1 // Copyright 2012-2014 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.
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.
11 /// An implementation of a set using a bit vector as an underlying
12 /// representation for holding unsigned numerical elements.
14 /// It should also be noted that the amount of storage necessary for holding a
15 /// set of objects is proportional to the maximum of the objects when viewed
21 /// use bit_set::BitSet;
23 /// // It's a regular set
24 /// let mut s = BitSet::new();
31 /// if !s.contains(&7) {
32 /// println!("There is no 7");
35 /// // Can initialize from a `BitVec`
36 /// let other = BitSet::from_bytes(&[0b11010000]);
38 /// s.union_with(&other);
40 /// // Print 0, 1, 3 in some order
41 /// for x in s.iter() {
42 /// println!("{}", x);
45 /// // Can convert back to a `BitVec`
46 /// let bv = s.into_bit_vec();
54 use bit_vec::{BitVec, Blocks, BitBlock};
55 use std::cmp::Ordering;
59 use std::iter::{Chain, Enumerate, Repeat, Skip, Take, repeat};
60 use std::iter::{self, FromIterator};
62 type MatchWords<'a, B> = Chain<Enumerate<Blocks<'a, B>>, Skip<Take<Enumerate<Repeat<B>>>>>;
64 /// Computes how many blocks are needed to store that many bits
65 fn blocks_for_bits<B: BitBlock>(bits: usize) -> usize {
66 // If we want 17 bits, dividing by 32 will produce 0. So we add 1 to make sure we
67 // reserve enough. But if we want exactly a multiple of 32, this will actually allocate
68 // one too many. So we need to check if that's the case. We can do that by computing if
69 // bitwise AND by `32 - 1` is 0. But LLVM should be able to optimize the semantically
70 // superior modulo operator on a power of two to this.
72 // Note that we can technically avoid this branch with the expression
73 // `(nbits + u32::BITS - 1) / 32::BITS`, but if nbits is almost usize::MAX this will overflow.
74 if bits % B::bits() == 0 {
81 // Take two BitVec's, and return iterators of their words, where the shorter one
82 // has been padded with 0's
83 fn match_words<'a,'b, B: BitBlock>(a: &'a BitVec<B>, b: &'b BitVec<B>)
84 -> (MatchWords<'a, B>, MatchWords<'b, B>) {
85 let a_len = a.storage().len();
86 let b_len = b.storage().len();
88 // have to uselessly pretend to pad the longer one for type matching
90 (a.blocks().enumerate().chain(iter::repeat(B::zero()).enumerate().take(b_len).skip(a_len)),
91 b.blocks().enumerate().chain(iter::repeat(B::zero()).enumerate().take(0).skip(0)))
93 (a.blocks().enumerate().chain(iter::repeat(B::zero()).enumerate().take(0).skip(0)),
94 b.blocks().enumerate().chain(iter::repeat(B::zero()).enumerate().take(a_len).skip(b_len)))
98 pub struct BitSet<B=u32> {
102 impl<B: BitBlock> Clone for BitSet<B> {
103 fn clone(&self) -> Self {
105 bit_vec: self.bit_vec.clone(),
110 impl<B: BitBlock> Default for BitSet<B> {
112 fn default() -> Self { BitSet { bit_vec: Default::default() } }
115 impl<B: BitBlock> FromIterator<usize> for BitSet<B> {
116 fn from_iter<I: IntoIterator<Item=usize>>(iter: I) -> Self {
117 let mut ret: Self = Default::default();
123 impl<B: BitBlock> Extend<usize> for BitSet<B> {
125 fn extend<I: IntoIterator<Item=usize>>(&mut self, iter: I) {
132 impl<B: BitBlock> PartialOrd for BitSet<B> {
134 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
135 Some(self.cmp(other))
139 impl<B: BitBlock> Ord for BitSet<B> {
141 fn cmp(&self, other: &Self) -> Ordering {
142 let mut a = self.iter();
143 let mut b = other.iter();
145 match (a.next(), b.next()) {
146 (Some(x), Some(y)) => match x.cmp(&y) {
147 Ordering::Equal => {}
148 otherwise => return otherwise,
150 (None, None) => return Ordering::Equal,
151 (None, _) => return Ordering::Less,
152 (_, None) => return Ordering::Greater,
158 impl<B: BitBlock> cmp::PartialEq for BitSet<B> {
160 fn eq(&self, other: &Self) -> bool {
161 self.cmp(other) == Ordering::Equal
165 impl<B: BitBlock> cmp::Eq for BitSet<B> {}
168 /// Creates a new empty `BitSet`.
