src/libstd/collections/hash/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 use borrow::Borrow;
  12 use fmt;
  13 use hash::{Hash, BuildHasher};
  14 use iter::{Chain, FromIterator, FusedIterator};
  15 use ops::{BitOr, BitAnd, BitXor, Sub};
  16
  17 use super::Recover;
  18 use super::map::{self, HashMap, Keys, RandomState};
  19
  20 // Future Optimization (FIXME!)
  21 // =============================
  22 //
  23 // Iteration over zero sized values is a noop. There is no need
  24 // for `bucket.val` in the case of HashSet. I suppose we would need HKT
  25 // to get rid of it properly.
  26
  27 /// A hash set implemented as a `HashMap` where the value is `()`.
  28 ///
  29 /// As with the [`HashMap`] type, a `HashSet` requires that the elements
  30 /// implement the [`Eq`] and [`Hash`] traits. This can frequently be achieved by
  31 /// using `#[derive(PartialEq, Eq, Hash)]`. If you implement these yourself,
  32 /// it is important that the following property holds:
  33 ///
  34 /// ```text
  35 /// k1 == k2 -> hash(k1) == hash(k2)
  36 /// ```
  37 ///
  38 /// In other words, if two keys are equal, their hashes must be equal.
  39 ///
  40 ///
  41 /// It is a logic error for an item to be modified in such a way that the
  42 /// item's hash, as determined by the [`Hash`] trait, or its equality, as
  43 /// determined by the [`Eq`] trait, changes while it is in the set. This is
  44 /// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or
  45 /// unsafe code.
  46 ///
  47 /// # Examples
  48 ///
  49 /// ```
  50 /// use std::collections::HashSet;
  51 /// // Type inference lets us omit an explicit type signature (which
  52 /// // would be `HashSet<&str>` in this example).
  53 /// let mut books = HashSet::new();
  54 ///
  55 /// // Add some books.
  56 /// books.insert("A Dance With Dragons");
  57 /// books.insert("To Kill a Mockingbird");
  58 /// books.insert("The Odyssey");
  59 /// books.insert("The Great Gatsby");
  60 ///
  61 /// // Check for a specific one.
  62 /// if !books.contains("The Winds of Winter") {
  63 ///     println!("We have {} books, but The Winds of Winter ain't one.",
  64 ///              books.len());
  65 /// }
  66 ///
  67 /// // Remove a book.
  68 /// books.remove("The Odyssey");
  69 ///
  70 /// // Iterate over everything.
  71 /// for book in &books {
  72 ///     println!("{}", book);
  73 /// }
  74 /// ```
  75 ///
  76 /// The easiest way to use `HashSet` with a custom type is to derive
  77 /// [`Eq`] and [`Hash`]. We must also derive [`PartialEq`], this will in the
  78 /// future be implied by [`Eq`].
  79 ///
  80 /// ```
  81 /// use std::collections::HashSet;
  82 /// #[derive(Hash, Eq, PartialEq, Debug)]
  83 /// struct Viking<'a> {
  84 ///     name: &'a str,
  85 ///     power: usize,
  86 /// }
  87 ///
  88 /// let mut vikings = HashSet::new();
  89 ///
  90 /// vikings.insert(Viking { name: "Einar", power: 9 });
  91 /// vikings.insert(Viking { name: "Einar", power: 9 });
  92 /// vikings.insert(Viking { name: "Olaf", power: 4 });
  93 /// vikings.insert(Viking { name: "Harald", power: 8 });
  94 ///
  95 /// // Use derived implementation to print the vikings.
  96 /// for x in &vikings {
  97 ///     println!("{:?}", x);
  98 /// }
  99 /// ```
 100 ///
 101 /// A `HashSet` with fixed list of elements can be initialized from an array:
 102 ///
 103 /// ```
 104 /// use std::collections::HashSet;
 105 ///
 106 /// fn main() {
 107 ///     let viking_names: HashSet<&str> =
 108 ///         [ "Einar", "Olaf", "Harald" ].iter().cloned().collect();
 109 ///     // use the values stored in the set
 110 /// }
 111 /// ```
 112 ///
 113 /// [`Cell`]: ../../std/cell/struct.Cell.html
 114 /// [`Eq`]: ../../std/cmp/trait.Eq.html
 115 /// [`Hash`]: ../../std/hash/trait.Hash.html
 116 /// [`HashMap`]: struct.HashMap.html
 117 /// [`PartialEq`]: ../../std/cmp/trait.PartialEq.html
 118 /// [`RefCell`]: ../../std/cell/struct.RefCell.html
 119 #[derive(Clone)]
 120 #[stable(feature = "rust1", since = "1.0.0")]
 121 pub struct HashSet<T, S = RandomState> {
 122     map: HashMap<T, (), S>,
 123 }
 124
 125 impl<T: Hash + Eq> HashSet<T, RandomState> {
 126     /// Creates an empty `HashSet`.
 127     ///
 128     /// # Examples
 129     ///
 130     /// ```
 131     /// use std::collections::HashSet;
 132     /// let set: HashSet<i32> = HashSet::new();
 133     /// ```
 134     #[inline]
 135     #[stable(feature = "rust1", since = "1.0.0")]
 136     pub fn new() -> HashSet<T, RandomState> {
 137         HashSet { map: HashMap::new() }
 138     }
 139
 140     /// Creates an empty `HashSet` with the specified capacity.
 141     ///
 142     /// The hash set will be able to hold at least `capacity` elements without
 143     /// reallocating. If `capacity` is 0, the hash set will not allocate.
 144     ///
 145     /// # Examples
 146     ///
 147     /// ```
 148     /// use std::collections::HashSet;
 149     /// let set: HashSet<i32> = HashSet::with_capacity(10);
 150     /// assert!(set.capacity() >= 10);
 151     /// ```
 152     #[inline]
 153     #[stable(feature = "rust1", since = "1.0.0")]
 154     pub fn with_capacity(capacity: usize) -> HashSet<T, RandomState> {
 155         HashSet { map: HashMap::with_capacity(capacity) }
 156     }
 157 }
 158
 159 impl<T, S> HashSet<T, S>
 160     where T: Eq + Hash,
 161           S: BuildHasher
 162 {
 163     /// Creates a new empty hash set which will use the given hasher to hash
 164     /// keys.
 165     ///
 166     /// The hash set is also created with the default initial capacity.
 167     ///
 168     /// Warning: `hasher` is normally randomly generated, and
 169     /// is designed to allow `HashSet`s to be resistant to attacks that
 170     /// cause many collisions and very poor performance. Setting it
 171     /// manually using this function can expose a DoS attack vector.
 172     ///
 173     /// # Examples
 174     ///
 175     /// ```
 176     /// use std::collections::HashSet;
 177     /// use std::collections::hash_map::RandomState;
 178     ///
 179     /// let s = RandomState::new();
 180     /// let mut set = HashSet::with_hasher(s);
 181     /// set.insert(2);
 182     /// ```
 183     #[inline]
 184     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
 185     pub fn with_hasher(hasher: S) -> HashSet<T, S> {
 186         HashSet { map: HashMap::with_hasher(hasher) }
 187     }
 188
 189     /// Creates an empty `HashSet` with with the specified capacity, using
 190     /// `hasher` to hash the keys.
 191     ///
 192     /// The hash set will be able to hold at least `capacity` elements without
 193     /// reallocating. If `capacity` is 0, the hash set will not allocate.
 194     ///
 195     /// Warning: `hasher` is normally randomly generated, and
 196     /// is designed to allow `HashSet`s to be resistant to attacks that
 197     /// cause many collisions and very poor performance. Setting it
 198     /// manually using this function can expose a DoS attack vector.
