1 // Copyright 2015 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 use core::cmp::Ordering;
13 use core::hash::{Hash, Hasher};
14 use core::iter::{FromIterator, Peekable, FusedIterator};
15 use core::marker::PhantomData;
16 use core::ops::Bound::{Excluded, Included, Unbounded};
18 use core::ops::RangeBounds;
19 use core::{fmt, intrinsics, mem, ptr};
23 use super::node::{self, Handle, NodeRef, marker};
26 use super::node::InsertResult::*;
27 use super::node::ForceResult::*;
28 use super::search::SearchResult::*;
29 use self::UnderflowResult::*;
32 /// A map based on a B-Tree.
34 /// B-Trees represent a fundamental compromise between cache-efficiency and actually minimizing
35 /// the amount of work performed in a search. In theory, a binary search tree (BST) is the optimal
36 /// choice for a sorted map, as a perfectly balanced BST performs the theoretical minimum amount of
37 /// comparisons necessary to find an element (log<sub>2</sub>n). However, in practice the way this
38 /// is done is *very* inefficient for modern computer architectures. In particular, every element
39 /// is stored in its own individually heap-allocated node. This means that every single insertion
40 /// triggers a heap-allocation, and every single comparison should be a cache-miss. Since these
41 /// are both notably expensive things to do in practice, we are forced to at very least reconsider
44 /// A B-Tree instead makes each node contain B-1 to 2B-1 elements in a contiguous array. By doing
45 /// this, we reduce the number of allocations by a factor of B, and improve cache efficiency in
46 /// searches. However, this does mean that searches will have to do *more* comparisons on average.
47 /// The precise number of comparisons depends on the node search strategy used. For optimal cache
48 /// efficiency, one could search the nodes linearly. For optimal comparisons, one could search
49 /// the node using binary search. As a compromise, one could also perform a linear search
50 /// that initially only checks every i<sup>th</sup> element for some choice of i.
52 /// Currently, our implementation simply performs naive linear search. This provides excellent
53 /// performance on *small* nodes of elements which are cheap to compare. However in the future we
54 /// would like to further explore choosing the optimal search strategy based on the choice of B,
55 /// and possibly other factors. Using linear search, searching for a random element is expected
56 /// to take O(B log<sub>B</sub>n) comparisons, which is generally worse than a BST. In practice,
57 /// however, performance is excellent.
59 /// It is a logic error for a key to be modified in such a way that the key's ordering relative to
60 /// any other key, as determined by the [`Ord`] trait, changes while it is in the map. This is
61 /// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
63 /// [`Ord`]: ../../std/cmp/trait.Ord.html
64 /// [`Cell`]: ../../std/cell/struct.Cell.html
65 /// [`RefCell`]: ../../std/cell/struct.RefCell.html
70 /// use std::collections::BTreeMap;
72 /// // type inference lets us omit an explicit type signature (which
73 /// // would be `BTreeMap<&str, &str>` in this example).
74 /// let mut movie_reviews = BTreeMap::new();
76 /// // review some movies.
77 /// movie_reviews.insert("Office Space", "Deals with real issues in the workplace.");
78 /// movie_reviews.insert("Pulp Fiction", "Masterpiece.");
79 /// movie_reviews.insert("The Godfather", "Very enjoyable.");
80 /// movie_reviews.insert("The Blues Brothers", "Eye lyked it a lot.");
82 /// // check for a specific one.
83 /// if !movie_reviews.contains_key("Les Misérables") {
84 /// println!("We've got {} reviews, but Les Misérables ain't one.",
85 /// movie_reviews.len());
88 /// // oops, this review has a lot of spelling mistakes, let's delete it.
89 /// movie_reviews.remove("The Blues Brothers");
91 /// // look up the values associated with some keys.
92 /// let to_find = ["Up!", "Office Space"];
93 /// for book in &to_find {
94 /// match movie_reviews.get(book) {
95 /// Some(review) => println!("{}: {}", book, review),
96 /// None => println!("{} is unreviewed.", book)
100 /// // iterate over everything.
101 /// for (movie, review) in &movie_reviews {
102 /// println!("{}: \"{}\"", movie, review);
106 /// `BTreeMap` also implements an [`Entry API`](#method.entry), which allows
107 /// for more complex methods of getting, setting, updating and removing keys and
111 /// use std::collections::BTreeMap;
113 /// // type inference lets us omit an explicit type signature (which
114 /// // would be `BTreeMap<&str, u8>` in this example).
115 /// let mut player_stats = BTreeMap::new();
117 /// fn random_stat_buff() -> u8 {
118 /// // could actually return some random value here - let's just return
119 /// // some fixed value for now
123 /// // insert a key only if it doesn't already exist
124 /// player_stats.entry("health").or_insert(100);
126 /// // insert a key using a function that provides a new value only if it
127 /// // doesn't already exist
128 /// player_stats.entry("defence").or_insert_with(random_stat_buff);
130 /// // update a key, guarding against the key possibly not being set
131 /// let stat = player_stats.entry("attack").or_insert(100);
132 /// *stat += random_stat_buff();
134 #[stable(feature = "rust1", since = "1.0.0")]
135 pub struct BTreeMap<K, V> {
136 root: node::Root<K, V>,
140 #[stable(feature = "btree_drop", since = "1.7.0")]
141 unsafe impl<#[may_dangle] K, #[may_dangle] V> Drop for BTreeMap<K, V> {
144 drop(ptr::read(self).into_iter());
149 #[stable(feature = "rust1", since = "1.0.0")]
150 impl<K: Clone, V: Clone> Clone for BTreeMap<K, V> {
151 fn clone(&self) -> BTreeMap<K, V> {
152 fn clone_subtree<'a, K: Clone, V: Clone>(
153 node: node::NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
159 let mut out_tree = BTreeMap {
160 root: node::Root::new_leaf(),
165 let mut out_node = match out_tree.root.as_mut().force() {
167 Internal(_) => unreachable!(),
170 let mut in_edge = leaf.first_edge();
171 while let Ok(kv) = in_edge.right_kv() {
172 let (k, v) = kv.into_kv();
173 in_edge = kv.right_edge();
175 out_node.push(k.clone(), v.clone());
176 out_tree.length += 1;
182 Internal(internal) => {
183 let mut out_tree = clone_subtree(internal.first_edge().descend());
186 let mut out_node = out_tree.root.push_level();
187 let mut in_edge = internal.first_edge();
188 while let Ok(kv) = in_edge.right_kv() {
189 let (k, v) = kv.into_kv();
190 in_edge = kv.right_edge();
192 let k = (*k).clone();
193 let v = (*v).clone();
194 let subtree = clone_subtree(in_edge.descend());
196 // We can't destructure subtree directly
197 // because BTreeMap implements Drop
198 let (subroot, sublength) = unsafe {
199 let root = ptr::read(&subtree.root);
200 let length = subtree.length;
201 mem::forget(subtree);
205 out_node.push(k, v, subroot);
206 out_tree.length += 1 + sublength;
216 // Ideally we'd call `BTreeMap::new` here, but that has the `K:
217 // Ord` constraint, which this method lacks.
219 root: node::Root::shared_empty_root(),
223 clone_subtree(self.root.as_ref())
228 impl<K, Q: ?Sized> super::Recover<Q> for BTreeMap<K, ()>
229 where K: Borrow<Q> + Ord,
234 fn get(&self, key: &Q) -> Option<&K> {
235 match search::search_tree(self.root.as_ref(), key) {
236 Found(handle) => Some(handle.into_kv().0),
241 fn take(&mut self, key: &Q) -> Option<K> {
242 match search::search_tree(self.root.as_mut(), key) {
246 length: &mut self.length,
247 _marker: PhantomData,
256 fn replace(&mut self, key: K) -> Option<K> {
257 self.ensure_root_is_owned();
258 match search::search_tree::<marker::Mut, K, (), K>(self.root.as_mut(), &key) {
259 Found(handle) => Some(mem::replace(handle.into_kv_mut().0, key)),
264 length: &mut self.length,
265 _marker: PhantomData,
274 /// An iterator over the entries of a `BTreeMap`.
276 /// This `struct` is created by the [`iter`] method on [`BTreeMap`]. See its
277 /// documentation for more.
279 /// [`iter`]: struct.BTreeMap.html#method.iter
280 /// [`BTreeMap`]: struct.BTreeMap.html
281 #[stable(feature = "rust1", since = "1.0.0")]
282 pub struct Iter<'a, K: 'a, V: 'a> {
283 range: Range<'a, K, V>,
287 #[stable(feature = "collection_debug", since = "1.17.0")]
288 impl<'a, K: 'a + fmt::Debug, V: 'a + fmt::Debug> fmt::Debug for Iter<'a, K, V> {
289 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
290 f.debug_list().entries(self.clone()).finish()
294 /// A mutable iterator over the entries of a `BTreeMap`.
