1 use core::borrow::Borrow;
2 use core::cmp::Ordering;
4 use core::hash::{Hash, Hasher};
5 use core::iter::{FromIterator, Peekable, FusedIterator};
6 use core::marker::PhantomData;
7 use core::ops::Bound::{Excluded, Included, Unbounded};
8 use core::ops::{Index, RangeBounds};
9 use core::{fmt, intrinsics, mem, ptr};
11 use super::node::{self, Handle, NodeRef, marker, InsertResult::*, ForceResult::*};
12 use super::search::{self, SearchResult::*};
14 use UnderflowResult::*;
17 /// A map based on a B-Tree.
19 /// B-Trees represent a fundamental compromise between cache-efficiency and actually minimizing
20 /// the amount of work performed in a search. In theory, a binary search tree (BST) is the optimal
21 /// choice for a sorted map, as a perfectly balanced BST performs the theoretical minimum amount of
22 /// comparisons necessary to find an element (log<sub>2</sub>n). However, in practice the way this
23 /// is done is *very* inefficient for modern computer architectures. In particular, every element
24 /// is stored in its own individually heap-allocated node. This means that every single insertion
25 /// triggers a heap-allocation, and every single comparison should be a cache-miss. Since these
26 /// are both notably expensive things to do in practice, we are forced to at very least reconsider
29 /// A B-Tree instead makes each node contain B-1 to 2B-1 elements in a contiguous array. By doing
30 /// this, we reduce the number of allocations by a factor of B, and improve cache efficiency in
31 /// searches. However, this does mean that searches will have to do *more* comparisons on average.
32 /// The precise number of comparisons depends on the node search strategy used. For optimal cache
33 /// efficiency, one could search the nodes linearly. For optimal comparisons, one could search
34 /// the node using binary search. As a compromise, one could also perform a linear search
35 /// that initially only checks every i<sup>th</sup> element for some choice of i.
37 /// Currently, our implementation simply performs naive linear search. This provides excellent
38 /// performance on *small* nodes of elements which are cheap to compare. However in the future we
39 /// would like to further explore choosing the optimal search strategy based on the choice of B,
40 /// and possibly other factors. Using linear search, searching for a random element is expected
41 /// to take O(B log<sub>B</sub>n) comparisons, which is generally worse than a BST. In practice,
42 /// however, performance is excellent.
44 /// It is a logic error for a key to be modified in such a way that the key's ordering relative to
45 /// any other key, as determined by the [`Ord`] trait, changes while it is in the map. This is
46 /// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
48 /// [`Ord`]: ../../std/cmp/trait.Ord.html
49 /// [`Cell`]: ../../std/cell/struct.Cell.html
50 /// [`RefCell`]: ../../std/cell/struct.RefCell.html
55 /// use std::collections::BTreeMap;
57 /// // type inference lets us omit an explicit type signature (which
58 /// // would be `BTreeMap<&str, &str>` in this example).
59 /// let mut movie_reviews = BTreeMap::new();
61 /// // review some movies.
62 /// movie_reviews.insert("Office Space", "Deals with real issues in the workplace.");
63 /// movie_reviews.insert("Pulp Fiction", "Masterpiece.");
64 /// movie_reviews.insert("The Godfather", "Very enjoyable.");
65 /// movie_reviews.insert("The Blues Brothers", "Eye lyked it a lot.");
67 /// // check for a specific one.
68 /// if !movie_reviews.contains_key("Les Misérables") {
69 /// println!("We've got {} reviews, but Les Misérables ain't one.",
70 /// movie_reviews.len());
73 /// // oops, this review has a lot of spelling mistakes, let's delete it.
74 /// movie_reviews.remove("The Blues Brothers");
76 /// // look up the values associated with some keys.
77 /// let to_find = ["Up!", "Office Space"];
78 /// for movie in &to_find {
79 /// match movie_reviews.get(movie) {
80 /// Some(review) => println!("{}: {}", movie, review),
81 /// None => println!("{} is unreviewed.", movie)
85 /// // Look up the value for a key (will panic if the key is not found).
86 /// println!("Movie review: {}", movie_reviews["Office Space"]);
88 /// // iterate over everything.
89 /// for (movie, review) in &movie_reviews {
90 /// println!("{}: \"{}\"", movie, review);
94 /// `BTreeMap` also implements an [`Entry API`](#method.entry), which allows
95 /// for more complex methods of getting, setting, updating and removing keys and
99 /// use std::collections::BTreeMap;
101 /// // type inference lets us omit an explicit type signature (which
102 /// // would be `BTreeMap<&str, u8>` in this example).
103 /// let mut player_stats = BTreeMap::new();
105 /// fn random_stat_buff() -> u8 {
106 /// // could actually return some random value here - let's just return
107 /// // some fixed value for now
111 /// // insert a key only if it doesn't already exist
112 /// player_stats.entry("health").or_insert(100);
114 /// // insert a key using a function that provides a new value only if it
115 /// // doesn't already exist
116 /// player_stats.entry("defence").or_insert_with(random_stat_buff);
118 /// // update a key, guarding against the key possibly not being set
119 /// let stat = player_stats.entry("attack").or_insert(100);
120 /// *stat += random_stat_buff();
122 #[stable(feature = "rust1", since = "1.0.0")]
123 pub struct BTreeMap<K, V> {
124 root: node::Root<K, V>,
128 #[stable(feature = "btree_drop", since = "1.7.0")]
129 unsafe impl<#[may_dangle] K, #[may_dangle] V> Drop for BTreeMap<K, V> {
132 drop(ptr::read(self).into_iter());
137 #[stable(feature = "rust1", since = "1.0.0")]
138 impl<K: Clone, V: Clone> Clone for BTreeMap<K, V> {
139 fn clone(&self) -> BTreeMap<K, V> {
140 fn clone_subtree<'a, K: Clone, V: Clone>(
141 node: node::NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
147 let mut out_tree = BTreeMap {
148 root: node::Root::new_leaf(),
153 let mut out_node = match out_tree.root.as_mut().force() {
155 Internal(_) => unreachable!(),
158 let mut in_edge = leaf.first_edge();
159 while let Ok(kv) = in_edge.right_kv() {
160 let (k, v) = kv.into_kv();
161 in_edge = kv.right_edge();
163 out_node.push(k.clone(), v.clone());
164 out_tree.length += 1;
170 Internal(internal) => {
171 let mut out_tree = clone_subtree(internal.first_edge().descend());
174 let mut out_node = out_tree.root.push_level();
175 let mut in_edge = internal.first_edge();
176 while let Ok(kv) = in_edge.right_kv() {
177 let (k, v) = kv.into_kv();
178 in_edge = kv.right_edge();
180 let k = (*k).clone();
181 let v = (*v).clone();
182 let subtree = clone_subtree(in_edge.descend());
184 // We can't destructure subtree directly
185 // because BTreeMap implements Drop
186 let (subroot, sublength) = unsafe {
187 let root = ptr::read(&subtree.root);
188 let length = subtree.length;
189 mem::forget(subtree);
193 out_node.push(k, v, subroot);
194 out_tree.length += 1 + sublength;
204 // Ideally we'd call `BTreeMap::new` here, but that has the `K:
205 // Ord` constraint, which this method lacks.
207 root: node::Root::shared_empty_root(),
211 clone_subtree(self.root.as_ref())
216 impl<K, Q: ?Sized> super::Recover<Q> for BTreeMap<K, ()>
217 where K: Borrow<Q> + Ord,
222 fn get(&self, key: &Q) -> Option<&K> {
223 match search::search_tree(self.root.as_ref(), key) {
224 Found(handle) => Some(handle.into_kv().0),
229 fn take(&mut self, key: &Q) -> Option<K> {
230 match search::search_tree(self.root.as_mut(), key) {
234 length: &mut self.length,
235 _marker: PhantomData,
244 fn replace(&mut self, key: K) -> Option<K> {
245 self.ensure_root_is_owned();
246 match search::search_tree::<marker::Mut<'_>, K, (), K>(self.root.as_mut(), &key) {
247 Found(handle) => Some(mem::replace(handle.into_kv_mut().0, key)),
252 length: &mut self.length,
253 _marker: PhantomData,
262 /// An iterator over the entries of a `BTreeMap`.
264 /// This `struct` is created by the [`iter`] method on [`BTreeMap`]. See its
265 /// documentation for more.
267 /// [`iter`]: struct.BTreeMap.html#method.iter
268 /// [`BTreeMap`]: struct.BTreeMap.html
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub struct Iter<'a, K: 'a, V: 'a> {
271 range: Range<'a, K, V>,
275 #[stable(feature = "collection_debug", since = "1.17.0")]
276 impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for Iter<'_, K, V> {
277 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
278 f.debug_list().entries(self.clone()).finish()
282 /// A mutable iterator over the entries of a `BTreeMap`.