 199     ///
 200     /// # Examples
 201     ///
 202     /// ```
 203     /// use std::collections::HashSet;
 204     /// use std::collections::hash_map::RandomState;
 205     ///
 206     /// let s = RandomState::new();
 207     /// let mut set = HashSet::with_capacity_and_hasher(10, s);
 208     /// set.insert(1);
 209     /// ```
 210     #[inline]
 211     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
 212     pub fn with_capacity_and_hasher(capacity: usize, hasher: S) -> HashSet<T, S> {
 213         HashSet { map: HashMap::with_capacity_and_hasher(capacity, hasher) }
 214     }
 215
 216     /// Returns a reference to the set's [`BuildHasher`].
 217     ///
 218     /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
 219     ///
 220     /// # Examples
 221     ///
 222     /// ```
 223     /// use std::collections::HashSet;
 224     /// use std::collections::hash_map::RandomState;
 225     ///
 226     /// let hasher = RandomState::new();
 227     /// let set: HashSet<i32> = HashSet::with_hasher(hasher);
 228     /// let hasher: &RandomState = set.hasher();
 229     /// ```
 230     #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
 231     pub fn hasher(&self) -> &S {
 232         self.map.hasher()
 233     }
 234
 235     /// Returns the number of elements the set can hold without reallocating.
 236     ///
 237     /// # Examples
 238     ///
 239     /// ```
 240     /// use std::collections::HashSet;
 241     /// let set: HashSet<i32> = HashSet::with_capacity(100);
 242     /// assert!(set.capacity() >= 100);
 243     /// ```
 244     #[inline]
 245     #[stable(feature = "rust1", since = "1.0.0")]
 246     pub fn capacity(&self) -> usize {
 247         self.map.capacity()
 248     }
 249
 250     /// Reserves capacity for at least `additional` more elements to be inserted
 251     /// in the `HashSet`. The collection may reserve more space to avoid
 252     /// frequent reallocations.
 253     ///
 254     /// # Panics
 255     ///
 256     /// Panics if the new allocation size overflows `usize`.
 257     ///
 258     /// # Examples
 259     ///
 260     /// ```
 261     /// use std::collections::HashSet;
 262     /// let mut set: HashSet<i32> = HashSet::new();
 263     /// set.reserve(10);
 264     /// assert!(set.capacity() >= 10);
 265     /// ```
 266     #[stable(feature = "rust1", since = "1.0.0")]
 267     pub fn reserve(&mut self, additional: usize) {
 268         self.map.reserve(additional)
 269     }
 270
 271     /// Shrinks the capacity of the set as much as possible. It will drop
 272     /// down as much as possible while maintaining the internal rules
 273     /// and possibly leaving some space in accordance with the resize policy.
 274     ///
 275     /// # Examples
 276     ///
 277     /// ```
 278     /// use std::collections::HashSet;
 279     ///
 280     /// let mut set = HashSet::with_capacity(100);
 281     /// set.insert(1);
 282     /// set.insert(2);
 283     /// assert!(set.capacity() >= 100);
 284     /// set.shrink_to_fit();
 285     /// assert!(set.capacity() >= 2);
 286     /// ```
 287     #[stable(feature = "rust1", since = "1.0.0")]
 288     pub fn shrink_to_fit(&mut self) {
 289         self.map.shrink_to_fit()
 290     }
 291
 292     /// An iterator visiting all elements in arbitrary order.
 293     /// The iterator element type is `&'a T`.
 294     ///
 295     /// # Examples
 296     ///
 297     /// ```
 298     /// use std::collections::HashSet;
 299     /// let mut set = HashSet::new();
 300     /// set.insert("a");
 301     /// set.insert("b");
 302     ///
 303     /// // Will print in an arbitrary order.
 304     /// for x in set.iter() {
 305     ///     println!("{}", x);
 306     /// }
 307     /// ```
 308     #[stable(feature = "rust1", since = "1.0.0")]
 309     pub fn iter(&self) -> Iter<T> {
 310         Iter { iter: self.map.keys() }
 311     }
 312
 313     /// Visits the values representing the difference,
 314     /// i.e. the values that are in `self` but not in `other`.
 315     ///
 316     /// # Examples
 317     ///
 318     /// ```
 319     /// use std::collections::HashSet;
 320     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 321     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
 322     ///
 323     /// // Can be seen as `a - b`.
 324     /// for x in a.difference(&b) {
 325     ///     println!("{}", x); // Print 1
 326     /// }
 327     ///
 328     /// let diff: HashSet<_> = a.difference(&b).collect();
 329     /// assert_eq!(diff, [1].iter().collect());
 330     ///
 331     /// // Note that difference is not symmetric,
 332     /// // and `b - a` means something else:
 333     /// let diff: HashSet<_> = b.difference(&a).collect();
 334     /// assert_eq!(diff, [4].iter().collect());
 335     /// ```
 336     #[stable(feature = "rust1", since = "1.0.0")]
 337     pub fn difference<'a>(&'a self, other: &'a HashSet<T, S>) -> Difference<'a, T, S> {
 338         Difference {
 339             iter: self.iter(),
 340             other,
 341         }
 342     }
 343
 344     /// Visits the values representing the symmetric difference,
 345     /// i.e. the values that are in `self` or in `other` but not in both.
 346     ///
 347     /// # Examples
 348     ///
 349     /// ```
 350     /// use std::collections::HashSet;
 351     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 352     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
 353     ///
 354     /// // Print 1, 4 in arbitrary order.
 355     /// for x in a.symmetric_difference(&b) {
 356     ///     println!("{}", x);
 357     /// }
 358     ///
 359     /// let diff1: HashSet<_> = a.symmetric_difference(&b).collect();
 360     /// let diff2: HashSet<_> = b.symmetric_difference(&a).collect();
 361     ///
 362     /// assert_eq!(diff1, diff2);
 363     /// assert_eq!(diff1, [1, 4].iter().collect());
 364     /// ```
 365     #[stable(feature = "rust1", since = "1.0.0")]
 366     pub fn symmetric_difference<'a>(&'a self,
 367                                     other: &'a HashSet<T, S>)
 368                                     -> SymmetricDifference<'a, T, S> {
 369         SymmetricDifference { iter: self.difference(other).chain(other.difference(self)) }
 370     }
 371
 372     /// Visits the values representing the intersection,
 373     /// i.e. the values that are both in `self` and `other`.
 374     ///
 375     /// # Examples
 376     ///
 377     /// ```
 378     /// use std::collections::HashSet;
 379     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 380     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
 381     ///
 382     /// // Print 2, 3 in arbitrary order.
 383     /// for x in a.intersection(&b) {
 384     ///     println!("{}", x);
 385     /// }
 386     ///
 387     /// let intersection: HashSet<_> = a.intersection(&b).collect();
 388     /// assert_eq!(intersection, [2, 3].iter().collect());
 389     /// ```
 390     #[stable(feature = "rust1", since = "1.0.0")]
 391     pub fn intersection<'a>(&'a self, other: &'a HashSet<T, S>) -> Intersection<'a, T, S> {
 392         Intersection {
 393             iter: self.iter(),
 394             other,
 395         }
 396     }
 397
 398     /// Visits the values representing the union,
 399     /// i.e. all the values in `self` or `other`, without duplicates.
 400     ///
 401     /// # Examples
 402     ///
 403     /// ```
 404     /// use std::collections::HashSet;
 405     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 406     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
 407     ///
 408     /// // Print 1, 2, 3, 4 in arbitrary order.
