 301         let (other_min, other_max) =
 302             if let (Some(other_min), Some(other_max)) = (other.first(), other.last()) {
 303                 (other_min, other_max)
 304             } else {
 305                 return Difference { inner: DifferenceInner::Iterate(self.iter()) };
 306             };
 307         Difference {
 308             inner: match (self_min.cmp(other_max), self_max.cmp(other_min)) {
 309                 (Greater, _) | (_, Less) => DifferenceInner::Iterate(self.iter()),
 310                 (Equal, _) => {
 311                     let mut self_iter = self.iter();
 312                     self_iter.next();
 313                     DifferenceInner::Iterate(self_iter)
 314                 }
 315                 (_, Equal) => {
 316                     let mut self_iter = self.iter();
 317                     self_iter.next_back();
 318                     DifferenceInner::Iterate(self_iter)
 319                 }
 320                 _ if self.len() <= other.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
 321                     DifferenceInner::Search { self_iter: self.iter(), other_set: other }
 322                 }
 323                 _ => DifferenceInner::Stitch {
 324                     self_iter: self.iter(),
 325                     other_iter: other.iter().peekable(),
 326                 },
 327             },
 328         }
 329     }
 330
 331     /// Visits the values representing the symmetric difference,
 332     /// i.e., the values that are in `self` or in `other` but not in both,
 333     /// in ascending order.
 334     ///
 335     /// # Examples
 336     ///
 337     /// ```
 338     /// use std::collections::BTreeSet;
 339     ///
 340     /// let mut a = BTreeSet::new();
 341     /// a.insert(1);
 342     /// a.insert(2);
 343     ///
 344     /// let mut b = BTreeSet::new();
 345     /// b.insert(2);
 346     /// b.insert(3);
 347     ///
 348     /// let sym_diff: Vec<_> = a.symmetric_difference(&b).cloned().collect();
 349     /// assert_eq!(sym_diff, [1, 3]);
 350     /// ```
 351     #[stable(feature = "rust1", since = "1.0.0")]
 352     pub fn symmetric_difference<'a>(
 353         &'a self,
 354         other: &'a BTreeSet<T>,
 355     ) -> SymmetricDifference<'a, T> {
 356         SymmetricDifference(MergeIterInner::new(self.iter(), other.iter()))
 357     }
 358
 359     /// Visits the values representing the intersection,
 360     /// i.e., the values that are both in `self` and `other`,
 361     /// in ascending order.
 362     ///
 363     /// # Examples
 364     ///
 365     /// ```
 366     /// use std::collections::BTreeSet;
 367     ///
 368     /// let mut a = BTreeSet::new();
 369     /// a.insert(1);
 370     /// a.insert(2);
 371     ///
 372     /// let mut b = BTreeSet::new();
 373     /// b.insert(2);
 374     /// b.insert(3);
 375     ///
 376     /// let intersection: Vec<_> = a.intersection(&b).cloned().collect();
 377     /// assert_eq!(intersection, [2]);
 378     /// ```
 379     #[stable(feature = "rust1", since = "1.0.0")]
 380     pub fn intersection<'a>(&'a self, other: &'a BTreeSet<T>) -> Intersection<'a, T> {
 381         let (self_min, self_max) =
 382             if let (Some(self_min), Some(self_max)) = (self.first(), self.last()) {
 383                 (self_min, self_max)
 384             } else {
 385                 return Intersection { inner: IntersectionInner::Answer(None) };
 386             };
 387         let (other_min, other_max) =
 388             if let (Some(other_min), Some(other_max)) = (other.first(), other.last()) {
 389                 (other_min, other_max)
 390             } else {
 391                 return Intersection { inner: IntersectionInner::Answer(None) };
 392             };
 393         Intersection {
 394             inner: match (self_min.cmp(other_max), self_max.cmp(other_min)) {
 395                 (Greater, _) | (_, Less) => IntersectionInner::Answer(None),
 396                 (Equal, _) => IntersectionInner::Answer(Some(self_min)),
 397                 (_, Equal) => IntersectionInner::Answer(Some(self_max)),
 398                 _ if self.len() <= other.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
 399                     IntersectionInner::Search { small_iter: self.iter(), large_set: other }
 400                 }
 401                 _ if other.len() <= self.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
 402                     IntersectionInner::Search { small_iter: other.iter(), large_set: self }
 403                 }
 404                 _ => IntersectionInner::Stitch { a: self.iter(), b: other.iter() },
 405             },
 406         }
 407     }
 408
 409     /// Visits the values representing the union,
 410     /// i.e., all the values in `self` or `other`, without duplicates,
 411     /// in ascending order.
 412     ///
 413     /// # Examples
 414     ///
 415     /// ```
 416     /// use std::collections::BTreeSet;
 417     ///
 418     /// let mut a = BTreeSet::new();
 419     /// a.insert(1);
 420     ///
 421     /// let mut b = BTreeSet::new();
 422     /// b.insert(2);
 423     ///
 424     /// let union: Vec<_> = a.union(&b).cloned().collect();
 425     /// assert_eq!(union, [1, 2]);
 426     /// ```
 427     #[stable(feature = "rust1", since = "1.0.0")]
 428     pub fn union<'a>(&'a self, other: &'a BTreeSet<T>) -> Union<'a, T> {
 429         Union(MergeIterInner::new(self.iter(), other.iter()))
 430     }
 431
 432     /// Clears the set, removing all values.
 433     ///
 434     /// # Examples
 435     ///
 436     /// ```
 437     /// use std::collections::BTreeSet;
 438     ///
 439     /// let mut v = BTreeSet::new();
 440     /// v.insert(1);
 441     /// v.clear();
 442     /// assert!(v.is_empty());
 443     /// ```
 444     #[stable(feature = "rust1", since = "1.0.0")]
 445     pub fn clear(&mut self) {
 446         self.map.clear()
 447     }
 448
 449     /// Returns `true` if the set contains a value.
