1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
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 // This implementation is largely based on the high-level description and analysis of B-Trees
12 // found in *Open Data Structures* (ODS). Although our implementation does not use any of
13 // the source found in ODS, if one wishes to review the high-level design of this structure, it
14 // can be freely downloaded at http://opendatastructures.org/. Its contents are as of this
15 // writing (August 2014) freely licensed under the following Creative Commons Attribution
16 // License: [CC BY 2.5 CA](http://creativecommons.org/licenses/by/2.5/ca/).
22 use core::cmp::Ordering;
24 use core::hash::{Hash, Hasher};
25 use core::iter::{Map, FromIterator};
27 use core::{iter, fmt, mem, usize};
28 use Bound::{self, Included, Excluded, Unbounded};
31 use vec_deque::VecDeque;
33 use self::Continuation::{Continue, Finished};
35 use super::node::ForceResult::{Leaf, Internal};
36 use super::node::TraversalItem::{self, Elem, Edge};
37 use super::node::{Traversal, MutTraversal, MoveTraversal};
38 use super::node::{self, Node, Found, GoDown};
40 /// A map based on a B-Tree.
42 /// B-Trees represent a fundamental compromise between cache-efficiency and actually minimizing
43 /// the amount of work performed in a search. In theory, a binary search tree (BST) is the optimal
44 /// choice for a sorted map, as a perfectly balanced BST performs the theoretical minimum amount of
45 /// comparisons necessary to find an element (log<sub>2</sub>n). However, in practice the way this
46 /// is done is *very* inefficient for modern computer architectures. In particular, every element
47 /// is stored in its own individually heap-allocated node. This means that every single insertion
48 /// triggers a heap-allocation, and every single comparison should be a cache-miss. Since these
49 /// are both notably expensive things to do in practice, we are forced to at very least reconsider
52 /// A B-Tree instead makes each node contain B-1 to 2B-1 elements in a contiguous array. By doing
53 /// this, we reduce the number of allocations by a factor of B, and improve cache efficiency in
54 /// searches. However, this does mean that searches will have to do *more* comparisons on average.
55 /// The precise number of comparisons depends on the node search strategy used. For optimal cache
56 /// efficiency, one could search the nodes linearly. For optimal comparisons, one could search
57 /// the node using binary search. As a compromise, one could also perform a linear search
58 /// that initially only checks every i<sup>th</sup> element for some choice of i.
60 /// Currently, our implementation simply performs naive linear search. This provides excellent
61 /// performance on *small* nodes of elements which are cheap to compare. However in the future we
62 /// would like to further explore choosing the optimal search strategy based on the choice of B,
63 /// and possibly other factors. Using linear search, searching for a random element is expected
64 /// to take O(B log<sub>B</sub>n) comparisons, which is generally worse than a BST. In practice,
65 /// however, performance is excellent.
67 /// It is a logic error for a key to be modified in such a way that the key's ordering relative to
68 /// any other key, as determined by the `Ord` trait, changes while it is in the map. This is
69 /// normally only possible through `Cell`, `RefCell`, global state, I/O, or unsafe code.
71 #[stable(feature = "rust1", since = "1.0.0")]
72 pub struct BTreeMap<K, V> {
79 /// An abstract base over-which all other BTree iterators are built.
82 traversals: VecDeque<T>,
86 /// An iterator over a BTreeMap's entries.
87 #[stable(feature = "rust1", since = "1.0.0")]
88 pub struct Iter<'a, K: 'a, V: 'a> {
89 inner: AbsIter<Traversal<'a, K, V>>
92 /// A mutable iterator over a BTreeMap's entries.
93 #[stable(feature = "rust1", since = "1.0.0")]
94 pub struct IterMut<'a, K: 'a, V: 'a> {
95 inner: AbsIter<MutTraversal<'a, K, V>>
98 /// An owning iterator over a BTreeMap's entries.
99 #[stable(feature = "rust1", since = "1.0.0")]
100 pub struct IntoIter<K, V> {
101 inner: AbsIter<MoveTraversal<K, V>>
104 /// An iterator over a BTreeMap's keys.