296 /// This `struct` is created by the [`iter_mut`] method on [`BTreeMap`]. See its
297 /// documentation for more.
299 /// [`iter_mut`]: struct.BTreeMap.html#method.iter_mut
300 /// [`BTreeMap`]: struct.BTreeMap.html
301 #[stable(feature = "rust1", since = "1.0.0")]
303 pub struct IterMut<'a, K: 'a, V: 'a> {
304 range: RangeMut<'a, K, V>,
308 /// An owning iterator over the entries of a `BTreeMap`.
310 /// This `struct` is created by the [`into_iter`] method on [`BTreeMap`][`BTreeMap`]
311 /// (provided by the `IntoIterator` trait). See its documentation for more.
313 /// [`into_iter`]: struct.BTreeMap.html#method.into_iter
314 /// [`BTreeMap`]: struct.BTreeMap.html
315 #[stable(feature = "rust1", since = "1.0.0")]
316 pub struct IntoIter<K, V> {
317 front: Handle<NodeRef<marker::Owned, K, V, marker::Leaf>, marker::Edge>,
318 back: Handle<NodeRef<marker::Owned, K, V, marker::Leaf>, marker::Edge>,
322 #[stable(feature = "collection_debug", since = "1.17.0")]
323 impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IntoIter<K, V> {
324 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
326 front: self.front.reborrow(),
327 back: self.back.reborrow(),
329 f.debug_list().entries(range).finish()
333 /// An iterator over the keys of a `BTreeMap`.
335 /// This `struct` is created by the [`keys`] method on [`BTreeMap`]. See its
336 /// documentation for more.
338 /// [`keys`]: struct.BTreeMap.html#method.keys
339 /// [`BTreeMap`]: struct.BTreeMap.html
340 #[stable(feature = "rust1", since = "1.0.0")]
341 pub struct Keys<'a, K: 'a, V: 'a> {
342 inner: Iter<'a, K, V>,
345 #[stable(feature = "collection_debug", since = "1.17.0")]
346 impl<'a, K: 'a + fmt::Debug, V: 'a> fmt::Debug for Keys<'a, K, V> {
347 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
348 f.debug_list().entries(self.clone()).finish()
352 /// An iterator over the values of a `BTreeMap`.
354 /// This `struct` is created by the [`values`] method on [`BTreeMap`]. See its
355 /// documentation for more.
357 /// [`values`]: struct.BTreeMap.html#method.values
358 /// [`BTreeMap`]: struct.BTreeMap.html
359 #[stable(feature = "rust1", since = "1.0.0")]
360 pub struct Values<'a, K: 'a, V: 'a> {
361 inner: Iter<'a, K, V>,
364 #[stable(feature = "collection_debug", since = "1.17.0")]
365 impl<'a, K: 'a, V: 'a + fmt::Debug> fmt::Debug for Values<'a, K, V> {
366 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
367 f.debug_list().entries(self.clone()).finish()
371 /// A mutable iterator over the values of a `BTreeMap`.
373 /// This `struct` is created by the [`values_mut`] method on [`BTreeMap`]. See its
374 /// documentation for more.
376 /// [`values_mut`]: struct.BTreeMap.html#method.values_mut
377 /// [`BTreeMap`]: struct.BTreeMap.html
378 #[stable(feature = "map_values_mut", since = "1.10.0")]
380 pub struct ValuesMut<'a, K: 'a, V: 'a> {
381 inner: IterMut<'a, K, V>,
384 /// An iterator over a sub-range of entries in a `BTreeMap`.
386 /// This `struct` is created by the [`range`] method on [`BTreeMap`]. See its
387 /// documentation for more.
389 /// [`range`]: struct.BTreeMap.html#method.range
390 /// [`BTreeMap`]: struct.BTreeMap.html
391 #[stable(feature = "btree_range", since = "1.17.0")]
392 pub struct Range<'a, K: 'a, V: 'a> {
393 front: Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Edge>,
394 back: Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Edge>,
397 #[stable(feature = "collection_debug", since = "1.17.0")]
398 impl<'a, K: 'a + fmt::Debug, V: 'a + fmt::Debug> fmt::Debug for Range<'a, K, V> {
399 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
400 f.debug_list().entries(self.clone()).finish()
404 /// A mutable iterator over a sub-range of entries in a `BTreeMap`.
406 /// This `struct` is created by the [`range_mut`] method on [`BTreeMap`]. See its
407 /// documentation for more.
409 /// [`range_mut`]: struct.BTreeMap.html#method.range_mut
410 /// [`BTreeMap`]: struct.BTreeMap.html
411 #[stable(feature = "btree_range", since = "1.17.0")]
412 pub struct RangeMut<'a, K: 'a, V: 'a> {
413 front: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>,
414 back: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>,
416 // Be invariant in `K` and `V`
417 _marker: PhantomData<&'a mut (K, V)>,
420 #[stable(feature = "collection_debug", since = "1.17.0")]
421 impl<'a, K: 'a + fmt::Debug, V: 'a + fmt::Debug> fmt::Debug for RangeMut<'a, K, V> {
422 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
424 front: self.front.reborrow(),
425 back: self.back.reborrow(),
427 f.debug_list().entries(range).finish()
431 /// A view into a single entry in a map, which may either be vacant or occupied.
433 /// This `enum` is constructed from the [`entry`] method on [`BTreeMap`].
435 /// [`BTreeMap`]: struct.BTreeMap.html
436 /// [`entry`]: struct.BTreeMap.html#method.entry
437 #[stable(feature = "rust1", since = "1.0.0")]
438 pub enum Entry<'a, K: 'a, V: 'a> {
440 #[stable(feature = "rust1", since = "1.0.0")]
441 Vacant(#[stable(feature = "rust1", since = "1.0.0")]
442 VacantEntry<'a, K, V>),
444 /// An occupied entry.
445 #[stable(feature = "rust1", since = "1.0.0")]
446 Occupied(#[stable(feature = "rust1", since = "1.0.0")]
447 OccupiedEntry<'a, K, V>),
450 #[stable(feature= "debug_btree_map", since = "1.12.0")]
451 impl<'a, K: 'a + Debug + Ord, V: 'a + Debug> Debug for Entry<'a, K, V> {
452 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
454 Vacant(ref v) => f.debug_tuple("Entry")
457 Occupied(ref o) => f.debug_tuple("Entry")
464 /// A view into a vacant entry in a `BTreeMap`.
465 /// It is part of the [`Entry`] enum.
467 /// [`Entry`]: enum.Entry.html
468 #[stable(feature = "rust1", since = "1.0.0")]
469 pub struct VacantEntry<'a, K: 'a, V: 'a> {
471 handle: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>,
472 length: &'a mut usize,
474 // Be invariant in `K` and `V`
475 _marker: PhantomData<&'a mut (K, V)>,
478 #[stable(feature= "debug_btree_map", since = "1.12.0")]
479 impl<'a, K: 'a + Debug + Ord, V: 'a> Debug for VacantEntry<'a, K, V> {
480 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
481 f.debug_tuple("VacantEntry")
487 /// A view into an occupied entry in a `BTreeMap`.
488 /// It is part of the [`Entry`] enum.
490 /// [`Entry`]: enum.Entry.html
491 #[stable(feature = "rust1", since = "1.0.0")]
492 pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
493 handle: Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV>,
495 length: &'a mut usize,
497 // Be invariant in `K` and `V`
498 _marker: PhantomData<&'a mut (K, V)>,
501 #[stable(feature= "debug_btree_map", since = "1.12.0")]
502 impl<'a, K: 'a + Debug + Ord, V: 'a + Debug> Debug for OccupiedEntry<'a, K, V> {
503 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
504 f.debug_struct("OccupiedEntry")
505 .field("key", self.key())
506 .field("value", self.get())
511 // An iterator for merging two sorted sequences into one
512 struct MergeIter<K, V, I: Iterator<Item = (K, V)>> {
517 impl<K: Ord, V> BTreeMap<K, V> {
518 /// Makes a new empty BTreeMap with a reasonable choice for B.
525 /// use std::collections::BTreeMap;
527 /// let mut map = BTreeMap::new();
529 /// // entries can now be inserted into the empty map
530 /// map.insert(1, "a");
532 #[stable(feature = "rust1", since = "1.0.0")]
533 pub fn new() -> BTreeMap<K, V> {
535 root: node::Root::shared_empty_root(),
540 /// Clears the map, removing all values.