 450     ///
 451     /// The value may be any borrowed form of the set's value type,
 452     /// but the ordering on the borrowed form *must* match the
 453     /// ordering on the value type.
 454     ///
 455     /// # Examples
 456     ///
 457     /// ```
 458     /// use std::collections::BTreeSet;
 459     ///
 460     /// let set: BTreeSet<_> = [1, 2, 3].iter().cloned().collect();
 461     /// assert_eq!(set.contains(&1), true);
 462     /// assert_eq!(set.contains(&4), false);
 463     /// ```
 464     #[stable(feature = "rust1", since = "1.0.0")]
 465     pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool
 466     where
 467         T: Borrow<Q>,
 468         Q: Ord,
 469     {
 470         self.map.contains_key(value)
 471     }
 472
 473     /// Returns a reference to the value in the set, if any, that is equal to the given value.
 474     ///
 475     /// The value may be any borrowed form of the set's value type,
 476     /// but the ordering on the borrowed form *must* match the
 477     /// ordering on the value type.
 478     ///
 479     /// # Examples
 480     ///
 481     /// ```
 482     /// use std::collections::BTreeSet;
 483     ///
 484     /// let set: BTreeSet<_> = [1, 2, 3].iter().cloned().collect();
 485     /// assert_eq!(set.get(&2), Some(&2));
 486     /// assert_eq!(set.get(&4), None);
 487     /// ```
 488     #[stable(feature = "set_recovery", since = "1.9.0")]
 489     pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>
 490     where
 491         T: Borrow<Q>,
 492         Q: Ord,
 493     {
 494         Recover::get(&self.map, value)
 495     }
 496
 497     /// Returns `true` if `self` has no elements in common with `other`.
 498     /// This is equivalent to checking for an empty intersection.
 499     ///
 500     /// # Examples
 501     ///
 502     /// ```
 503     /// use std::collections::BTreeSet;
 504     ///
 505     /// let a: BTreeSet<_> = [1, 2, 3].iter().cloned().collect();
 506     /// let mut b = BTreeSet::new();
 507     ///
 508     /// assert_eq!(a.is_disjoint(&b), true);
 509     /// b.insert(4);
 510     /// assert_eq!(a.is_disjoint(&b), true);
 511     /// b.insert(1);
 512     /// assert_eq!(a.is_disjoint(&b), false);
 513     /// ```
 514     #[stable(feature = "rust1", since = "1.0.0")]
 515     pub fn is_disjoint(&self, other: &BTreeSet<T>) -> bool {
 516         self.intersection(other).next().is_none()
 517     }
 518
 519     /// Returns `true` if the set is a subset of another,
 520     /// i.e., `other` contains at least all the values in `self`.
 521     ///
 522     /// # Examples
 523     ///
 524     /// ```
 525     /// use std::collections::BTreeSet;
 526     ///
 527     /// let sup: BTreeSet<_> = [1, 2, 3].iter().cloned().collect();
 528     /// let mut set = BTreeSet::new();
 529     ///
 530     /// assert_eq!(set.is_subset(&sup), true);
 531     /// set.insert(2);
 532     /// assert_eq!(set.is_subset(&sup), true);
 533     /// set.insert(4);
 534     /// assert_eq!(set.is_subset(&sup), false);
 535     /// ```
 536     #[stable(feature = "rust1", since = "1.0.0")]
 537     pub fn is_subset(&self, other: &BTreeSet<T>) -> bool {
 538         // Same result as self.difference(other).next().is_none()
 539         // but the code below is faster (hugely in some cases).
 540         if self.len() > other.len() {
 541             return false;
 542         }
 543         let (self_min, self_max) =
 544             if let (Some(self_min), Some(self_max)) = (self.first(), self.last()) {
 545                 (self_min, self_max)
 546             } else {
 547                 return true; // self is empty
 548             };
 549         let (other_min, other_max) =
 550             if let (Some(other_min), Some(other_max)) = (other.first(), other.last()) {
 551                 (other_min, other_max)
 552             } else {
 553                 return false; // other is empty
 554             };
 555         let mut self_iter = self.iter();
 556         match self_min.cmp(other_min) {
 557             Less => return false,
 558             Equal => {
 559                 self_iter.next();
 560             }
 561             Greater => (),
 562         }
 563         match self_max.cmp(other_max) {
 564             Greater => return false,
 565             Equal => {
 566                 self_iter.next_back();
 567             }
 568             Less => (),
 569         }
 570         if self_iter.len() <= other.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF {
 571             for next in self_iter {
 572                 if !other.contains(next) {
 573                     return false;
 574                 }
 575             }
 576         } else {
 577             let mut other_iter = other.iter();
 578             other_iter.next();
 579             other_iter.next_back();
 580             let mut self_next = self_iter.next();
 581             while let Some(self1) = self_next {
 582                 match other_iter.next().map_or(Less, |other1| self1.cmp(other1)) {
 583                     Less => return false,
 584                     Equal => self_next = self_iter.next(),
 585                     Greater => (),
 586                 }
 587             }
 588         }
 589         true
 590     }
 591
 592     /// Returns `true` if the set is a superset of another,
 593     /// i.e., `self` contains at least all the values in `other`.
 594     ///
 595     /// # Examples
 596     ///
 597     /// ```
 598     /// use std::collections::BTreeSet;
 599     ///
 600     /// let sub: BTreeSet<_> = [1, 2].iter().cloned().collect();
 601     /// let mut set = BTreeSet::new();
 602     ///
 603     /// assert_eq!(set.is_superset(&sub), false);
 604     ///
 605     /// set.insert(0);
 606     /// set.insert(1);
 607     /// assert_eq!(set.is_superset(&sub), false);
 608     ///
 609     /// set.insert(2);
 610     /// assert_eq!(set.is_superset(&sub), true);
 611     /// ```
 612     #[stable(feature = "rust1", since = "1.0.0")]
 613     pub fn is_superset(&self, other: &BTreeSet<T>) -> bool {
 614         other.is_subset(self)
 615     }
 616
 617     /// Returns a reference to the first value in the set, if any.
