library/std/src/collections/hash/set.rs

   1 #[cfg(test)]
   2 mod tests;
   3
   4 use hashbrown::hash_set as base;
   5
   6 use crate::borrow::Borrow;
   7 use crate::collections::TryReserveError;
   8 use crate::fmt;
   9 use crate::hash::{BuildHasher, Hash};
  10 use crate::iter::{Chain, FromIterator, FusedIterator};
  11 use crate::ops::{BitAnd, BitOr, BitXor, Sub};
  12
  13 use super::map::{map_try_reserve_error, RandomState};
  14
  15 // Future Optimization (FIXME!)
  16 // ============================
  17 //
  18 // Iteration over zero sized values is a noop. There is no need
  19 // for `bucket.val` in the case of HashSet. I suppose we would need HKT
  20 // to get rid of it properly.
  21
  22 /// A hash set implemented as a `HashMap` where the value is `()`.
  23 ///
  24 /// As with the [`HashMap`] type, a `HashSet` requires that the elements
  25 /// implement the [`Eq`] and [`Hash`] traits. This can frequently be achieved by
  26 /// using `#[derive(PartialEq, Eq, Hash)]`. If you implement these yourself,
  27 /// it is important that the following property holds:
  28 ///
  29 /// ```text
  30 /// k1 == k2 -> hash(k1) == hash(k2)
  31 /// ```
  32 ///
  33 /// In other words, if two keys are equal, their hashes must be equal.
  34 ///
  35 ///
  36 /// It is a logic error for an item to be modified in such a way that the
  37 /// item's hash, as determined by the [`Hash`] trait, or its equality, as
  38 /// determined by the [`Eq`] trait, changes while it is in the set. This is
  39 /// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or
  40 /// unsafe code.
  41 ///
  42 /// # Examples
  43 ///
  44 /// ```
  45 /// use std::collections::HashSet;
  46 /// // Type inference lets us omit an explicit type signature (which
  47 /// // would be `HashSet<String>` in this example).
  48 /// let mut books = HashSet::new();
  49 ///
  50 /// // Add some books.
  51 /// books.insert("A Dance With Dragons".to_string());
  52 /// books.insert("To Kill a Mockingbird".to_string());
  53 /// books.insert("The Odyssey".to_string());
  54 /// books.insert("The Great Gatsby".to_string());
  55 ///
  56 /// // Check for a specific one.
  57 /// if !books.contains("The Winds of Winter") {
  58 ///     println!("We have {} books, but The Winds of Winter ain't one.",
  59 ///              books.len());
  60 /// }
  61 ///
  62 /// // Remove a book.
  63 /// books.remove("The Odyssey");
  64 ///
  65 /// // Iterate over everything.
  66 /// for book in &books {
  67 ///     println!("{}", book);
  68 /// }
  69 /// ```
  70 ///
  71 /// The easiest way to use `HashSet` with a custom type is to derive
  72 /// [`Eq`] and [`Hash`]. We must also derive [`PartialEq`], this will in the
  73 /// future be implied by [`Eq`].
  74 ///
  75 /// ```
  76 /// use std::collections::HashSet;
  77 /// #[derive(Hash, Eq, PartialEq, Debug)]
  78 /// struct Viking {
  79 ///     name: String,
  80 ///     power: usize,
  81 /// }
  82 ///
  83 /// let mut vikings = HashSet::new();
  84 ///
  85 /// vikings.insert(Viking { name: "Einar".to_string(), power: 9 });
  86 /// vikings.insert(Viking { name: "Einar".to_string(), power: 9 });
  87 /// vikings.insert(Viking { name: "Olaf".to_string(), power: 4 });
  88 /// vikings.insert(Viking { name: "Harald".to_string(), power: 8 });
  89 ///
  90 /// // Use derived implementation to print the vikings.
  91 /// for x in &vikings {
  92 ///     println!("{:?}", x);
  93 /// }
  94 /// ```
  95 ///
  96 /// A `HashSet` with fixed list of elements can be initialized from an array:
  97 ///
  98 /// ```
  99 /// use std::collections::HashSet;
 100 ///
 101 /// let viking_names: HashSet<&'static str> =
 102 ///     [ "Einar", "Olaf", "Harald" ].iter().cloned().collect();
 103 /// // use the values stored in the set
 104 /// ```
 105 ///
 106 /// [`HashMap`]: crate::collections::HashMap
 107 /// [`RefCell`]: crate::cell::RefCell
 108 /// [`Cell`]: crate::cell::Cell
 109 #[derive(Clone)]
 110 #[cfg_attr(not(test), rustc_diagnostic_item = "hashset_type")]
 111 #[stable(feature = "rust1", since = "1.0.0")]
 112 pub struct HashSet<T, S = RandomState> {
 113     base: base::HashSet<T, S>,
 114 }
 115
 116 impl<T> HashSet<T, RandomState> {
 117     /// Creates an empty `HashSet`.
 118     ///
 119     /// The hash set is initially created with a capacity of 0, so it will not allocate until it
 120     /// is first inserted into.
 121     ///
 122     /// # Examples
 123     ///
 124     /// ```
 125     /// use std::collections::HashSet;
 126     /// let set: HashSet<i32> = HashSet::new();
 127     /// ```
 128     #[inline]
 129     #[stable(feature = "rust1", since = "1.0.0")]
 130     pub fn new() -> HashSet<T, RandomState> {
 131         Default::default()
 132     }
 133
 134     /// Creates an empty `HashSet` with the specified capacity.
 135     ///
 136     /// The hash set will be able to hold at least `capacity` elements without
 137     /// reallocating. If `capacity` is 0, the hash set will not allocate.
 138     ///
 139     /// # Examples
 140     ///
 141     /// ```
 142     /// use std::collections::HashSet;
 143     /// let set: HashSet<i32> = HashSet::with_capacity(10);
 144     /// assert!(set.capacity() >= 10);
 145     /// ```
 146     #[inline]
 147     #[stable(feature = "rust1", since = "1.0.0")]
 148     pub fn with_capacity(capacity: usize) -> HashSet<T, RandomState> {
 149         HashSet { base: base::HashSet::with_capacity_and_hasher(capacity, Default::default()) }
 150     }
 151 }
 152
 153 impl<T, S> HashSet<T, S> {
 154     /// Returns the number of elements the set can hold without reallocating.
 155     ///
 156     /// # Examples
 157     ///
 158     /// ```
 159     /// use std::collections::HashSet;
 160     /// let set: HashSet<i32> = HashSet::with_capacity(100);
 161     /// assert!(set.capacity() >= 100);
 162     /// ```
 163     #[inline]
 164     #[stable(feature = "rust1", since = "1.0.0")]
 165     pub fn capacity(&self) -> usize {
 166         self.base.capacity()
 167     }
 168
 169     /// An iterator visiting all elements in arbitrary order.
 170     /// The iterator element type is `&'a T`.
 171     ///
 172     /// # Examples
 173     ///
 174     /// ```
 175     /// use std::collections::HashSet;
 176     /// let mut set = HashSet::new();
 177     /// set.insert("a");
 178     /// set.insert("b");
 179     ///
 180     /// // Will print in an arbitrary order.
 181     /// for x in set.iter() {
 182     ///     println!("{}", x);
 183     /// }
 184     /// ```
 185     #[inline]
 186     #[stable(feature = "rust1", since = "1.0.0")]
 187     pub fn iter(&self) -> Iter<'_, T> {
 188         Iter { base: self.base.iter() }
 189     }
 190
 191     /// Returns the number of elements in the set.