284 /// This `struct` is created by the [`iter_mut`] method on [`BTreeMap`]. See its
285 /// documentation for more.
287 /// [`iter_mut`]: struct.BTreeMap.html#method.iter_mut
288 /// [`BTreeMap`]: struct.BTreeMap.html
289 #[stable(feature = "rust1", since = "1.0.0")]
291 pub struct IterMut<'a, K: 'a, V: 'a> {
292 range: RangeMut<'a, K, V>,
296 /// An owning iterator over the entries of a `BTreeMap`.
298 /// This `struct` is created by the [`into_iter`] method on [`BTreeMap`][`BTreeMap`]
299 /// (provided by the `IntoIterator` trait). See its documentation for more.
301 /// [`into_iter`]: struct.BTreeMap.html#method.into_iter
302 /// [`BTreeMap`]: struct.BTreeMap.html
303 #[stable(feature = "rust1", since = "1.0.0")]
304 pub struct IntoIter<K, V> {
305 front: Handle<NodeRef<marker::Owned, K, V, marker::Leaf>, marker::Edge>,
306 back: Handle<NodeRef<marker::Owned, K, V, marker::Leaf>, marker::Edge>,
310 #[stable(feature = "collection_debug", since = "1.17.0")]
311 impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IntoIter<K, V> {
312 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
314 front: self.front.reborrow(),
315 back: self.back.reborrow(),
317 f.debug_list().entries(range).finish()
321 /// An iterator over the keys of a `BTreeMap`.
323 /// This `struct` is created by the [`keys`] method on [`BTreeMap`]. See its
324 /// documentation for more.
326 /// [`keys`]: struct.BTreeMap.html#method.keys
327 /// [`BTreeMap`]: struct.BTreeMap.html
328 #[stable(feature = "rust1", since = "1.0.0")]
329 pub struct Keys<'a, K: 'a, V: 'a> {
330 inner: Iter<'a, K, V>,
333 #[stable(feature = "collection_debug", since = "1.17.0")]
334 impl<K: fmt::Debug, V> fmt::Debug for Keys<'_, K, V> {
335 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
336 f.debug_list().entries(self.clone()).finish()
340 /// An iterator over the values of a `BTreeMap`.
342 /// This `struct` is created by the [`values`] method on [`BTreeMap`]. See its
343 /// documentation for more.
345 /// [`values`]: struct.BTreeMap.html#method.values
346 /// [`BTreeMap`]: struct.BTreeMap.html
347 #[stable(feature = "rust1", since = "1.0.0")]
348 pub struct Values<'a, K: 'a, V: 'a> {
349 inner: Iter<'a, K, V>,
352 #[stable(feature = "collection_debug", since = "1.17.0")]
353 impl<K, V: fmt::Debug> fmt::Debug for Values<'_, K, V> {
354 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
355 f.debug_list().entries(self.clone()).finish()
359 /// A mutable iterator over the values of a `BTreeMap`.
361 /// This `struct` is created by the [`values_mut`] method on [`BTreeMap`]. See its
362 /// documentation for more.
364 /// [`values_mut`]: struct.BTreeMap.html#method.values_mut
365 /// [`BTreeMap`]: struct.BTreeMap.html
366 #[stable(feature = "map_values_mut", since = "1.10.0")]
368 pub struct ValuesMut<'a, K: 'a, V: 'a> {
369 inner: IterMut<'a, K, V>,
372 /// An iterator over a sub-range of entries in a `BTreeMap`.
374 /// This `struct` is created by the [`range`] method on [`BTreeMap`]. See its
375 /// documentation for more.
377 /// [`range`]: struct.BTreeMap.html#method.range
378 /// [`BTreeMap`]: struct.BTreeMap.html
379 #[stable(feature = "btree_range", since = "1.17.0")]
380 pub struct Range<'a, K: 'a, V: 'a> {
381 front: Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Edge>,
382 back: Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Edge>,
385 #[stable(feature = "collection_debug", since = "1.17.0")]
386 impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for Range<'_, K, V> {
387 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
388 f.debug_list().entries(self.clone()).finish()
392 /// A mutable iterator over a sub-range of entries in a `BTreeMap`.
394 /// This `struct` is created by the [`range_mut`] method on [`BTreeMap`]. See its
395 /// documentation for more.
397 /// [`range_mut`]: struct.BTreeMap.html#method.range_mut
398 /// [`BTreeMap`]: struct.BTreeMap.html
399 #[stable(feature = "btree_range", since = "1.17.0")]
400 pub struct RangeMut<'a, K: 'a, V: 'a> {
401 front: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>,
402 back: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>,
404 // Be invariant in `K` and `V`
405 _marker: PhantomData<&'a mut (K, V)>,
408 #[stable(feature = "collection_debug", since = "1.17.0")]
409 impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for RangeMut<'_, K, V> {
410 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
412 front: self.front.reborrow(),
413 back: self.back.reborrow(),
415 f.debug_list().entries(range).finish()
419 /// A view into a single entry in a map, which may either be vacant or occupied.
421 /// This `enum` is constructed from the [`entry`] method on [`BTreeMap`].
423 /// [`BTreeMap`]: struct.BTreeMap.html
424 /// [`entry`]: struct.BTreeMap.html#method.entry
425 #[stable(feature = "rust1", since = "1.0.0")]
426 pub enum Entry<'a, K: 'a, V: 'a> {
428 #[stable(feature = "rust1", since = "1.0.0")]
429 Vacant(#[stable(feature = "rust1", since = "1.0.0")]
430 VacantEntry<'a, K, V>),
432 /// An occupied entry.
433 #[stable(feature = "rust1", since = "1.0.0")]
434 Occupied(#[stable(feature = "rust1", since = "1.0.0")]
435 OccupiedEntry<'a, K, V>),
438 #[stable(feature= "debug_btree_map", since = "1.12.0")]
439 impl<K: Debug + Ord, V: Debug> Debug for Entry<'_, K, V> {
440 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
442 Vacant(ref v) => f.debug_tuple("Entry")
445 Occupied(ref o) => f.debug_tuple("Entry")
452 /// A view into a vacant entry in a `BTreeMap`.
453 /// It is part of the [`Entry`] enum.
455 /// [`Entry`]: enum.Entry.html
456 #[stable(feature = "rust1", since = "1.0.0")]
457 pub struct VacantEntry<'a, K: 'a, V: 'a> {
459 handle: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>,
460 length: &'a mut usize,
462 // Be invariant in `K` and `V`
463 _marker: PhantomData<&'a mut (K, V)>,
466 #[stable(feature= "debug_btree_map", since = "1.12.0")]
467 impl<K: Debug + Ord, V> Debug for VacantEntry<'_, K, V> {
468 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
469 f.debug_tuple("VacantEntry")
475 /// A view into an occupied entry in a `BTreeMap`.
476 /// It is part of the [`Entry`] enum.
478 /// [`Entry`]: enum.Entry.html
479 #[stable(feature = "rust1", since = "1.0.0")]
480 pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
481 handle: Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV>,
483 length: &'a mut usize,
485 // Be invariant in `K` and `V`
486 _marker: PhantomData<&'a mut (K, V)>,
489 #[stable(feature= "debug_btree_map", since = "1.12.0")]
490 impl<K: Debug + Ord, V: Debug> Debug for OccupiedEntry<'_, K, V> {
491 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
492 f.debug_struct("OccupiedEntry")
493 .field("key", self.key())
494 .field("value", self.get())
499 // An iterator for merging two sorted sequences into one
500 struct MergeIter<K, V, I: Iterator<Item = (K, V)>> {
505 impl<K: Ord, V> BTreeMap<K, V> {
506 /// Makes a new empty BTreeMap with a reasonable choice for B.
513 /// use std::collections::BTreeMap;
515 /// let mut map = BTreeMap::new();
517 /// // entries can now be inserted into the empty map
518 /// map.insert(1, "a");
520 #[stable(feature = "rust1", since = "1.0.0")]
521 pub fn new() -> BTreeMap<K, V> {
523 root: node::Root::shared_empty_root(),
528 /// Clears the map, removing all values.
535 /// use std::collections::BTreeMap;
537 /// let mut a = BTreeMap::new();
538 /// a.insert(1, "a");
540 /// assert!(a.is_empty());
542 #[stable(feature = "rust1", since = "1.0.0")]
543 pub fn clear(&mut self) {
544 *self = BTreeMap::new();
547 /// Returns a reference to the value corresponding to the key.
549 /// The key may be any borrowed form of the map's key type, but the ordering
550 /// on the borrowed form *must* match the ordering on the key type.