 618     /// This value is always the minimum of all values in the set.
 619     ///
 620     /// # Examples
 621     ///
 622     /// Basic usage:
 623     ///
 624     /// ```
 625     /// #![feature(map_first_last)]
 626     /// use std::collections::BTreeSet;
 627     ///
 628     /// let mut map = BTreeSet::new();
 629     /// assert_eq!(map.first(), None);
 630     /// map.insert(1);
 631     /// assert_eq!(map.first(), Some(&1));
 632     /// map.insert(2);
 633     /// assert_eq!(map.first(), Some(&1));
 634     /// ```
 635     #[unstable(feature = "map_first_last", issue = "62924")]
 636     pub fn first(&self) -> Option<&T> {
 637         self.map.first_key_value().map(|(k, _)| k)
 638     }
 639
 640     /// Returns a reference to the last value in the set, if any.
 641     /// This value is always the maximum of all values in the set.
 642     ///
 643     /// # Examples
 644     ///
 645     /// Basic usage:
 646     ///
 647     /// ```
 648     /// #![feature(map_first_last)]
 649     /// use std::collections::BTreeSet;
 650     ///
 651     /// let mut map = BTreeSet::new();
 652     /// assert_eq!(map.first(), None);
 653     /// map.insert(1);
 654     /// assert_eq!(map.last(), Some(&1));
 655     /// map.insert(2);
 656     /// assert_eq!(map.last(), Some(&2));
 657     /// ```
 658     #[unstable(feature = "map_first_last", issue = "62924")]
 659     pub fn last(&self) -> Option<&T> {
 660         self.map.last_key_value().map(|(k, _)| k)
 661     }
 662
 663     /// Removes the first value from the set and returns it, if any.
 664     /// The first value is always the minimum value in the set.
 665     ///
 666     /// # Examples
 667     ///
 668     /// ```
 669     /// #![feature(map_first_last)]
 670     /// use std::collections::BTreeSet;
 671     ///
 672     /// let mut set = BTreeSet::new();
 673     ///
 674     /// set.insert(1);
 675     /// while let Some(n) = set.pop_first() {
 676     ///     assert_eq!(n, 1);
 677     /// }
 678     /// assert!(set.is_empty());
 679     /// ```
 680     #[unstable(feature = "map_first_last", issue = "62924")]
 681     pub fn pop_first(&mut self) -> Option<T> {
 682         self.map.pop_first().map(|kv| kv.0)
 683     }
 684
 685     /// Removes the last value from the set and returns it, if any.
 686     /// The last value is always the maximum value in the set.
 687     ///
 688     /// # Examples
 689     ///
 690     /// ```
 691     /// #![feature(map_first_last)]
 692     /// use std::collections::BTreeSet;
 693     ///
 694     /// let mut set = BTreeSet::new();
 695     ///
 696     /// set.insert(1);
 697     /// while let Some(n) = set.pop_last() {
 698     ///     assert_eq!(n, 1);
 699     /// }
 700     /// assert!(set.is_empty());
 701     /// ```
 702     #[unstable(feature = "map_first_last", issue = "62924")]
 703     pub fn pop_last(&mut self) -> Option<T> {
 704         self.map.pop_last().map(|kv| kv.0)
 705     }
 706
 707     /// Adds a value to the set.
 708     ///
 709     /// If the set did not have this value present, `true` is returned.
 710     ///
 711     /// If the set did have this value present, `false` is returned, and the
 712     /// entry is not updated. See the [module-level documentation] for more.
 713     ///
 714     /// [module-level documentation]: index.html#insert-and-complex-keys
 715     ///
 716     /// # Examples
 717     ///
 718     /// ```
 719     /// use std::collections::BTreeSet;
 720     ///
 721     /// let mut set = BTreeSet::new();
 722     ///
 723     /// assert_eq!(set.insert(2), true);
 724     /// assert_eq!(set.insert(2), false);
 725     /// assert_eq!(set.len(), 1);
 726     /// ```
 727     #[stable(feature = "rust1", since = "1.0.0")]
 728     pub fn insert(&mut self, value: T) -> bool {
 729         self.map.insert(value, ()).is_none()
 730     }
 731
 732     /// Adds a value to the set, replacing the existing value, if any, that is equal to the given
 733     /// one. Returns the replaced value.
 734     ///
 735     /// # Examples
 736     ///
 737     /// ```
 738     /// use std::collections::BTreeSet;
 739     ///
 740     /// let mut set = BTreeSet::new();
 741     /// set.insert(Vec::<i32>::new());
 742     ///
 743     /// assert_eq!(set.get(&[][..]).unwrap().capacity(), 0);
 744     /// set.replace(Vec::with_capacity(10));
 745     /// assert_eq!(set.get(&[][..]).unwrap().capacity(), 10);
 746     /// ```
 747     #[stable(feature = "set_recovery", since = "1.9.0")]
 748     pub fn replace(&mut self, value: T) -> Option<T> {
 749         Recover::replace(&mut self.map, value)
 750     }
 751
 752     /// Removes a value from the set. Returns whether the value was
 753     /// present in the set.
 754     ///
 755     /// The value may be any borrowed form of the set's value type,
 756     /// but the ordering on the borrowed form *must* match the
 757     /// ordering on the value type.
 758     ///
 759     /// # Examples
 760     ///
 761     /// ```
 762     /// use std::collections::BTreeSet;
 763     ///
 764     /// let mut set = BTreeSet::new();
 765     ///
 766     /// set.insert(2);
 767     /// assert_eq!(set.remove(&2), true);
 768     /// assert_eq!(set.remove(&2), false);
 769     /// ```
 770     #[stable(feature = "rust1", since = "1.0.0")]
 771     pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool
 772     where
 773         T: Borrow<Q>,
 774         Q: Ord,
 775     {
 776         self.map.remove(value).is_some()
 777     }
 778
 779     /// Removes and returns the value in the set, if any, that is equal to the given one.