 192     ///
 193     /// # Examples
 194     ///
 195     /// ```
 196     /// use std::collections::HashSet;
 197     ///
 198     /// let mut v = HashSet::new();
 199     /// assert_eq!(v.len(), 0);
 200     /// v.insert(1);
 201     /// assert_eq!(v.len(), 1);
 202     /// ```
 203     #[inline]
 204     #[stable(feature = "rust1", since = "1.0.0")]
 205     pub fn len(&self) -> usize {
 206         self.base.len()
 207     }
 208
 209     /// Returns `true` if the set contains no elements.
 210     ///
 211     /// # Examples
 212     ///
 213     /// ```
 214     /// use std::collections::HashSet;
 215     ///
 216     /// let mut v = HashSet::new();
 217     /// assert!(v.is_empty());
 218     /// v.insert(1);
 219     /// assert!(!v.is_empty());
 220     /// ```
 221     #[inline]
 222     #[stable(feature = "rust1", since = "1.0.0")]
 223     pub fn is_empty(&self) -> bool {
 224         self.base.is_empty()
 225     }
 226
 227     /// Clears the set, returning all elements in an iterator.
 228     ///
 229     /// # Examples
 230     ///
 231     /// ```
 232     /// use std::collections::HashSet;
 233     ///
 234     /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 235     /// assert!(!set.is_empty());
 236     ///
 237     /// // print 1, 2, 3 in an arbitrary order
 238     /// for i in set.drain() {
 239     ///     println!("{}", i);
 240     /// }
 241     ///
 242     /// assert!(set.is_empty());
 243     /// ```
 244     #[inline]
 245     #[stable(feature = "drain", since = "1.6.0")]
 246     pub fn drain(&mut self) -> Drain<'_, T> {
 247         Drain { base: self.base.drain() }
 248     }
 249
 250     /// Creates an iterator which uses a closure to determine if a value should be removed.
 251     ///
 252     /// If the closure returns true, then the value is removed and yielded.
 253     /// If the closure returns false, the value will remain in the list and will not be yielded
 254     /// by the iterator.
 255     ///
 256     /// If the iterator is only partially consumed or not consumed at all, each of the remaining
 257     /// values will still be subjected to the closure and removed and dropped if it returns true.
 258     ///
 259     /// It is unspecified how many more values will be subjected to the closure
 260     /// if a panic occurs in the closure, or if a panic occurs while dropping a value, or if the
 261     /// `DrainFilter` itself is leaked.
 262     ///
 263     /// # Examples
 264     ///
 265     /// Splitting a set into even and odd values, reusing the original set:
 266     ///
 267     /// ```
 268     /// #![feature(hash_drain_filter)]
 269     /// use std::collections::HashSet;
 270     ///
 271     /// let mut set: HashSet<i32> = (0..8).collect();
 272     /// let drained: HashSet<i32> = set.drain_filter(|v| v % 2 == 0).collect();
 273     ///
 274     /// let mut evens = drained.into_iter().collect::<Vec<_>>();
 275     /// let mut odds = set.into_iter().collect::<Vec<_>>();
 276     /// evens.sort();
 277     /// odds.sort();
 278     ///
 279     /// assert_eq!(evens, vec![0, 2, 4, 6]);
 280     /// assert_eq!(odds, vec![1, 3, 5, 7]);
 281     /// ```
 282     #[inline]
 283     #[unstable(feature = "hash_drain_filter", issue = "59618")]
 284     pub fn drain_filter<F>(&mut self, pred: F) -> DrainFilter<'_, T, F>
 285     where
 286         F: FnMut(&T) -> bool,
 287     {
 288         DrainFilter { base: self.base.drain_filter(pred) }
 289     }
 290
 291     /// Clears the set, removing all values.
 292     ///
 293     /// # Examples
 294     ///
 295     /// ```
 296     /// use std::collections::HashSet;
 297     ///
 298     /// let mut v = HashSet::new();
 299     /// v.insert(1);
 300     /// v.clear();
 301     /// assert!(v.is_empty());
 302     /// ```
 303     #[inline]
 304     #[stable(feature = "rust1", since = "1.0.0")]
 305     pub fn clear(&mut self) {
 306         self.base.clear()
 307     }
 308
 309     /// Creates a new empty hash set which will use the given hasher to hash
 310     /// keys.
 311     ///
 312     /// The hash set is also created with the default initial capacity.
 313     ///
 314     /// Warning: `hasher` is normally randomly generated, and
 315     /// is designed to allow `HashSet`s to be resistant to attacks that
 316     /// cause many collisions and very poor performance. Setting it
 317     /// manually using this function can expose a DoS attack vector.
 318     ///
 319     /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
 320     /// the HashMap to be useful, see its documentation for details.
 321     ///
 322     /// # Examples
 323     ///
 324     /// ```
 325     /// use std::collections::HashSet;
 326     /// use std::collections::hash_map::RandomState;
 327     ///
 328     /// let s = RandomState::new();
 329     /// let mut set = HashSet::with_hasher(s);
 330     /// set.insert(2);
 331     /// ```
 332     #[inline]
 333     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
 334     pub fn with_hasher(hasher: S) -> HashSet<T, S> {
 335         HashSet { base: base::HashSet::with_hasher(hasher) }
 336     }
 337
 338     /// Creates an empty `HashSet` with the specified capacity, using
 339     /// `hasher` to hash the keys.
 340     ///
 341     /// The hash set will be able to hold at least `capacity` elements without
 342     /// reallocating. If `capacity` is 0, the hash set will not allocate.
 343     ///
 344     /// Warning: `hasher` is normally randomly generated, and
 345     /// is designed to allow `HashSet`s to be resistant to attacks that
 346     /// cause many collisions and very poor performance. Setting it
 347     /// manually using this function can expose a DoS attack vector.
 348     ///
 349     /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
 350     /// the HashMap to be useful, see its documentation for details.
 351     ///
 352     /// # Examples
 353     ///
 354     /// ```
 355     /// use std::collections::HashSet;
 356     /// use std::collections::hash_map::RandomState;
 357     ///
 358     /// let s = RandomState::new();
 359     /// let mut set = HashSet::with_capacity_and_hasher(10, s);
 360     /// set.insert(1);
 361     /// ```
 362     #[inline]
 363     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
 364     pub fn with_capacity_and_hasher(capacity: usize, hasher: S) -> HashSet<T, S> {
 365         HashSet { base: base::HashSet::with_capacity_and_hasher(capacity, hasher) }
 366     }
 367
 368     /// Returns a reference to the set's [`BuildHasher`].
 369     ///
 370     /// # Examples
 371     ///
 372     /// ```
 373     /// use std::collections::HashSet;
 374     /// use std::collections::hash_map::RandomState;
 375     ///
 376     /// let hasher = RandomState::new();
 377     /// let set: HashSet<i32> = HashSet::with_hasher(hasher);
 378     /// let hasher: &RandomState = set.hasher();
 379     /// ```
 380     #[inline]
 381     #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
 382     pub fn hasher(&self) -> &S {
 383         self.base.hasher()
 384     }
 385 }
 386
 387 impl<T, S> HashSet<T, S>
 388 where
 389     T: Eq + Hash,
 390     S: BuildHasher,
 391 {
 392     /// Reserves capacity for at least `additional` more elements to be inserted
 393     /// in the `HashSet`. The collection may reserve more space to avoid
 394     /// frequent reallocations.
 395     ///
 396     /// # Panics
 397     ///
 398     /// Panics if the new allocation size overflows `usize`.
 399     ///
 400     /// # Examples
 401     ///
 402     /// ```
 403     /// use std::collections::HashSet;
 404     /// let mut set: HashSet<i32> = HashSet::new();
 405     /// set.reserve(10);
 406     /// assert!(set.capacity() >= 10);
 407     /// ```
 408     #[inline]
 409     #[stable(feature = "rust1", since = "1.0.0")]
 410     pub fn reserve(&mut self, additional: usize) {
 411         self.base.reserve(additional)
 412     }
 413
 414     /// Tries to reserve capacity for at least `additional` more elements to be inserted
 415     /// in the given `HashSet<K, V>`. The collection may reserve more space to avoid
 416     /// frequent reallocations.