557 /// use std::collections::BTreeMap;
559 /// let mut map = BTreeMap::new();
560 /// map.insert(1, "a");
561 /// assert_eq!(map.get(&1), Some(&"a"));
562 /// assert_eq!(map.get(&2), None);
564 #[stable(feature = "rust1", since = "1.0.0")]
565 pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&V>
569 match search::search_tree(self.root.as_ref(), key) {
570 Found(handle) => Some(handle.into_kv().1),
575 /// Returns the key-value pair corresponding to the supplied key.
577 /// The supplied key may be any borrowed form of the map's key type, but the ordering
578 /// on the borrowed form *must* match the ordering on the key type.
583 /// #![feature(map_get_key_value)]
584 /// use std::collections::BTreeMap;
586 /// let mut map = BTreeMap::new();
587 /// map.insert(1, "a");
588 /// assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
589 /// assert_eq!(map.get_key_value(&2), None);
591 #[unstable(feature = "map_get_key_value", issue = "49347")]
592 pub fn get_key_value<Q: ?Sized>(&self, k: &Q) -> Option<(&K, &V)>
596 match search::search_tree(self.root.as_ref(), k) {
597 Found(handle) => Some(handle.into_kv()),
602 /// Returns `true` if the map contains a value for the specified key.
604 /// The key may be any borrowed form of the map's key type, but the ordering
605 /// on the borrowed form *must* match the ordering on the key type.
612 /// use std::collections::BTreeMap;
614 /// let mut map = BTreeMap::new();
615 /// map.insert(1, "a");
616 /// assert_eq!(map.contains_key(&1), true);
617 /// assert_eq!(map.contains_key(&2), false);
619 #[stable(feature = "rust1", since = "1.0.0")]
620 pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
624 self.get(key).is_some()
627 /// Returns a mutable reference to the value corresponding to the key.
629 /// The key may be any borrowed form of the map's key type, but the ordering
630 /// on the borrowed form *must* match the ordering on the key type.
637 /// use std::collections::BTreeMap;
639 /// let mut map = BTreeMap::new();
640 /// map.insert(1, "a");
641 /// if let Some(x) = map.get_mut(&1) {
644 /// assert_eq!(map[&1], "b");
646 // See `get` for implementation notes, this is basically a copy-paste with mut's added
647 #[stable(feature = "rust1", since = "1.0.0")]
648 pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V>
652 match search::search_tree(self.root.as_mut(), key) {
653 Found(handle) => Some(handle.into_kv_mut().1),
658 /// Inserts a key-value pair into the map.
660 /// If the map did not have this key present, `None` is returned.
662 /// If the map did have this key present, the value is updated, and the old
663 /// value is returned. The key is not updated, though; this matters for
664 /// types that can be `==` without being identical. See the [module-level
665 /// documentation] for more.
667 /// [module-level documentation]: index.html#insert-and-complex-keys
674 /// use std::collections::BTreeMap;
676 /// let mut map = BTreeMap::new();
677 /// assert_eq!(map.insert(37, "a"), None);
678 /// assert_eq!(map.is_empty(), false);
680 /// map.insert(37, "b");
681 /// assert_eq!(map.insert(37, "c"), Some("b"));
682 /// assert_eq!(map[&37], "c");
684 #[stable(feature = "rust1", since = "1.0.0")]
685 pub fn insert(&mut self, key: K, value: V) -> Option<V> {
686 match self.entry(key) {
687 Occupied(mut entry) => Some(entry.insert(value)),
695 /// Removes a key from the map, returning the value at the key if the key
696 /// was previously in the map.
698 /// The key may be any borrowed form of the map's key type, but the ordering
699 /// on the borrowed form *must* match the ordering on the key type.
706 /// use std::collections::BTreeMap;
708 /// let mut map = BTreeMap::new();
709 /// map.insert(1, "a");
710 /// assert_eq!(map.remove(&1), Some("a"));
711 /// assert_eq!(map.remove(&1), None);
713 #[stable(feature = "rust1", since = "1.0.0")]
714 pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
718 match search::search_tree(self.root.as_mut(), key) {
722 length: &mut self.length,
723 _marker: PhantomData,
731 /// Moves all elements from `other` into `Self`, leaving `other` empty.
736 /// use std::collections::BTreeMap;
738 /// let mut a = BTreeMap::new();
739 /// a.insert(1, "a");
740 /// a.insert(2, "b");
741 /// a.insert(3, "c");
743 /// let mut b = BTreeMap::new();
744 /// b.insert(3, "d");
745 /// b.insert(4, "e");
746 /// b.insert(5, "f");
748 /// a.append(&mut b);
750 /// assert_eq!(a.len(), 5);
751 /// assert_eq!(b.len(), 0);
753 /// assert_eq!(a[&1], "a");
754 /// assert_eq!(a[&2], "b");
755 /// assert_eq!(a[&3], "d");
756 /// assert_eq!(a[&4], "e");
757 /// assert_eq!(a[&5], "f");
759 #[stable(feature = "btree_append", since = "1.11.0")]
760 pub fn append(&mut self, other: &mut Self) {
761 // Do we have to append anything at all?
762 if other.len() == 0 {
766 // We can just swap `self` and `other` if `self` is empty.
768 mem::swap(self, other);
772 // First, we merge `self` and `other` into a sorted sequence in linear time.
773 let self_iter = mem::take(self).into_iter();
774 let other_iter = mem::take(other).into_iter();
775 let iter = MergeIter {
776 left: self_iter.peekable(),
777 right: other_iter.peekable(),
780 // Second, we build a tree from the sorted sequence in linear time.
781 self.from_sorted_iter(iter);
782 self.fix_right_edge();
785 /// Constructs a double-ended iterator over a sub-range of elements in the map.
786 /// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will
787 /// yield elements from min (inclusive) to max (exclusive).
788 /// The range may also be entered as `(Bound<T>, Bound<T>)`, so for example
789 /// `range((Excluded(4), Included(10)))` will yield a left-exclusive, right-inclusive
790 /// range from 4 to 10.
794 /// Panics if range `start > end`.
795 /// Panics if range `start == end` and both bounds are `Excluded`.
802 /// use std::collections::BTreeMap;
803 /// use std::ops::Bound::Included;
805 /// let mut map = BTreeMap::new();
806 /// map.insert(3, "a");
807 /// map.insert(5, "b");
808 /// map.insert(8, "c");
809 /// for (&key, &value) in map.range((Included(&4), Included(&8))) {
810 /// println!("{}: {}", key, value);
812 /// assert_eq!(Some((&5, &"b")), map.range(4..).next());
814 #[stable(feature = "btree_range", since = "1.17.0")]
815 pub fn range<T: ?Sized, R>(&self, range: R) -> Range<'_, K, V>
816 where T: Ord, K: Borrow<T>, R: RangeBounds<T>
818 let root1 = self.root.as_ref();
819 let root2 = self.root.as_ref();
820 let (f, b) = range_search(root1, root2, range);
822 Range { front: f, back: b}
825 /// Constructs a mutable double-ended iterator over a sub-range of elements in the map.
826 /// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will
827 /// yield elements from min (inclusive) to max (exclusive).
828 /// The range may also be entered as `(Bound<T>, Bound<T>)`, so for example
829 /// `range((Excluded(4), Included(10)))` will yield a left-exclusive, right-inclusive
830 /// range from 4 to 10.
834 /// Panics if range `start > end`.
835 /// Panics if range `start == end` and both bounds are `Excluded`.
842 /// use std::collections::BTreeMap;
844 /// let mut map: BTreeMap<&str, i32> = ["Alice", "Bob", "Carol", "Cheryl"]
846 /// .map(|&s| (s, 0))
848 /// for (_, balance) in map.range_mut("B".."Cheryl") {
851 /// for (name, balance) in &map {
852 /// println!("{} => {}", name, balance);
855 #[stable(feature = "btree_range", since = "1.17.0")]
856 pub fn range_mut<T: ?Sized, R>(&mut self, range: R) -> RangeMut<'_, K, V>
857 where T: Ord, K: Borrow<T>, R: RangeBounds<T>
859 let root1 = self.root.as_mut();
860 let root2 = unsafe { ptr::read(&root1) };
861 let (f, b) = range_search(root1, root2, range);
866 _marker: PhantomData,
870 /// Gets the given key's corresponding entry in the map for in-place manipulation.