105 #[stable(feature = "rust1", since = "1.0.0")]
106 pub struct Keys<'a, K: 'a, V: 'a> {
107 inner: Map<Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a K>
110 /// An iterator over a BTreeMap's values.
111 #[stable(feature = "rust1", since = "1.0.0")]
112 pub struct Values<'a, K: 'a, V: 'a> {
113 inner: Map<Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a V>
116 /// An iterator over a sub-range of BTreeMap's entries.
117 pub struct Range<'a, K: 'a, V: 'a> {
118 inner: AbsIter<Traversal<'a, K, V>>
121 /// A mutable iterator over a sub-range of BTreeMap's entries.
122 pub struct RangeMut<'a, K: 'a, V: 'a> {
123 inner: AbsIter<MutTraversal<'a, K, V>>
126 /// A view into a single entry in a map, which may either be vacant or occupied.
127 #[stable(feature = "rust1", since = "1.0.0")]
128 pub enum Entry<'a, K:'a, V:'a> {
130 #[stable(feature = "rust1", since = "1.0.0")]
131 Vacant(VacantEntry<'a, K, V>),
133 /// An occupied Entry
134 #[stable(feature = "rust1", since = "1.0.0")]
135 Occupied(OccupiedEntry<'a, K, V>),
139 #[stable(feature = "rust1", since = "1.0.0")]
140 pub struct VacantEntry<'a, K:'a, V:'a> {
142 stack: stack::SearchStack<'a, K, V, node::handle::Edge, node::handle::Leaf>,
145 /// An occupied Entry.
146 #[stable(feature = "rust1", since = "1.0.0")]
147 pub struct OccupiedEntry<'a, K:'a, V:'a> {
148 stack: stack::SearchStack<'a, K, V, node::handle::KV, node::handle::LeafOrInternal>,
151 impl<K: Ord, V> BTreeMap<K, V> {
152 /// Makes a new empty BTreeMap with a reasonable choice for B.
153 #[stable(feature = "rust1", since = "1.0.0")]
154 pub fn new() -> BTreeMap<K, V> {
155 //FIXME(Gankro): Tune this as a function of size_of<K/V>?
159 /// Makes a new empty BTreeMap with the given B.
161 /// B cannot be less than 2.
162 pub fn with_b(b: usize) -> BTreeMap<K, V> {
163 assert!(b > 1, "B must be greater than 1");
167 root: Node::make_leaf_root(b),
172 /// Clears the map, removing all values.
177 /// use std::collections::BTreeMap;
179 /// let mut a = BTreeMap::new();
180 /// a.insert(1, "a");
182 /// assert!(a.is_empty());
184 #[stable(feature = "rust1", since = "1.0.0")]
185 pub fn clear(&mut self) {
187 // avoid recursive destructors by manually traversing the tree
188 for _ in mem::replace(self, BTreeMap::with_b(b)) {};
191 // Searching in a B-Tree is pretty straightforward.
193 // Start at the root. Try to find the key in the current node. If we find it, return it.
194 // If it's not in there, follow the edge *before* the smallest key larger than
195 // the search key. If no such key exists (they're *all* smaller), then just take the last
196 // edge in the node. If we're in a leaf and we don't find our key, then it's not
199 /// Returns a reference to the value corresponding to the key.
201 /// The key may be any borrowed form of the map's key type, but the ordering
202 /// on the borrowed form *must* match the ordering on the key type.
207 /// use std::collections::BTreeMap;
209 /// let mut map = BTreeMap::new();
210 /// map.insert(1, "a");
211 /// assert_eq!(map.get(&1), Some(&"a"));
212 /// assert_eq!(map.get(&2), None);
214 #[stable(feature = "rust1", since = "1.0.0")]
215 pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&V> where K: Borrow<Q>, Q: Ord {
216 let mut cur_node = &self.root;
218 match Node::search(cur_node, key) {
219 Found(handle) => return Some(handle.into_kv().1),
220 GoDown(handle) => match handle.force() {
221 Leaf(_) => return None,
222 Internal(internal_handle) => {
223 cur_node = internal_handle.into_edge();
231 /// Returns true if the map contains a value for the specified key.