 417     ///
 418     /// # Errors
 419     ///
 420     /// If the capacity overflows, or the allocator reports a failure, then an error
 421     /// is returned.
 422     ///
 423     /// # Examples
 424     ///
 425     /// ```
 426     /// #![feature(try_reserve)]
 427     /// use std::collections::HashSet;
 428     /// let mut set: HashSet<i32> = HashSet::new();
 429     /// set.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");
 430     /// ```
 431     #[inline]
 432     #[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
 433     pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
 434         self.base.try_reserve(additional).map_err(map_try_reserve_error)
 435     }
 436
 437     /// Shrinks the capacity of the set as much as possible. It will drop
 438     /// down as much as possible while maintaining the internal rules
 439     /// and possibly leaving some space in accordance with the resize policy.
 440     ///
 441     /// # Examples
 442     ///
 443     /// ```
 444     /// use std::collections::HashSet;
 445     ///
 446     /// let mut set = HashSet::with_capacity(100);
 447     /// set.insert(1);
 448     /// set.insert(2);
 449     /// assert!(set.capacity() >= 100);
 450     /// set.shrink_to_fit();
 451     /// assert!(set.capacity() >= 2);
 452     /// ```
 453     #[inline]
 454     #[stable(feature = "rust1", since = "1.0.0")]
 455     pub fn shrink_to_fit(&mut self) {
 456         self.base.shrink_to_fit()
 457     }
 458
 459     /// Shrinks the capacity of the set with a lower limit. It will drop
 460     /// down no lower than the supplied limit while maintaining the internal rules
 461     /// and possibly leaving some space in accordance with the resize policy.
 462     ///
 463     /// Panics if the current capacity is smaller than the supplied
 464     /// minimum capacity.
 465     ///
 466     /// # Examples
 467     ///
 468     /// ```
 469     /// #![feature(shrink_to)]
 470     /// use std::collections::HashSet;
 471     ///
 472     /// let mut set = HashSet::with_capacity(100);
 473     /// set.insert(1);
 474     /// set.insert(2);
 475     /// assert!(set.capacity() >= 100);
 476     /// set.shrink_to(10);
 477     /// assert!(set.capacity() >= 10);
 478     /// set.shrink_to(0);
 479     /// assert!(set.capacity() >= 2);
 480     /// ```
 481     #[inline]
 482     #[unstable(feature = "shrink_to", reason = "new API", issue = "56431")]
 483     pub fn shrink_to(&mut self, min_capacity: usize) {
 484         self.base.shrink_to(min_capacity)
 485     }
 486
 487     /// Visits the values representing the difference,
 488     /// i.e., the values that are in `self` but not in `other`.
 489     ///
 490     /// # Examples
 491     ///
 492     /// ```
 493     /// use std::collections::HashSet;
 494     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 495     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
 496     ///
 497     /// // Can be seen as `a - b`.
 498     /// for x in a.difference(&b) {
 499     ///     println!("{}", x); // Print 1
 500     /// }
 501     ///
 502     /// let diff: HashSet<_> = a.difference(&b).collect();
 503     /// assert_eq!(diff, [1].iter().collect());
 504     ///
 505     /// // Note that difference is not symmetric,
 506     /// // and `b - a` means something else:
 507     /// let diff: HashSet<_> = b.difference(&a).collect();
 508     /// assert_eq!(diff, [4].iter().collect());
 509     /// ```
 510     #[inline]
 511     #[stable(feature = "rust1", since = "1.0.0")]
 512     pub fn difference<'a>(&'a self, other: &'a HashSet<T, S>) -> Difference<'a, T, S> {
 513         Difference { iter: self.iter(), other }
 514     }
 515
 516     /// Visits the values representing the symmetric difference,
 517     /// i.e., the values that are in `self` or in `other` but not in both.
 518     ///
 519     /// # Examples
 520     ///
 521     /// ```
 522     /// use std::collections::HashSet;
 523     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 524     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
 525     ///
 526     /// // Print 1, 4 in arbitrary order.
 527     /// for x in a.symmetric_difference(&b) {
 528     ///     println!("{}", x);
 529     /// }
 530     ///
 531     /// let diff1: HashSet<_> = a.symmetric_difference(&b).collect();
 532     /// let diff2: HashSet<_> = b.symmetric_difference(&a).collect();
 533     ///
 534     /// assert_eq!(diff1, diff2);
 535     /// assert_eq!(diff1, [1, 4].iter().collect());
 536     /// ```
 537     #[inline]
 538     #[stable(feature = "rust1", since = "1.0.0")]
 539     pub fn symmetric_difference<'a>(
 540         &'a self,
 541         other: &'a HashSet<T, S>,
 542     ) -> SymmetricDifference<'a, T, S> {
 543         SymmetricDifference { iter: self.difference(other).chain(other.difference(self)) }
 544     }
 545
 546     /// Visits the values representing the intersection,
 547     /// i.e., the values that are both in `self` and `other`.
 548     ///
 549     /// # Examples
 550     ///
 551     /// ```
 552     /// use std::collections::HashSet;
 553     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 554     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
 555     ///
 556     /// // Print 2, 3 in arbitrary order.
 557     /// for x in a.intersection(&b) {
 558     ///     println!("{}", x);
 559     /// }
 560     ///
 561     /// let intersection: HashSet<_> = a.intersection(&b).collect();
 562     /// assert_eq!(intersection, [2, 3].iter().collect());
 563     /// ```
 564     #[inline]
 565     #[stable(feature = "rust1", since = "1.0.0")]
 566     pub fn intersection<'a>(&'a self, other: &'a HashSet<T, S>) -> Intersection<'a, T, S> {
 567         if self.len() <= other.len() {
 568             Intersection { iter: self.iter(), other }
 569         } else {
 570             Intersection { iter: other.iter(), other: self }
 571         }
 572     }
 573
 574     /// Visits the values representing the union,
 575     /// i.e., all the values in `self` or `other`, without duplicates.
 576     ///
 577     /// # Examples
 578     ///
 579     /// ```
 580     /// use std::collections::HashSet;
 581     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 582     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
 583     ///
 584     /// // Print 1, 2, 3, 4 in arbitrary order.
 585     /// for x in a.union(&b) {
 586     ///     println!("{}", x);
 587     /// }
 588     ///
 589     /// let union: HashSet<_> = a.union(&b).collect();
 590     /// assert_eq!(union, [1, 2, 3, 4].iter().collect());
 591     /// ```
 592     #[inline]
 593     #[stable(feature = "rust1", since = "1.0.0")]
 594     pub fn union<'a>(&'a self, other: &'a HashSet<T, S>) -> Union<'a, T, S> {
 595         if self.len() >= other.len() {
 596             Union { iter: self.iter().chain(other.difference(self)) }
 597         } else {
 598             Union { iter: other.iter().chain(self.difference(other)) }
 599         }
 600     }
 601
 602     /// Returns `true` if the set contains a value.
 603     ///
 604     /// The value may be any borrowed form of the set's value type, but
 605     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
 606     /// the value type.
 607     ///
 608     /// # Examples
 609     ///
 610     /// ```
 611     /// use std::collections::HashSet;
 612     ///
 613     /// let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 614     /// assert_eq!(set.contains(&1), true);
 615     /// assert_eq!(set.contains(&4), false);
 616     /// ```
 617     #[inline]
 618     #[stable(feature = "rust1", since = "1.0.0")]
 619     pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool
 620     where
 621         T: Borrow<Q>,
 622         Q: Hash + Eq,
 623     {
 624         self.base.contains(value)
 625     }
 626
 627     /// Returns a reference to the value in the set, if any, that is equal to the given value.