 409     /// for x in a.union(&b) {
 410     ///     println!("{}", x);
 411     /// }
 412     ///
 413     /// let union: HashSet<_> = a.union(&b).collect();
 414     /// assert_eq!(union, [1, 2, 3, 4].iter().collect());
 415     /// ```
 416     #[stable(feature = "rust1", since = "1.0.0")]
 417     pub fn union<'a>(&'a self, other: &'a HashSet<T, S>) -> Union<'a, T, S> {
 418         Union { iter: self.iter().chain(other.difference(self)) }
 419     }
 420
 421     /// Returns the number of elements in the set.
 422     ///
 423     /// # Examples
 424     ///
 425     /// ```
 426     /// use std::collections::HashSet;
 427     ///
 428     /// let mut v = HashSet::new();
 429     /// assert_eq!(v.len(), 0);
 430     /// v.insert(1);
 431     /// assert_eq!(v.len(), 1);
 432     /// ```
 433     #[stable(feature = "rust1", since = "1.0.0")]
 434     pub fn len(&self) -> usize {
 435         self.map.len()
 436     }
 437
 438     /// Returns true if the set contains no elements.
 439     ///
 440     /// # Examples
 441     ///
 442     /// ```
 443     /// use std::collections::HashSet;
 444     ///
 445     /// let mut v = HashSet::new();
 446     /// assert!(v.is_empty());
 447     /// v.insert(1);
 448     /// assert!(!v.is_empty());
 449     /// ```
 450     #[stable(feature = "rust1", since = "1.0.0")]
 451     pub fn is_empty(&self) -> bool {
 452         self.map.is_empty()
 453     }
 454
 455     /// Clears the set, returning all elements in an iterator.
 456     ///
 457     /// # Examples
 458     ///
 459     /// ```
 460     /// use std::collections::HashSet;
 461     ///
 462     /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 463     /// assert!(!set.is_empty());
 464     ///
 465     /// // print 1, 2, 3 in an arbitrary order
 466     /// for i in set.drain() {
 467     ///     println!("{}", i);
 468     /// }
 469     ///
 470     /// assert!(set.is_empty());
 471     /// ```
 472     #[inline]
 473     #[stable(feature = "drain", since = "1.6.0")]
 474     pub fn drain(&mut self) -> Drain<T> {
 475         Drain { iter: self.map.drain() }
 476     }
 477
 478     /// Clears the set, removing all values.
 479     ///
 480     /// # Examples
 481     ///
 482     /// ```
 483     /// use std::collections::HashSet;
 484     ///
 485     /// let mut v = HashSet::new();
 486     /// v.insert(1);
 487     /// v.clear();
 488     /// assert!(v.is_empty());
 489     /// ```
 490     #[stable(feature = "rust1", since = "1.0.0")]
 491     pub fn clear(&mut self) {
 492         self.map.clear()
 493     }
 494
 495     /// Returns `true` if the set contains a value.
 496     ///
 497     /// The value may be any borrowed form of the set's value type, but
 498     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
 499     /// the value type.
 500     ///
 501     /// # Examples
 502     ///
 503     /// ```
 504     /// use std::collections::HashSet;
 505     ///
 506     /// let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 507     /// assert_eq!(set.contains(&1), true);
 508     /// assert_eq!(set.contains(&4), false);
 509     /// ```
 510     ///
 511     /// [`Eq`]: ../../std/cmp/trait.Eq.html
 512     /// [`Hash`]: ../../std/hash/trait.Hash.html
 513     #[stable(feature = "rust1", since = "1.0.0")]
 514     pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool
 515         where T: Borrow<Q>,
 516               Q: Hash + Eq
 517     {
 518         self.map.contains_key(value)
 519     }
 520
 521     /// Returns a reference to the value in the set, if any, that is equal to the given value.
 522     ///
 523     /// The value may be any borrowed form of the set's value type, but
 524     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
 525     /// the value type.
 526     ///
 527     /// [`Eq`]: ../../std/cmp/trait.Eq.html
 528     /// [`Hash`]: ../../std/hash/trait.Hash.html
 529     #[stable(feature = "set_recovery", since = "1.9.0")]
 530     pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>
 531         where T: Borrow<Q>,
 532               Q: Hash + Eq
 533     {
 534         Recover::get(&self.map, value)
 535     }
 536
 537     /// Returns `true` if `self` has no elements in common with `other`.
 538     /// This is equivalent to checking for an empty intersection.
 539     ///
 540     /// # Examples
 541     ///
 542     /// ```
 543     /// use std::collections::HashSet;
 544     ///
 545     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 546     /// let mut b = HashSet::new();
 547     ///
 548     /// assert_eq!(a.is_disjoint(&b), true);
 549     /// b.insert(4);
 550     /// assert_eq!(a.is_disjoint(&b), true);
 551     /// b.insert(1);
 552     /// assert_eq!(a.is_disjoint(&b), false);
 553     /// ```
 554     #[stable(feature = "rust1", since = "1.0.0")]
 555     pub fn is_disjoint(&self, other: &HashSet<T, S>) -> bool {
 556         self.iter().all(|v| !other.contains(v))
 557     }
 558
 559     /// Returns `true` if the set is a subset of another,
 560     /// i.e. `other` contains at least all the values in `self`.
 561     ///
 562     /// # Examples
 563     ///
 564     /// ```
 565     /// use std::collections::HashSet;
 566     ///
 567     /// let sup: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 568     /// let mut set = HashSet::new();
 569     ///
 570     /// assert_eq!(set.is_subset(&sup), true);
 571     /// set.insert(2);
 572     /// assert_eq!(set.is_subset(&sup), true);
 573     /// set.insert(4);
 574     /// assert_eq!(set.is_subset(&sup), false);
 575     /// ```
 576     #[stable(feature = "rust1", since = "1.0.0")]
 577     pub fn is_subset(&self, other: &HashSet<T, S>) -> bool {
 578         self.iter().all(|v| other.contains(v))
 579     }
 580
 581     /// Returns `true` if the set is a superset of another,
 582     /// i.e. `self` contains at least all the values in `other`.
 583     ///
 584     /// # Examples
 585     ///
 586     /// ```
 587     /// use std::collections::HashSet;
 588     ///
 589     /// let sub: HashSet<_> = [1, 2].iter().cloned().collect();
 590     /// let mut set = HashSet::new();
 591     ///
 592     /// assert_eq!(set.is_superset(&sub), false);
 593     ///
 594     /// set.insert(0);
 595     /// set.insert(1);
 596     /// assert_eq!(set.is_superset(&sub), false);
 597     ///
 598     /// set.insert(2);
 599     /// assert_eq!(set.is_superset(&sub), true);
 600     /// ```
 601     #[inline]
 602     #[stable(feature = "rust1", since = "1.0.0")]
 603     pub fn is_superset(&self, other: &HashSet<T, S>) -> bool {
 604         other.is_subset(self)
 605     }
 606
 607     /// Adds a value to the set.
 608     ///
 609     /// If the set did not have this value present, `true` is returned.
 610     ///
 611     /// If the set did have this value present, `false` is returned.
 612     ///
 613     /// # Examples
 614     ///
 615     /// ```
 616     /// use std::collections::HashSet;
 617     ///
 618     /// let mut set = HashSet::new();
 619     ///
 620     /// assert_eq!(set.insert(2), true);
 621     /// assert_eq!(set.insert(2), false);
 622     /// assert_eq!(set.len(), 1);
 623     /// ```
 624     #[stable(feature = "rust1", since = "1.0.0")]
 625     pub fn insert(&mut self, value: T) -> bool {
 626         self.map.insert(value, ()).is_none()
 627     }
 628
 629     /// Adds a value to the set, replacing the existing value, if any, that is equal to the given
 630     /// one. Returns the replaced value.