 780     ///
 781     /// The value may be any borrowed form of the set's value type,
 782     /// but the ordering on the borrowed form *must* match the
 783     /// ordering on the value type.
 784     ///
 785     /// # Examples
 786     ///
 787     /// ```
 788     /// use std::collections::BTreeSet;
 789     ///
 790     /// let mut set: BTreeSet<_> = [1, 2, 3].iter().cloned().collect();
 791     /// assert_eq!(set.take(&2), Some(2));
 792     /// assert_eq!(set.take(&2), None);
 793     /// ```
 794     #[stable(feature = "set_recovery", since = "1.9.0")]
 795     pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
 796     where
 797         T: Borrow<Q>,
 798         Q: Ord,
 799     {
 800         Recover::take(&mut self.map, value)
 801     }
 802
 803     /// Retains only the elements specified by the predicate.
 804     ///
 805     /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
 806     ///
 807     /// # Examples
 808     ///
 809     /// ```
 810     /// #![feature(btree_retain)]
 811     /// use std::collections::BTreeSet;
 812     ///
 813     /// let xs = [1, 2, 3, 4, 5, 6];
 814     /// let mut set: BTreeSet<i32> = xs.iter().cloned().collect();
 815     /// // Keep only the even numbers.
 816     /// set.retain(|&k| k % 2 == 0);
 817     /// assert!(set.iter().eq([2, 4, 6].iter()));
 818     /// ```
 819     #[unstable(feature = "btree_retain", issue = "79025")]
 820     pub fn retain<F>(&mut self, mut f: F)
 821     where
 822         F: FnMut(&T) -> bool,
 823     {
 824         self.drain_filter(|v| !f(v));
 825     }
 826
 827     /// Moves all elements from `other` into `Self`, leaving `other` empty.
 828     ///
 829     /// # Examples
 830     ///
 831     /// ```
 832     /// use std::collections::BTreeSet;
 833     ///
 834     /// let mut a = BTreeSet::new();
 835     /// a.insert(1);
 836     /// a.insert(2);
 837     /// a.insert(3);
 838     ///
 839     /// let mut b = BTreeSet::new();
 840     /// b.insert(3);
 841     /// b.insert(4);
 842     /// b.insert(5);
 843     ///
 844     /// a.append(&mut b);
 845     ///
 846     /// assert_eq!(a.len(), 5);
 847     /// assert_eq!(b.len(), 0);
 848     ///
 849     /// assert!(a.contains(&1));
 850     /// assert!(a.contains(&2));
 851     /// assert!(a.contains(&3));
 852     /// assert!(a.contains(&4));
 853     /// assert!(a.contains(&5));
 854     /// ```
 855     #[stable(feature = "btree_append", since = "1.11.0")]
 856     pub fn append(&mut self, other: &mut Self) {
 857         self.map.append(&mut other.map);
 858     }
 859
 860     /// Splits the collection into two at the given key. Returns everything after the given key,
 861     /// including the key.
 862     ///
 863     /// # Examples
 864     ///
 865     /// Basic usage:
 866     ///
 867     /// ```
 868     /// use std::collections::BTreeSet;
 869     ///
 870     /// let mut a = BTreeSet::new();
 871     /// a.insert(1);
 872     /// a.insert(2);
 873     /// a.insert(3);
 874     /// a.insert(17);
 875     /// a.insert(41);
 876     ///
 877     /// let b = a.split_off(&3);
 878     ///
 879     /// assert_eq!(a.len(), 2);
 880     /// assert_eq!(b.len(), 3);
 881     ///
 882     /// assert!(a.contains(&1));
 883     /// assert!(a.contains(&2));
 884     ///
 885     /// assert!(b.contains(&3));
 886     /// assert!(b.contains(&17));
 887     /// assert!(b.contains(&41));
 888     /// ```
 889     #[stable(feature = "btree_split_off", since = "1.11.0")]
 890     pub fn split_off<Q: ?Sized + Ord>(&mut self, key: &Q) -> Self
 891     where
 892         T: Borrow<Q>,
 893     {
 894         BTreeSet { map: self.map.split_off(key) }
 895     }
 896
 897     /// Creates an iterator which uses a closure to determine if a value should be removed.
 898     ///
 899     /// If the closure returns true, then the value is removed and yielded.
 900     /// If the closure returns false, the value will remain in the list and will not be yielded
 901     /// by the iterator.
 902     ///
 903     /// If the iterator is only partially consumed or not consumed at all, each of the remaining
 904     /// values will still be subjected to the closure and removed and dropped if it returns true.
 905     ///
 906     /// It is unspecified how many more values will be subjected to the closure
 907     /// if a panic occurs in the closure, or if a panic occurs while dropping a value, or if the
 908     /// `DrainFilter` itself is leaked.
 909     ///
 910     /// # Examples
 911     ///
 912     /// Splitting a set into even and odd values, reusing the original set:
 913     ///
 914     /// ```
 915     /// #![feature(btree_drain_filter)]
 916     /// use std::collections::BTreeSet;
 917     ///
 918     /// let mut set: BTreeSet<i32> = (0..8).collect();
 919     /// let evens: BTreeSet<_> = set.drain_filter(|v| v % 2 == 0).collect();
 920     /// let odds = set;
 921     /// assert_eq!(evens.into_iter().collect::<Vec<_>>(), vec![0, 2, 4, 6]);
 922     /// assert_eq!(odds.into_iter().collect::<Vec<_>>(), vec![1, 3, 5, 7]);
 923     /// ```
 924     #[unstable(feature = "btree_drain_filter", issue = "70530")]
 925     pub fn drain_filter<'a, F>(&'a mut self, pred: F) -> DrainFilter<'a, T, F>
 926     where
 927         F: 'a + FnMut(&T) -> bool,
 928     {
 929         DrainFilter { pred, inner: self.map.drain_filter_inner() }
 930     }
 931 }
 932
 933 impl<T> BTreeSet<T> {
 934     /// Gets an iterator that visits the values in the `BTreeSet` in ascending order.