 628     ///
 629     /// The value may be any borrowed form of the set's value type, but
 630     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
 631     /// the value type.
 632     ///
 633     /// # Examples
 634     ///
 635     /// ```
 636     /// use std::collections::HashSet;
 637     ///
 638     /// let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 639     /// assert_eq!(set.get(&2), Some(&2));
 640     /// assert_eq!(set.get(&4), None);
 641     /// ```
 642     #[inline]
 643     #[stable(feature = "set_recovery", since = "1.9.0")]
 644     pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>
 645     where
 646         T: Borrow<Q>,
 647         Q: Hash + Eq,
 648     {
 649         self.base.get(value)
 650     }
 651
 652     /// Inserts the given `value` into the set if it is not present, then
 653     /// returns a reference to the value in the set.
 654     ///
 655     /// # Examples
 656     ///
 657     /// ```
 658     /// #![feature(hash_set_entry)]
 659     ///
 660     /// use std::collections::HashSet;
 661     ///
 662     /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 663     /// assert_eq!(set.len(), 3);
 664     /// assert_eq!(set.get_or_insert(2), &2);
 665     /// assert_eq!(set.get_or_insert(100), &100);
 666     /// assert_eq!(set.len(), 4); // 100 was inserted
 667     /// ```
 668     #[inline]
 669     #[unstable(feature = "hash_set_entry", issue = "60896")]
 670     pub fn get_or_insert(&mut self, value: T) -> &T {
 671         // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with
 672         // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`.
 673         self.base.get_or_insert(value)
 674     }
 675
 676     /// Inserts an owned copy of the given `value` into the set if it is not
 677     /// present, then returns a reference to the value in the set.
 678     ///
 679     /// # Examples
 680     ///
 681     /// ```
 682     /// #![feature(hash_set_entry)]
 683     ///
 684     /// use std::collections::HashSet;
 685     ///
 686     /// let mut set: HashSet<String> = ["cat", "dog", "horse"]
 687     ///     .iter().map(|&pet| pet.to_owned()).collect();
 688     ///
 689     /// assert_eq!(set.len(), 3);
 690     /// for &pet in &["cat", "dog", "fish"] {
 691     ///     let value = set.get_or_insert_owned(pet);
 692     ///     assert_eq!(value, pet);
 693     /// }
 694     /// assert_eq!(set.len(), 4); // a new "fish" was inserted
 695     /// ```
 696     #[inline]
 697     #[unstable(feature = "hash_set_entry", issue = "60896")]
 698     pub fn get_or_insert_owned<Q: ?Sized>(&mut self, value: &Q) -> &T
 699     where
 700         T: Borrow<Q>,
 701         Q: Hash + Eq + ToOwned<Owned = T>,
 702     {
 703         // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with
 704         // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`.
 705         self.base.get_or_insert_owned(value)
 706     }
 707
 708     /// Inserts a value computed from `f` into the set if the given `value` is
 709     /// not present, then returns a reference to the value in the set.
 710     ///
 711     /// # Examples
 712     ///
 713     /// ```
 714     /// #![feature(hash_set_entry)]
 715     ///
 716     /// use std::collections::HashSet;
 717     ///
 718     /// let mut set: HashSet<String> = ["cat", "dog", "horse"]
 719     ///     .iter().map(|&pet| pet.to_owned()).collect();
 720     ///
 721     /// assert_eq!(set.len(), 3);
 722     /// for &pet in &["cat", "dog", "fish"] {
 723     ///     let value = set.get_or_insert_with(pet, str::to_owned);
 724     ///     assert_eq!(value, pet);
 725     /// }
 726     /// assert_eq!(set.len(), 4); // a new "fish" was inserted
 727     /// ```
 728     #[inline]
 729     #[unstable(feature = "hash_set_entry", issue = "60896")]
 730     pub fn get_or_insert_with<Q: ?Sized, F>(&mut self, value: &Q, f: F) -> &T
 731     where
 732         T: Borrow<Q>,
 733         Q: Hash + Eq,
 734         F: FnOnce(&Q) -> T,
 735     {
 736         // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with
 737         // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`.
 738         self.base.get_or_insert_with(value, f)
 739     }
 740
 741     /// Returns `true` if `self` has no elements in common with `other`.
 742     /// This is equivalent to checking for an empty intersection.
 743     ///
 744     /// # Examples
 745     ///
 746     /// ```
 747     /// use std::collections::HashSet;
 748     ///
 749     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 750     /// let mut b = HashSet::new();
 751     ///
 752     /// assert_eq!(a.is_disjoint(&b), true);
 753     /// b.insert(4);
 754     /// assert_eq!(a.is_disjoint(&b), true);
 755     /// b.insert(1);
 756     /// assert_eq!(a.is_disjoint(&b), false);
 757     /// ```
 758     #[stable(feature = "rust1", since = "1.0.0")]
 759     pub fn is_disjoint(&self, other: &HashSet<T, S>) -> bool {
 760         if self.len() <= other.len() {
 761             self.iter().all(|v| !other.contains(v))
 762         } else {
 763             other.iter().all(|v| !self.contains(v))
 764         }
 765     }
 766
 767     /// Returns `true` if the set is a subset of another,
 768     /// i.e., `other` contains at least all the values in `self`.
 769     ///
 770     /// # Examples
 771     ///
 772     /// ```
 773     /// use std::collections::HashSet;
 774     ///
 775     /// let sup: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 776     /// let mut set = HashSet::new();
 777     ///
 778     /// assert_eq!(set.is_subset(&sup), true);
 779     /// set.insert(2);
 780     /// assert_eq!(set.is_subset(&sup), true);
 781     /// set.insert(4);
 782     /// assert_eq!(set.is_subset(&sup), false);
 783     /// ```
 784     #[stable(feature = "rust1", since = "1.0.0")]
 785     pub fn is_subset(&self, other: &HashSet<T, S>) -> bool {
 786         if self.len() <= other.len() { self.iter().all(|v| other.contains(v)) } else { false }
 787     }
 788
 789     /// Returns `true` if the set is a superset of another,
 790     /// i.e., `self` contains at least all the values in `other`.
 791     ///
 792     /// # Examples
 793     ///
 794     /// ```
 795     /// use std::collections::HashSet;
 796     ///
 797     /// let sub: HashSet<_> = [1, 2].iter().cloned().collect();
 798     /// let mut set = HashSet::new();
 799     ///
 800     /// assert_eq!(set.is_superset(&sub), false);
 801     ///
 802     /// set.insert(0);
 803     /// set.insert(1);
 804     /// assert_eq!(set.is_superset(&sub), false);
 805     ///
 806     /// set.insert(2);
 807     /// assert_eq!(set.is_superset(&sub), true);
 808     /// ```
 809     #[inline]
 810     #[stable(feature = "rust1", since = "1.0.0")]
 811     pub fn is_superset(&self, other: &HashSet<T, S>) -> bool {
 812         other.is_subset(self)
 813     }
 814
 815     /// Adds a value to the set.
 816     ///
 817     /// If the set did not have this value present, `true` is returned.
 818     ///
 819     /// If the set did have this value present, `false` is returned.
 820     ///
 821     /// # Examples
 822     ///
 823     /// ```
 824     /// use std::collections::HashSet;
 825     ///
 826     /// let mut set = HashSet::new();
 827     ///
 828     /// assert_eq!(set.insert(2), true);
 829     /// assert_eq!(set.insert(2), false);
 830     /// assert_eq!(set.len(), 1);
 831     /// ```
 832     #[inline]
 833     #[stable(feature = "rust1", since = "1.0.0")]
 834     pub fn insert(&mut self, value: T) -> bool {
 835         self.base.insert(value)
 836     }
 837
 838     /// Adds a value to the set, replacing the existing value, if any, that is equal to the given
 839     /// one. Returns the replaced value.