 631     #[stable(feature = "set_recovery", since = "1.9.0")]
 632     pub fn replace(&mut self, value: T) -> Option<T> {
 633         Recover::replace(&mut self.map, value)
 634     }
 635
 636     /// Removes a value from the set. Returns `true` if the value was
 637     /// present in the set.
 638     ///
 639     /// The value may be any borrowed form of the set's value type, but
 640     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
 641     /// the value type.
 642     ///
 643     /// # Examples
 644     ///
 645     /// ```
 646     /// use std::collections::HashSet;
 647     ///
 648     /// let mut set = HashSet::new();
 649     ///
 650     /// set.insert(2);
 651     /// assert_eq!(set.remove(&2), true);
 652     /// assert_eq!(set.remove(&2), false);
 653     /// ```
 654     ///
 655     /// [`Eq`]: ../../std/cmp/trait.Eq.html
 656     /// [`Hash`]: ../../std/hash/trait.Hash.html
 657     #[stable(feature = "rust1", since = "1.0.0")]
 658     pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool
 659         where T: Borrow<Q>,
 660               Q: Hash + Eq
 661     {
 662         self.map.remove(value).is_some()
 663     }
 664
 665     /// Removes and returns the value in the set, if any, that is equal to the given one.
 666     ///
 667     /// The value may be any borrowed form of the set's value type, but
 668     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
 669     /// the value type.
 670     ///
 671     /// [`Eq`]: ../../std/cmp/trait.Eq.html
 672     /// [`Hash`]: ../../std/hash/trait.Hash.html
 673     #[stable(feature = "set_recovery", since = "1.9.0")]
 674     pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
 675         where T: Borrow<Q>,
 676               Q: Hash + Eq
 677     {
 678         Recover::take(&mut self.map, value)
 679     }
 680
 681     /// Retains only the elements specified by the predicate.
 682     ///
 683     /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
 684     ///
 685     /// # Examples
 686     ///
 687     /// ```
 688     /// use std::collections::HashSet;
 689     ///
 690     /// let xs = [1,2,3,4,5,6];
 691     /// let mut set: HashSet<isize> = xs.iter().cloned().collect();
 692     /// set.retain(|&k| k % 2 == 0);
 693     /// assert_eq!(set.len(), 3);
 694     /// ```
 695     #[stable(feature = "retain_hash_collection", since = "1.18.0")]
 696     pub fn retain<F>(&mut self, mut f: F)
 697         where F: FnMut(&T) -> bool
 698     {
 699         self.map.retain(|k, _| f(k));
 700     }
 701 }
 702
 703 #[stable(feature = "rust1", since = "1.0.0")]
 704 impl<T, S> PartialEq for HashSet<T, S>
 705     where T: Eq + Hash,
 706           S: BuildHasher
 707 {
 708     fn eq(&self, other: &HashSet<T, S>) -> bool {
 709         if self.len() != other.len() {
 710             return false;
 711         }
 712
 713         self.iter().all(|key| other.contains(key))
 714     }
 715 }
 716
 717 #[stable(feature = "rust1", since = "1.0.0")]
 718 impl<T, S> Eq for HashSet<T, S>
 719     where T: Eq + Hash,
 720           S: BuildHasher
 721 {
 722 }
 723
 724 #[stable(feature = "rust1", since = "1.0.0")]
 725 impl<T, S> fmt::Debug for HashSet<T, S>
 726     where T: Eq + Hash + fmt::Debug,
 727           S: BuildHasher
 728 {
 729     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 730         f.debug_set().entries(self.iter()).finish()
 731     }
 732 }
 733
 734 #[stable(feature = "rust1", since = "1.0.0")]
 735 impl<T, S> FromIterator<T> for HashSet<T, S>
 736     where T: Eq + Hash,
 737           S: BuildHasher + Default
 738 {
 739     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> HashSet<T, S> {
 740         let mut set = HashSet::with_hasher(Default::default());
 741         set.extend(iter);
 742         set
 743     }
 744 }
 745
 746 #[stable(feature = "rust1", since = "1.0.0")]
 747 impl<T, S> Extend<T> for HashSet<T, S>
 748     where T: Eq + Hash,
 749           S: BuildHasher
 750 {
 751     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
 752         self.map.extend(iter.into_iter().map(|k| (k, ())));
 753     }
 754 }
 755
 756 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
 757 impl<'a, T, S> Extend<&'a T> for HashSet<T, S>
 758     where T: 'a + Eq + Hash + Copy,
 759           S: BuildHasher
 760 {
 761     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
 762         self.extend(iter.into_iter().cloned());
 763     }
 764 }
 765
 766 #[stable(feature = "rust1", since = "1.0.0")]
 767 impl<T, S> Default for HashSet<T, S>
 768     where T: Eq + Hash,
 769           S: BuildHasher + Default
 770 {
 771     /// Creates an empty `HashSet<T, S>` with the `Default` value for the hasher.
 772     fn default() -> HashSet<T, S> {
 773         HashSet { map: HashMap::default() }
 774     }
 775 }
 776
 777 #[stable(feature = "rust1", since = "1.0.0")]
 778 impl<'a, 'b, T, S> BitOr<&'b HashSet<T, S>> for &'a HashSet<T, S>
 779     where T: Eq + Hash + Clone,
 780           S: BuildHasher + Default
 781 {
 782     type Output = HashSet<T, S>;
 783
 784     /// Returns the union of `self` and `rhs` as a new `HashSet<T, S>`.
 785     ///
 786     /// # Examples
 787     ///
 788     /// ```
 789     /// use std::collections::HashSet;
 790     ///
 791     /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
 792     /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
 793     ///
 794     /// let set = &a | &b;
 795     ///
 796     /// let mut i = 0;
 797     /// let expected = [1, 2, 3, 4, 5];
 798     /// for x in &set {
 799     ///     assert!(expected.contains(x));
 800     ///     i += 1;
 801     /// }
 802     /// assert_eq!(i, expected.len());
 803     /// ```
 804     fn bitor(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
 805         self.union(rhs).cloned().collect()
 806     }
 807 }
 808
 809 #[stable(feature = "rust1", since = "1.0.0")]
 810 impl<'a, 'b, T, S> BitAnd<&'b HashSet<T, S>> for &'a HashSet<T, S>
 811     where T: Eq + Hash + Clone,
 812           S: BuildHasher + Default
 813 {
 814     type Output = HashSet<T, S>;
 815
 816     /// Returns the intersection of `self` and `rhs` as a new `HashSet<T, S>`.
 817     ///
 818     /// # Examples
 819     ///
 820     /// ```
 821     /// use std::collections::HashSet;
 822     ///
 823     /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
 824     /// let b: HashSet<_> = vec![2, 3, 4].into_iter().collect();
 825     ///
 826     /// let set = &a & &b;
 827     ///
 828     /// let mut i = 0;
 829     /// let expected = [2, 3];
 830     /// for x in &set {
 831     ///     assert!(expected.contains(x));
 832     ///     i += 1;
 833     /// }
 834     /// assert_eq!(i, expected.len());
 835     /// ```
 836     fn bitand(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
 837         self.intersection(rhs).cloned().collect()
 838     }
 839 }
 840
 841 #[stable(feature = "rust1", since = "1.0.0")]
 842 impl<'a, 'b, T, S> BitXor<&'b HashSet<T, S>> for &'a HashSet<T, S>
 843     where T: Eq + Hash + Clone,
 844           S: BuildHasher + Default
 845 {
 846     type Output = HashSet<T, S>;
 847
 848     /// Returns the symmetric difference of `self` and `rhs` as a new `HashSet<T, S>`.