547 /// use std::collections::BTreeMap;
549 /// let mut a = BTreeMap::new();
550 /// a.insert(1, "a");
552 /// assert!(a.is_empty());
554 #[stable(feature = "rust1", since = "1.0.0")]
555 pub fn clear(&mut self) {
556 *self = BTreeMap::new();
559 /// Returns a reference to the value corresponding to the key.
561 /// The key may be any borrowed form of the map's key type, but the ordering
562 /// on the borrowed form *must* match the ordering on the key type.
569 /// use std::collections::BTreeMap;
571 /// let mut map = BTreeMap::new();
572 /// map.insert(1, "a");
573 /// assert_eq!(map.get(&1), Some(&"a"));
574 /// assert_eq!(map.get(&2), None);
576 #[stable(feature = "rust1", since = "1.0.0")]
577 pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&V>
581 match search::search_tree(self.root.as_ref(), key) {
582 Found(handle) => Some(handle.into_kv().1),
587 /// Returns the key-value pair corresponding to the supplied key.
589 /// The supplied key may be any borrowed form of the map's key type, but the ordering
590 /// on the borrowed form *must* match the ordering on the key type.
595 /// #![feature(map_get_key_value)]
596 /// use std::collections::BTreeMap;
598 /// let mut map = BTreeMap::new();
599 /// map.insert(1, "a");
600 /// assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
601 /// assert_eq!(map.get_key_value(&2), None);
603 #[unstable(feature = "map_get_key_value", issue = "49347")]
604 pub fn get_key_value<Q: ?Sized>(&self, k: &Q) -> Option<(&K, &V)>
608 match search::search_tree(self.root.as_ref(), k) {
609 Found(handle) => Some(handle.into_kv()),
614 /// Returns `true` if the map contains a value for the specified key.
616 /// The key may be any borrowed form of the map's key type, but the ordering
617 /// on the borrowed form *must* match the ordering on the key type.
624 /// use std::collections::BTreeMap;
626 /// let mut map = BTreeMap::new();
627 /// map.insert(1, "a");
628 /// assert_eq!(map.contains_key(&1), true);
629 /// assert_eq!(map.contains_key(&2), false);
631 #[stable(feature = "rust1", since = "1.0.0")]
632 pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
636 self.get(key).is_some()
639 /// Returns a mutable reference to the value corresponding to the key.
641 /// The key may be any borrowed form of the map's key type, but the ordering
642 /// on the borrowed form *must* match the ordering on the key type.
649 /// use std::collections::BTreeMap;
651 /// let mut map = BTreeMap::new();
652 /// map.insert(1, "a");
653 /// if let Some(x) = map.get_mut(&1) {
656 /// assert_eq!(map[&1], "b");
658 // See `get` for implementation notes, this is basically a copy-paste with mut's added
659 #[stable(feature = "rust1", since = "1.0.0")]
660 pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V>
664 match search::search_tree(self.root.as_mut(), key) {
665 Found(handle) => Some(handle.into_kv_mut().1),
670 /// Inserts a key-value pair into the map.
672 /// If the map did not have this key present, `None` is returned.
674 /// If the map did have this key present, the value is updated, and the old
675 /// value is returned. The key is not updated, though; this matters for
676 /// types that can be `==` without being identical. See the [module-level
677 /// documentation] for more.
679 /// [module-level documentation]: index.html#insert-and-complex-keys
686 /// use std::collections::BTreeMap;
688 /// let mut map = BTreeMap::new();
689 /// assert_eq!(map.insert(37, "a"), None);
690 /// assert_eq!(map.is_empty(), false);
692 /// map.insert(37, "b");
693 /// assert_eq!(map.insert(37, "c"), Some("b"));
694 /// assert_eq!(map[&37], "c");
696 #[stable(feature = "rust1", since = "1.0.0")]
697 pub fn insert(&mut self, key: K, value: V) -> Option<V> {
698 match self.entry(key) {
699 Occupied(mut entry) => Some(entry.insert(value)),
707 /// Removes a key from the map, returning the value at the key if the key
708 /// was previously in the map.
710 /// The key may be any borrowed form of the map's key type, but the ordering
711 /// on the borrowed form *must* match the ordering on the key type.
718 /// use std::collections::BTreeMap;
720 /// let mut map = BTreeMap::new();
721 /// map.insert(1, "a");
722 /// assert_eq!(map.remove(&1), Some("a"));
723 /// assert_eq!(map.remove(&1), None);
725 #[stable(feature = "rust1", since = "1.0.0")]
726 pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
730 match search::search_tree(self.root.as_mut(), key) {
734 length: &mut self.length,
735 _marker: PhantomData,
743 /// Moves all elements from `other` into `Self`, leaving `other` empty.
748 /// use std::collections::BTreeMap;
750 /// let mut a = BTreeMap::new();
751 /// a.insert(1, "a");
752 /// a.insert(2, "b");
753 /// a.insert(3, "c");
755 /// let mut b = BTreeMap::new();
756 /// b.insert(3, "d");
757 /// b.insert(4, "e");
758 /// b.insert(5, "f");
760 /// a.append(&mut b);
762 /// assert_eq!(a.len(), 5);
763 /// assert_eq!(b.len(), 0);
765 /// assert_eq!(a[&1], "a");
766 /// assert_eq!(a[&2], "b");
767 /// assert_eq!(a[&3], "d");
768 /// assert_eq!(a[&4], "e");
769 /// assert_eq!(a[&5], "f");
771 #[stable(feature = "btree_append", since = "1.11.0")]
772 pub fn append(&mut self, other: &mut Self) {
773 // Do we have to append anything at all?
774 if other.len() == 0 {
778 // We can just swap `self` and `other` if `self` is empty.
780 mem::swap(self, other);
784 // First, we merge `self` and `other` into a sorted sequence in linear time.
785 let self_iter = mem::replace(self, BTreeMap::new()).into_iter();
786 let other_iter = mem::replace(other, BTreeMap::new()).into_iter();
787 let iter = MergeIter {
788 left: self_iter.peekable(),
789 right: other_iter.peekable(),
792 // Second, we build a tree from the sorted sequence in linear time.
793 self.from_sorted_iter(iter);
794 self.fix_right_edge();
797 /// Constructs a double-ended iterator over a sub-range of elements in the map.
798 /// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will
799 /// yield elements from min (inclusive) to max (exclusive).
800 /// The range may also be entered as `(Bound<T>, Bound<T>)`, so for example
801 /// `range((Excluded(4), Included(10)))` will yield a left-exclusive, right-inclusive
802 /// range from 4 to 10.
806 /// Panics if range `start > end`.
807 /// Panics if range `start == end` and both bounds are `Excluded`.
814 /// use std::collections::BTreeMap;
815 /// use std::ops::Bound::Included;
817 /// let mut map = BTreeMap::new();
818 /// map.insert(3, "a");
819 /// map.insert(5, "b");
820 /// map.insert(8, "c");
821 /// for (&key, &value) in map.range((Included(&4), Included(&8))) {
822 /// println!("{}: {}", key, value);
824 /// assert_eq!(Some((&5, &"b")), map.range(4..).next());
826 #[stable(feature = "btree_range", since = "1.17.0")]
827 pub fn range<T: ?Sized, R>(&self, range: R) -> Range<K, V>
828 where T: Ord, K: Borrow<T>, R: RangeBounds<T>
830 let root1 = self.root.as_ref();
831 let root2 = self.root.as_ref();
832 let (f, b) = range_search(root1, root2, range);
834 Range { front: f, back: b}
837 /// Constructs a mutable double-ended iterator over a sub-range of elements in the map.
838 /// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will
839 /// yield elements from min (inclusive) to max (exclusive).
840 /// The range may also be entered as `(Bound<T>, Bound<T>)`, so for example
841 /// `range((Excluded(4), Included(10)))` will yield a left-exclusive, right-inclusive
842 /// range from 4 to 10.
846 /// Panics if range `start > end`.
847 /// Panics if range `start == end` and both bounds are `Excluded`.
854 /// use std::collections::BTreeMap;
856 /// let mut map: BTreeMap<&str, i32> = ["Alice", "Bob", "Carol", "Cheryl"].iter()
857 /// .map(|&s| (s, 0))
859 /// for (_, balance) in map.range_mut("B".."Cheryl") {
862 /// for (name, balance) in &map {
863 /// println!("{} => {}", name, balance);
866 #[stable(feature = "btree_range", since = "1.17.0")]
867 pub fn range_mut<T: ?Sized, R>(&mut self, range: R) -> RangeMut<K, V>
868 where T: Ord, K: Borrow<T>, R: RangeBounds<T>
870 let root1 = self.root.as_mut();
871 let root2 = unsafe { ptr::read(&root1) };
872 let (f, b) = range_search(root1, root2, range);
877 _marker: PhantomData,
881 /// Gets the given key's corresponding entry in the map for in-place manipulation.