 840     ///
 841     /// # Examples
 842     ///
 843     /// ```
 844     /// use std::collections::HashSet;
 845     ///
 846     /// let mut set = HashSet::new();
 847     /// set.insert(Vec::<i32>::new());
 848     ///
 849     /// assert_eq!(set.get(&[][..]).unwrap().capacity(), 0);
 850     /// set.replace(Vec::with_capacity(10));
 851     /// assert_eq!(set.get(&[][..]).unwrap().capacity(), 10);
 852     /// ```
 853     #[inline]
 854     #[stable(feature = "set_recovery", since = "1.9.0")]
 855     pub fn replace(&mut self, value: T) -> Option<T> {
 856         self.base.replace(value)
 857     }
 858
 859     /// Removes a value from the set. Returns whether the value was
 860     /// present in the set.
 861     ///
 862     /// The value may be any borrowed form of the set's value type, but
 863     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
 864     /// the value type.
 865     ///
 866     /// # Examples
 867     ///
 868     /// ```
 869     /// use std::collections::HashSet;
 870     ///
 871     /// let mut set = HashSet::new();
 872     ///
 873     /// set.insert(2);
 874     /// assert_eq!(set.remove(&2), true);
 875     /// assert_eq!(set.remove(&2), false);
 876     /// ```
 877     #[inline]
 878     #[stable(feature = "rust1", since = "1.0.0")]
 879     pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool
 880     where
 881         T: Borrow<Q>,
 882         Q: Hash + Eq,
 883     {
 884         self.base.remove(value)
 885     }
 886
 887     /// Removes and returns the value in the set, if any, that is equal to the given one.
 888     ///
 889     /// The value may be any borrowed form of the set's value type, but
 890     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
 891     /// the value type.
 892     ///
 893     /// # Examples
 894     ///
 895     /// ```
 896     /// use std::collections::HashSet;
 897     ///
 898     /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
 899     /// assert_eq!(set.take(&2), Some(2));
 900     /// assert_eq!(set.take(&2), None);
 901     /// ```
 902     #[inline]
 903     #[stable(feature = "set_recovery", since = "1.9.0")]
 904     pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
 905     where
 906         T: Borrow<Q>,
 907         Q: Hash + Eq,
 908     {
 909         self.base.take(value)
 910     }
 911
 912     /// Retains only the elements specified by the predicate.
 913     ///
 914     /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
 915     ///
 916     /// # Examples
 917     ///
 918     /// ```
 919     /// use std::collections::HashSet;
 920     ///
 921     /// let xs = [1, 2, 3, 4, 5, 6];
 922     /// let mut set: HashSet<i32> = xs.iter().cloned().collect();
 923     /// set.retain(|&k| k % 2 == 0);
 924     /// assert_eq!(set.len(), 3);
 925     /// ```
 926     #[stable(feature = "retain_hash_collection", since = "1.18.0")]
 927     pub fn retain<F>(&mut self, f: F)
 928     where
 929         F: FnMut(&T) -> bool,
 930     {
 931         self.base.retain(f)
 932     }
 933 }
 934
 935 #[stable(feature = "rust1", since = "1.0.0")]
 936 impl<T, S> PartialEq for HashSet<T, S>
 937 where
 938     T: Eq + Hash,
 939     S: BuildHasher,
 940 {
 941     fn eq(&self, other: &HashSet<T, S>) -> bool {
 942         if self.len() != other.len() {
 943             return false;
 944         }
 945
 946         self.iter().all(|key| other.contains(key))
 947     }
 948 }
 949
 950 #[stable(feature = "rust1", since = "1.0.0")]
 951 impl<T, S> Eq for HashSet<T, S>
 952 where
 953     T: Eq + Hash,
 954     S: BuildHasher,
 955 {
 956 }
 957
 958 #[stable(feature = "rust1", since = "1.0.0")]
 959 impl<T, S> fmt::Debug for HashSet<T, S>
 960 where
 961     T: fmt::Debug,
 962 {
 963     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 964         f.debug_set().entries(self.iter()).finish()
 965     }
 966 }
 967
 968 #[stable(feature = "rust1", since = "1.0.0")]
 969 impl<T, S> FromIterator<T> for HashSet<T, S>
 970 where
 971     T: Eq + Hash,
 972     S: BuildHasher + Default,
 973 {
 974     #[inline]
 975     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> HashSet<T, S> {
 976         let mut set = HashSet::with_hasher(Default::default());
 977         set.extend(iter);
 978         set
 979     }
 980 }
 981
 982 #[stable(feature = "rust1", since = "1.0.0")]
 983 impl<T, S> Extend<T> for HashSet<T, S>
 984 where
 985     T: Eq + Hash,
 986     S: BuildHasher,
 987 {
 988     #[inline]
 989     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
 990         self.base.extend(iter);
 991     }
 992
 993     #[inline]
 994     fn extend_one(&mut self, item: T) {
 995         self.base.insert(item);
 996     }
 997
 998     #[inline]
 999     fn extend_reserve(&mut self, additional: usize) {
1000         self.base.extend_reserve(additional);
1001     }
1002 }
1003
1004 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
1005 impl<'a, T, S> Extend<&'a T> for HashSet<T, S>
1006 where
1007     T: 'a + Eq + Hash + Copy,
1008     S: BuildHasher,
1009 {
1010     #[inline]
1011     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
1012         self.extend(iter.into_iter().cloned());
1013     }
1014
1015     #[inline]
1016     fn extend_one(&mut self, &item: &'a T) {
1017         self.base.insert(item);
1018     }
1019
1020     #[inline]
1021     fn extend_reserve(&mut self, additional: usize) {
1022         Extend::<T>::extend_reserve(self, additional)
1023     }
1024 }
1025
1026 #[stable(feature = "rust1", since = "1.0.0")]
1027 impl<T, S> Default for HashSet<T, S>
1028 where
1029     S: Default,
1030 {
1031     /// Creates an empty `HashSet<T, S>` with the `Default` value for the hasher.
1032     #[inline]
1033     fn default() -> HashSet<T, S> {
1034         HashSet { base: Default::default() }
1035     }
1036 }
1037
1038 #[stable(feature = "rust1", since = "1.0.0")]
1039 impl<T, S> BitOr<&HashSet<T, S>> for &HashSet<T, S>
1040 where
1041     T: Eq + Hash + Clone,
1042     S: BuildHasher + Default,
1043 {
1044     type Output = HashSet<T, S>;
1045
1046     /// Returns the union of `self` and `rhs` as a new `HashSet<T, S>`.
1047     ///
1048     /// # Examples
1049     ///
1050     /// ```
1051     /// use std::collections::HashSet;
1052     ///
1053     /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
1054     /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
1055     ///
1056     /// let set = &a | &b;
1057     ///
1058     /// let mut i = 0;
1059     /// let expected = [1, 2, 3, 4, 5];
1060     /// for x in &set {
1061     ///     assert!(expected.contains(x));
1062     ///     i += 1;
1063     /// }
1064     /// assert_eq!(i, expected.len());
1065     /// ```
1066     fn bitor(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
1067         self.union(rhs).cloned().collect()
1068     }
1069 }
1070
1071 #[stable(feature = "rust1", since = "1.0.0")]
1072 impl<T, S> BitAnd<&HashSet<T, S>> for &HashSet<T, S>
1073 where
1074     T: Eq + Hash + Clone,
1075     S: BuildHasher + Default,
1076 {
1077     type Output = HashSet<T, S>;
1078
1079     /// Returns the intersection of `self` and `rhs` as a new `HashSet<T, S>`.