877 /// use std::collections::BTreeMap;
879 /// let mut count: BTreeMap<&str, usize> = BTreeMap::new();
881 /// // count the number of occurrences of letters in the vec
882 /// for x in vec!["a","b","a","c","a","b"] {
883 /// *count.entry(x).or_insert(0) += 1;
886 /// assert_eq!(count["a"], 3);
888 #[stable(feature = "rust1", since = "1.0.0")]
889 pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
890 // FIXME(@porglezomp) Avoid allocating if we don't insert
891 self.ensure_root_is_owned();
892 match search::search_tree(self.root.as_mut(), &key) {
894 Occupied(OccupiedEntry {
896 length: &mut self.length,
897 _marker: PhantomData,
904 length: &mut self.length,
905 _marker: PhantomData,
911 fn from_sorted_iter<I: Iterator<Item = (K, V)>>(&mut self, iter: I) {
912 self.ensure_root_is_owned();
913 let mut cur_node = last_leaf_edge(self.root.as_mut()).into_node();
914 // Iterate through all key-value pairs, pushing them into nodes at the right level.
915 for (key, value) in iter {
916 // Try to push key-value pair into the current leaf node.
917 if cur_node.len() < node::CAPACITY {
918 cur_node.push(key, value);
920 // No space left, go up and push there.
922 let mut test_node = cur_node.forget_type();
924 match test_node.ascend() {
926 let parent = parent.into_node();
927 if parent.len() < node::CAPACITY {
928 // Found a node with space left, push here.
933 test_node = parent.forget_type();
937 // We are at the top, create a new root node and push there.
938 open_node = node.into_root_mut().push_level();
944 // Push key-value pair and new right subtree.
945 let tree_height = open_node.height() - 1;
946 let mut right_tree = node::Root::new_leaf();
947 for _ in 0..tree_height {
948 right_tree.push_level();
950 open_node.push(key, value, right_tree);
952 // Go down to the right-most leaf again.
953 cur_node = last_leaf_edge(open_node.forget_type()).into_node();
960 fn fix_right_edge(&mut self) {
961 // Handle underfull nodes, start from the top.
962 let mut cur_node = self.root.as_mut();
963 while let Internal(internal) = cur_node.force() {
964 // Check if right-most child is underfull.
965 let mut last_edge = internal.last_edge();
966 let right_child_len = last_edge.reborrow().descend().len();
967 if right_child_len < node::MIN_LEN {
969 let mut last_kv = match last_edge.left_kv() {
971 Err(_) => unreachable!(),
973 last_kv.bulk_steal_left(node::MIN_LEN - right_child_len);
974 last_edge = last_kv.right_edge();
978 cur_node = last_edge.descend();
982 /// Splits the collection into two at the given key. Returns everything after the given key,
983 /// including the key.
990 /// use std::collections::BTreeMap;
992 /// let mut a = BTreeMap::new();
993 /// a.insert(1, "a");
994 /// a.insert(2, "b");
995 /// a.insert(3, "c");
996 /// a.insert(17, "d");
997 /// a.insert(41, "e");
999 /// let b = a.split_off(&3);
1001 /// assert_eq!(a.len(), 2);
1002 /// assert_eq!(b.len(), 3);
1004 /// assert_eq!(a[&1], "a");
1005 /// assert_eq!(a[&2], "b");
1007 /// assert_eq!(b[&3], "c");
1008 /// assert_eq!(b[&17], "d");
1009 /// assert_eq!(b[&41], "e");
1011 #[stable(feature = "btree_split_off", since = "1.11.0")]
1012 pub fn split_off<Q: ?Sized + Ord>(&mut self, key: &Q) -> Self
1015 if self.is_empty() {
1019 let total_num = self.len();
1021 let mut right = Self::new();
1022 right.root = node::Root::new_leaf();
1023 for _ in 0..(self.root.as_ref().height()) {
1024 right.root.push_level();
1028 let mut left_node = self.root.as_mut();
1029 let mut right_node = right.root.as_mut();
1032 let mut split_edge = match search::search_node(left_node, key) {
1033 // key is going to the right tree
1034 Found(handle) => handle.left_edge(),
1035 GoDown(handle) => handle,
1038 split_edge.move_suffix(&mut right_node);
1040 match (split_edge.force(), right_node.force()) {
1041 (Internal(edge), Internal(node)) => {
1042 left_node = edge.descend();
1043 right_node = node.first_edge().descend();
1045 (Leaf(_), Leaf(_)) => {
1055 self.fix_right_border();
1056 right.fix_left_border();
1058 if self.root.as_ref().height() < right.root.as_ref().height() {
1059 self.recalc_length();
1060 right.length = total_num - self.len();
1062 right.recalc_length();
1063 self.length = total_num - right.len();
1069 /// Calculates the number of elements if it is incorrect.
1070 fn recalc_length(&mut self) {
1072 node: NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
1076 let mut res = node.len();
1078 if let Internal(node) = node.force() {
1079 let mut edge = node.first_edge();
1081 res += dfs(edge.reborrow().descend());
1082 match edge.right_kv() {
1084 edge = right_kv.right_edge();
1096 self.length = dfs(self.root.as_ref());
1099 /// Removes empty levels on the top.
1100 fn fix_top(&mut self) {
1103 let node = self.root.as_ref();
1104 if node.height() == 0 || node.len() > 0 {
1108 self.root.pop_level();
1112 fn fix_right_border(&mut self) {
1116 let mut cur_node = self.root.as_mut();
1118 while let Internal(node) = cur_node.force() {
1119 let mut last_kv = node.last_kv();
1121 if last_kv.can_merge() {
1122 cur_node = last_kv.merge().descend();
1124 let right_len = last_kv.reborrow().right_edge().descend().len();
1125 // `MINLEN + 1` to avoid readjust if merge happens on the next level.
1126 if right_len < node::MIN_LEN + 1 {
1127 last_kv.bulk_steal_left(node::MIN_LEN + 1 - right_len);
1129 cur_node = last_kv.right_edge().descend();
1137 /// The symmetric clone of `fix_right_border`.
1138 fn fix_left_border(&mut self) {
1142 let mut cur_node = self.root.as_mut();
1144 while let Internal(node) = cur_node.force() {
1145 let mut first_kv = node.first_kv();
1147 if first_kv.can_merge() {
1148 cur_node = first_kv.merge().descend();
1150 let left_len = first_kv.reborrow().left_edge().descend().len();
1151 if left_len < node::MIN_LEN + 1 {
1152 first_kv.bulk_steal_right(node::MIN_LEN + 1 - left_len);
1154 cur_node = first_kv.left_edge().descend();
1162 /// If the root node is the shared root node, allocate our own node.