 935     ///
 936     /// # Examples
 937     ///
 938     /// ```
 939     /// use std::collections::BTreeSet;
 940     ///
 941     /// let set: BTreeSet<usize> = [1, 2, 3].iter().cloned().collect();
 942     /// let mut set_iter = set.iter();
 943     /// assert_eq!(set_iter.next(), Some(&1));
 944     /// assert_eq!(set_iter.next(), Some(&2));
 945     /// assert_eq!(set_iter.next(), Some(&3));
 946     /// assert_eq!(set_iter.next(), None);
 947     /// ```
 948     ///
 949     /// Values returned by the iterator are returned in ascending order:
 950     ///
 951     /// ```
 952     /// use std::collections::BTreeSet;
 953     ///
 954     /// let set: BTreeSet<usize> = [3, 1, 2].iter().cloned().collect();
 955     /// let mut set_iter = set.iter();
 956     /// assert_eq!(set_iter.next(), Some(&1));
 957     /// assert_eq!(set_iter.next(), Some(&2));
 958     /// assert_eq!(set_iter.next(), Some(&3));
 959     /// assert_eq!(set_iter.next(), None);
 960     /// ```
 961     #[stable(feature = "rust1", since = "1.0.0")]
 962     pub fn iter(&self) -> Iter<'_, T> {
 963         Iter { iter: self.map.keys() }
 964     }
 965
 966     /// Returns the number of elements in the set.
 967     ///
 968     /// # Examples
 969     ///
 970     /// ```
 971     /// use std::collections::BTreeSet;
 972     ///
 973     /// let mut v = BTreeSet::new();
 974     /// assert_eq!(v.len(), 0);
 975     /// v.insert(1);
 976     /// assert_eq!(v.len(), 1);
 977     /// ```
 978     #[stable(feature = "rust1", since = "1.0.0")]
 979     #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
 980     pub const fn len(&self) -> usize {
 981         self.map.len()
 982     }
 983
 984     /// Returns `true` if the set contains no elements.
 985     ///
 986     /// # Examples
 987     ///
 988     /// ```
 989     /// use std::collections::BTreeSet;
 990     ///
 991     /// let mut v = BTreeSet::new();
 992     /// assert!(v.is_empty());
 993     /// v.insert(1);
 994     /// assert!(!v.is_empty());
 995     /// ```
 996     #[stable(feature = "rust1", since = "1.0.0")]
 997     #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
 998     pub const fn is_empty(&self) -> bool {
 999         self.len() == 0
1000     }
1001 }
1002
1003 #[stable(feature = "rust1", since = "1.0.0")]
1004 impl<T: Ord> FromIterator<T> for BTreeSet<T> {
1005     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> BTreeSet<T> {
1006         let mut set = BTreeSet::new();
1007         set.extend(iter);
1008         set
1009     }
1010 }
1011
1012 #[stable(feature = "rust1", since = "1.0.0")]
1013 impl<T> IntoIterator for BTreeSet<T> {
1014     type Item = T;
1015     type IntoIter = IntoIter<T>;
1016
1017     /// Gets an iterator for moving out the `BTreeSet`'s contents.
1018     ///
1019     /// # Examples
1020     ///
1021     /// ```
1022     /// use std::collections::BTreeSet;
1023     ///
1024     /// let set: BTreeSet<usize> = [1, 2, 3, 4].iter().cloned().collect();
1025     ///
1026     /// let v: Vec<_> = set.into_iter().collect();
1027     /// assert_eq!(v, [1, 2, 3, 4]);
1028     /// ```
1029     fn into_iter(self) -> IntoIter<T> {
1030         IntoIter { iter: self.map.into_iter() }
1031     }
1032 }
1033
1034 #[stable(feature = "rust1", since = "1.0.0")]
1035 impl<'a, T> IntoIterator for &'a BTreeSet<T> {
1036     type Item = &'a T;
1037     type IntoIter = Iter<'a, T>;
1038
1039     fn into_iter(self) -> Iter<'a, T> {
1040         self.iter()
1041     }
1042 }
1043
1044 /// An iterator produced by calling `drain_filter` on BTreeSet.