 849     ///
 850     /// # Examples
 851     ///
 852     /// ```
 853     /// use std::collections::HashSet;
 854     ///
 855     /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
 856     /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
 857     ///
 858     /// let set = &a ^ &b;
 859     ///
 860     /// let mut i = 0;
 861     /// let expected = [1, 2, 4, 5];
 862     /// for x in &set {
 863     ///     assert!(expected.contains(x));
 864     ///     i += 1;
 865     /// }
 866     /// assert_eq!(i, expected.len());
 867     /// ```
 868     fn bitxor(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
 869         self.symmetric_difference(rhs).cloned().collect()
 870     }
 871 }
 872
 873 #[stable(feature = "rust1", since = "1.0.0")]
 874 impl<'a, 'b, T, S> Sub<&'b HashSet<T, S>> for &'a HashSet<T, S>
 875     where T: Eq + Hash + Clone,
 876           S: BuildHasher + Default
 877 {
 878     type Output = HashSet<T, S>;
 879
 880     /// Returns the difference of `self` and `rhs` as a new `HashSet<T, S>`.
 881     ///
 882     /// # Examples
 883     ///
 884     /// ```
 885     /// use std::collections::HashSet;
 886     ///
 887     /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
 888     /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
 889     ///
 890     /// let set = &a - &b;
 891     ///
 892     /// let mut i = 0;
 893     /// let expected = [1, 2];
 894     /// for x in &set {
 895     ///     assert!(expected.contains(x));
 896     ///     i += 1;
 897     /// }
 898     /// assert_eq!(i, expected.len());
 899     /// ```
 900     fn sub(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
 901         self.difference(rhs).cloned().collect()
 902     }
 903 }
 904
 905 /// An iterator over the items of a `HashSet`.
 906 ///
 907 /// This `struct` is created by the [`iter`] method on [`HashSet`].
 908 /// See its documentation for more.
 909 ///
 910 /// [`HashSet`]: struct.HashSet.html
 911 /// [`iter`]: struct.HashSet.html#method.iter
 912 #[stable(feature = "rust1", since = "1.0.0")]
 913 pub struct Iter<'a, K: 'a> {
 914     iter: Keys<'a, K, ()>,
 915 }
 916
 917 /// An owning iterator over the items of a `HashSet`.
 918 ///
 919 /// This `struct` is created by the [`into_iter`] method on [`HashSet`][`HashSet`]
 920 /// (provided by the `IntoIterator` trait). See its documentation for more.
 921 ///
 922 /// [`HashSet`]: struct.HashSet.html
 923 /// [`into_iter`]: struct.HashSet.html#method.into_iter
 924 #[stable(feature = "rust1", since = "1.0.0")]
 925 pub struct IntoIter<K> {
 926     iter: map::IntoIter<K, ()>,
 927 }
 928
 929 /// A draining iterator over the items of a `HashSet`.
 930 ///
 931 /// This `struct` is created by the [`drain`] method on [`HashSet`].
 932 /// See its documentation for more.
 933 ///
 934 /// [`HashSet`]: struct.HashSet.html
 935 /// [`drain`]: struct.HashSet.html#method.drain
 936 #[stable(feature = "rust1", since = "1.0.0")]
 937 pub struct Drain<'a, K: 'a> {
 938     iter: map::Drain<'a, K, ()>,
 939 }
 940
 941 /// A lazy iterator producing elements in the intersection of `HashSet`s.
 942 ///
 943 /// This `struct` is created by the [`intersection`] method on [`HashSet`].
 944 /// See its documentation for more.
 945 ///
 946 /// [`HashSet`]: struct.HashSet.html
 947 /// [`intersection`]: struct.HashSet.html#method.intersection
 948 #[stable(feature = "rust1", since = "1.0.0")]
 949 pub struct Intersection<'a, T: 'a, S: 'a> {
 950     // iterator of the first set
 951     iter: Iter<'a, T>,
 952     // the second set
 953     other: &'a HashSet<T, S>,
 954 }
 955
 956 /// A lazy iterator producing elements in the difference of `HashSet`s.
 957 ///
 958 /// This `struct` is created by the [`difference`] method on [`HashSet`].
 959 /// See its documentation for more.
 960 ///
 961 /// [`HashSet`]: struct.HashSet.html
 962 /// [`difference`]: struct.HashSet.html#method.difference
 963 #[stable(feature = "rust1", since = "1.0.0")]
 964 pub struct Difference<'a, T: 'a, S: 'a> {
 965     // iterator of the first set
 966     iter: Iter<'a, T>,
 967     // the second set
 968     other: &'a HashSet<T, S>,
 969 }
 970
 971 /// A lazy iterator producing elements in the symmetric difference of `HashSet`s.
 972 ///
 973 /// This `struct` is created by the [`symmetric_difference`] method on
 974 /// [`HashSet`]. See its documentation for more.
 975 ///
 976 /// [`HashSet`]: struct.HashSet.html
 977 /// [`symmetric_difference`]: struct.HashSet.html#method.symmetric_difference
 978 #[stable(feature = "rust1", since = "1.0.0")]
 979 pub struct SymmetricDifference<'a, T: 'a, S: 'a> {
 980     iter: Chain<Difference<'a, T, S>, Difference<'a, T, S>>,
 981 }
 982
 983 /// A lazy iterator producing elements in the union of `HashSet`s.
 984 ///
 985 /// This `struct` is created by the [`union`] method on [`HashSet`].
 986 /// See its documentation for more.
 987 ///
 988 /// [`HashSet`]: struct.HashSet.html
 989 /// [`union`]: struct.HashSet.html#method.union
 990 #[stable(feature = "rust1", since = "1.0.0")]
 991 pub struct Union<'a, T: 'a, S: 'a> {
 992     iter: Chain<Iter<'a, T>, Difference<'a, T, S>>,
 993 }
 994
 995 #[stable(feature = "rust1", since = "1.0.0")]
 996 impl<'a, T, S> IntoIterator for &'a HashSet<T, S>
 997     where T: Eq + Hash,
 998           S: BuildHasher
 999 {
1000     type Item = &'a T;
1001     type IntoIter = Iter<'a, T>;
1002
1003     fn into_iter(self) -> Iter<'a, T> {
1004         self.iter()
1005     }
1006 }
1007
1008 #[stable(feature = "rust1", since = "1.0.0")]
1009 impl<T, S> IntoIterator for HashSet<T, S>
1010     where T: Eq + Hash,
1011           S: BuildHasher
1012 {
1013     type Item = T;
1014     type IntoIter = IntoIter<T>;
1015
1016     /// Creates a consuming iterator, that is, one that moves each value out
1017     /// of the set in arbitrary order. The set cannot be used after calling
1018     /// this.
1019     ///
1020     /// # Examples
1021     ///
1022     /// ```
1023     /// use std::collections::HashSet;
1024     /// let mut set = HashSet::new();
1025     /// set.insert("a".to_string());
1026     /// set.insert("b".to_string());
1027     ///
1028     /// // Not possible to collect to a Vec<String> with a regular `.iter()`.
1029     /// let v: Vec<String> = set.into_iter().collect();
1030     ///
1031     /// // Will print in an arbitrary order.