173 /// use bit_set::BitSet;
175 /// let mut s = BitSet::new();
178 pub fn new() -> Self {
182 /// Creates a new `BitSet` with initially no contents, able to
183 /// hold `nbits` elements without resizing.
188 /// use bit_set::BitSet;
190 /// let mut s = BitSet::with_capacity(100);
191 /// assert!(s.capacity() >= 100);
194 pub fn with_capacity(nbits: usize) -> Self {
195 let bit_vec = BitVec::from_elem(nbits, false);
196 BitSet::from_bit_vec(bit_vec)
199 /// Creates a new `BitSet` from the given bit vector.
204 /// extern crate bit_vec;
205 /// extern crate bit_set;
208 /// use bit_vec::BitVec;
209 /// use bit_set::BitSet;
211 /// let bv = BitVec::from_bytes(&[0b01100000]);
212 /// let s = BitSet::from_bit_vec(bv);
214 /// // Print 1, 2 in arbitrary order
215 /// for x in s.iter() {
216 /// println!("{}", x);
221 pub fn from_bit_vec(bit_vec: BitVec) -> Self {
222 BitSet { bit_vec: bit_vec }
225 pub fn from_bytes(bytes: &[u8]) -> Self {
226 BitSet { bit_vec: BitVec::from_bytes(bytes) }
230 impl<B: BitBlock> BitSet<B> {
232 /// Returns the capacity in bits for this bit vector. Inserting any
233 /// element less than this amount will not trigger a resizing.
238 /// use bit_set::BitSet;
240 /// let mut s = BitSet::with_capacity(100);
241 /// assert!(s.capacity() >= 100);
244 pub fn capacity(&self) -> usize {
245 self.bit_vec.capacity()
248 /// Reserves capacity for the given `BitSet` to contain `len` distinct elements. In the case
249 /// of `BitSet` this means reallocations will not occur as long as all inserted elements
250 /// are less than `len`.
252 /// The collection may reserve more space to avoid frequent reallocations.
258 /// use bit_set::BitSet;
260 /// let mut s = BitSet::new();
261 /// s.reserve_len(10);
262 /// assert!(s.capacity() >= 10);
264 pub fn reserve_len(&mut self, len: usize) {
265 let cur_len = self.bit_vec.len();
267 self.bit_vec.reserve(len - cur_len);
271 /// Reserves the minimum capacity for the given `BitSet` to contain `len` distinct elements.
272 /// In the case of `BitSet` this means reallocations will not occur as long as all inserted
273 /// elements are less than `len`.
275 /// Note that the allocator may give the collection more space than it requests. Therefore
276 /// capacity can not be relied upon to be precisely minimal. Prefer `reserve_len` if future
277 /// insertions are expected.
283 /// use bit_set::BitSet;
285 /// let mut s = BitSet::new();
286 /// s.reserve_len_exact(10);
287 /// assert!(s.capacity() >= 10);
289 pub fn reserve_len_exact(&mut self, len: usize) {
290 let cur_len = self.bit_vec.len();
292 self.bit_vec.reserve_exact(len - cur_len);
297 /// Consumes this set to return the underlying bit vector.
302 /// use bit_set::BitSet;
304 /// let mut s = BitSet::new();
308 /// let bv = s.into_bit_vec();
313 pub fn into_bit_vec(self) -> BitVec<B> {
317 /// Returns a reference to the underlying bit vector.