1045 #[unstable(feature = "btree_drain_filter", issue = "70530")]
1046 pub struct DrainFilter<'a, T, F>
1047 where
1048     T: 'a,
1049     F: 'a + FnMut(&T) -> bool,
1050 {
1051     pred: F,
1052     inner: super::map::DrainFilterInner<'a, T, ()>,
1053 }
1054
1055 #[unstable(feature = "btree_drain_filter", issue = "70530")]
1056 impl<T, F> Drop for DrainFilter<'_, T, F>
1057 where
1058     F: FnMut(&T) -> bool,
1059 {
1060     fn drop(&mut self) {
1061         self.for_each(drop);
1062     }
1063 }
1064
1065 #[unstable(feature = "btree_drain_filter", issue = "70530")]
1066 impl<T, F> fmt::Debug for DrainFilter<'_, T, F>
1067 where
1068     T: fmt::Debug,
1069     F: FnMut(&T) -> bool,
1070 {
1071     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1072         f.debug_tuple("DrainFilter").field(&self.inner.peek().map(|(k, _)| k)).finish()
1073     }
1074 }
1075
1076 #[unstable(feature = "btree_drain_filter", issue = "70530")]
1077 impl<'a, T, F> Iterator for DrainFilter<'_, T, F>
1078 where
1079     F: 'a + FnMut(&T) -> bool,
1080 {
1081     type Item = T;
1082
1083     fn next(&mut self) -> Option<T> {
1084         let pred = &mut self.pred;
1085         let mut mapped_pred = |k: &T, _v: &mut ()| pred(k);
1086         self.inner.next(&mut mapped_pred).map(|(k, _)| k)
1087     }
1088
1089     fn size_hint(&self) -> (usize, Option<usize>) {
1090         self.inner.size_hint()
1091     }
1092 }
1093
1094 #[unstable(feature = "btree_drain_filter", issue = "70530")]
1095 impl<T, F> FusedIterator for DrainFilter<'_, T, F> where F: FnMut(&T) -> bool {}
1096
1097 #[stable(feature = "rust1", since = "1.0.0")]
1098 impl<T: Ord> Extend<T> for BTreeSet<T> {
1099     #[inline]
1100     fn extend<Iter: IntoIterator<Item = T>>(&mut self, iter: Iter) {
1101         iter.into_iter().for_each(move |elem| {
1102             self.insert(elem);
1103         });
1104     }
1105
1106     #[inline]
1107     fn extend_one(&mut self, elem: T) {
1108         self.insert(elem);
1109     }
1110 }
1111
1112 #[stable(feature = "extend_ref", since = "1.2.0")]
1113 impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BTreeSet<T> {
1114     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
1115         self.extend(iter.into_iter().cloned());
1116     }
1117
1118     #[inline]
1119     fn extend_one(&mut self, &elem: &'a T) {
1120         self.insert(elem);
1121     }
1122 }
1123
1124 #[stable(feature = "rust1", since = "1.0.0")]
1125 impl<T: Ord> Default for BTreeSet<T> {
1126     /// Creates an empty `BTreeSet`.
1127     fn default() -> BTreeSet<T> {
1128         BTreeSet::new()
1129     }
1130 }
1131
1132 #[stable(feature = "rust1", since = "1.0.0")]
1133 impl<T: Ord + Clone> Sub<&BTreeSet<T>> for &BTreeSet<T> {
1134     type Output = BTreeSet<T>;
1135
1136     /// Returns the difference of `self` and `rhs` as a new `BTreeSet<T>`.
1137     ///
1138     /// # Examples
1139     ///
1140     /// ```
1141     /// use std::collections::BTreeSet;
1142     ///
1143     /// let a: BTreeSet<_> = vec![1, 2, 3].into_iter().collect();
1144     /// let b: BTreeSet<_> = vec![3, 4, 5].into_iter().collect();
1145     ///
1146     /// let result = &a - &b;
1147     /// let result_vec: Vec<_> = result.into_iter().collect();
1148     /// assert_eq!(result_vec, [1, 2]);
1149     /// ```
1150     fn sub(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
1151         self.difference(rhs).cloned().collect()
1152     }
1153 }
1154
1155 #[stable(feature = "rust1", since = "1.0.0")]
1156 impl<T: Ord + Clone> BitXor<&BTreeSet<T>> for &BTreeSet<T> {
1157     type Output = BTreeSet<T>;
1158
1159     /// Returns the symmetric difference of `self` and `rhs` as a new `BTreeSet<T>`.
1160     ///
1161     /// # Examples
1162     ///
1163     /// ```
1164     /// use std::collections::BTreeSet;
1165     ///
1166     /// let a: BTreeSet<_> = vec![1, 2, 3].into_iter().collect();
1167     /// let b: BTreeSet<_> = vec![2, 3, 4].into_iter().collect();
1168     ///
1169     /// let result = &a ^ &b;
1170     /// let result_vec: Vec<_> = result.into_iter().collect();
1171     /// assert_eq!(result_vec, [1, 4]);
1172     /// ```
1173     fn bitxor(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
1174         self.symmetric_difference(rhs).cloned().collect()
1175     }
1176 }
1177
1178 #[stable(feature = "rust1", since = "1.0.0")]
1179 impl<T: Ord + Clone> BitAnd<&BTreeSet<T>> for &BTreeSet<T> {
1180     type Output = BTreeSet<T>;
1181
1182     /// Returns the intersection of `self` and `rhs` as a new `BTreeSet<T>`.
1183     ///
1184     /// # Examples
1185     ///
1186     /// ```
1187     /// use std::collections::BTreeSet;
1188     ///
1189     /// let a: BTreeSet<_> = vec![1, 2, 3].into_iter().collect();
1190     /// let b: BTreeSet<_> = vec![2, 3, 4].into_iter().collect();
1191     ///
1192     /// let result = &a & &b;
1193     /// let result_vec: Vec<_> = result.into_iter().collect();
1194     /// assert_eq!(result_vec, [2, 3]);
1195     /// ```
1196     fn bitand(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
1197         self.intersection(rhs).cloned().collect()
1198     }
1199 }
1200
1201 #[stable(feature = "rust1", since = "1.0.0")]
1202 impl<T: Ord + Clone> BitOr<&BTreeSet<T>> for &BTreeSet<T> {
1203     type Output = BTreeSet<T>;
1204
1205     /// Returns the union of `self` and `rhs` as a new `BTreeSet<T>`.