1032     /// for x in &v {
1033     ///     println!("{}", x);
1034     /// }
1035     /// ```
1036     fn into_iter(self) -> IntoIter<T> {
1037         IntoIter { iter: self.map.into_iter() }
1038     }
1039 }
1040
1041 #[stable(feature = "rust1", since = "1.0.0")]
1042 impl<'a, K> Clone for Iter<'a, K> {
1043     fn clone(&self) -> Iter<'a, K> {
1044         Iter { iter: self.iter.clone() }
1045     }
1046 }
1047 #[stable(feature = "rust1", since = "1.0.0")]
1048 impl<'a, K> Iterator for Iter<'a, K> {
1049     type Item = &'a K;
1050
1051     fn next(&mut self) -> Option<&'a K> {
1052         self.iter.next()
1053     }
1054     fn size_hint(&self) -> (usize, Option<usize>) {
1055         self.iter.size_hint()
1056     }
1057 }
1058 #[stable(feature = "rust1", since = "1.0.0")]
1059 impl<'a, K> ExactSizeIterator for Iter<'a, K> {
1060     fn len(&self) -> usize {
1061         self.iter.len()
1062     }
1063 }
1064 #[unstable(feature = "fused", issue = "35602")]
1065 impl<'a, K> FusedIterator for Iter<'a, K> {}
1066
1067 #[stable(feature = "std_debug", since = "1.16.0")]
1068 impl<'a, K: fmt::Debug> fmt::Debug for Iter<'a, K> {
1069     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1070         f.debug_list().entries(self.clone()).finish()
1071     }
1072 }
1073
1074 #[stable(feature = "rust1", since = "1.0.0")]
1075 impl<K> Iterator for IntoIter<K> {
1076     type Item = K;
1077
1078     fn next(&mut self) -> Option<K> {
1079         self.iter.next().map(|(k, _)| k)
1080     }
1081     fn size_hint(&self) -> (usize, Option<usize>) {
1082         self.iter.size_hint()
1083     }
1084 }
1085 #[stable(feature = "rust1", since = "1.0.0")]
1086 impl<K> ExactSizeIterator for IntoIter<K> {
1087     fn len(&self) -> usize {
1088         self.iter.len()
1089     }
1090 }
1091 #[unstable(feature = "fused", issue = "35602")]
1092 impl<K> FusedIterator for IntoIter<K> {}
1093
1094 #[stable(feature = "std_debug", since = "1.16.0")]
1095 impl<K: fmt::Debug> fmt::Debug for IntoIter<K> {
1096     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1097         let entries_iter = self.iter
1098             .inner
1099             .iter()
1100             .map(|(k, _)| k);
1101         f.debug_list().entries(entries_iter).finish()
1102     }
1103 }
1104
1105 #[stable(feature = "rust1", since = "1.0.0")]
1106 impl<'a, K> Iterator for Drain<'a, K> {
1107     type Item = K;
1108
1109     fn next(&mut self) -> Option<K> {
1110         self.iter.next().map(|(k, _)| k)
1111     }
1112     fn size_hint(&self) -> (usize, Option<usize>) {
1113         self.iter.size_hint()
1114     }
1115 }
1116 #[stable(feature = "rust1", since = "1.0.0")]
1117 impl<'a, K> ExactSizeIterator for Drain<'a, K> {
1118     fn len(&self) -> usize {
1119         self.iter.len()
1120     }
1121 }
1122 #[unstable(feature = "fused", issue = "35602")]
1123 impl<'a, K> FusedIterator for Drain<'a, K> {}
1124
1125 #[stable(feature = "std_debug", since = "1.16.0")]
1126 impl<'a, K: fmt::Debug> fmt::Debug for Drain<'a, K> {
1127     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1128         let entries_iter = self.iter
1129             .inner
1130             .iter()
1131             .map(|(k, _)| k);
1132         f.debug_list().entries(entries_iter).finish()
1133     }
1134 }
1135
1136 #[stable(feature = "rust1", since = "1.0.0")]
1137 impl<'a, T, S> Clone for Intersection<'a, T, S> {
1138     fn clone(&self) -> Intersection<'a, T, S> {
1139         Intersection { iter: self.iter.clone(), ..*self }
1140     }
1141 }
1142
1143 #[stable(feature = "rust1", since = "1.0.0")]
1144 impl<'a, T, S> Iterator for Intersection<'a, T, S>
1145     where T: Eq + Hash,
1146           S: BuildHasher
1147 {
1148     type Item = &'a T;
1149
1150     fn next(&mut self) -> Option<&'a T> {
1151         loop {
1152             match self.iter.next() {
1153                 None => return None,
1154                 Some(elt) => {
1155                     if self.other.contains(elt) {
1156                         return Some(elt);
1157                     }
1158                 }
1159             }
1160         }
1161     }
1162
1163     fn size_hint(&self) -> (usize, Option<usize>) {
1164         let (_, upper) = self.iter.size_hint();
1165         (0, upper)
1166     }
1167 }
1168
1169 #[stable(feature = "std_debug", since = "1.16.0")]
1170 impl<'a, T, S> fmt::Debug for Intersection<'a, T, S>
1171     where T: fmt::Debug + Eq + Hash,
1172           S: BuildHasher
1173 {
1174     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1175         f.debug_list().entries(self.clone()).finish()
1176     }
1177 }
1178
1179 #[unstable(feature = "fused", issue = "35602")]
1180 impl<'a, T, S> FusedIterator for Intersection<'a, T, S>
1181     where T: Eq + Hash,
1182           S: BuildHasher
1183 {
1184 }
1185
1186 #[stable(feature = "rust1", since = "1.0.0")]
1187 impl<'a, T, S> Clone for Difference<'a, T, S> {
1188     fn clone(&self) -> Difference<'a, T, S> {
1189         Difference { iter: self.iter.clone(), ..*self }
1190     }
1191 }
1192
1193 #[stable(feature = "rust1", since = "1.0.0")]
1194 impl<'a, T, S> Iterator for Difference<'a, T, S>
1195     where T: Eq + Hash,
1196           S: BuildHasher
1197 {
1198     type Item = &'a T;
1199
1200     fn next(&mut self) -> Option<&'a T> {
1201         loop {
1202             match self.iter.next() {
1203                 None => return None,
1204                 Some(elt) => {
1205                     if !self.other.contains(elt) {
1206                         return Some(elt);
1207                     }
1208                 }
1209             }
1210         }
1211     }
1212
1213     fn size_hint(&self) -> (usize, Option<usize>) {
1214         let (_, upper) = self.iter.size_hint();
1215         (0, upper)
1216     }
1217 }
1218
1219 #[unstable(feature = "fused", issue = "35602")]
1220 impl<'a, T, S> FusedIterator for Difference<'a, T, S>
1221     where T: Eq + Hash,
1222           S: BuildHasher
1223 {
1224 }
1225
1226 #[stable(feature = "std_debug", since = "1.16.0")]
1227 impl<'a, T, S> fmt::Debug for Difference<'a, T, S>
1228     where T: fmt::Debug + Eq + Hash,
1229           S: BuildHasher
1230 {
1231     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1232         f.debug_list().entries(self.clone()).finish()
1233     }
1234 }
1235
1236 #[stable(feature = "rust1", since = "1.0.0")]
1237 impl<'a, T, S> Clone for SymmetricDifference<'a, T, S> {
1238     fn clone(&self) -> SymmetricDifference<'a, T, S> {
1239         SymmetricDifference { iter: self.iter.clone() }
1240     }
1241 }
1242
1243 #[stable(feature = "rust1", since = "1.0.0")]
1244 impl<'a, T, S> Iterator for SymmetricDifference<'a, T, S>
1245     where T: Eq + Hash,
1246           S: BuildHasher
1247 {
1248     type Item = &'a T;
1249
1250     fn next(&mut self) -> Option<&'a T> {
1251         self.iter.next()
1252     }
1253     fn size_hint(&self) -> (usize, Option<usize>) {
1254         self.iter.size_hint()
1255     }
1256 }
1257