888 /// use std::collections::BTreeMap;
890 /// let mut count: BTreeMap<&str, usize> = BTreeMap::new();
892 /// // count the number of occurrences of letters in the vec
893 /// for x in vec!["a","b","a","c","a","b"] {
894 /// *count.entry(x).or_insert(0) += 1;
897 /// assert_eq!(count["a"], 3);
899 #[stable(feature = "rust1", since = "1.0.0")]
900 pub fn entry(&mut self, key: K) -> Entry<K, V> {
901 // FIXME(@porglezomp) Avoid allocating if we don't insert
902 self.ensure_root_is_owned();
903 match search::search_tree(self.root.as_mut(), &key) {
905 Occupied(OccupiedEntry {
907 length: &mut self.length,
908 _marker: PhantomData,
915 length: &mut self.length,
916 _marker: PhantomData,
922 fn from_sorted_iter<I: Iterator<Item = (K, V)>>(&mut self, iter: I) {
923 self.ensure_root_is_owned();
924 let mut cur_node = last_leaf_edge(self.root.as_mut()).into_node();
925 // Iterate through all key-value pairs, pushing them into nodes at the right level.
926 for (key, value) in iter {
927 // Try to push key-value pair into the current leaf node.
928 if cur_node.len() < node::CAPACITY {
929 cur_node.push(key, value);
931 // No space left, go up and push there.
933 let mut test_node = cur_node.forget_type();
935 match test_node.ascend() {
937 let parent = parent.into_node();
938 if parent.len() < node::CAPACITY {
939 // Found a node with space left, push here.
944 test_node = parent.forget_type();
948 // We are at the top, create a new root node and push there.
949 open_node = node.into_root_mut().push_level();
955 // Push key-value pair and new right subtree.
956 let tree_height = open_node.height() - 1;
957 let mut right_tree = node::Root::new_leaf();
958 for _ in 0..tree_height {
959 right_tree.push_level();
961 open_node.push(key, value, right_tree);
963 // Go down to the right-most leaf again.
964 cur_node = last_leaf_edge(open_node.forget_type()).into_node();
971 fn fix_right_edge(&mut self) {
972 // Handle underfull nodes, start from the top.
973 let mut cur_node = self.root.as_mut();
974 while let Internal(internal) = cur_node.force() {
975 // Check if right-most child is underfull.
976 let mut last_edge = internal.last_edge();
977 let right_child_len = last_edge.reborrow().descend().len();
978 if right_child_len < node::MIN_LEN {
980 let mut last_kv = match last_edge.left_kv() {
982 Err(_) => unreachable!(),
984 last_kv.bulk_steal_left(node::MIN_LEN - right_child_len);
985 last_edge = last_kv.right_edge();
989 cur_node = last_edge.descend();
993 /// Splits the collection into two at the given key. Returns everything after the given key,
994 /// including the key.
1001 /// use std::collections::BTreeMap;
1003 /// let mut a = BTreeMap::new();
1004 /// a.insert(1, "a");
1005 /// a.insert(2, "b");
1006 /// a.insert(3, "c");
1007 /// a.insert(17, "d");
1008 /// a.insert(41, "e");
1010 /// let b = a.split_off(&3);
1012 /// assert_eq!(a.len(), 2);
1013 /// assert_eq!(b.len(), 3);
1015 /// assert_eq!(a[&1], "a");
1016 /// assert_eq!(a[&2], "b");
1018 /// assert_eq!(b[&3], "c");
1019 /// assert_eq!(b[&17], "d");
1020 /// assert_eq!(b[&41], "e");
1022 #[stable(feature = "btree_split_off", since = "1.11.0")]
1023 pub fn split_off<Q: ?Sized + Ord>(&mut self, key: &Q) -> Self
1026 if self.is_empty() {
1030 let total_num = self.len();
1032 let mut right = Self::new();
1033 right.root = node::Root::new_leaf();
1034 for _ in 0..(self.root.as_ref().height()) {
1035 right.root.push_level();
1039 let mut left_node = self.root.as_mut();
1040 let mut right_node = right.root.as_mut();
1043 let mut split_edge = match search::search_node(left_node, key) {
1044 // key is going to the right tree
1045 Found(handle) => handle.left_edge(),
1046 GoDown(handle) => handle,
1049 split_edge.move_suffix(&mut right_node);
1051 match (split_edge.force(), right_node.force()) {
1052 (Internal(edge), Internal(node)) => {
1053 left_node = edge.descend();
1054 right_node = node.first_edge().descend();
1056 (Leaf(_), Leaf(_)) => {
1066 self.fix_right_border();
1067 right.fix_left_border();
1069 if self.root.as_ref().height() < right.root.as_ref().height() {
1070 self.recalc_length();
1071 right.length = total_num - self.len();
1073 right.recalc_length();
1074 self.length = total_num - right.len();
1080 /// Calculates the number of elements if it is incorrect.
1081 fn recalc_length(&mut self) {
1083 node: NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>
1087 let mut res = node.len();
1089 if let Internal(node) = node.force() {
1090 let mut edge = node.first_edge();
1092 res += dfs(edge.reborrow().descend());
1093 match edge.right_kv() {
1095 edge = right_kv.right_edge();
1107 self.length = dfs(self.root.as_ref());
1110 /// Removes empty levels on the top.
1111 fn fix_top(&mut self) {
1114 let node = self.root.as_ref();
1115 if node.height() == 0 || node.len() > 0 {
1119 self.root.pop_level();
1123 fn fix_right_border(&mut self) {
1127 let mut cur_node = self.root.as_mut();
1129 while let Internal(node) = cur_node.force() {
1130 let mut last_kv = node.last_kv();
1132 if last_kv.can_merge() {
1133 cur_node = last_kv.merge().descend();
1135 let right_len = last_kv.reborrow().right_edge().descend().len();
1136 // `MINLEN + 1` to avoid readjust if merge happens on the next level.
1137 if right_len < node::MIN_LEN + 1 {
1138 last_kv.bulk_steal_left(node::MIN_LEN + 1 - right_len);
1140 cur_node = last_kv.right_edge().descend();
1148 /// The symmetric clone of `fix_right_border`.
1149 fn fix_left_border(&mut self) {
1153 let mut cur_node = self.root.as_mut();
1155 while let Internal(node) = cur_node.force() {
1156 let mut first_kv = node.first_kv();
1158 if first_kv.can_merge() {
1159 cur_node = first_kv.merge().descend();
1161 let left_len = first_kv.reborrow().left_edge().descend().len();
1162 if left_len < node::MIN_LEN + 1 {
1163 first_kv.bulk_steal_right(node::MIN_LEN + 1 - left_len);
1165 cur_node = first_kv.left_edge().descend();
1173 /// If the root node is the shared root node, allocate our own node.