1163 fn ensure_root_is_owned(&mut self) {
1164 if self.root.is_shared_root() {
1165 self.root = node::Root::new_leaf();
1170 #[stable(feature = "rust1", since = "1.0.0")]
1171 impl<'a, K: 'a, V: 'a> IntoIterator for &'a BTreeMap<K, V> {
1172 type Item = (&'a K, &'a V);
1173 type IntoIter = Iter<'a, K, V>;
1175 fn into_iter(self) -> Iter<'a, K, V> {
1180 #[stable(feature = "rust1", since = "1.0.0")]
1181 impl<'a, K: 'a, V: 'a> Iterator for Iter<'a, K, V> {
1182 type Item = (&'a K, &'a V);
1184 fn next(&mut self) -> Option<(&'a K, &'a V)> {
1185 if self.length == 0 {
1189 unsafe { Some(self.range.next_unchecked()) }
1193 fn size_hint(&self) -> (usize, Option<usize>) {
1194 (self.length, Some(self.length))
1197 fn last(mut self) -> Option<(&'a K, &'a V)> {
1202 #[stable(feature = "fused", since = "1.26.0")]
1203 impl<K, V> FusedIterator for Iter<'_, K, V> {}
1205 #[stable(feature = "rust1", since = "1.0.0")]
1206 impl<'a, K: 'a, V: 'a> DoubleEndedIterator for Iter<'a, K, V> {
1207 fn next_back(&mut self) -> Option<(&'a K, &'a V)> {
1208 if self.length == 0 {
1212 unsafe { Some(self.range.next_back_unchecked()) }
1217 #[stable(feature = "rust1", since = "1.0.0")]
1218 impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
1219 fn len(&self) -> usize {
1224 #[stable(feature = "rust1", since = "1.0.0")]
1225 impl<K, V> Clone for Iter<'_, K, V> {
1226 fn clone(&self) -> Self {
1228 range: self.range.clone(),
1229 length: self.length,
1234 #[stable(feature = "rust1", since = "1.0.0")]
1235 impl<'a, K: 'a, V: 'a> IntoIterator for &'a mut BTreeMap<K, V> {
1236 type Item = (&'a K, &'a mut V);
1237 type IntoIter = IterMut<'a, K, V>;
1239 fn into_iter(self) -> IterMut<'a, K, V> {
1244 #[stable(feature = "rust1", since = "1.0.0")]
1245 impl<'a, K: 'a, V: 'a> Iterator for IterMut<'a, K, V> {
1246 type Item = (&'a K, &'a mut V);
1248 fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
1249 if self.length == 0 {
1253 unsafe { Some(self.range.next_unchecked()) }
1257 fn size_hint(&self) -> (usize, Option<usize>) {
1258 (self.length, Some(self.length))
1261 fn last(mut self) -> Option<(&'a K, &'a mut V)> {
1266 #[stable(feature = "rust1", since = "1.0.0")]
1267 impl<'a, K: 'a, V: 'a> DoubleEndedIterator for IterMut<'a, K, V> {
1268 fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> {
1269 if self.length == 0 {
1273 unsafe { Some(self.range.next_back_unchecked()) }
1278 #[stable(feature = "rust1", since = "1.0.0")]
1279 impl<K, V> ExactSizeIterator for IterMut<'_, K, V> {
1280 fn len(&self) -> usize {
1285 #[stable(feature = "fused", since = "1.26.0")]
1286 impl<K, V> FusedIterator for IterMut<'_, K, V> {}
1288 #[stable(feature = "rust1", since = "1.0.0")]
1289 impl<K, V> IntoIterator for BTreeMap<K, V> {
1291 type IntoIter = IntoIter<K, V>;
1293 fn into_iter(self) -> IntoIter<K, V> {
1294 let root1 = unsafe { ptr::read(&self.root).into_ref() };
1295 let root2 = unsafe { ptr::read(&self.root).into_ref() };
1296 let len = self.length;
1300 front: first_leaf_edge(root1),
1301 back: last_leaf_edge(root2),
1307 #[stable(feature = "btree_drop", since = "1.7.0")]
1308 impl<K, V> Drop for IntoIter<K, V> {
1309 fn drop(&mut self) {
1310 self.for_each(drop);
1312 let leaf_node = ptr::read(&self.front).into_node();
1313 if leaf_node.is_shared_root() {
1317 if let Some(first_parent) = leaf_node.deallocate_and_ascend() {
1318 let mut cur_node = first_parent.into_node();
1319 while let Some(parent) = cur_node.deallocate_and_ascend() {
1320 cur_node = parent.into_node()
1327 #[stable(feature = "rust1", since = "1.0.0")]
1328 impl<K, V> Iterator for IntoIter<K, V> {
1331 fn next(&mut self) -> Option<(K, V)> {
1332 if self.length == 0 {
1338 let handle = unsafe { ptr::read(&self.front) };
1340 let mut cur_handle = match handle.right_kv() {
1342 let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
1343 let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
1344 self.front = kv.right_edge();
1345 return Some((k, v));
1347 Err(last_edge) => unsafe {
1348 unwrap_unchecked(last_edge.into_node().deallocate_and_ascend())
1353 match cur_handle.right_kv() {
1355 let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
1356 let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
1357 self.front = first_leaf_edge(kv.right_edge().descend());
1358 return Some((k, v));
1360 Err(last_edge) => unsafe {
1361 cur_handle = unwrap_unchecked(last_edge.into_node().deallocate_and_ascend());
1367 fn size_hint(&self) -> (usize, Option<usize>) {
1368 (self.length, Some(self.length))
1372 #[stable(feature = "rust1", since = "1.0.0")]
1373 impl<K, V> DoubleEndedIterator for IntoIter<K, V> {
1374 fn next_back(&mut self) -> Option<(K, V)> {
1375 if self.length == 0 {
1381 let handle = unsafe { ptr::read(&self.back) };
1383 let mut cur_handle = match handle.left_kv() {
1385 let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
1386 let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
1387 self.back = kv.left_edge();
1388 return Some((k, v));
1390 Err(last_edge) => unsafe {
1391 unwrap_unchecked(last_edge.into_node().deallocate_and_ascend())
1396 match cur_handle.left_kv() {
1398 let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
1399 let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
1400 self.back = last_leaf_edge(kv.left_edge().descend());
1401 return Some((k, v));
1403 Err(last_edge) => unsafe {
1404 cur_handle = unwrap_unchecked(last_edge.into_node().deallocate_and_ascend());
1411 #[stable(feature = "rust1", since = "1.0.0")]
1412 impl<K, V> ExactSizeIterator for IntoIter<K, V> {
1413 fn len(&self) -> usize {
1418 #[stable(feature = "fused", since = "1.26.0")]
1419 impl<K, V> FusedIterator for IntoIter<K, V> {}
1421 #[stable(feature = "rust1", since = "1.0.0")]
1422 impl<'a, K, V> Iterator for Keys<'a, K, V> {
1425 fn next(&mut self) -> Option<&'a K> {
1426 self.inner.next().map(|(k, _)| k)
1429 fn size_hint(&self) -> (usize, Option<usize>) {
1430 self.inner.size_hint()
1433 fn last(mut self) -> Option<&'a K> {
1438 #[stable(feature = "rust1", since = "1.0.0")]
1439 impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V> {
1440 fn next_back(&mut self) -> Option<&'a K> {
1441 self.inner.next_back().map(|(k, _)| k)
1445 #[stable(feature = "rust1", since = "1.0.0")]
1446 impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
1447 fn len(&self) -> usize {
1452 #[stable(feature = "fused", since = "1.26.0")]
1453 impl<K, V> FusedIterator for Keys<'_, K, V> {}
1455 #[stable(feature = "rust1", since = "1.0.0")]
1456 impl<K, V> Clone for Keys<'_, K, V> {
1457 fn clone(&self) -> Self {
1458 Keys { inner: self.inner.clone() }
1462 #[stable(feature = "rust1", since = "1.0.0")]
1463 impl<'a, K, V> Iterator for Values<'a, K, V> {
1466 fn next(&mut self) -> Option<&'a V> {
1467 self.inner.next().map(|(_, v)| v)
1470 fn size_hint(&self) -> (usize, Option<usize>) {
1471 self.inner.size_hint()
1474 fn last(mut self) -> Option<&'a V> {
1479 #[stable(feature = "rust1", since = "1.0.0")]
1480 impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V> {
1481 fn next_back(&mut self) -> Option<&'a V> {
1482 self.inner.next_back().map(|(_, v)| v)
1486 #[stable(feature = "rust1", since = "1.0.0")]
1487 impl<K, V> ExactSizeIterator for Values<'_, K, V> {
1488 fn len(&self) -> usize {
1493 #[stable(feature = "fused", since = "1.26.0")]
1494 impl<K, V> FusedIterator for Values<'_, K, V> {}
1496 #[stable(feature = "rust1", since = "1.0.0")]
1497 impl<K, V> Clone for Values<'_, K, V> {
1498 fn clone(&self) -> Self {
1499 Values { inner: self.inner.clone() }
1503 #[stable(feature = "btree_range", since = "1.17.0")]
1504 impl<'a, K, V> Iterator for Range<'a, K, V> {
1505 type Item = (&'a K, &'a V);
1507 fn next(&mut self) -> Option<(&'a K, &'a V)> {
1508 if self.front == self.back {
1511 unsafe { Some(self.next_unchecked()) }
1515 fn last(mut self) -> Option<(&'a K, &'a V)> {
1520 #[stable(feature = "map_values_mut", since = "1.10.0")]
1521 impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
1522 type Item = &'a mut V;
1524 fn next(&mut self) -> Option<&'a mut V> {
1525 self.inner.next().map(|(_, v)| v)
1528 fn size_hint(&self) -> (usize, Option<usize>) {
1529 self.inner.size_hint()
1532 fn last(mut self) -> Option<&'a mut V> {
1537 #[stable(feature = "map_values_mut", since = "1.10.0")]
1538 impl<'a, K, V> DoubleEndedIterator for ValuesMut<'a, K, V> {
1539 fn next_back(&mut self) -> Option<&'a mut V> {
1540 self.inner.next_back().map(|(_, v)| v)
1544 #[stable(feature = "map_values_mut", since = "1.10.0")]
1545 impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
1546 fn len(&self) -> usize {
1551 #[stable(feature = "fused", since = "1.26.0")]
1552 impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}
1554 impl<'a, K, V> Range<'a, K, V> {
1555 unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
1556 let handle = self.front;
1558 let mut cur_handle = match handle.right_kv() {
1560 let ret = kv.into_kv();
1561 self.front = kv.right_edge();
1565 let next_level = last_edge.into_node().ascend().ok();
1566 unwrap_unchecked(next_level)
1571 match cur_handle.right_kv() {
1573 let ret = kv.into_kv();
1574 self.front = first_leaf_edge(kv.right_edge().descend());
1578 let next_level = last_edge.into_node().ascend().ok();
1579 cur_handle = unwrap_unchecked(next_level);
1586 #[stable(feature = "btree_range", since = "1.17.0")]
1587 impl<'a, K, V> DoubleEndedIterator for Range<'a, K, V> {
1588 fn next_back(&mut self) -> Option<(&'a K, &'a V)> {
1589 if self.front == self.back {
1592 unsafe { Some(self.next_back_unchecked()) }
1597 impl<'a, K, V> Range<'a, K, V> {
1598 unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
1599 let handle = self.back;
1601 let mut cur_handle = match handle.left_kv() {
1603 let ret = kv.into_kv();
1604 self.back = kv.left_edge();
1608 let next_level = last_edge.into_node().ascend().ok();
1609 unwrap_unchecked(next_level)
1614 match cur_handle.left_kv() {
1616 let ret = kv.into_kv();
1617 self.back = last_leaf_edge(kv.left_edge().descend());
1621 let next_level = last_edge.into_node().ascend().ok();
1622 cur_handle = unwrap_unchecked(next_level);
1629 #[stable(feature = "fused", since = "1.26.0")]
1630 impl<K, V> FusedIterator for Range<'_, K, V> {}
1632 #[stable(feature = "btree_range", since = "1.17.0")]
1633 impl<K, V> Clone for Range<'_, K, V> {
1634 fn clone(&self) -> Self {
1642 #[stable(feature = "btree_range", since = "1.17.0")]
1643 impl<'a, K, V> Iterator for RangeMut<'a, K, V> {
1644 type Item = (&'a K, &'a mut V);
1646 fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
1647 if self.front == self.back {
1650 unsafe { Some(self.next_unchecked()) }
1654 fn last(mut self) -> Option<(&'a K, &'a mut V)> {
1659 impl<'a, K, V> RangeMut<'a, K, V> {
1660 unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
1661 let handle = ptr::read(&self.front);
1663 let mut cur_handle = match handle.right_kv() {
1665 self.front = ptr::read(&kv).right_edge();
1666 // Doing the descend invalidates the references returned by `into_kv_mut`,
1667 // so we have to do this last.