1258 #[unstable(feature = "fused", issue = "35602")]
1259 impl<'a, T, S> FusedIterator for SymmetricDifference<'a, T, S>
1260     where T: Eq + Hash,
1261           S: BuildHasher
1262 {
1263 }
1264
1265 #[stable(feature = "std_debug", since = "1.16.0")]
1266 impl<'a, T, S> fmt::Debug for SymmetricDifference<'a, T, S>
1267     where T: fmt::Debug + Eq + Hash,
1268           S: BuildHasher
1269 {
1270     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1271         f.debug_list().entries(self.clone()).finish()
1272     }
1273 }
1274
1275 #[stable(feature = "rust1", since = "1.0.0")]
1276 impl<'a, T, S> Clone for Union<'a, T, S> {
1277     fn clone(&self) -> Union<'a, T, S> {
1278         Union { iter: self.iter.clone() }
1279     }
1280 }
1281
1282 #[unstable(feature = "fused", issue = "35602")]
1283 impl<'a, T, S> FusedIterator for Union<'a, T, S>
1284     where T: Eq + Hash,
1285           S: BuildHasher
1286 {
1287 }
1288
1289 #[stable(feature = "std_debug", since = "1.16.0")]
1290 impl<'a, T, S> fmt::Debug for Union<'a, T, S>
1291     where T: fmt::Debug + Eq + Hash,
1292           S: BuildHasher
1293 {
1294     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1295         f.debug_list().entries(self.clone()).finish()
1296     }
1297 }
1298
1299 #[stable(feature = "rust1", since = "1.0.0")]
1300 impl<'a, T, S> Iterator for Union<'a, T, S>
1301     where T: Eq + Hash,
1302           S: BuildHasher
1303 {
1304     type Item = &'a T;
1305
1306     fn next(&mut self) -> Option<&'a T> {
1307         self.iter.next()
1308     }
1309     fn size_hint(&self) -> (usize, Option<usize>) {
1310         self.iter.size_hint()
1311     }
1312 }
1313
1314 #[allow(dead_code)]
1315 fn assert_covariance() {
1316     fn set<'new>(v: HashSet<&'static str>) -> HashSet<&'new str> {
1317         v
1318     }
1319     fn iter<'a, 'new>(v: Iter<'a, &'static str>) -> Iter<'a, &'new str> {
1320         v
1321     }
1322     fn into_iter<'new>(v: IntoIter<&'static str>) -> IntoIter<&'new str> {
1323         v
1324     }
1325     fn difference<'a, 'new>(v: Difference<'a, &'static str, RandomState>)
1326                             -> Difference<'a, &'new str, RandomState> {
1327         v
1328     }
1329     fn symmetric_difference<'a, 'new>(v: SymmetricDifference<'a, &'static str, RandomState>)
1330                                       -> SymmetricDifference<'a, &'new str, RandomState> {
1331         v
1332     }
1333     fn intersection<'a, 'new>(v: Intersection<'a, &'static str, RandomState>)
1334                               -> Intersection<'a, &'new str, RandomState> {
1335         v
1336     }
1337     fn union<'a, 'new>(v: Union<'a, &'static str, RandomState>)
1338                        -> Union<'a, &'new str, RandomState> {
1339         v
1340     }
1341     fn drain<'new>(d: Drain<'static, &'static str>) -> Drain<'new, &'new str> {
1342         d
1343     }
1344 }
1345
1346 #[cfg(test)]
1347 mod test_set {
1348     use super::HashSet;
1349     use super::super::map::RandomState;
1350
1351     #[test]
1352     fn test_zero_capacities() {
1353         type HS = HashSet<i32>;
1354
1355         let s = HS::new();
1356         assert_eq!(s.capacity(), 0);
1357
1358         let s = HS::default();
1359         assert_eq!(s.capacity(), 0);
1360
1361         let s = HS::with_hasher(RandomState::new());
1362         assert_eq!(s.capacity(), 0);
1363
1364         let s = HS::with_capacity(0);
1365         assert_eq!(s.capacity(), 0);
1366
1367         let s = HS::with_capacity_and_hasher(0, RandomState::new());
1368         assert_eq!(s.capacity(), 0);
1369
1370         let mut s = HS::new();
1371         s.insert(1);
1372         s.insert(2);
1373         s.remove(&1);
1374         s.remove(&2);
1375         s.shrink_to_fit();
1376         assert_eq!(s.capacity(), 0);
1377
1378         let mut s = HS::new();
1379         s.reserve(0);
1380         assert_eq!(s.capacity(), 0);
1381     }
1382
1383     #[test]
1384     fn test_disjoint() {
1385         let mut xs = HashSet::new();
1386         let mut ys = HashSet::new();
1387         assert!(xs.is_disjoint(&ys));
1388         assert!(ys.is_disjoint(&xs));
1389         assert!(xs.insert(5));
1390         assert!(ys.insert(11));
1391         assert!(xs.is_disjoint(&ys));
1392         assert!(ys.is_disjoint(&xs));
1393         assert!(xs.insert(7));
1394         assert!(xs.insert(19));
1395         assert!(xs.insert(4));
1396         assert!(ys.insert(2));
1397         assert!(ys.insert(-11));
1398         assert!(xs.is_disjoint(&ys));
1399         assert!(ys.is_disjoint(&xs));
1400         assert!(ys.insert(7));
1401         assert!(!xs.is_disjoint(&ys));
1402         assert!(!ys.is_disjoint(&xs));
1403     }
1404
1405     #[test]
1406     fn test_subset_and_superset() {
1407         let mut a = HashSet::new();
1408         assert!(a.insert(0));
1409         assert!(a.insert(5));
1410         assert!(a.insert(11));
1411         assert!(a.insert(7));
1412
1413         let mut b = HashSet::new();
1414         assert!(b.insert(0));
1415         assert!(b.insert(7));
1416         assert!(b.insert(19));
1417         assert!(b.insert(250));
1418         assert!(b.insert(11));
1419         assert!(b.insert(200));
1420
1421         assert!(!a.is_subset(&b));
1422         assert!(!a.is_superset(&b));
1423         assert!(!b.is_subset(&a));
1424         assert!(!b.is_superset(&a));
1425
1426         assert!(b.insert(5));
1427
1428         assert!(a.is_subset(&b));
1429         assert!(!a.is_superset(&b));
1430         assert!(!b.is_subset(&a));
1431         assert!(b.is_superset(&a));
1432     }
1433
1434     #[test]
1435     fn test_iterate() {
1436         let mut a = HashSet::new();
1437         for i in 0..32 {
1438             assert!(a.insert(i));
1439         }
1440         let mut observed: u32 = 0;
1441         for k in &a {
1442             observed |= 1 << *k;
1443         }
1444         assert_eq!(observed, 0xFFFF_FFFF);
1445     }
1446
1447     #[test]
1448     fn test_intersection() {
1449         let mut a = HashSet::new();
1450         let mut b = HashSet::new();
1451
1452         assert!(a.insert(11));
1453         assert!(a.insert(1));
1454         assert!(a.insert(3));
1455         assert!(a.insert(77));
1456         assert!(a.insert(103));
1457         assert!(a.insert(5));
1458         assert!(a.insert(-5));
1459
1460         assert!(b.insert(2));
1461         assert!(b.insert(11));
1462         assert!(b.insert(77));
1463         assert!(b.insert(-9));
1464         assert!(b.insert(-42));
1465         assert!(b.insert(5));
1466         assert!(b.insert(3));
1467
1468         let mut i = 0;
1469         let expected = [3, 5, 11, 77];
1470         for x in a.intersection(&b) {
1471             assert!(expected.contains(x));
1472             i += 1
1473         }
1474         assert_eq!(i, expected.len());
1475     }
1476
1477     #[test]
1478     fn test_difference() {
1479         let mut a = HashSet::new();
1480         let mut b = HashSet::new();
1481