1174 fn ensure_root_is_owned(&mut self) {
1175 if self.root.is_shared_root() {
1176 self.root = node::Root::new_leaf();
1181 #[stable(feature = "rust1", since = "1.0.0")]
1182 impl<'a, K: 'a, V: 'a> IntoIterator for &'a BTreeMap<K, V> {
1183 type Item = (&'a K, &'a V);
1184 type IntoIter = Iter<'a, K, V>;
1186 fn into_iter(self) -> Iter<'a, K, V> {
1191 #[stable(feature = "rust1", since = "1.0.0")]
1192 impl<'a, K: 'a, V: 'a> Iterator for Iter<'a, K, V> {
1193 type Item = (&'a K, &'a V);
1195 fn next(&mut self) -> Option<(&'a K, &'a V)> {
1196 if self.length == 0 {
1200 unsafe { Some(self.range.next_unchecked()) }
1204 fn size_hint(&self) -> (usize, Option<usize>) {
1205 (self.length, Some(self.length))
1209 #[stable(feature = "fused", since = "1.26.0")]
1210 impl<'a, K, V> FusedIterator for Iter<'a, K, V> {}
1212 #[stable(feature = "rust1", since = "1.0.0")]
1213 impl<'a, K: 'a, V: 'a> DoubleEndedIterator for Iter<'a, K, V> {
1214 fn next_back(&mut self) -> Option<(&'a K, &'a V)> {
1215 if self.length == 0 {
1219 unsafe { Some(self.range.next_back_unchecked()) }
1224 #[stable(feature = "rust1", since = "1.0.0")]
1225 impl<'a, K: 'a, V: 'a> ExactSizeIterator for Iter<'a, K, V> {
1226 fn len(&self) -> usize {
1231 #[stable(feature = "rust1", since = "1.0.0")]
1232 impl<'a, K, V> Clone for Iter<'a, K, V> {
1233 fn clone(&self) -> Iter<'a, K, V> {
1235 range: self.range.clone(),
1236 length: self.length,
1241 #[stable(feature = "rust1", since = "1.0.0")]
1242 impl<'a, K: 'a, V: 'a> IntoIterator for &'a mut BTreeMap<K, V> {
1243 type Item = (&'a K, &'a mut V);
1244 type IntoIter = IterMut<'a, K, V>;
1246 fn into_iter(self) -> IterMut<'a, K, V> {
1251 #[stable(feature = "rust1", since = "1.0.0")]
1252 impl<'a, K: 'a, V: 'a> Iterator for IterMut<'a, K, V> {
1253 type Item = (&'a K, &'a mut V);
1255 fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
1256 if self.length == 0 {
1260 unsafe { Some(self.range.next_unchecked()) }
1264 fn size_hint(&self) -> (usize, Option<usize>) {
1265 (self.length, Some(self.length))
1269 #[stable(feature = "rust1", since = "1.0.0")]
1270 impl<'a, K: 'a, V: 'a> DoubleEndedIterator for IterMut<'a, K, V> {
1271 fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> {
1272 if self.length == 0 {
1276 unsafe { Some(self.range.next_back_unchecked()) }
1281 #[stable(feature = "rust1", since = "1.0.0")]
1282 impl<'a, K: 'a, V: 'a> ExactSizeIterator for IterMut<'a, K, V> {
1283 fn len(&self) -> usize {
1288 #[stable(feature = "fused", since = "1.26.0")]
1289 impl<'a, K, V> FusedIterator for IterMut<'a, K, V> {}
1291 #[stable(feature = "rust1", since = "1.0.0")]
1292 impl<K, V> IntoIterator for BTreeMap<K, V> {
1294 type IntoIter = IntoIter<K, V>;
1296 fn into_iter(self) -> IntoIter<K, V> {
1297 let root1 = unsafe { ptr::read(&self.root).into_ref() };
1298 let root2 = unsafe { ptr::read(&self.root).into_ref() };
1299 let len = self.length;
1303 front: first_leaf_edge(root1),
1304 back: last_leaf_edge(root2),
1310 #[stable(feature = "btree_drop", since = "1.7.0")]
1311 impl<K, V> Drop for IntoIter<K, V> {
1312 fn drop(&mut self) {
1313 self.for_each(drop);
1315 let leaf_node = ptr::read(&self.front).into_node();
1316 if leaf_node.is_shared_root() {
1320 if let Some(first_parent) = leaf_node.deallocate_and_ascend() {
1321 let mut cur_node = first_parent.into_node();
1322 while let Some(parent) = cur_node.deallocate_and_ascend() {
1323 cur_node = parent.into_node()
1330 #[stable(feature = "rust1", since = "1.0.0")]
1331 impl<K, V> Iterator for IntoIter<K, V> {
1334 fn next(&mut self) -> Option<(K, V)> {
1335 if self.length == 0 {
1341 let handle = unsafe { ptr::read(&self.front) };
1343 let mut cur_handle = match handle.right_kv() {
1345 let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
1346 let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
1347 self.front = kv.right_edge();
1348 return Some((k, v));
1350 Err(last_edge) => unsafe {
1351 unwrap_unchecked(last_edge.into_node().deallocate_and_ascend())
1356 match cur_handle.right_kv() {
1358 let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
1359 let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
1360 self.front = first_leaf_edge(kv.right_edge().descend());
1361 return Some((k, v));
1363 Err(last_edge) => unsafe {
1364 cur_handle = unwrap_unchecked(last_edge.into_node().deallocate_and_ascend());
1370 fn size_hint(&self) -> (usize, Option<usize>) {
1371 (self.length, Some(self.length))
1375 #[stable(feature = "rust1", since = "1.0.0")]
1376 impl<K, V> DoubleEndedIterator for IntoIter<K, V> {
1377 fn next_back(&mut self) -> Option<(K, V)> {
1378 if self.length == 0 {
1384 let handle = unsafe { ptr::read(&self.back) };
1386 let mut cur_handle = match handle.left_kv() {
1388 let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
1389 let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
1390 self.back = kv.left_edge();
1391 return Some((k, v));
1393 Err(last_edge) => unsafe {
1394 unwrap_unchecked(last_edge.into_node().deallocate_and_ascend())
1399 match cur_handle.left_kv() {
1401 let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
1402 let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
1403 self.back = last_leaf_edge(kv.left_edge().descend());
1404 return Some((k, v));
1406 Err(last_edge) => unsafe {
1407 cur_handle = unwrap_unchecked(last_edge.into_node().deallocate_and_ascend());
1414 #[stable(feature = "rust1", since = "1.0.0")]
1415 impl<K, V> ExactSizeIterator for IntoIter<K, V> {
1416 fn len(&self) -> usize {
1421 #[stable(feature = "fused", since = "1.26.0")]
1422 impl<K, V> FusedIterator for IntoIter<K, V> {}
1424 #[stable(feature = "rust1", since = "1.0.0")]
1425 impl<'a, K, V> Iterator for Keys<'a, K, V> {
1428 fn next(&mut self) -> Option<&'a K> {
1429 self.inner.next().map(|(k, _)| k)
1432 fn size_hint(&self) -> (usize, Option<usize>) {
1433 self.inner.size_hint()
1437 #[stable(feature = "rust1", since = "1.0.0")]
1438 impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V> {
1439 fn next_back(&mut self) -> Option<&'a K> {
1440 self.inner.next_back().map(|(k, _)| k)
1444 #[stable(feature = "rust1", since = "1.0.0")]
1445 impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
1446 fn len(&self) -> usize {
1451 #[stable(feature = "fused", since = "1.26.0")]
1452 impl<'a, K, V> FusedIterator for Keys<'a, K, V> {}
1454 #[stable(feature = "rust1", since = "1.0.0")]
1455 impl<'a, K, V> Clone for Keys<'a, K, V> {
1456 fn clone(&self) -> Keys<'a, K, V> {
1457 Keys { inner: self.inner.clone() }
1461 #[stable(feature = "rust1", since = "1.0.0")]
1462 impl<'a, K, V> Iterator for Values<'a, K, V> {
1465 fn next(&mut self) -> Option<&'a V> {
1466 self.inner.next().map(|(_, v)| v)
1469 fn size_hint(&self) -> (usize, Option<usize>) {
1470 self.inner.size_hint()
1474 #[stable(feature = "rust1", since = "1.0.0")]
1475 impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V> {
1476 fn next_back(&mut self) -> Option<&'a V> {
1477 self.inner.next_back().map(|(_, v)| v)
1481 #[stable(feature = "rust1", since = "1.0.0")]
1482 impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
1483 fn len(&self) -> usize {
1488 #[stable(feature = "fused", since = "1.26.0")]
1489 impl<'a, K, V> FusedIterator for Values<'a, K, V> {}
1491 #[stable(feature = "rust1", since = "1.0.0")]
1492 impl<'a, K, V> Clone for Values<'a, K, V> {
1493 fn clone(&self) -> Values<'a, K, V> {
1494 Values { inner: self.inner.clone() }
1498 #[stable(feature = "btree_range", since = "1.17.0")]
1499 impl<'a, K, V> Iterator for Range<'a, K, V> {
1500 type Item = (&'a K, &'a V);
1502 fn next(&mut self) -> Option<(&'a K, &'a V)> {
1503 if self.front == self.back {
1506 unsafe { Some(self.next_unchecked()) }
1511 #[stable(feature = "map_values_mut", since = "1.10.0")]
1512 impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
1513 type Item = &'a mut V;
1515 fn next(&mut self) -> Option<&'a mut V> {
1516 self.inner.next().map(|(_, v)| v)
1519 fn size_hint(&self) -> (usize, Option<usize>) {
1520 self.inner.size_hint()
1524 #[stable(feature = "map_values_mut", since = "1.10.0")]
1525 impl<'a, K, V> DoubleEndedIterator for ValuesMut<'a, K, V> {
1526 fn next_back(&mut self) -> Option<&'a mut V> {
1527 self.inner.next_back().map(|(_, v)| v)
1531 #[stable(feature = "map_values_mut", since = "1.10.0")]
1532 impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V> {
1533 fn len(&self) -> usize {
1538 #[stable(feature = "fused", since = "1.26.0")]
1539 impl<'a, K, V> FusedIterator for ValuesMut<'a, K, V> {}
1542 impl<'a, K, V> Range<'a, K, V> {
1543 unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
1544 let handle = self.front;
1546 let mut cur_handle = match handle.right_kv() {
1548 let ret = kv.into_kv();
1549 self.front = kv.right_edge();
1553 let next_level = last_edge.into_node().ascend().ok();