1080     ///
1081     /// # Examples
1082     ///
1083     /// ```
1084     /// use std::collections::HashSet;
1085     ///
1086     /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
1087     /// let b: HashSet<_> = vec![2, 3, 4].into_iter().collect();
1088     ///
1089     /// let set = &a & &b;
1090     ///
1091     /// let mut i = 0;
1092     /// let expected = [2, 3];
1093     /// for x in &set {
1094     ///     assert!(expected.contains(x));
1095     ///     i += 1;
1096     /// }
1097     /// assert_eq!(i, expected.len());
1098     /// ```
1099     fn bitand(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
1100         self.intersection(rhs).cloned().collect()
1101     }
1102 }
1103
1104 #[stable(feature = "rust1", since = "1.0.0")]
1105 impl<T, S> BitXor<&HashSet<T, S>> for &HashSet<T, S>
1106 where
1107     T: Eq + Hash + Clone,
1108     S: BuildHasher + Default,
1109 {
1110     type Output = HashSet<T, S>;
1111
1112     /// Returns the symmetric difference of `self` and `rhs` as a new `HashSet<T, S>`.
1113     ///
1114     /// # Examples
1115     ///
1116     /// ```
1117     /// use std::collections::HashSet;
1118     ///
1119     /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
1120     /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
1121     ///
1122     /// let set = &a ^ &b;
1123     ///
1124     /// let mut i = 0;
1125     /// let expected = [1, 2, 4, 5];
1126     /// for x in &set {
1127     ///     assert!(expected.contains(x));
1128     ///     i += 1;
1129     /// }
1130     /// assert_eq!(i, expected.len());
1131     /// ```
1132     fn bitxor(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
1133         self.symmetric_difference(rhs).cloned().collect()
1134     }
1135 }
1136
1137 #[stable(feature = "rust1", since = "1.0.0")]
1138 impl<T, S> Sub<&HashSet<T, S>> for &HashSet<T, S>
1139 where
1140     T: Eq + Hash + Clone,
1141     S: BuildHasher + Default,
1142 {
1143     type Output = HashSet<T, S>;
1144
1145     /// Returns the difference of `self` and `rhs` as a new `HashSet<T, S>`.
1146     ///
1147     /// # Examples
1148     ///
1149     /// ```
1150     /// use std::collections::HashSet;
1151     ///
1152     /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
1153     /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
1154     ///
1155     /// let set = &a - &b;
1156     ///
1157     /// let mut i = 0;
1158     /// let expected = [1, 2];
1159     /// for x in &set {
1160     ///     assert!(expected.contains(x));
1161     ///     i += 1;
1162     /// }
1163     /// assert_eq!(i, expected.len());
1164     /// ```
1165     fn sub(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
1166         self.difference(rhs).cloned().collect()
1167     }
1168 }
1169
1170 /// An iterator over the items of a `HashSet`.
1171 ///
1172 /// This `struct` is created by the [`iter`] method on [`HashSet`].
1173 /// See its documentation for more.
1174 ///
1175 /// [`iter`]: HashSet::iter
1176 ///
1177 /// # Examples
1178 ///
1179 /// ```
1180 /// use std::collections::HashSet;
1181 ///
1182 /// let a: HashSet<u32> = vec![1, 2, 3].into_iter().collect();
1183 ///
1184 /// let mut iter = a.iter();
1185 /// ```
1186 #[stable(feature = "rust1", since = "1.0.0")]
1187 pub struct Iter<'a, K: 'a> {
1188     base: base::Iter<'a, K>,
1189 }
1190
1191 /// An owning iterator over the items of a `HashSet`.
1192 ///
1193 /// This `struct` is created by the [`into_iter`] method on [`HashSet`]
1194 /// (provided by the `IntoIterator` trait). See its documentation for more.
1195 ///
1196 /// [`into_iter`]: IntoIterator::into_iter
1197 ///
1198 /// # Examples
1199 ///
1200 /// ```
1201 /// use std::collections::HashSet;
1202 ///
1203 /// let a: HashSet<u32> = vec![1, 2, 3].into_iter().collect();
1204 ///
1205 /// let mut iter = a.into_iter();
1206 /// ```
1207 #[stable(feature = "rust1", since = "1.0.0")]
1208 pub struct IntoIter<K> {
1209     base: base::IntoIter<K>,
1210 }
1211
1212 /// A draining iterator over the items of a `HashSet`.
1213 ///
1214 /// This `struct` is created by the [`drain`] method on [`HashSet`].
1215 /// See its documentation for more.
1216 ///
1217 /// [`drain`]: HashSet::drain
1218 ///
1219 /// # Examples
1220 ///
1221 /// ```
1222 /// use std::collections::HashSet;
1223 ///
1224 /// let mut a: HashSet<u32> = vec![1, 2, 3].into_iter().collect();
1225 ///
1226 /// let mut drain = a.drain();
1227 /// ```
1228 #[stable(feature = "rust1", since = "1.0.0")]
1229 pub struct Drain<'a, K: 'a> {
1230     base: base::Drain<'a, K>,
1231 }
1232
1233 /// A draining, filtering iterator over the items of a `HashSet`.
1234 ///
1235 /// This `struct` is created by the [`drain_filter`] method on [`HashSet`].
1236 ///
1237 /// [`drain_filter`]: HashSet::drain_filter
1238 ///
1239 /// # Examples
1240 ///
1241 /// ```
1242 /// #![feature(hash_drain_filter)]
1243 ///
1244 /// use std::collections::HashSet;
1245 ///
1246 /// let mut a: HashSet<u32> = vec![1, 2, 3].into_iter().collect();
1247 ///
1248 /// let mut drain_filtered = a.drain_filter(|v| v % 2 == 0);
1249 /// ```
1250 #[unstable(feature = "hash_drain_filter", issue = "59618")]
1251 pub struct DrainFilter<'a, K, F>
1252 where
1253     F: FnMut(&K) -> bool,
1254 {
1255     base: base::DrainFilter<'a, K, F>,
1256 }
1257
1258 /// A lazy iterator producing elements in the intersection of `HashSet`s.
1259 ///
1260 /// This `struct` is created by the [`intersection`] method on [`HashSet`].
1261 /// See its documentation for more.
1262 ///
1263 /// [`intersection`]: HashSet::intersection
1264 ///
1265 /// # Examples
1266 ///
1267 /// ```
1268 /// use std::collections::HashSet;
1269 ///
1270 /// let a: HashSet<u32> = vec![1, 2, 3].into_iter().collect();
1271 /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
1272 ///
1273 /// let mut intersection = a.intersection(&b);
1274 /// ```
1275 #[stable(feature = "rust1", since = "1.0.0")]
1276 pub struct Intersection<'a, T: 'a, S: 'a> {
1277     // iterator of the first set
1278     iter: Iter<'a, T>,
1279     // the second set
1280     other: &'a HashSet<T, S>,
1281 }
1282
1283 /// A lazy iterator producing elements in the difference of `HashSet`s.
1284 ///
1285 /// This `struct` is created by the [`difference`] method on [`HashSet`].
1286 /// See its documentation for more.
1287 ///
1288 /// [`difference`]: HashSet::difference
1289 ///
1290 /// # Examples
1291 ///
1292 /// ```
1293 /// use std::collections::HashSet;
1294 ///
1295 /// let a: HashSet<u32> = vec![1, 2, 3].into_iter().collect();
1296 /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
1297 ///
1298 /// let mut difference = a.difference(&b);
1299 /// ```
1300 #[stable(feature = "rust1", since = "1.0.0")]
1301 pub struct Difference<'a, T: 'a, S: 'a> {
1302     // iterator of the first set
1303     iter: Iter<'a, T>,
1304     // the second set
1305     other: &'a HashSet<T, S>,
1306 }
1307
1308 /// A lazy iterator producing elements in the symmetric difference of `HashSet`s.