233 /// The key may be any borrowed form of the map's key type, but the ordering
234 /// on the borrowed form *must* match the ordering on the key type.
239 /// use std::collections::BTreeMap;
241 /// let mut map = BTreeMap::new();
242 /// map.insert(1, "a");
243 /// assert_eq!(map.contains_key(&1), true);
244 /// assert_eq!(map.contains_key(&2), false);
246 #[stable(feature = "rust1", since = "1.0.0")]
247 pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool where K: Borrow<Q>, Q: Ord {
248 self.get(key).is_some()
251 /// Returns a mutable reference to the value corresponding to the key.
253 /// The key may be any borrowed form of the map's key type, but the ordering
254 /// on the borrowed form *must* match the ordering on the key type.
259 /// use std::collections::BTreeMap;
261 /// let mut map = BTreeMap::new();
262 /// map.insert(1, "a");
263 /// if let Some(x) = map.get_mut(&1) {
266 /// assert_eq!(map[&1], "b");
268 // See `get` for implementation notes, this is basically a copy-paste with mut's added
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V> where K: Borrow<Q>, Q: Ord {
271 // temp_node is a Borrowck hack for having a mutable value outlive a loop iteration
272 let mut temp_node = &mut self.root;
274 let cur_node = temp_node;
275 match Node::search(cur_node, key) {
276 Found(handle) => return Some(handle.into_kv_mut().1),
277 GoDown(handle) => match handle.force() {
278 Leaf(_) => return None,
279 Internal(internal_handle) => {
280 temp_node = internal_handle.into_edge_mut();
288 // Insertion in a B-Tree is a bit complicated.
290 // First we do the same kind of search described in `find`. But we need to maintain a stack of
291 // all the nodes/edges in our search path. If we find a match for the key we're trying to
292 // insert, just swap the vals and return the old ones. However, when we bottom out in a leaf,
293 // we attempt to insert our key-value pair at the same location we would want to follow another
296 // If the node has room, then this is done in the obvious way by shifting elements. However,
297 // if the node itself is full, we split node into two, and give its median key-value
298 // pair to its parent to insert the new node with. Of course, the parent may also be
299 // full, and insertion can propagate until we reach the root. If we reach the root, and
300 // it is *also* full, then we split the root and place the two nodes under a newly made root.
302 // Note that we subtly deviate from Open Data Structures in our implementation of split.
303 // ODS describes inserting into the node *regardless* of its capacity, and then
304 // splitting *afterwards* if it happens to be overfull. However, this is inefficient.
305 // Instead, we split beforehand, and then insert the key-value pair into the appropriate
306 // result node. This has two consequences:
308 // 1) While ODS produces a left node of size B-1, and a right node of size B,
309 // we may potentially reverse this. However, this shouldn't effect the analysis.
311 // 2) While ODS may potentially return the pair we *just* inserted after
312 // the split, we will never do this. Again, this shouldn't effect the analysis.
314 /// Inserts a key-value pair into the map. If the key already had a value
315 /// present in the map, that value is returned. Otherwise, `None` is returned.
320 /// use std::collections::BTreeMap;
322 /// let mut map = BTreeMap::new();
323 /// assert_eq!(map.insert(37, "a"), None);
324 /// assert_eq!(map.is_empty(), false);
326 /// map.insert(37, "b");
327 /// assert_eq!(map.insert(37, "c"), Some("b"));
328 /// assert_eq!(map[&37], "c");
330 #[stable(feature = "rust1", since = "1.0.0")]
331 pub fn insert(&mut self, mut key: K, mut value: V) -> Option<V> {
332 // This is a stack of rawptrs to nodes paired with indices, respectively
333 // representing the nodes and edges of our search path. We have to store rawptrs
334 // because as far as Rust is concerned, we can mutate aliased data with such a
335 // stack. It is of course correct, but what it doesn't know is that we will only
336 // be popping and using these ptrs one at a time in child-to-parent order. The alternative
337 // to doing this is to take the Nodes from their parents. This actually makes
338 // borrowck *really* happy and everything is pretty smooth. However, this creates
339 // *tons* of pointless writes, and requires us to always walk all the way back to
340 // the root after an insertion, even if we only needed to change a leaf. Therefore,
341 // we accept this potential unsafety and complexity in the name of performance.