1554 unwrap_unchecked(next_level)
1559 match cur_handle.right_kv() {
1561 let ret = kv.into_kv();
1562 self.front = first_leaf_edge(kv.right_edge().descend());
1566 let next_level = last_edge.into_node().ascend().ok();
1567 cur_handle = unwrap_unchecked(next_level);
1574 #[stable(feature = "btree_range", since = "1.17.0")]
1575 impl<'a, K, V> DoubleEndedIterator for Range<'a, K, V> {
1576 fn next_back(&mut self) -> Option<(&'a K, &'a V)> {
1577 if self.front == self.back {
1580 unsafe { Some(self.next_back_unchecked()) }
1585 impl<'a, K, V> Range<'a, K, V> {
1586 unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
1587 let handle = self.back;
1589 let mut cur_handle = match handle.left_kv() {
1591 let ret = kv.into_kv();
1592 self.back = kv.left_edge();
1596 let next_level = last_edge.into_node().ascend().ok();
1597 unwrap_unchecked(next_level)
1602 match cur_handle.left_kv() {
1604 let ret = kv.into_kv();
1605 self.back = last_leaf_edge(kv.left_edge().descend());
1609 let next_level = last_edge.into_node().ascend().ok();
1610 cur_handle = unwrap_unchecked(next_level);
1617 #[stable(feature = "fused", since = "1.26.0")]
1618 impl<'a, K, V> FusedIterator for Range<'a, K, V> {}
1620 #[stable(feature = "btree_range", since = "1.17.0")]
1621 impl<'a, K, V> Clone for Range<'a, K, V> {
1622 fn clone(&self) -> Range<'a, K, V> {
1630 #[stable(feature = "btree_range", since = "1.17.0")]
1631 impl<'a, K, V> Iterator for RangeMut<'a, K, V> {
1632 type Item = (&'a K, &'a mut V);
1634 fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
1635 if self.front == self.back {
1638 unsafe { Some(self.next_unchecked()) }
1643 impl<'a, K, V> RangeMut<'a, K, V> {
1644 unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
1645 let handle = ptr::read(&self.front);
1647 let mut cur_handle = match handle.right_kv() {
1649 let (k, v) = ptr::read(&kv).into_kv_mut();
1650 self.front = kv.right_edge();
1654 let next_level = last_edge.into_node().ascend().ok();
1655 unwrap_unchecked(next_level)
1660 match cur_handle.right_kv() {
1662 let (k, v) = ptr::read(&kv).into_kv_mut();
1663 self.front = first_leaf_edge(kv.right_edge().descend());
1667 let next_level = last_edge.into_node().ascend().ok();
1668 cur_handle = unwrap_unchecked(next_level);
1675 #[stable(feature = "btree_range", since = "1.17.0")]
1676 impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V> {
1677 fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> {
1678 if self.front == self.back {
1681 unsafe { Some(self.next_back_unchecked()) }
1686 #[stable(feature = "fused", since = "1.26.0")]
1687 impl<'a, K, V> FusedIterator for RangeMut<'a, K, V> {}
1689 impl<'a, K, V> RangeMut<'a, K, V> {
1690 unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
1691 let handle = ptr::read(&self.back);
1693 let mut cur_handle = match handle.left_kv() {
1695 let (k, v) = ptr::read(&kv).into_kv_mut();
1696 self.back = kv.left_edge();
1700 let next_level = last_edge.into_node().ascend().ok();
1701 unwrap_unchecked(next_level)
1706 match cur_handle.left_kv() {
1708 let (k, v) = ptr::read(&kv).into_kv_mut();
1709 self.back = last_leaf_edge(kv.left_edge().descend());
1713 let next_level = last_edge.into_node().ascend().ok();
1714 cur_handle = unwrap_unchecked(next_level);
1721 #[stable(feature = "rust1", since = "1.0.0")]
1722 impl<K: Ord, V> FromIterator<(K, V)> for BTreeMap<K, V> {
1723 fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> BTreeMap<K, V> {
1724 let mut map = BTreeMap::new();
1730 #[stable(feature = "rust1", since = "1.0.0")]
1731 impl<K: Ord, V> Extend<(K, V)> for BTreeMap<K, V> {
1733 fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
1734 for (k, v) in iter {
1740 #[stable(feature = "extend_ref", since = "1.2.0")]
1741 impl<'a, K: Ord + Copy, V: Copy> Extend<(&'a K, &'a V)> for BTreeMap<K, V> {
1742 fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: I) {
1743 self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
1747 #[stable(feature = "rust1", since = "1.0.0")]
1748 impl<K: Hash, V: Hash> Hash for BTreeMap<K, V> {
1749 fn hash<H: Hasher>(&self, state: &mut H) {
1756 #[stable(feature = "rust1", since = "1.0.0")]
1757 impl<K: Ord, V> Default for BTreeMap<K, V> {
1758 /// Creates an empty `BTreeMap<K, V>`.
1759 fn default() -> BTreeMap<K, V> {
1764 #[stable(feature = "rust1", since = "1.0.0")]
1765 impl<K: PartialEq, V: PartialEq> PartialEq for BTreeMap<K, V> {
1766 fn eq(&self, other: &BTreeMap<K, V>) -> bool {
1767 self.len() == other.len() && self.iter().zip(other).all(|(a, b)| a == b)
1771 #[stable(feature = "rust1", since = "1.0.0")]
1772 impl<K: Eq, V: Eq> Eq for BTreeMap<K, V> {}
1774 #[stable(feature = "rust1", since = "1.0.0")]
1775 impl<K: PartialOrd, V: PartialOrd> PartialOrd for BTreeMap<K, V> {
1777 fn partial_cmp(&self, other: &BTreeMap<K, V>) -> Option<Ordering> {
1778 self.iter().partial_cmp(other.iter())
1782 #[stable(feature = "rust1", since = "1.0.0")]
1783 impl<K: Ord, V: Ord> Ord for BTreeMap<K, V> {
1785 fn cmp(&self, other: &BTreeMap<K, V>) -> Ordering {
1786 self.iter().cmp(other.iter())
1790 #[stable(feature = "rust1", since = "1.0.0")]
1791 impl<K: Debug, V: Debug> Debug for BTreeMap<K, V> {
1792 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1793 f.debug_map().entries(self.iter()).finish()
1797 #[stable(feature = "rust1", since = "1.0.0")]
1798 impl<'a, K: Ord, Q: ?Sized, V> Index<&'a Q> for BTreeMap<K, V>
1804 /// Returns a reference to the value corresponding to the supplied key.
1808 /// Panics if the key is not present in the `BTreeMap`.
1810 fn index(&self, key: &Q) -> &V {
1811 self.get(key).expect("no entry found for key")
1815 fn first_leaf_edge<BorrowType, K, V>
1816 (mut node: NodeRef<BorrowType, K, V, marker::LeafOrInternal>)
1817 -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
1819 match node.force() {
1820 Leaf(leaf) => return leaf.first_edge(),
1821 Internal(internal) => {
1822 node = internal.first_edge().descend();
1828 fn last_leaf_edge<BorrowType, K, V>
1829 (mut node: NodeRef<BorrowType, K, V, marker::LeafOrInternal>)
1830 -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
1832 match node.force() {
1833 Leaf(leaf) => return leaf.last_edge(),
1834 Internal(internal) => {
1835 node = internal.last_edge().descend();
1841 fn range_search<BorrowType, K, V, Q: ?Sized, R: RangeBounds<Q>>(
1842 root1: NodeRef<BorrowType, K, V, marker::LeafOrInternal>,
1843 root2: NodeRef<BorrowType, K, V, marker::LeafOrInternal>,
1845 )-> (Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>,
1846 Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>)
1847 where Q: Ord, K: Borrow<Q>
1849 match (range.start_bound(), range.end_bound()) {
1850 (Excluded(s), Excluded(e)) if s==e =>
1851 panic!("range start and end are equal and excluded in BTreeMap"),
1852 (Included(s), Included(e)) |
1853 (Included(s), Excluded(e)) |
1854 (Excluded(s), Included(e)) |
1855 (Excluded(s), Excluded(e)) if s>e =>
1856 panic!("range start is greater than range end in BTreeMap"),
1860 let mut min_node = root1;
1861 let mut max_node = root2;
1862 let mut min_found = false;
1863 let mut max_found = false;
1864 let mut diverged = false;
1867 let min_edge = match (min_found, range.start_bound()) {
1868 (false, Included(key)) => match search::search_linear(&min_node, key) {
1869 (i, true) => { min_found = true; i },
1872 (false, Excluded(key)) => match search::search_linear(&min_node, key) {
1873 (i, true) => { min_found = true; i+1 },
1876 (_, Unbounded) => 0,
1877 (true, Included(_)) => min_node.keys().len(),
1878 (true, Excluded(_)) => 0,
1881 let max_edge = match (max_found, range.end_bound()) {
1882 (false, Included(key)) => match search::search_linear(&max_node, key) {
1883 (i, true) => { max_found = true; i+1 },
1886 (false, Excluded(key)) => match search::search_linear(&max_node, key) {
1887 (i, true) => { max_found = true; i },
1890 (_, Unbounded) => max_node.keys().len(),
1891 (true, Included(_)) => 0,
1892 (true, Excluded(_)) => max_node.keys().len(),
1896 if max_edge < min_edge { panic!("Ord is ill-defined in BTreeMap range") }
1897 if min_edge != max_edge { diverged = true; }
1900 let front = Handle::new_edge(min_node, min_edge);
1901 let back = Handle::new_edge(max_node, max_edge);
1902 match (front.force(), back.force()) {
1903 (Leaf(f), Leaf(b)) => {
1906 (Internal(min_int), Internal(max_int)) => {
1907 min_node = min_int.descend();
1908 max_node = max_int.descend();
1910 _ => unreachable!("BTreeMap has different depths"),
1916 unsafe fn unwrap_unchecked<T>(val: Option<T>) -> T {
1917 val.unwrap_or_else(|| {
1918 if cfg!(debug_assertions) {
1919 panic!("'unchecked' unwrap on None in BTreeMap");
1921 intrinsics::unreachable();
1926 impl<K, V> BTreeMap<K, V> {
1927 /// Gets an iterator over the entries of the map, sorted by key.