1668 let (k, v) = kv.into_kv_mut();
1669 return (k, v); // coerce k from `&mut K` to `&K`
1672 let next_level = last_edge.into_node().ascend().ok();
1673 unwrap_unchecked(next_level)
1678 match cur_handle.right_kv() {
1680 self.front = first_leaf_edge(ptr::read(&kv).right_edge().descend());
1681 // Doing the descend invalidates the references returned by `into_kv_mut`,
1682 // so we have to do this last.
1683 let (k, v) = kv.into_kv_mut();
1684 return (k, v); // coerce k from `&mut K` to `&K`
1687 let next_level = last_edge.into_node().ascend().ok();
1688 cur_handle = unwrap_unchecked(next_level);
1695 #[stable(feature = "btree_range", since = "1.17.0")]
1696 impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V> {
1697 fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> {
1698 if self.front == self.back {
1701 unsafe { Some(self.next_back_unchecked()) }
1706 #[stable(feature = "fused", since = "1.26.0")]
1707 impl<K, V> FusedIterator for RangeMut<'_, K, V> {}
1709 impl<'a, K, V> RangeMut<'a, K, V> {
1710 unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
1711 let handle = ptr::read(&self.back);
1713 let mut cur_handle = match handle.left_kv() {
1715 self.back = ptr::read(&kv).left_edge();
1716 // Doing the descend invalidates the references returned by `into_kv_mut`,
1717 // so we have to do this last.
1718 let (k, v) = kv.into_kv_mut();
1719 return (k, v); // coerce k from `&mut K` to `&K`
1722 let next_level = last_edge.into_node().ascend().ok();
1723 unwrap_unchecked(next_level)
1728 match cur_handle.left_kv() {
1730 self.back = last_leaf_edge(ptr::read(&kv).left_edge().descend());
1731 // Doing the descend invalidates the references returned by `into_kv_mut`,
1732 // so we have to do this last.
1733 let (k, v) = kv.into_kv_mut();
1734 return (k, v); // coerce k from `&mut K` to `&K`
1737 let next_level = last_edge.into_node().ascend().ok();
1738 cur_handle = unwrap_unchecked(next_level);
1745 #[stable(feature = "rust1", since = "1.0.0")]
1746 impl<K: Ord, V> FromIterator<(K, V)> for BTreeMap<K, V> {
1747 fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> BTreeMap<K, V> {
1748 let mut map = BTreeMap::new();
1754 #[stable(feature = "rust1", since = "1.0.0")]
1755 impl<K: Ord, V> Extend<(K, V)> for BTreeMap<K, V> {
1757 fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
1758 iter.into_iter().for_each(move |(k, v)| {
1764 #[stable(feature = "extend_ref", since = "1.2.0")]
1765 impl<'a, K: Ord + Copy, V: Copy> Extend<(&'a K, &'a V)> for BTreeMap<K, V> {
1766 fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: I) {
1767 self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
1771 #[stable(feature = "rust1", since = "1.0.0")]
1772 impl<K: Hash, V: Hash> Hash for BTreeMap<K, V> {
1773 fn hash<H: Hasher>(&self, state: &mut H) {
1780 #[stable(feature = "rust1", since = "1.0.0")]
1781 impl<K: Ord, V> Default for BTreeMap<K, V> {
1782 /// Creates an empty `BTreeMap<K, V>`.
1783 fn default() -> BTreeMap<K, V> {
1788 #[stable(feature = "rust1", since = "1.0.0")]
1789 impl<K: PartialEq, V: PartialEq> PartialEq for BTreeMap<K, V> {
1790 fn eq(&self, other: &BTreeMap<K, V>) -> bool {
1791 self.len() == other.len() && self.iter().zip(other).all(|(a, b)| a == b)
1795 #[stable(feature = "rust1", since = "1.0.0")]
1796 impl<K: Eq, V: Eq> Eq for BTreeMap<K, V> {}
1798 #[stable(feature = "rust1", since = "1.0.0")]
1799 impl<K: PartialOrd, V: PartialOrd> PartialOrd for BTreeMap<K, V> {
1801 fn partial_cmp(&self, other: &BTreeMap<K, V>) -> Option<Ordering> {
1802 self.iter().partial_cmp(other.iter())
1806 #[stable(feature = "rust1", since = "1.0.0")]
1807 impl<K: Ord, V: Ord> Ord for BTreeMap<K, V> {
1809 fn cmp(&self, other: &BTreeMap<K, V>) -> Ordering {
1810 self.iter().cmp(other.iter())
1814 #[stable(feature = "rust1", since = "1.0.0")]
1815 impl<K: Debug, V: Debug> Debug for BTreeMap<K, V> {
1816 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1817 f.debug_map().entries(self.iter()).finish()
1821 #[stable(feature = "rust1", since = "1.0.0")]
1822 impl<K: Ord, Q: ?Sized, V> Index<&Q> for BTreeMap<K, V>
1828 /// Returns a reference to the value corresponding to the supplied key.
1832 /// Panics if the key is not present in the `BTreeMap`.
1834 fn index(&self, key: &Q) -> &V {
1835 self.get(key).expect("no entry found for key")
1839 fn first_leaf_edge<BorrowType, K, V>
1840 (mut node: NodeRef<BorrowType, K, V, marker::LeafOrInternal>)
1841 -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
1843 match node.force() {
1844 Leaf(leaf) => return leaf.first_edge(),
1845 Internal(internal) => {
1846 node = internal.first_edge().descend();
1852 fn last_leaf_edge<BorrowType, K, V>
1853 (mut node: NodeRef<BorrowType, K, V, marker::LeafOrInternal>)
1854 -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
1856 match node.force() {
1857 Leaf(leaf) => return leaf.last_edge(),
1858 Internal(internal) => {
1859 node = internal.last_edge().descend();
1865 fn range_search<BorrowType, K, V, Q: ?Sized, R: RangeBounds<Q>>(
1866 root1: NodeRef<BorrowType, K, V, marker::LeafOrInternal>,
1867 root2: NodeRef<BorrowType, K, V, marker::LeafOrInternal>,
1869 )-> (Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>,
1870 Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>)
1871 where Q: Ord, K: Borrow<Q>
1873 match (range.start_bound(), range.end_bound()) {
1874 (Excluded(s), Excluded(e)) if s==e =>
1875 panic!("range start and end are equal and excluded in BTreeMap"),
1876 (Included(s), Included(e)) |
1877 (Included(s), Excluded(e)) |
1878 (Excluded(s), Included(e)) |
1879 (Excluded(s), Excluded(e)) if s>e =>
1880 panic!("range start is greater than range end in BTreeMap"),
1884 let mut min_node = root1;
1885 let mut max_node = root2;
1886 let mut min_found = false;
1887 let mut max_found = false;
1888 let mut diverged = false;
1891 let min_edge = match (min_found, range.start_bound()) {
1892 (false, Included(key)) => match search::search_linear(&min_node, key) {
1893 (i, true) => { min_found = true; i },
1896 (false, Excluded(key)) => match search::search_linear(&min_node, key) {
1897 (i, true) => { min_found = true; i+1 },
1900 (_, Unbounded) => 0,
1901 (true, Included(_)) => min_node.keys().len(),
1902 (true, Excluded(_)) => 0,
1905 let max_edge = match (max_found, range.end_bound()) {
1906 (false, Included(key)) => match search::search_linear(&max_node, key) {
1907 (i, true) => { max_found = true; i+1 },
1910 (false, Excluded(key)) => match search::search_linear(&max_node, key) {
1911 (i, true) => { max_found = true; i },
1914 (_, Unbounded) => max_node.keys().len(),
1915 (true, Included(_)) => 0,
1916 (true, Excluded(_)) => max_node.keys().len(),
1920 if max_edge < min_edge { panic!("Ord is ill-defined in BTreeMap range") }
1921 if min_edge != max_edge { diverged = true; }
1924 let front = Handle::new_edge(min_node, min_edge);
1925 let back = Handle::new_edge(max_node, max_edge);
1926 match (front.force(), back.force()) {
1927 (Leaf(f), Leaf(b)) => {
1930 (Internal(min_int), Internal(max_int)) => {
1931 min_node = min_int.descend();
1932 max_node = max_int.descend();
1934 _ => unreachable!("BTreeMap has different depths"),
1940 unsafe fn unwrap_unchecked<T>(val: Option<T>) -> T {
1941 val.unwrap_or_else(|| {
1942 if cfg!(debug_assertions) {
1943 panic!("'unchecked' unwrap on None in BTreeMap");
1945 intrinsics::unreachable();
1950 impl<K, V> BTreeMap<K, V> {
1951 /// Gets an iterator over the entries of the map, sorted by key.