343 // Regardless, the actual dangerous logic is completely abstracted away from BTreeMap
344 // by the stack module. All it can do is immutably read nodes, and ask the search stack
345 // to proceed down some edge by index. This makes the search logic we'll be reusing in a
346 // few different methods much neater, and of course drastically improves safety.
347 let mut stack = stack::PartialSearchStack::new(self);
350 let result = stack.with(move |pusher, node| {
351 // Same basic logic as found in `find`, but with PartialSearchStack mediating the
352 // actual nodes for us
353 match Node::search(node, &key) {
354 Found(mut handle) => {
355 // Perfect match, swap the values and return the old one
356 mem::swap(handle.val_mut(), &mut value);
357 Finished(Some(value))
360 // We need to keep searching, try to get the search stack
361 // to go down further
362 match handle.force() {
363 Leaf(leaf_handle) => {
364 // We've reached a leaf, perform the insertion here
365 pusher.seal(leaf_handle).insert(key, value);
368 Internal(internal_handle) => {
369 // We've found the subtree to insert this key/value pair in,
371 Continue((pusher.push(internal_handle), key, value))
378 Finished(ret) => return ret,
379 Continue((new_stack, renewed_key, renewed_val)) => {
388 // Deletion is the most complicated operation for a B-Tree.
390 // First we do the same kind of search described in
391 // `find`. But we need to maintain a stack of all the nodes/edges in our search path.
392 // If we don't find the key, then we just return `None` and do nothing. If we do find the
393 // key, we perform two operations: remove the item, and then possibly handle underflow.
395 // # removing the item
396 // If the node is a leaf, we just remove the item, and shift
397 // any items after it back to fill the hole.
399 // If the node is an internal node, we *swap* the item with the smallest item in
400 // in its right subtree (which must reside in a leaf), and then revert to the leaf
403 // # handling underflow
404 // After removing an item, there may be too few items in the node. We want nodes
405 // to be mostly full for efficiency, although we make an exception for the root, which
406 // may have as few as one item. If this is the case, we may first try to steal
407 // an item from our left or right neighbour.
409 // To steal from the left (right) neighbour,
410 // we take the largest (smallest) item and child from it. We then swap the taken item
411 // with the item in their mutual parent that separates them, and then insert the
412 // parent's item and the taken child into the first (last) index of the underflowed node.
414 // However, stealing has the possibility of underflowing our neighbour. If this is the
415 // case, we instead *merge* with our neighbour. This of course reduces the number of
416 // children in the parent. Therefore, we also steal the item that separates the now
417 // merged nodes, and insert it into the merged node.
419 // Merging may cause the parent to underflow. If this is the case, then we must repeat
420 // the underflow handling process on the parent. If merging merges the last two children
421 // of the root, then we replace the root with the merged node.
423 /// Removes a key from the map, returning the value at the key if the key
424 /// was previously in the map.
426 /// The key may be any borrowed form of the map's key type, but the ordering
427 /// on the borrowed form *must* match the ordering on the key type.
432 /// use std::collections::BTreeMap;
434 /// let mut map = BTreeMap::new();
435 /// map.insert(1, "a");
436 /// assert_eq!(map.remove(&1), Some("a"));
437 /// assert_eq!(map.remove(&1), None);
439 #[stable(feature = "rust1", since = "1.0.0")]
440 pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V> where K: Borrow<Q>, Q: Ord {
441 // See `swap` for a more thorough description of the stuff going on in here
442 let mut stack = stack::PartialSearchStack::new(self);
444 let result = stack.with(move |pusher, node| {
445 match Node::search(node, key) {
447 // Perfect match. Terminate the stack here, and remove the entry
448 Finished(Some(pusher.seal(handle).remove()))
451 // We need to keep searching, try to go down the next edge
452 match handle.force() {
453 // We're at a leaf; the key isn't in here
454 Leaf(_) => Finished(None),
455 Internal(internal_handle) => Continue(pusher.push(internal_handle))
461 Finished(ret) => return ret,
462 Continue(new_stack) => stack = new_stack
468 #[stable(feature = "rust1", since = "1.0.0")]
469 impl<K, V> IntoIterator for BTreeMap<K, V> {
471 type IntoIter = IntoIter<K, V>;
473 /// Gets an owning iterator over the entries of the map.