1934 /// use std::collections::BTreeMap;
1936 /// let mut map = BTreeMap::new();
1937 /// map.insert(3, "c");
1938 /// map.insert(2, "b");
1939 /// map.insert(1, "a");
1941 /// for (key, value) in map.iter() {
1942 /// println!("{}: {}", key, value);
1945 /// let (first_key, first_value) = map.iter().next().unwrap();
1946 /// assert_eq!((*first_key, *first_value), (1, "a"));
1948 #[stable(feature = "rust1", since = "1.0.0")]
1949 pub fn iter(&self) -> Iter<K, V> {
1952 front: first_leaf_edge(self.root.as_ref()),
1953 back: last_leaf_edge(self.root.as_ref()),
1955 length: self.length,
1959 /// Gets a mutable iterator over the entries of the map, sorted by key.
1966 /// use std::collections::BTreeMap;
1968 /// let mut map = BTreeMap::new();
1969 /// map.insert("a", 1);
1970 /// map.insert("b", 2);
1971 /// map.insert("c", 3);
1973 /// // add 10 to the value if the key isn't "a"
1974 /// for (key, value) in map.iter_mut() {
1975 /// if key != &"a" {
1980 #[stable(feature = "rust1", since = "1.0.0")]
1981 pub fn iter_mut(&mut self) -> IterMut<K, V> {
1982 let root1 = self.root.as_mut();
1983 let root2 = unsafe { ptr::read(&root1) };
1986 front: first_leaf_edge(root1),
1987 back: last_leaf_edge(root2),
1988 _marker: PhantomData,
1990 length: self.length,
1994 /// Gets an iterator over the keys of the map, in sorted order.
2001 /// use std::collections::BTreeMap;
2003 /// let mut a = BTreeMap::new();
2004 /// a.insert(2, "b");
2005 /// a.insert(1, "a");
2007 /// let keys: Vec<_> = a.keys().cloned().collect();
2008 /// assert_eq!(keys, [1, 2]);
2010 #[stable(feature = "rust1", since = "1.0.0")]
2011 pub fn keys<'a>(&'a self) -> Keys<'a, K, V> {
2012 Keys { inner: self.iter() }
2015 /// Gets an iterator over the values of the map, in order by key.
2022 /// use std::collections::BTreeMap;
2024 /// let mut a = BTreeMap::new();
2025 /// a.insert(1, "hello");
2026 /// a.insert(2, "goodbye");
2028 /// let values: Vec<&str> = a.values().cloned().collect();
2029 /// assert_eq!(values, ["hello", "goodbye"]);
2031 #[stable(feature = "rust1", since = "1.0.0")]
2032 pub fn values<'a>(&'a self) -> Values<'a, K, V> {
2033 Values { inner: self.iter() }
2036 /// Gets a mutable iterator over the values of the map, in order by key.
2043 /// use std::collections::BTreeMap;
2045 /// let mut a = BTreeMap::new();
2046 /// a.insert(1, String::from("hello"));
2047 /// a.insert(2, String::from("goodbye"));
2049 /// for value in a.values_mut() {
2050 /// value.push_str("!");
2053 /// let values: Vec<String> = a.values().cloned().collect();
2054 /// assert_eq!(values, [String::from("hello!"),
2055 /// String::from("goodbye!")]);
2057 #[stable(feature = "map_values_mut", since = "1.10.0")]
2058 pub fn values_mut(&mut self) -> ValuesMut<K, V> {
2059 ValuesMut { inner: self.iter_mut() }
2062 /// Returns the number of elements in the map.
2069 /// use std::collections::BTreeMap;
2071 /// let mut a = BTreeMap::new();
2072 /// assert_eq!(a.len(), 0);
2073 /// a.insert(1, "a");
2074 /// assert_eq!(a.len(), 1);
2076 #[stable(feature = "rust1", since = "1.0.0")]
2077 pub const fn len(&self) -> usize {
2081 /// Returns `true` if the map contains no elements.
2088 /// use std::collections::BTreeMap;
2090 /// let mut a = BTreeMap::new();
2091 /// assert!(a.is_empty());
2092 /// a.insert(1, "a");
2093 /// assert!(!a.is_empty());
2095 #[stable(feature = "rust1", since = "1.0.0")]
2096 pub const fn is_empty(&self) -> bool {
2101 impl<'a, K: Ord, V> Entry<'a, K, V> {
2102 /// Ensures a value is in the entry by inserting the default if empty, and returns
2103 /// a mutable reference to the value in the entry.
2108 /// use std::collections::BTreeMap;
2110 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2111 /// map.entry("poneyland").or_insert(12);
2113 /// assert_eq!(map["poneyland"], 12);
2115 #[stable(feature = "rust1", since = "1.0.0")]
2116 pub fn or_insert(self, default: V) -> &'a mut V {
2118 Occupied(entry) => entry.into_mut(),
2119 Vacant(entry) => entry.insert(default),
2123 /// Ensures a value is in the entry by inserting the result of the default function if empty,
2124 /// and returns a mutable reference to the value in the entry.
2129 /// use std::collections::BTreeMap;
2131 /// let mut map: BTreeMap<&str, String> = BTreeMap::new();
2132 /// let s = "hoho".to_string();
2134 /// map.entry("poneyland").or_insert_with(|| s);
2136 /// assert_eq!(map["poneyland"], "hoho".to_string());
2138 #[stable(feature = "rust1", since = "1.0.0")]
2139 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
2141 Occupied(entry) => entry.into_mut(),
2142 Vacant(entry) => entry.insert(default()),
2146 /// Returns a reference to this entry's key.
2151 /// use std::collections::BTreeMap;
2153 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2154 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2156 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2157 pub fn key(&self) -> &K {
2159 Occupied(ref entry) => entry.key(),
2160 Vacant(ref entry) => entry.key(),
2164 /// Provides in-place mutable access to an occupied entry before any
2165 /// potential inserts into the map.
2170 /// use std::collections::BTreeMap;
2172 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2174 /// map.entry("poneyland")
2175 /// .and_modify(|e| { *e += 1 })
2177 /// assert_eq!(map["poneyland"], 42);
2179 /// map.entry("poneyland")
2180 /// .and_modify(|e| { *e += 1 })
2182 /// assert_eq!(map["poneyland"], 43);
2184 #[stable(feature = "entry_and_modify", since = "1.26.0")]
2185 pub fn and_modify<F>(self, f: F) -> Self
2186 where F: FnOnce(&mut V)
2189 Occupied(mut entry) => {
2193 Vacant(entry) => Vacant(entry),
2198 impl<'a, K: Ord, V: Default> Entry<'a, K, V> {
2199 #[stable(feature = "entry_or_default", since = "1.28.0")]
2200 /// Ensures a value is in the entry by inserting the default value if empty,
2201 /// and returns a mutable reference to the value in the entry.