1206     ///
1207     /// # Examples
1208     ///
1209     /// ```
1210     /// use std::collections::BTreeSet;
1211     ///
1212     /// let a: BTreeSet<_> = vec![1, 2, 3].into_iter().collect();
1213     /// let b: BTreeSet<_> = vec![3, 4, 5].into_iter().collect();
1214     ///
1215     /// let result = &a | &b;
1216     /// let result_vec: Vec<_> = result.into_iter().collect();
1217     /// assert_eq!(result_vec, [1, 2, 3, 4, 5]);
1218     /// ```
1219     fn bitor(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
1220         self.union(rhs).cloned().collect()
1221     }
1222 }
1223
1224 #[stable(feature = "rust1", since = "1.0.0")]
1225 impl<T: Debug> Debug for BTreeSet<T> {
1226     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1227         f.debug_set().entries(self.iter()).finish()
1228     }
1229 }
1230
1231 #[stable(feature = "rust1", since = "1.0.0")]
1232 impl<T> Clone for Iter<'_, T> {
1233     fn clone(&self) -> Self {
1234         Iter { iter: self.iter.clone() }
1235     }
1236 }
1237 #[stable(feature = "rust1", since = "1.0.0")]
1238 impl<'a, T> Iterator for Iter<'a, T> {
1239     type Item = &'a T;
1240
1241     fn next(&mut self) -> Option<&'a T> {
1242         self.iter.next()
1243     }
1244
1245     fn size_hint(&self) -> (usize, Option<usize>) {
1246         self.iter.size_hint()
1247     }
1248
1249     fn last(mut self) -> Option<&'a T> {
1250         self.next_back()
1251     }
1252
1253     fn min(mut self) -> Option<&'a T> {
1254         self.next()
1255     }
1256
1257     fn max(mut self) -> Option<&'a T> {
1258         self.next_back()
1259     }
1260 }
1261 #[stable(feature = "rust1", since = "1.0.0")]
1262 impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
1263     fn next_back(&mut self) -> Option<&'a T> {
1264         self.iter.next_back()
1265     }
1266 }
1267 #[stable(feature = "rust1", since = "1.0.0")]
1268 impl<T> ExactSizeIterator for Iter<'_, T> {
1269     fn len(&self) -> usize {
1270         self.iter.len()
1271     }
1272 }
1273
1274 #[stable(feature = "fused", since = "1.26.0")]
1275 impl<T> FusedIterator for Iter<'_, T> {}
1276
1277 #[stable(feature = "rust1", since = "1.0.0")]
1278 impl<T> Iterator for IntoIter<T> {
1279     type Item = T;
1280
1281     fn next(&mut self) -> Option<T> {
1282         self.iter.next().map(|(k, _)| k)
1283     }
1284
1285     fn size_hint(&self) -> (usize, Option<usize>) {
1286         self.iter.size_hint()
1287     }
1288 }
1289 #[stable(feature = "rust1", since = "1.0.0")]
1290 impl<T> DoubleEndedIterator for IntoIter<T> {
1291     fn next_back(&mut self) -> Option<T> {
1292         self.iter.next_back().map(|(k, _)| k)
1293     }
1294 }
1295 #[stable(feature = "rust1", since = "1.0.0")]
1296 impl<T> ExactSizeIterator for IntoIter<T> {
1297     fn len(&self) -> usize {
1298         self.iter.len()
1299     }
1300 }
1301
1302 #[stable(feature = "fused", since = "1.26.0")]
1303 impl<T> FusedIterator for IntoIter<T> {}
1304
1305 #[stable(feature = "btree_range", since = "1.17.0")]
1306 impl<T> Clone for Range<'_, T> {
1307     fn clone(&self) -> Self {
1308         Range { iter: self.iter.clone() }
1309     }
1310 }
1311
1312 #[stable(feature = "btree_range", since = "1.17.0")]
1313 impl<'a, T> Iterator for Range<'a, T> {
1314     type Item = &'a T;
1315
1316     fn next(&mut self) -> Option<&'a T> {
1317         self.iter.next().map(|(k, _)| k)
1318     }
1319
1320     fn last(mut self) -> Option<&'a T> {
1321         self.next_back()
1322     }
1323
1324     fn min(mut self) -> Option<&'a T> {
1325         self.next()
1326     }
1327
1328     fn max(mut self) -> Option<&'a T> {
1329         self.next_back()
1330     }
1331 }
1332
1333 #[stable(feature = "btree_range", since = "1.17.0")]
1334 impl<'a, T> DoubleEndedIterator for Range<'a, T> {
1335     fn next_back(&mut self) -> Option<&'a T> {
1336         self.iter.next_back().map(|(k, _)| k)
1337     }
1338 }
1339
1340 #[stable(feature = "fused", since = "1.26.0")]
1341 impl<T> FusedIterator for Range<'_, T> {}
1342
1343 #[stable(feature = "rust1", since = "1.0.0")]
1344 impl<T> Clone for Difference<'_, T> {
1345     fn clone(&self) -> Self {
1346         Difference {
1347             inner: match &self.inner {
1348                 DifferenceInner::Stitch { self_iter, other_iter } => DifferenceInner::Stitch {
1349                     self_iter: self_iter.clone(),
1350                     other_iter: other_iter.clone(),
1351                 },
1352                 DifferenceInner::Search { self_iter, other_set } => {
1353                     DifferenceInner::Search { self_iter: self_iter.clone(), other_set }
1354                 }
1355                 DifferenceInner::Iterate(iter) => DifferenceInner::Iterate(iter.clone()),
1356             },
1357         }
1358     }
1359 }
1360 #[stable(feature = "rust1", since = "1.0.0")]
1361 impl<'a, T: Ord> Iterator for Difference<'a, T> {
1362     type Item = &'a T;
1363
1364     fn next(&mut self) -> Option<&'a T> {
1365         match &mut self.inner {
1366             DifferenceInner::Stitch { self_iter, other_iter } => {
1367                 let mut self_next = self_iter.next()?;
1368                 loop {
1369                     match other_iter.peek().map_or(Less, |other_next| self_next.cmp(other_next)) {
1370                         Less => return Some(self_next),
1371                         Equal => {
1372                             self_next = self_iter.next()?;
1373                             other_iter.next();
1374                         }
1375                         Greater => {
1376                             other_iter.next();
1377                         }
1378                     }
1379                 }
1380             }