322 /// use bit_set::BitSet;
324 /// let mut s = BitSet::new();
327 /// let bv = s.get_ref();
328 /// assert_eq!(bv[0], true);
331 pub fn get_ref(&self) -> &BitVec<B> {
336 fn other_op<F>(&mut self, other: &Self, mut f: F) where F: FnMut(B, B) -> B {
338 let self_bit_vec = &mut self.bit_vec;
339 let other_bit_vec = &other.bit_vec;
341 let self_len = self_bit_vec.len();
342 let other_len = other_bit_vec.len();
344 // Expand the vector if necessary
345 if self_len < other_len {
346 self_bit_vec.grow(other_len - self_len, false);
349 // virtually pad other with 0's for equal lengths
351 let (_, result) = match_words(self_bit_vec, other_bit_vec);
355 // Apply values found in other
356 for (i, w) in other_words {
357 let old = self_bit_vec.storage()[i];
360 self_bit_vec.storage_mut()[i] = new;
365 /// Truncates the underlying vector to the least length required.
370 /// use bit_set::BitSet;
372 /// let mut s = BitSet::new();
373 /// s.insert(32183231);
374 /// s.remove(&32183231);
376 /// // Internal storage will probably be bigger than necessary
377 /// println!("old capacity: {}", s.capacity());
379 /// // Now should be smaller
380 /// s.shrink_to_fit();
381 /// println!("new capacity: {}", s.capacity());
384 pub fn shrink_to_fit(&mut self) {
385 let bit_vec = &mut self.bit_vec;
386 // Obtain original length
387 let old_len = bit_vec.storage().len();
388 // Obtain coarse trailing zero length
389 let n = bit_vec.storage().iter().rev().take_while(|&&n| n == B::zero()).count();
391 let trunc_len = cmp::max(old_len - n, 1);
393 bit_vec.storage_mut().truncate(trunc_len);
394 bit_vec.set_len(trunc_len * B::bits());
398 /// Iterator over each usize stored in the `BitSet`.
403 /// use bit_set::BitSet;
405 /// let s = BitSet::from_bytes(&[0b01001010]);
407 /// // Print 1, 4, 6 in arbitrary order
408 /// for x in s.iter() {
409 /// println!("{}", x);
413 pub fn iter(&self) -> Iter<B> {
414 Iter(BlockIter::from_blocks(self.bit_vec.blocks()))
417 /// Iterator over each usize stored in `self` union `other`.
418 /// See [union_with](#method.union_with) for an efficient in-place version.
423 /// use bit_set::BitSet;
425 /// let a = BitSet::from_bytes(&[0b01101000]);
426 /// let b = BitSet::from_bytes(&[0b10100000]);
428 /// // Print 0, 1, 2, 4 in arbitrary order
429 /// for x in a.union(&b) {
430 /// println!("{}", x);
434 pub fn union<'a>(&'a self, other: &'a Self) -> Union<'a, B> {
435 fn or<B: BitBlock>(w1: B, w2: B) -> B { w1 | w2 }
437 Union(BlockIter::from_blocks(TwoBitPositions {
438 set: self.bit_vec.blocks(),
439 other: other.bit_vec.blocks(),
444 /// Iterator over each usize stored in `self` intersect `other`.
445 /// See [intersect_with](#method.intersect_with) for an efficient in-place version.
450 /// use bit_set::BitSet;
452 /// let a = BitSet::from_bytes(&[0b01101000]);
453 /// let b = BitSet::from_bytes(&[0b10100000]);
456 /// for x in a.intersection(&b) {
457 /// println!("{}", x);
461 pub fn intersection<'a>(&'a self, other: &'a Self) -> Intersection<'a, B> {
462 fn bitand<B: BitBlock>(w1: B, w2: B) -> B { w1 & w2 }
463 let min = cmp::min(self.bit_vec.len(), other.bit_vec.len());
465 Intersection(BlockIter::from_blocks(TwoBitPositions {
466 set: self.bit_vec.blocks(),
467 other: other.bit_vec.blocks(),
472 /// Iterator over each usize stored in the `self` setminus `other`.
473 /// See [difference_with](#method.difference_with) for an efficient in-place version.
478 /// use bit_set::BitSet;
480 /// let a = BitSet::from_bytes(&[0b01101000]);
481 /// let b = BitSet::from_bytes(&[0b10100000]);
483 /// // Print 1, 4 in arbitrary order
484 /// for x in a.difference(&b) {
485 /// println!("{}", x);
488 /// // Note that difference is not symmetric,
489 /// // and `b - a` means something else.