1309 ///
1310 /// This `struct` is created by the [`symmetric_difference`] method on
1311 /// [`HashSet`]. See its documentation for more.
1312 ///
1313 /// [`symmetric_difference`]: HashSet::symmetric_difference
1314 ///
1315 /// # Examples
1316 ///
1317 /// ```
1318 /// use std::collections::HashSet;
1319 ///
1320 /// let a: HashSet<u32> = vec![1, 2, 3].into_iter().collect();
1321 /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
1322 ///
1323 /// let mut intersection = a.symmetric_difference(&b);
1324 /// ```
1325 #[stable(feature = "rust1", since = "1.0.0")]
1326 pub struct SymmetricDifference<'a, T: 'a, S: 'a> {
1327     iter: Chain<Difference<'a, T, S>, Difference<'a, T, S>>,
1328 }
1329
1330 /// A lazy iterator producing elements in the union of `HashSet`s.
1331 ///
1332 /// This `struct` is created by the [`union`] method on [`HashSet`].
1333 /// See its documentation for more.
1334 ///
1335 /// [`union`]: HashSet::union
1336 ///
1337 /// # Examples
1338 ///
1339 /// ```
1340 /// use std::collections::HashSet;
1341 ///
1342 /// let a: HashSet<u32> = vec![1, 2, 3].into_iter().collect();
1343 /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
1344 ///
1345 /// let mut union_iter = a.union(&b);
1346 /// ```
1347 #[stable(feature = "rust1", since = "1.0.0")]
1348 pub struct Union<'a, T: 'a, S: 'a> {
1349     iter: Chain<Iter<'a, T>, Difference<'a, T, S>>,
1350 }
1351
1352 #[stable(feature = "rust1", since = "1.0.0")]
1353 impl<'a, T, S> IntoIterator for &'a HashSet<T, S> {
1354     type Item = &'a T;
1355     type IntoIter = Iter<'a, T>;
1356
1357     #[inline]
1358     fn into_iter(self) -> Iter<'a, T> {
1359         self.iter()
1360     }
1361 }
1362
1363 #[stable(feature = "rust1", since = "1.0.0")]
1364 impl<T, S> IntoIterator for HashSet<T, S> {
1365     type Item = T;
1366     type IntoIter = IntoIter<T>;
1367
1368     /// Creates a consuming iterator, that is, one that moves each value out
1369     /// of the set in arbitrary order. The set cannot be used after calling
1370     /// this.
1371     ///
1372     /// # Examples
1373     ///
1374     /// ```
1375     /// use std::collections::HashSet;
1376     /// let mut set = HashSet::new();
1377     /// set.insert("a".to_string());
1378     /// set.insert("b".to_string());
1379     ///
1380     /// // Not possible to collect to a Vec<String> with a regular `.iter()`.
1381     /// let v: Vec<String> = set.into_iter().collect();
1382     ///
1383     /// // Will print in an arbitrary order.
1384     /// for x in &v {
1385     ///     println!("{}", x);
1386     /// }
1387     /// ```
1388     #[inline]
1389     fn into_iter(self) -> IntoIter<T> {
1390         IntoIter { base: self.base.into_iter() }
1391     }
1392 }
1393
1394 #[stable(feature = "rust1", since = "1.0.0")]
1395 impl<K> Clone for Iter<'_, K> {
1396     #[inline]
1397     fn clone(&self) -> Self {
1398         Iter { base: self.base.clone() }
1399     }
1400 }
1401 #[stable(feature = "rust1", since = "1.0.0")]
1402 impl<'a, K> Iterator for Iter<'a, K> {
1403     type Item = &'a K;
1404
1405     #[inline]
1406     fn next(&mut self) -> Option<&'a K> {
1407         self.base.next()
1408     }
1409     #[inline]
1410     fn size_hint(&self) -> (usize, Option<usize>) {
1411         self.base.size_hint()
1412     }
1413 }
1414 #[stable(feature = "rust1", since = "1.0.0")]
1415 impl<K> ExactSizeIterator for Iter<'_, K> {
1416     #[inline]
1417     fn len(&self) -> usize {
1418         self.base.len()
1419     }
1420 }
1421 #[stable(feature = "fused", since = "1.26.0")]
1422 impl<K> FusedIterator for Iter<'_, K> {}
1423
1424 #[stable(feature = "std_debug", since = "1.16.0")]
1425 impl<K: fmt::Debug> fmt::Debug for Iter<'_, K> {
1426     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1427         f.debug_list().entries(self.clone()).finish()
1428     }
1429 }
1430
1431 #[stable(feature = "rust1", since = "1.0.0")]
1432 impl<K> Iterator for IntoIter<K> {
1433     type Item = K;
1434
1435     #[inline]
1436     fn next(&mut self) -> Option<K> {
1437         self.base.next()
1438     }
1439     #[inline]
1440     fn size_hint(&self) -> (usize, Option<usize>) {
1441         self.base.size_hint()
1442     }
1443 }
1444 #[stable(feature = "rust1", since = "1.0.0")]
1445 impl<K> ExactSizeIterator for IntoIter<K> {
1446     #[inline]
1447     fn len(&self) -> usize {
1448         self.base.len()
1449     }
1450 }
1451 #[stable(feature = "fused", since = "1.26.0")]
1452 impl<K> FusedIterator for IntoIter<K> {}
1453
1454 #[stable(feature = "std_debug", since = "1.16.0")]
1455 impl<K: fmt::Debug> fmt::Debug for IntoIter<K> {
1456     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1457         fmt::Debug::fmt(&self.base, f)
1458     }
1459 }
1460
1461 #[stable(feature = "rust1", since = "1.0.0")]
1462 impl<'a, K> Iterator for Drain<'a, K> {
1463     type Item = K;
1464
1465     #[inline]
1466     fn next(&mut self) -> Option<K> {
1467         self.base.next()
1468     }
1469     #[inline]
1470     fn size_hint(&self) -> (usize, Option<usize>) {
1471         self.base.size_hint()
1472     }
1473 }
1474 #[stable(feature = "rust1", since = "1.0.0")]
1475 impl<K> ExactSizeIterator for Drain<'_, K> {
1476     #[inline]
1477     fn len(&self) -> usize {
1478         self.base.len()
1479     }
1480 }
1481 #[stable(feature = "fused", since = "1.26.0")]
1482 impl<K> FusedIterator for Drain<'_, K> {}
1483
1484 #[stable(feature = "std_debug", since = "1.16.0")]
1485 impl<K: fmt::Debug> fmt::Debug for Drain<'_, K> {
1486     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1487         fmt::Debug::fmt(&self.base, f)
1488     }
1489 }
1490
1491 #[unstable(feature = "hash_drain_filter", issue = "59618")]
1492 impl<K, F> Iterator for DrainFilter<'_, K, F>
1493 where
1494     F: FnMut(&K) -> bool,
1495 {
1496     type Item = K;
1497
1498     #[inline]
1499     fn next(&mut self) -> Option<K> {
1500         self.base.next()
1501     }
1502     #[inline]
1503     fn size_hint(&self) -> (usize, Option<usize>) {
1504         self.base.size_hint()
1505     }
1506 }
1507
1508 #[unstable(feature = "hash_drain_filter", issue = "59618")]
1509 impl<K, F> FusedIterator for DrainFilter<'_, K, F> where F: FnMut(&K) -> bool {}
1510
1511 #[unstable(feature = "hash_drain_filter", issue = "59618")]
1512 impl<'a, K, F> fmt::Debug for DrainFilter<'a, K, F>
1513 where
1514     F: FnMut(&K) -> bool,
1515 {
1516     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1517         f.pad("DrainFilter { .. }")