1958 /// use std::collections::BTreeMap;
1960 /// let mut map = BTreeMap::new();
1961 /// map.insert(3, "c");
1962 /// map.insert(2, "b");
1963 /// map.insert(1, "a");
1965 /// for (key, value) in map.iter() {
1966 /// println!("{}: {}", key, value);
1969 /// let (first_key, first_value) = map.iter().next().unwrap();
1970 /// assert_eq!((*first_key, *first_value), (1, "a"));
1972 #[stable(feature = "rust1", since = "1.0.0")]
1973 pub fn iter(&self) -> Iter<'_, K, V> {
1976 front: first_leaf_edge(self.root.as_ref()),
1977 back: last_leaf_edge(self.root.as_ref()),
1979 length: self.length,
1983 /// Gets a mutable iterator over the entries of the map, sorted by key.
1990 /// use std::collections::BTreeMap;
1992 /// let mut map = BTreeMap::new();
1993 /// map.insert("a", 1);
1994 /// map.insert("b", 2);
1995 /// map.insert("c", 3);
1997 /// // add 10 to the value if the key isn't "a"
1998 /// for (key, value) in map.iter_mut() {
1999 /// if key != &"a" {
2004 #[stable(feature = "rust1", since = "1.0.0")]
2005 pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
2006 let root1 = self.root.as_mut();
2007 let root2 = unsafe { ptr::read(&root1) };
2010 front: first_leaf_edge(root1),
2011 back: last_leaf_edge(root2),
2012 _marker: PhantomData,
2014 length: self.length,
2018 /// Gets an iterator over the keys of the map, in sorted order.
2025 /// use std::collections::BTreeMap;
2027 /// let mut a = BTreeMap::new();
2028 /// a.insert(2, "b");
2029 /// a.insert(1, "a");
2031 /// let keys: Vec<_> = a.keys().cloned().collect();
2032 /// assert_eq!(keys, [1, 2]);
2034 #[stable(feature = "rust1", since = "1.0.0")]
2035 pub fn keys(&self) -> Keys<'_, K, V> {
2036 Keys { inner: self.iter() }
2039 /// Gets an iterator over the values of the map, in order by key.
2046 /// use std::collections::BTreeMap;
2048 /// let mut a = BTreeMap::new();
2049 /// a.insert(1, "hello");
2050 /// a.insert(2, "goodbye");
2052 /// let values: Vec<&str> = a.values().cloned().collect();
2053 /// assert_eq!(values, ["hello", "goodbye"]);
2055 #[stable(feature = "rust1", since = "1.0.0")]
2056 pub fn values(&self) -> Values<'_, K, V> {
2057 Values { inner: self.iter() }
2060 /// Gets a mutable iterator over the values of the map, in order by key.
2067 /// use std::collections::BTreeMap;
2069 /// let mut a = BTreeMap::new();
2070 /// a.insert(1, String::from("hello"));
2071 /// a.insert(2, String::from("goodbye"));
2073 /// for value in a.values_mut() {
2074 /// value.push_str("!");
2077 /// let values: Vec<String> = a.values().cloned().collect();
2078 /// assert_eq!(values, [String::from("hello!"),
2079 /// String::from("goodbye!")]);
2081 #[stable(feature = "map_values_mut", since = "1.10.0")]
2082 pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
2083 ValuesMut { inner: self.iter_mut() }
2086 /// Returns the number of elements in the map.
2093 /// use std::collections::BTreeMap;
2095 /// let mut a = BTreeMap::new();
2096 /// assert_eq!(a.len(), 0);
2097 /// a.insert(1, "a");
2098 /// assert_eq!(a.len(), 1);
2100 #[stable(feature = "rust1", since = "1.0.0")]
2101 pub fn len(&self) -> usize {
2105 /// Returns `true` if the map contains no elements.
2112 /// use std::collections::BTreeMap;
2114 /// let mut a = BTreeMap::new();
2115 /// assert!(a.is_empty());
2116 /// a.insert(1, "a");
2117 /// assert!(!a.is_empty());
2119 #[stable(feature = "rust1", since = "1.0.0")]
2120 pub fn is_empty(&self) -> bool {
2125 impl<'a, K: Ord, V> Entry<'a, K, V> {
2126 /// Ensures a value is in the entry by inserting the default if empty, and returns
2127 /// a mutable reference to the value in the entry.
2132 /// use std::collections::BTreeMap;
2134 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2135 /// map.entry("poneyland").or_insert(12);
2137 /// assert_eq!(map["poneyland"], 12);
2139 #[stable(feature = "rust1", since = "1.0.0")]
2140 pub fn or_insert(self, default: V) -> &'a mut V {
2142 Occupied(entry) => entry.into_mut(),
2143 Vacant(entry) => entry.insert(default),
2147 /// Ensures a value is in the entry by inserting the result of the default function if empty,
2148 /// and returns a mutable reference to the value in the entry.
2153 /// use std::collections::BTreeMap;
2155 /// let mut map: BTreeMap<&str, String> = BTreeMap::new();
2156 /// let s = "hoho".to_string();
2158 /// map.entry("poneyland").or_insert_with(|| s);
2160 /// assert_eq!(map["poneyland"], "hoho".to_string());
2162 #[stable(feature = "rust1", since = "1.0.0")]
2163 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
2165 Occupied(entry) => entry.into_mut(),
2166 Vacant(entry) => entry.insert(default()),
2170 /// Returns a reference to this entry's key.
2175 /// use std::collections::BTreeMap;
2177 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2178 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2180 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2181 pub fn key(&self) -> &K {
2183 Occupied(ref entry) => entry.key(),
2184 Vacant(ref entry) => entry.key(),
2188 /// Provides in-place mutable access to an occupied entry before any
2189 /// potential inserts into the map.
2194 /// use std::collections::BTreeMap;
2196 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2198 /// map.entry("poneyland")
2199 /// .and_modify(|e| { *e += 1 })
2201 /// assert_eq!(map["poneyland"], 42);
2203 /// map.entry("poneyland")
2204 /// .and_modify(|e| { *e += 1 })
2206 /// assert_eq!(map["poneyland"], 43);
2208 #[stable(feature = "entry_and_modify", since = "1.26.0")]
2209 pub fn and_modify<F>(self, f: F) -> Self
2210 where F: FnOnce(&mut V)
2213 Occupied(mut entry) => {
2217 Vacant(entry) => Vacant(entry),
2222 impl<'a, K: Ord, V: Default> Entry<'a, K, V> {
2223 #[stable(feature = "entry_or_default", since = "1.28.0")]
2224 /// Ensures a value is in the entry by inserting the default value if empty,
2225 /// and returns a mutable reference to the value in the entry.
2231 /// use std::collections::BTreeMap;
2233 /// let mut map: BTreeMap<&str, Option<usize>> = BTreeMap::new();
2234 /// map.entry("poneyland").or_default();
2236 /// assert_eq!(map["poneyland"], None);
2239 pub fn or_default(self) -> &'a mut V {
2241 Occupied(entry) => entry.into_mut(),
2242 Vacant(entry) => entry.insert(Default::default()),
2248 impl<'a, K: Ord, V> VacantEntry<'a, K, V> {
2249 /// Gets a reference to the key that would be used when inserting a value
2250 /// through the VacantEntry.