1482         assert!(a.insert(1));
1483         assert!(a.insert(3));
1484         assert!(a.insert(5));
1485         assert!(a.insert(9));
1486         assert!(a.insert(11));
1487
1488         assert!(b.insert(3));
1489         assert!(b.insert(9));
1490
1491         let mut i = 0;
1492         let expected = [1, 5, 11];
1493         for x in a.difference(&b) {
1494             assert!(expected.contains(x));
1495             i += 1
1496         }
1497         assert_eq!(i, expected.len());
1498     }
1499
1500     #[test]
1501     fn test_symmetric_difference() {
1502         let mut a = HashSet::new();
1503         let mut b = HashSet::new();
1504
1505         assert!(a.insert(1));
1506         assert!(a.insert(3));
1507         assert!(a.insert(5));
1508         assert!(a.insert(9));
1509         assert!(a.insert(11));
1510
1511         assert!(b.insert(-2));
1512         assert!(b.insert(3));
1513         assert!(b.insert(9));
1514         assert!(b.insert(14));
1515         assert!(b.insert(22));
1516
1517         let mut i = 0;
1518         let expected = [-2, 1, 5, 11, 14, 22];
1519         for x in a.symmetric_difference(&b) {
1520             assert!(expected.contains(x));
1521             i += 1
1522         }
1523         assert_eq!(i, expected.len());
1524     }
1525
1526     #[test]
1527     fn test_union() {
1528         let mut a = HashSet::new();
1529         let mut b = HashSet::new();
1530
1531         assert!(a.insert(1));
1532         assert!(a.insert(3));
1533         assert!(a.insert(5));
1534         assert!(a.insert(9));
1535         assert!(a.insert(11));
1536         assert!(a.insert(16));
1537         assert!(a.insert(19));
1538         assert!(a.insert(24));
1539
1540         assert!(b.insert(-2));
1541         assert!(b.insert(1));
1542         assert!(b.insert(5));
1543         assert!(b.insert(9));
1544         assert!(b.insert(13));
1545         assert!(b.insert(19));
1546
1547         let mut i = 0;
1548         let expected = [-2, 1, 3, 5, 9, 11, 13, 16, 19, 24];
1549         for x in a.union(&b) {
1550             assert!(expected.contains(x));
1551             i += 1
1552         }
1553         assert_eq!(i, expected.len());
1554     }
1555
1556     #[test]
1557     fn test_from_iter() {
1558         let xs = [1, 2, 3, 4, 5, 6, 7, 8, 9];
1559
1560         let set: HashSet<_> = xs.iter().cloned().collect();
1561
1562         for x in &xs {
1563             assert!(set.contains(x));
1564         }
1565     }
1566
1567     #[test]
1568     fn test_move_iter() {
1569         let hs = {
1570             let mut hs = HashSet::new();
1571
1572             hs.insert('a');
1573             hs.insert('b');
1574
1575             hs
1576         };
1577
1578         let v = hs.into_iter().collect::<Vec<char>>();
1579         assert!(v == ['a', 'b'] || v == ['b', 'a']);
1580     }
1581
1582     #[test]
1583     fn test_eq() {
1584         // These constants once happened to expose a bug in insert().
1585         // I'm keeping them around to prevent a regression.
1586         let mut s1 = HashSet::new();
1587
1588         s1.insert(1);
1589         s1.insert(2);
1590         s1.insert(3);
1591
1592         let mut s2 = HashSet::new();
1593
1594         s2.insert(1);
1595         s2.insert(2);
1596
1597         assert!(s1 != s2);
1598
1599         s2.insert(3);
1600
1601         assert_eq!(s1, s2);
1602     }
1603
1604     #[test]
1605     fn test_show() {
1606         let mut set = HashSet::new();
1607         let empty = HashSet::<i32>::new();
1608
1609         set.insert(1);
1610         set.insert(2);
1611
1612         let set_str = format!("{:?}", set);
1613
1614         assert!(set_str == "{1, 2}" || set_str == "{2, 1}");
1615         assert_eq!(format!("{:?}", empty), "{}");
1616     }
1617
1618     #[test]
1619     fn test_trivial_drain() {
1620         let mut s = HashSet::<i32>::new();
1621         for _ in s.drain() {}
1622         assert!(s.is_empty());
1623         drop(s);
1624
1625         let mut s = HashSet::<i32>::new();
1626         drop(s.drain());
1627         assert!(s.is_empty());
1628     }
1629
1630     #[test]
1631     fn test_drain() {
1632         let mut s: HashSet<_> = (1..100).collect();
1633
1634         // try this a bunch of times to make sure we don't screw up internal state.
1635         for _ in 0..20 {
1636             assert_eq!(s.len(), 99);
1637
1638             {
1639                 let mut last_i = 0;
1640                 let mut d = s.drain();
1641                 for (i, x) in d.by_ref().take(50).enumerate() {
1642                     last_i = i;
1643                     assert!(x != 0);
1644                 }
1645                 assert_eq!(last_i, 49);
1646             }
1647
1648             for _ in &s {
1649                 panic!("s should be empty!");
1650             }
1651
1652             // reset to try again.
1653             s.extend(1..100);
1654         }
1655     }
1656
1657     #[test]
1658     fn test_replace() {
1659         use hash;
1660
1661         #[derive(Debug)]
1662         struct Foo(&'static str, i32);
1663
1664         impl PartialEq for Foo {
1665             fn eq(&self, other: &Self) -> bool {
1666                 self.0 == other.0
1667             }
1668         }
1669
1670         impl Eq for Foo {}
1671
1672         impl hash::Hash for Foo {
1673             fn hash<H: hash::Hasher>(&self, h: &mut H) {
1674                 self.0.hash(h);
1675             }
1676         }
1677
1678         let mut s = HashSet::new();
1679         assert_eq!(s.replace(Foo("a", 1)), None);
1680         assert_eq!(s.len(), 1);
1681         assert_eq!(s.replace(Foo("a", 2)), Some(Foo("a", 1)));
1682         assert_eq!(s.len(), 1);
1683
1684         let mut it = s.iter();
1685         assert_eq!(it.next(), Some(&Foo("a", 2)));
1686         assert_eq!(it.next(), None);
1687     }
1688
1689     #[test]
1690     fn test_extend_ref() {
1691         let mut a = HashSet::new();
1692         a.insert(1);
1693
1694         a.extend(&[2, 3, 4]);
1695
1696         assert_eq!(a.len(), 4);
1697         assert!(a.contains(&1));
1698         assert!(a.contains(&2));
1699         assert!(a.contains(&3));
1700         assert!(a.contains(&4));
1701
1702         let mut b = HashSet::new();
1703         b.insert(5);
1704         b.insert(6);
1705
1706         a.extend(&b);
1707
1708         assert_eq!(a.len(), 6);
1709         assert!(a.contains(&1));
1710         assert!(a.contains(&2));
1711         assert!(a.contains(&3));
1712         assert!(a.contains(&4));
1713         assert!(a.contains(&5));
1714         assert!(a.contains(&6));
1715     }
1716
1717     #[test]
1718     fn test_retain() {
1719         let xs = [1, 2, 3, 4, 5, 6];
1720         let mut set: HashSet<isize> = xs.iter().cloned().collect();
1721         set.retain(|&k| k % 2 == 0);
1722         assert_eq!(set.len(), 3);
1723         assert!(set.contains(&2));
1724         assert!(set.contains(&4));
1725         assert!(set.contains(&6));
1726     }
1727 }