2207 /// use std::collections::BTreeMap;
2209 /// let mut map: BTreeMap<&str, Option<usize>> = BTreeMap::new();
2210 /// map.entry("poneyland").or_default();
2212 /// assert_eq!(map["poneyland"], None);
2215 pub fn or_default(self) -> &'a mut V {
2217 Occupied(entry) => entry.into_mut(),
2218 Vacant(entry) => entry.insert(Default::default()),
2224 impl<'a, K: Ord, V> VacantEntry<'a, K, V> {
2225 /// Gets a reference to the key that would be used when inserting a value
2226 /// through the VacantEntry.
2231 /// use std::collections::BTreeMap;
2233 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2234 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2236 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2237 pub fn key(&self) -> &K {
2241 /// Take ownership of the key.
2246 /// use std::collections::BTreeMap;
2247 /// use std::collections::btree_map::Entry;
2249 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2251 /// if let Entry::Vacant(v) = map.entry("poneyland") {
2255 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2256 pub fn into_key(self) -> K {
2260 /// Sets the value of the entry with the `VacantEntry`'s key,
2261 /// and returns a mutable reference to it.
2266 /// use std::collections::BTreeMap;
2268 /// let mut count: BTreeMap<&str, usize> = BTreeMap::new();
2270 /// // count the number of occurrences of letters in the vec
2271 /// for x in vec!["a","b","a","c","a","b"] {
2272 /// *count.entry(x).or_insert(0) += 1;
2275 /// assert_eq!(count["a"], 3);
2277 #[stable(feature = "rust1", since = "1.0.0")]
2278 pub fn insert(self, value: V) -> &'a mut V {
2287 let mut cur_parent = match self.handle.insert(self.key, value) {
2288 (Fit(handle), _) => return handle.into_kv_mut().1,
2289 (Split(left, k, v, right), ptr) => {
2294 left.ascend().map_err(|n| n.into_root_mut())
2301 match parent.insert(ins_k, ins_v, ins_edge) {
2302 Fit(_) => return unsafe { &mut *out_ptr },
2303 Split(left, k, v, right) => {
2307 cur_parent = left.ascend().map_err(|n| n.into_root_mut());
2312 root.push_level().push(ins_k, ins_v, ins_edge);
2313 return unsafe { &mut *out_ptr };
2320 impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
2321 /// Gets a reference to the key in the entry.
2326 /// use std::collections::BTreeMap;
2328 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2329 /// map.entry("poneyland").or_insert(12);
2330 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2332 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2333 pub fn key(&self) -> &K {
2334 self.handle.reborrow().into_kv().0
2337 /// Take ownership of the key and value from the map.
2342 /// use std::collections::BTreeMap;
2343 /// use std::collections::btree_map::Entry;
2345 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2346 /// map.entry("poneyland").or_insert(12);
2348 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2349 /// // We delete the entry from the map.
2350 /// o.remove_entry();
2353 /// // If now try to get the value, it will panic:
2354 /// // println!("{}", map["poneyland"]);
2356 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2357 pub fn remove_entry(self) -> (K, V) {
2361 /// Gets a reference to the value in the entry.
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 /// assert_eq!(o.get(), &12);
2376 #[stable(feature = "rust1", since = "1.0.0")]
2377 pub fn get(&self) -> &V {
2378 self.handle.reborrow().into_kv().1
2381 /// Gets a mutable reference to the value in the entry.
2383 /// If you need a reference to the `OccupiedEntry` which may outlive the
2384 /// destruction of the `Entry` value, see [`into_mut`].
2386 /// [`into_mut`]: #method.into_mut
2391 /// use std::collections::BTreeMap;
2392 /// use std::collections::btree_map::Entry;
2394 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2395 /// map.entry("poneyland").or_insert(12);
2397 /// assert_eq!(map["poneyland"], 12);
2398 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2399 /// *o.get_mut() += 10;
2400 /// assert_eq!(*o.get(), 22);
2402 /// // We can use the same Entry multiple times.
2403 /// *o.get_mut() += 2;
2405 /// assert_eq!(map["poneyland"], 24);
2407 #[stable(feature = "rust1", since = "1.0.0")]
2408 pub fn get_mut(&mut self) -> &mut V {
2409 self.handle.kv_mut().1
2412 /// Converts the entry into a mutable reference to its value.
2414 /// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].
2416 /// [`get_mut`]: #method.get_mut
2421 /// use std::collections::BTreeMap;
2422 /// use std::collections::btree_map::Entry;
2424 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2425 /// map.entry("poneyland").or_insert(12);
2427 /// assert_eq!(map["poneyland"], 12);
2428 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2429 /// *o.into_mut() += 10;
2431 /// assert_eq!(map["poneyland"], 22);
2433 #[stable(feature = "rust1", since = "1.0.0")]
2434 pub fn into_mut(self) -> &'a mut V {
2435 self.handle.into_kv_mut().1
2438 /// Sets the value of the entry with the `OccupiedEntry`'s key,
2439 /// and returns the entry's old value.
2444 /// use std::collections::BTreeMap;
2445 /// use std::collections::btree_map::Entry;
2447 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2448 /// map.entry("poneyland").or_insert(12);
2450 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2451 /// assert_eq!(o.insert(15), 12);
2453 /// assert_eq!(map["poneyland"], 15);
2455 #[stable(feature = "rust1", since = "1.0.0")]
2456 pub fn insert(&mut self, value: V) -> V {
2457 mem::replace(self.get_mut(), value)
2460 /// Takes the value of the entry out of the map, and returns it.
2465 /// use std::collections::BTreeMap;
2466 /// use std::collections::btree_map::Entry;
2468 /// let mut map: BTreeMap<&str, usize> = BTreeMap::new();
2469 /// map.entry("poneyland").or_insert(12);
2471 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2472 /// assert_eq!(o.remove(), 12);
2474 /// // If we try to get "poneyland"'s value, it'll panic:
2475 /// // println!("{}", map["poneyland"]);
2477 #[stable(feature = "rust1", since = "1.0.0")]
2478 pub fn remove(self) -> V {
2482 fn remove_kv(self) -> (K, V) {
2485 let (small_leaf, old_key, old_val) = match self.handle.force() {
2487 let (hole, old_key, old_val) = leaf.remove();
2488 (hole.into_node(), old_key, old_val)
2490 Internal(mut internal) => {
2491 let key_loc = internal.kv_mut().0 as *mut K;
2492 let val_loc = internal.kv_mut().1 as *mut V;
2494 let to_remove = first_leaf_edge(internal.right_edge().descend()).right_kv().ok();
2495 let to_remove = unsafe { unwrap_unchecked(to_remove) };
2497 let (hole, key, val) = to_remove.remove();
2499 let old_key = unsafe { mem::replace(&mut *key_loc, key) };
2500 let old_val = unsafe { mem::replace(&mut *val_loc, val) };
2502 (hole.into_node(), old_key, old_val)
2507 let mut cur_node = small_leaf.forget_type();
2508 while cur_node.len() < node::CAPACITY / 2 {
2509 match handle_underfull_node(cur_node) {
2511 EmptyParent(_) => unreachable!(),
2513 if parent.len() == 0 {
2514 // We must be at the root
2515 parent.into_root_mut().pop_level();
2518 cur_node = parent.forget_type();
2529 enum UnderflowResult<'a, K, V> {
2531 EmptyParent(NodeRef<marker::Mut<'a>, K, V, marker::Internal>),
2532 Merged(NodeRef<marker::Mut<'a>, K, V, marker::Internal>),
2533 Stole(NodeRef<marker::Mut<'a>, K, V, marker::Internal>),
2536 fn handle_underfull_node<'a, K, V>(node: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>)
2537 -> UnderflowResult<'a, K, V> {
2538 let parent = if let Ok(parent) = node.ascend() {
2544 let (is_left, mut handle) = match parent.left_kv() {
2545 Ok(left) => (true, left),
2547 match parent.right_kv() {
2548 Ok(right) => (false, right),
2550 return EmptyParent(parent.into_node());
2556 if handle.can_merge() {
2557 Merged(handle.merge().into_node())
2560 handle.steal_left();
2562 handle.steal_right();
2564 Stole(handle.into_node())
2568 impl<K: Ord, V, I: Iterator<Item = (K, V)>> Iterator for MergeIter<K, V, I> {
2571 fn next(&mut self) -> Option<(K, V)> {
2572 let res = match (self.left.peek(), self.right.peek()) {
2573 (Some(&(ref left_key, _)), Some(&(ref right_key, _))) => left_key.cmp(right_key),
2574 (Some(_), None) => Ordering::Less,
2575 (None, Some(_)) => Ordering::Greater,
2576 (None, None) => return None,
2579 // Check which elements comes first and only advance the corresponding iterator.
2580 // If two keys are equal, take the value from `right`.
2582 Ordering::Less => self.left.next(),
2583 Ordering::Greater => self.right.next(),
2584 Ordering::Equal => {