1381             DifferenceInner::Search { self_iter, other_set } => loop {
1382                 let self_next = self_iter.next()?;
1383                 if !other_set.contains(&self_next) {
1384                     return Some(self_next);
1385                 }
1386             },
1387             DifferenceInner::Iterate(iter) => iter.next(),
1388         }
1389     }
1390
1391     fn size_hint(&self) -> (usize, Option<usize>) {
1392         let (self_len, other_len) = match &self.inner {
1393             DifferenceInner::Stitch { self_iter, other_iter } => {
1394                 (self_iter.len(), other_iter.len())
1395             }
1396             DifferenceInner::Search { self_iter, other_set } => (self_iter.len(), other_set.len()),
1397             DifferenceInner::Iterate(iter) => (iter.len(), 0),
1398         };
1399         (self_len.saturating_sub(other_len), Some(self_len))
1400     }
1401
1402     fn min(mut self) -> Option<&'a T> {
1403         self.next()
1404     }
1405 }
1406
1407 #[stable(feature = "fused", since = "1.26.0")]
1408 impl<T: Ord> FusedIterator for Difference<'_, T> {}
1409
1410 #[stable(feature = "rust1", since = "1.0.0")]
1411 impl<T> Clone for SymmetricDifference<'_, T> {
1412     fn clone(&self) -> Self {
1413         SymmetricDifference(self.0.clone())
1414     }
1415 }
1416 #[stable(feature = "rust1", since = "1.0.0")]
1417 impl<'a, T: Ord> Iterator for SymmetricDifference<'a, T> {
1418     type Item = &'a T;
1419
1420     fn next(&mut self) -> Option<&'a T> {
1421         loop {
1422             let (a_next, b_next) = self.0.nexts(Self::Item::cmp);
1423             if a_next.and(b_next).is_none() {
1424                 return a_next.or(b_next);
1425             }
1426         }
1427     }
1428
1429     fn size_hint(&self) -> (usize, Option<usize>) {
1430         let (a_len, b_len) = self.0.lens();
1431         // No checked_add, because even if a and b refer to the same set,
1432         // and T is an empty type, the storage overhead of sets limits
1433         // the number of elements to less than half the range of usize.
1434         (0, Some(a_len + b_len))
1435     }
1436
1437     fn min(mut self) -> Option<&'a T> {
1438         self.next()
1439     }
1440 }
1441
1442 #[stable(feature = "fused", since = "1.26.0")]
1443 impl<T: Ord> FusedIterator for SymmetricDifference<'_, T> {}
1444
1445 #[stable(feature = "rust1", since = "1.0.0")]
1446 impl<T> Clone for Intersection<'_, T> {
1447     fn clone(&self) -> Self {
1448         Intersection {
1449             inner: match &self.inner {
1450                 IntersectionInner::Stitch { a, b } => {
1451                     IntersectionInner::Stitch { a: a.clone(), b: b.clone() }
1452                 }
1453                 IntersectionInner::Search { small_iter, large_set } => {
1454                     IntersectionInner::Search { small_iter: small_iter.clone(), large_set }
1455                 }
1456                 IntersectionInner::Answer(answer) => IntersectionInner::Answer(*answer),
1457             },
1458         }
1459     }
1460 }
1461 #[stable(feature = "rust1", since = "1.0.0")]
1462 impl<'a, T: Ord> Iterator for Intersection<'a, T> {
1463     type Item = &'a T;
1464
1465     fn next(&mut self) -> Option<&'a T> {
1466         match &mut self.inner {
1467             IntersectionInner::Stitch { a, b } => {
1468                 let mut a_next = a.next()?;
1469                 let mut b_next = b.next()?;
1470                 loop {
1471                     match a_next.cmp(b_next) {
1472                         Less => a_next = a.next()?,
1473                         Greater => b_next = b.next()?,
1474                         Equal => return Some(a_next),
1475                     }
1476                 }
1477             }
1478             IntersectionInner::Search { small_iter, large_set } => loop {
1479                 let small_next = small_iter.next()?;
1480                 if large_set.contains(&small_next) {
1481                     return Some(small_next);
1482                 }
1483             },
1484             IntersectionInner::Answer(answer) => answer.take(),
1485         }
1486     }
1487
1488     fn size_hint(&self) -> (usize, Option<usize>) {
1489         match &self.inner {
1490             IntersectionInner::Stitch { a, b } => (0, Some(min(a.len(), b.len()))),
1491             IntersectionInner::Search { small_iter, .. } => (0, Some(small_iter.len())),
1492             IntersectionInner::Answer(None) => (0, Some(0)),
1493             IntersectionInner::Answer(Some(_)) => (1, Some(1)),
1494         }
1495     }
1496
1497     fn min(mut self) -> Option<&'a T> {
1498         self.next()
1499     }
1500 }
1501
1502 #[stable(feature = "fused", since = "1.26.0")]
1503 impl<T: Ord> FusedIterator for Intersection<'_, T> {}
1504
1505 #[stable(feature = "rust1", since = "1.0.0")]
1506 impl<T> Clone for Union<'_, T> {
1507     fn clone(&self) -> Self {
1508         Union(self.0.clone())
1509     }
1510 }
1511 #[stable(feature = "rust1", since = "1.0.0")]
1512 impl<'a, T: Ord> Iterator for Union<'a, T> {
1513     type Item = &'a T;
1514
1515     fn next(&mut self) -> Option<&'a T> {
1516         let (a_next, b_next) = self.0.nexts(Self::Item::cmp);
1517         a_next.or(b_next)
1518     }
1519
1520     fn size_hint(&self) -> (usize, Option<usize>) {
1521         let (a_len, b_len) = self.0.lens();
1522         // No checked_add - see SymmetricDifference::size_hint.
1523         (max(a_len, b_len), Some(a_len + b_len))
1524     }
1525
1526     fn min(mut self) -> Option<&'a T> {
1527         self.next()
1528     }
1529 }
1530
1531 #[stable(feature = "fused", since = "1.26.0")]
1532 impl<T: Ord> FusedIterator for Union<'_, T> {}
1533
1534 #[cfg(test)]
1535 mod tests;