491 /// for x in b.difference(&a) {
492 /// println!("{}", x);
496 pub fn difference<'a>(&'a self, other: &'a Self) -> Difference<'a, B> {
497 fn diff<B: BitBlock>(w1: B, w2: B) -> B { w1 & !w2 }
499 Difference(BlockIter::from_blocks(TwoBitPositions {
500 set: self.bit_vec.blocks(),
501 other: other.bit_vec.blocks(),
506 /// Iterator over each usize stored in the symmetric difference of `self` and `other`.
507 /// See [symmetric_difference_with](#method.symmetric_difference_with) for
508 /// an efficient in-place version.
513 /// use bit_set::BitSet;
515 /// let a = BitSet::from_bytes(&[0b01101000]);
516 /// let b = BitSet::from_bytes(&[0b10100000]);
518 /// // Print 0, 1, 4 in arbitrary order
519 /// for x in a.symmetric_difference(&b) {
520 /// println!("{}", x);
524 pub fn symmetric_difference<'a>(&'a self, other: &'a Self) -> SymmetricDifference<'a, B> {
525 fn bitxor<B: BitBlock>(w1: B, w2: B) -> B { w1 ^ w2 }
527 SymmetricDifference(BlockIter::from_blocks(TwoBitPositions {
528 set: self.bit_vec.blocks(),
529 other: other.bit_vec.blocks(),
534 /// Unions in-place with the specified other bit vector.
539 /// use bit_set::BitSet;
541 /// let a = 0b01101000;
542 /// let b = 0b10100000;
543 /// let res = 0b11101000;
545 /// let mut a = BitSet::from_bytes(&[a]);
546 /// let b = BitSet::from_bytes(&[b]);
547 /// let res = BitSet::from_bytes(&[res]);
549 /// a.union_with(&b);
550 /// assert_eq!(a, res);
553 pub fn union_with(&mut self, other: &Self) {
554 self.other_op(other, |w1, w2| w1 | w2);
557 /// Intersects in-place with the specified other bit vector.
562 /// use bit_set::BitSet;
564 /// let a = 0b01101000;
565 /// let b = 0b10100000;
566 /// let res = 0b00100000;
568 /// let mut a = BitSet::from_bytes(&[a]);
569 /// let b = BitSet::from_bytes(&[b]);
570 /// let res = BitSet::from_bytes(&[res]);
572 /// a.intersect_with(&b);
573 /// assert_eq!(a, res);
576 pub fn intersect_with(&mut self, other: &Self) {
577 self.other_op(other, |w1, w2| w1 & w2);
580 /// Makes this bit vector the difference with the specified other bit vector
586 /// use bit_set::BitSet;
588 /// let a = 0b01101000;
589 /// let b = 0b10100000;
590 /// let a_b = 0b01001000; // a - b
591 /// let b_a = 0b10000000; // b - a
593 /// let mut bva = BitSet::from_bytes(&[a]);
594 /// let bvb = BitSet::from_bytes(&[b]);
595 /// let bva_b = BitSet::from_bytes(&[a_b]);
596 /// let bvb_a = BitSet::from_bytes(&[b_a]);
598 /// bva.difference_with(&bvb);
599 /// assert_eq!(bva, bva_b);
601 /// let bva = BitSet::from_bytes(&[a]);
602 /// let mut bvb = BitSet::from_bytes(&[b]);
604 /// bvb.difference_with(&bva);
605 /// assert_eq!(bvb, bvb_a);
608 pub fn difference_with(&mut self, other: &Self) {
609 self.other_op(other, |w1, w2| w1 & !w2);
612 /// Makes this bit vector the symmetric difference with the specified other
613 /// bit vector in-place.
618 /// use bit_set::BitSet;
620 /// let a = 0b01101000;
621 /// let b = 0b10100000;
622 /// let res = 0b11001000;
624 /// let mut a = BitSet::from_bytes(&[a]);
625 /// let b = BitSet::from_bytes(&[b]);
626 /// let res = BitSet::from_bytes(&[res]);
628 /// a.symmetric_difference_with(&b);
629 /// assert_eq!(a, res);
632 pub fn symmetric_difference_with(&mut self, other: &Self) {
633 self.other_op(other, |w1, w2| w1 ^ w2);
637 /// Moves all elements from `other` into `Self`, leaving `other` empty.