1518     }
1519 }
1520
1521 #[stable(feature = "rust1", since = "1.0.0")]
1522 impl<T, S> Clone for Intersection<'_, T, S> {
1523     #[inline]
1524     fn clone(&self) -> Self {
1525         Intersection { iter: self.iter.clone(), ..*self }
1526     }
1527 }
1528
1529 #[stable(feature = "rust1", since = "1.0.0")]
1530 impl<'a, T, S> Iterator for Intersection<'a, T, S>
1531 where
1532     T: Eq + Hash,
1533     S: BuildHasher,
1534 {
1535     type Item = &'a T;
1536
1537     #[inline]
1538     fn next(&mut self) -> Option<&'a T> {
1539         loop {
1540             let elt = self.iter.next()?;
1541             if self.other.contains(elt) {
1542                 return Some(elt);
1543             }
1544         }
1545     }
1546
1547     #[inline]
1548     fn size_hint(&self) -> (usize, Option<usize>) {
1549         let (_, upper) = self.iter.size_hint();
1550         (0, upper)
1551     }
1552 }
1553
1554 #[stable(feature = "std_debug", since = "1.16.0")]
1555 impl<T, S> fmt::Debug for Intersection<'_, T, S>
1556 where
1557     T: fmt::Debug + Eq + Hash,
1558     S: BuildHasher,
1559 {
1560     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1561         f.debug_list().entries(self.clone()).finish()
1562     }
1563 }
1564
1565 #[stable(feature = "fused", since = "1.26.0")]
1566 impl<T, S> FusedIterator for Intersection<'_, T, S>
1567 where
1568     T: Eq + Hash,
1569     S: BuildHasher,
1570 {
1571 }
1572
1573 #[stable(feature = "rust1", since = "1.0.0")]
1574 impl<T, S> Clone for Difference<'_, T, S> {
1575     #[inline]
1576     fn clone(&self) -> Self {
1577         Difference { iter: self.iter.clone(), ..*self }
1578     }
1579 }
1580
1581 #[stable(feature = "rust1", since = "1.0.0")]
1582 impl<'a, T, S> Iterator for Difference<'a, T, S>
1583 where
1584     T: Eq + Hash,
1585     S: BuildHasher,
1586 {
1587     type Item = &'a T;
1588
1589     #[inline]
1590     fn next(&mut self) -> Option<&'a T> {
1591         loop {
1592             let elt = self.iter.next()?;
1593             if !self.other.contains(elt) {
1594                 return Some(elt);
1595             }
1596         }
1597     }
1598
1599     #[inline]
1600     fn size_hint(&self) -> (usize, Option<usize>) {
1601         let (_, upper) = self.iter.size_hint();
1602         (0, upper)
1603     }
1604 }
1605
1606 #[stable(feature = "fused", since = "1.26.0")]
1607 impl<T, S> FusedIterator for Difference<'_, T, S>
1608 where
1609     T: Eq + Hash,
1610     S: BuildHasher,
1611 {
1612 }
1613
1614 #[stable(feature = "std_debug", since = "1.16.0")]
1615 impl<T, S> fmt::Debug for Difference<'_, T, S>
1616 where
1617     T: fmt::Debug + Eq + Hash,
1618     S: BuildHasher,
1619 {
1620     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1621         f.debug_list().entries(self.clone()).finish()
1622     }
1623 }
1624
1625 #[stable(feature = "rust1", since = "1.0.0")]
1626 impl<T, S> Clone for SymmetricDifference<'_, T, S> {
1627     #[inline]
1628     fn clone(&self) -> Self {
1629         SymmetricDifference { iter: self.iter.clone() }
1630     }
1631 }
1632
1633 #[stable(feature = "rust1", since = "1.0.0")]
1634 impl<'a, T, S> Iterator for SymmetricDifference<'a, T, S>
1635 where
1636     T: Eq + Hash,
1637     S: BuildHasher,
1638 {
1639     type Item = &'a T;
1640
1641     #[inline]
1642     fn next(&mut self) -> Option<&'a T> {
1643         self.iter.next()
1644     }
1645     #[inline]
1646     fn size_hint(&self) -> (usize, Option<usize>) {
1647         self.iter.size_hint()
1648     }
1649 }
1650
1651 #[stable(feature = "fused", since = "1.26.0")]
1652 impl<T, S> FusedIterator for SymmetricDifference<'_, T, S>
1653 where
1654     T: Eq + Hash,
1655     S: BuildHasher,
1656 {
1657 }
1658
1659 #[stable(feature = "std_debug", since = "1.16.0")]
1660 impl<T, S> fmt::Debug for SymmetricDifference<'_, T, S>
1661 where
1662     T: fmt::Debug + Eq + Hash,
1663     S: BuildHasher,
1664 {
1665     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1666         f.debug_list().entries(self.clone()).finish()
1667     }
1668 }
1669
1670 #[stable(feature = "rust1", since = "1.0.0")]
1671 impl<T, S> Clone for Union<'_, T, S> {
1672     #[inline]
1673     fn clone(&self) -> Self {
1674         Union { iter: self.iter.clone() }
1675     }
1676 }
1677
1678 #[stable(feature = "fused", since = "1.26.0")]
1679 impl<T, S> FusedIterator for Union<'_, T, S>
1680 where
1681     T: Eq + Hash,
1682     S: BuildHasher,
1683 {
1684 }
1685
1686 #[stable(feature = "std_debug", since = "1.16.0")]
1687 impl<T, S> fmt::Debug for Union<'_, T, S>
1688 where
1689     T: fmt::Debug + Eq + Hash,
1690     S: BuildHasher,
1691 {
1692     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1693         f.debug_list().entries(self.clone()).finish()
1694     }
1695 }
1696
1697 #[stable(feature = "rust1", since = "1.0.0")]
1698 impl<'a, T, S> Iterator for Union<'a, T, S>
1699 where
1700     T: Eq + Hash,
1701     S: BuildHasher,
1702 {
1703     type Item = &'a T;
1704
1705     #[inline]
1706     fn next(&mut self) -> Option<&'a T> {
1707         self.iter.next()
1708     }
1709     #[inline]
1710     fn size_hint(&self) -> (usize, Option<usize>) {
1711         self.iter.size_hint()
1712     }
1713 }
1714
1715 #[allow(dead_code)]
1716 fn assert_covariance() {
1717     fn set<'new>(v: HashSet<&'static str>) -> HashSet<&'new str> {
1718         v
1719     }
1720     fn iter<'a, 'new>(v: Iter<'a, &'static str>) -> Iter<'a, &'new str> {
1721         v
1722     }
1723     fn into_iter<'new>(v: IntoIter<&'static str>) -> IntoIter<&'new str> {
1724         v
1725     }
1726     fn difference<'a, 'new>(
1727         v: Difference<'a, &'static str, RandomState>,
1728     ) -> Difference<'a, &'new str, RandomState> {
1729         v
1730     }
1731     fn symmetric_difference<'a, 'new>(
1732         v: SymmetricDifference<'a, &'static str, RandomState>,
1733     ) -> SymmetricDifference<'a, &'new str, RandomState> {
1734         v
1735     }
1736     fn intersection<'a, 'new>(
1737         v: Intersection<'a, &'static str, RandomState>,
1738     ) -> Intersection<'a, &'new str, RandomState> {
1739         v
1740     }
1741     fn union<'a, 'new>(
1742         v: Union<'a, &'static str, RandomState>,
1743     ) -> Union<'a, &'new str, RandomState> {
1744         v
1745     }
1746     fn drain<'new>(d: Drain<'static, &'static str>) -> Drain<'new, &'new str> {
1747         d
1748     }
1749 }