2255 /// use std::collections::BTreeMap;
2257 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2258 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2260 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2261 pub fn key(&self) -> &K {
2265 /// Take ownership of the key.
2270 /// use std::collections::BTreeMap;
2271 /// use std::collections::btree_map::Entry;
2273 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2275 /// if let Entry::Vacant(v) = map.entry("poneyland") {
2279 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2280 pub fn into_key(self) -> K {
2284 /// Sets the value of the entry with the `VacantEntry`'s key,
2285 /// and returns a mutable reference to it.
2290 /// use std::collections::BTreeMap;
2292 /// let mut count: BTreeMap<&str, usize> = BTreeMap::new();
2294 /// // count the number of occurrences of letters in the vec
2295 /// for x in vec!["a","b","a","c","a","b"] {
2296 /// *count.entry(x).or_insert(0) += 1;
2299 /// assert_eq!(count["a"], 3);
2301 #[stable(feature = "rust1", since = "1.0.0")]
2302 pub fn insert(self, value: V) -> &'a mut V {
2311 let mut cur_parent = match self.handle.insert(self.key, value) {
2312 (Fit(handle), _) => return handle.into_kv_mut().1,
2313 (Split(left, k, v, right), ptr) => {
2318 left.ascend().map_err(|n| n.into_root_mut())
2325 match parent.insert(ins_k, ins_v, ins_edge) {
2326 Fit(_) => return unsafe { &mut *out_ptr },
2327 Split(left, k, v, right) => {
2331 cur_parent = left.ascend().map_err(|n| n.into_root_mut());
2336 root.push_level().push(ins_k, ins_v, ins_edge);
2337 return unsafe { &mut *out_ptr };
2344 impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
2345 /// Gets a reference to the key in the entry.
2350 /// use std::collections::BTreeMap;
2352 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2353 /// map.entry("poneyland").or_insert(12);
2354 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2356 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2357 pub fn key(&self) -> &K {
2358 self.handle.reborrow().into_kv().0
2361 /// Take ownership of the key and value from the map.
2366 /// use std::collections::BTreeMap;
2367 /// use std::collections::btree_map::Entry;
2369 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2370 /// map.entry("poneyland").or_insert(12);
2372 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2373 /// // We delete the entry from the map.
2374 /// o.remove_entry();
2377 /// // If now try to get the value, it will panic:
2378 /// // println!("{}", map["poneyland"]);
2380 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2381 pub fn remove_entry(self) -> (K, V) {
2385 /// Gets a reference to the value in the entry.
2390 /// use std::collections::BTreeMap;
2391 /// use std::collections::btree_map::Entry;
2393 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2394 /// map.entry("poneyland").or_insert(12);
2396 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2397 /// assert_eq!(o.get(), &12);
2400 #[stable(feature = "rust1", since = "1.0.0")]
2401 pub fn get(&self) -> &V {
2402 self.handle.reborrow().into_kv().1
2405 /// Gets a mutable reference to the value in the entry.
2407 /// If you need a reference to the `OccupiedEntry` that may outlive the
2408 /// destruction of the `Entry` value, see [`into_mut`].
2410 /// [`into_mut`]: #method.into_mut
2415 /// use std::collections::BTreeMap;
2416 /// use std::collections::btree_map::Entry;
2418 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2419 /// map.entry("poneyland").or_insert(12);
2421 /// assert_eq!(map["poneyland"], 12);
2422 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2423 /// *o.get_mut() += 10;
2424 /// assert_eq!(*o.get(), 22);
2426 /// // We can use the same Entry multiple times.
2427 /// *o.get_mut() += 2;
2429 /// assert_eq!(map["poneyland"], 24);
2431 #[stable(feature = "rust1", since = "1.0.0")]
2432 pub fn get_mut(&mut self) -> &mut V {
2433 self.handle.kv_mut().1
2436 /// Converts the entry into a mutable reference to its value.
2438 /// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].
2440 /// [`get_mut`]: #method.get_mut
2445 /// use std::collections::BTreeMap;
2446 /// use std::collections::btree_map::Entry;
2448 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2449 /// map.entry("poneyland").or_insert(12);
2451 /// assert_eq!(map["poneyland"], 12);
2452 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2453 /// *o.into_mut() += 10;
2455 /// assert_eq!(map["poneyland"], 22);
2457 #[stable(feature = "rust1", since = "1.0.0")]
2458 pub fn into_mut(self) -> &'a mut V {
2459 self.handle.into_kv_mut().1
2462 /// Sets the value of the entry with the `OccupiedEntry`'s key,
2463 /// and returns the entry's old value.
2468 /// use std::collections::BTreeMap;
2469 /// use std::collections::btree_map::Entry;
2471 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2472 /// map.entry("poneyland").or_insert(12);
2474 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2475 /// assert_eq!(o.insert(15), 12);
2477 /// assert_eq!(map["poneyland"], 15);
2479 #[stable(feature = "rust1", since = "1.0.0")]
2480 pub fn insert(&mut self, value: V) -> V {
2481 mem::replace(self.get_mut(), value)
2484 /// Takes the value of the entry out of the map, and returns it.
2489 /// use std::collections::BTreeMap;
2490 /// use std::collections::btree_map::Entry;
2492 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2493 /// map.entry("poneyland").or_insert(12);
2495 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2496 /// assert_eq!(o.remove(), 12);
2498 /// // If we try to get "poneyland"'s value, it'll panic:
2499 /// // println!("{}", map["poneyland"]);
2501 #[stable(feature = "rust1", since = "1.0.0")]
2502 pub fn remove(self) -> V {
2506 fn remove_kv(self) -> (K, V) {
2509 let (small_leaf, old_key, old_val) = match self.handle.force() {
2511 let (hole, old_key, old_val) = leaf.remove();
2512 (hole.into_node(), old_key, old_val)
2514 Internal(mut internal) => {
2515 let key_loc = internal.kv_mut().0 as *mut K;
2516 let val_loc = internal.kv_mut().1 as *mut V;
2518 let to_remove = first_leaf_edge(internal.right_edge().descend()).right_kv().ok();
2519 let to_remove = unsafe { unwrap_unchecked(to_remove) };
2521 let (hole, key, val) = to_remove.remove();
2523 let old_key = unsafe { mem::replace(&mut *key_loc, key) };
2524 let old_val = unsafe { mem::replace(&mut *val_loc, val) };
2526 (hole.into_node(), old_key, old_val)
2531 let mut cur_node = small_leaf.forget_type();
2532 while cur_node.len() < node::CAPACITY / 2 {
2533 match handle_underfull_node(cur_node) {
2535 EmptyParent(_) => unreachable!(),
2537 if parent.len() == 0 {
2538 // We must be at the root
2539 parent.into_root_mut().pop_level();
2542 cur_node = parent.forget_type();
2553 enum UnderflowResult<'a, K, V> {
2555 EmptyParent(NodeRef<marker::Mut<'a>, K, V, marker::Internal>),
2556 Merged(NodeRef<marker::Mut<'a>, K, V, marker::Internal>),
2557 Stole(NodeRef<marker::Mut<'a>, K, V, marker::Internal>),
2560 fn handle_underfull_node<K, V>(node: NodeRef<marker::Mut<'_>, K, V, marker::LeafOrInternal>)
2561 -> UnderflowResult<'_, K, V> {
2562 let parent = if let Ok(parent) = node.ascend() {
2568 let (is_left, mut handle) = match parent.left_kv() {
2569 Ok(left) => (true, left),
2571 match parent.right_kv() {
2572 Ok(right) => (false, right),
2574 return EmptyParent(parent.into_node());
2580 if handle.can_merge() {
2581 Merged(handle.merge().into_node())
2584 handle.steal_left();
2586 handle.steal_right();
2588 Stole(handle.into_node())
2592 impl<K: Ord, V, I: Iterator<Item = (K, V)>> Iterator for MergeIter<K, V, I> {
2595 fn next(&mut self) -> Option<(K, V)> {
2596 let res = match (self.left.peek(), self.right.peek()) {
2597 (Some(&(ref left_key, _)), Some(&(ref right_key, _))) => left_key.cmp(right_key),
2598 (Some(_), None) => Ordering::Less,
2599 (None, Some(_)) => Ordering::Greater,
2600 (None, None) => return None,
2603 // Check which elements comes first and only advance the corresponding iterator.
2604 // If two keys are equal, take the value from `right`.
2606 Ordering::Less => self.left.next(),
2607 Ordering::Greater => self.right.next(),
2608 Ordering::Equal => {