642 /// use bit_set::BitSet;
644 /// let mut a = BitSet::new();
648 /// let mut b = BitSet::new();
653 /// a.append(&mut b);
655 /// assert_eq!(a.len(), 4);
656 /// assert_eq!(b.len(), 0);
657 /// assert_eq!(a, BitSet::from_bytes(&[0b01110010]));
659 pub fn append(&mut self, other: &mut Self) {
660 self.union_with(other);
664 /// Splits the `BitSet` into two at the given key including the key.
665 /// Retains the first part in-place while returning the second part.
670 /// use bit_set::BitSet;
672 /// let mut a = BitSet::new();
678 /// let b = a.split_off(3);
680 /// assert_eq!(a.len(), 2);
681 /// assert_eq!(b.len(), 2);
682 /// assert_eq!(a, BitSet::from_bytes(&[0b01100000]));
683 /// assert_eq!(b, BitSet::from_bytes(&[0b00010010]));
685 pub fn split_off(&mut self, at: usize) -> Self {
686 let mut other = BitSet::new();
689 swap(self, &mut other);
691 } else if at >= self.bit_vec.len() {
695 // Calculate block and bit at which to split
696 let w = at / u32::BITS;
697 let b = at % u32::BITS;
699 // Pad `other` with `w` zero blocks,
700 // append `self`'s blocks in the range from `w` to the end to `other`
701 other.bit_vec.storage_mut().extend(repeat(0u32).take(w)
702 .chain(self.bit_vec.storage()[w..].iter().cloned()));
703 other.bit_vec.nbits = self.bit_vec.nbits;
706 other.bit_vec.storage_mut()[w] &= !0 << b;
709 // Sets `bit_vec.len()` and fixes the last block as well
710 self.bit_vec.truncate(at);
716 /// Returns the number of set bits in this set.
718 pub fn len(&self) -> usize {
719 self.bit_vec.blocks().fold(0, |acc, n| acc + n.count_ones() as usize)
722 /// Returns whether there are no bits set in this set
724 pub fn is_empty(&self) -> bool {
728 /// Clears all bits in this set
730 pub fn clear(&mut self) {
731 self.bit_vec.clear();
734 /// Returns `true` if this set contains the specified integer.
736 pub fn contains(&self, value: &usize) -> bool {
737 let bit_vec = &self.bit_vec;
738 *value < bit_vec.len() && bit_vec[*value]
741 /// Returns `true` if the set has no elements in common with `other`.
742 /// This is equivalent to checking for an empty intersection.
744 pub fn is_disjoint(&self, other: &Self) -> bool {
745 self.intersection(other).next().is_none()
748 /// Returns `true` if the set is a subset of another.
750 pub fn is_subset(&self, other: &Self) -> bool {
751 let self_bit_vec = &self.bit_vec;
752 let other_bit_vec = &other.bit_vec;
753 let other_blocks = blocks_for_bits::<B>(other_bit_vec.len());
755 // Check that `self` intersect `other` is self
756 self_bit_vec.blocks().zip(other_bit_vec.blocks()).all(|(w1, w2)| w1 & w2 == w1) &&
757 // Make sure if `self` has any more blocks than `other`, they're all 0
758 self_bit_vec.blocks().skip(other_blocks).all(|w| w == B::zero())
761 /// Returns `true` if the set is a superset of another.
763 pub fn is_superset(&self, other: &Self) -> bool {
764 other.is_subset(self)
767 /// Adds a value to the set. Returns `true` if the value was not already
768 /// present in the set.
769 pub fn insert(&mut self, value: usize) -> bool {
770 if self.contains(&value) {
774 // Ensure we have enough space to hold the new element
775 let len = self.bit_vec.len();
777 self.bit_vec.grow(value - len + 1, false)
780 self.bit_vec.set(value, true);
784 /// Removes a value from the set. Returns `true` if the value was
785 /// present in the set.
786 pub fn remove(&mut self, value: &usize) -> bool {
787 if !self.contains(value) {
791 self.bit_vec.set(*value, false);
797 impl<B: BitBlock> fmt::Debug for BitSet<B> {
798 fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
799 try!(write!(fmt, "{{"));
800 let mut first = true;
803 try!(write!(fmt, ", "));
805 try!(write!(fmt, "{:?}", n));
812 impl<B: BitBlock> hash::Hash for BitSet<B> {
813 fn hash<H: hash::Hasher>(&self, state: &mut H) {
821 struct BlockIter<T, B> {
827 impl<T, B: BitBlock> BlockIter<T, B> where T: Iterator<Item=B> {
828 fn from_blocks(mut blocks: T) -> BlockIter<T, B> {
829 let h = blocks.next().unwrap_or(B::zero());
830 BlockIter {tail: blocks, head: h, head_offset: 0}
834 /// An iterator combining two `BitSet` iterators.
836 struct TwoBitPositions<'a, B: 'a> {
838 other: Blocks<'a, B>,
839 merge: fn(B, B) -> B,
842 /// An iterator for `BitSet`.
844 pub struct Iter<'a, B: 'a>(BlockIter<Blocks<'a, B>, B>);
846 pub struct Union<'a, B: 'a>(BlockIter<TwoBitPositions<'a, B>, B>);
848 pub struct Intersection<'a, B: 'a>(Take<BlockIter<TwoBitPositions<'a, B>, B>>);
850 pub struct Difference<'a, B: 'a>(BlockIter<TwoBitPositions<'a, B>, B>);
852 pub struct SymmetricDifference<'a, B: 'a>(BlockIter<TwoBitPositions<'a, B>, B>);
854 impl<'a, T, B: BitBlock> Iterator for BlockIter<T, B> where T: Iterator<Item=B> {
857 fn next(&mut self) -> Option<usize> {
858 while self.head == B::zero() {
859 match self.tail.next() {
860 Some(w) => self.head = w,
863 self.head_offset += B::bits();
866 // from the current block, isolate the
867 // LSB and subtract 1, producing k:
868 // a block with a number of set bits
869 // equal to the index of the LSB
870 let k = (self.head & (!self.head + B::one())) - B::one();
871 // update block, removing the LSB
872 self.head = self.head & (self.head - B::one());
873 // return offset + (index of LSB)
874 Some(self.head_offset + (B::count_ones(k) as usize))
878 fn size_hint(&self) -> (usize, Option<usize>) {
879 match self.tail.size_hint() {
880 (_, Some(h)) => (0, Some(1 + h * B::bits())),
886 impl<'a, B: BitBlock> Iterator for TwoBitPositions<'a, B> {
889 fn next(&mut self) -> Option<B> {
890 match (self.set.next(), self.other.next()) {
891 (Some(a), Some(b)) => Some((self.merge)(a, b)),
892 (Some(a), None) => Some((self.merge)(a, B::zero())),
893 (None, Some(b)) => Some((self.merge)(B::zero(), b)),
899 fn size_hint(&self) -> (usize, Option<usize>) {
900 let (a, au) = self.set.size_hint();
901 let (b, bu) = self.other.size_hint();
903 let upper = match (au, bu) {
904 (Some(au), Some(bu)) => Some(cmp::max(au, bu)),
908 (cmp::max(a, b), upper)
912 impl<'a, B: BitBlock> Iterator for Iter<'a, B> {
915 #[inline] fn next(&mut self) -> Option<usize> { self.0.next() }
916 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.0.size_hint() }
919 impl<'a, B: BitBlock> Iterator for Union<'a, B> {
922 #[inline] fn next(&mut self) -> Option<usize> { self.0.next() }
923 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.0.size_hint() }
926 impl<'a, B: BitBlock> Iterator for Intersection<'a, B> {
929 #[inline] fn next(&mut self) -> Option<usize> { self.0.next() }
930 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.0.size_hint() }
933 impl<'a, B: BitBlock> Iterator for Difference<'a, B> {
936 #[inline] fn next(&mut self) -> Option<usize> { self.0.next() }
937 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.0.size_hint() }
940 impl<'a, B: BitBlock> Iterator for SymmetricDifference<'a, B> {
943 #[inline] fn next(&mut self) -> Option<usize> { self.0.next() }
944 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.0.size_hint() }
947 impl<'a, B: BitBlock> IntoIterator for &'a BitSet<B> {
949 type IntoIter = Iter<'a, B>;
951 fn into_iter(self) -> Iter<'a, B> {