478 /// use std::collections::BTreeMap;
480 /// let mut map = BTreeMap::new();
481 /// map.insert(1, "a");
482 /// map.insert(2, "b");
483 /// map.insert(3, "c");
485 /// for (key, value) in map.into_iter() {
486 /// println!("{}: {}", key, value);
489 fn into_iter(self) -> IntoIter<K, V> {
490 let len = self.len();
491 let mut lca = VecDeque::new();
492 lca.push_back(Traverse::traverse(self.root));
502 #[stable(feature = "rust1", since = "1.0.0")]
503 impl<'a, K, V> IntoIterator for &'a BTreeMap<K, V> {
504 type Item = (&'a K, &'a V);
505 type IntoIter = Iter<'a, K, V>;
507 fn into_iter(self) -> Iter<'a, K, V> {
512 #[stable(feature = "rust1", since = "1.0.0")]
513 impl<'a, K, V> IntoIterator for &'a mut BTreeMap<K, V> {
514 type Item = (&'a K, &'a mut V);
515 type IntoIter = IterMut<'a, K, V>;
517 fn into_iter(mut self) -> IterMut<'a, K, V> {
522 /// A helper enum useful for deciding whether to continue a loop since we can't
523 /// return from a closure
524 enum Continuation<A, B> {
529 /// The stack module provides a safe interface for constructing and manipulating a stack of ptrs
530 /// to nodes. By using this module much better safety guarantees can be made, and more search
531 /// boilerplate gets cut out.
533 use core::prelude::*;
536 use core::ops::{Deref, DerefMut};
538 use super::super::node::{self, Node, Fit, Split, Internal, Leaf};
539 use super::super::node::handle;
542 struct InvariantLifetime<'id>(
543 marker::PhantomData<::core::cell::Cell<&'id ()>>);
545 impl<'id> InvariantLifetime<'id> {
546 fn new() -> InvariantLifetime<'id> {
547 InvariantLifetime(marker::PhantomData)
551 /// A generic mutable reference, identical to `&mut` except for the fact that its lifetime
552 /// parameter is invariant. This means that wherever an `IdRef` is expected, only an `IdRef`
553 /// with the exact requested lifetime can be used. This is in contrast to normal references,
554 /// where `&'static` can be used in any function expecting any lifetime reference.
555 pub struct IdRef<'id, T: 'id> {
557 _marker: InvariantLifetime<'id>,
560 impl<'id, T> Deref for IdRef<'id, T> {
563 fn deref(&self) -> &T {
568 impl<'id, T> DerefMut for IdRef<'id, T> {
569 fn deref_mut(&mut self) -> &mut T {
574 type StackItem<K, V> = node::Handle<*mut Node<K, V>, handle::Edge, handle::Internal>;
575 type Stack<K, V> = Vec<StackItem<K, V>>;
577 /// A `PartialSearchStack` handles the construction of a search stack.
578 pub struct PartialSearchStack<'a, K:'a, V:'a> {
579 map: &'a mut BTreeMap<K, V>,
581 next: *mut Node<K, V>,
584 /// A `SearchStack` represents a full path to an element or an edge of interest. It provides
585 /// methods depending on the type of what the path points to for removing an element, inserting
586 /// a new element, and manipulating to element at the top of the stack.
587 pub struct SearchStack<'a, K:'a, V:'a, Type, NodeType> {
588 map: &'a mut BTreeMap<K, V>,
590 top: node::Handle<*mut Node<K, V>, Type, NodeType>,
593 /// A `PartialSearchStack` that doesn't hold a a reference to the next node, and is just
594 /// just waiting for a `Handle` to that next node to be pushed. See `PartialSearchStack::with`
595 /// for more details.
596 pub struct Pusher<'id, 'a, K:'a, V:'a> {
597 map: &'a mut BTreeMap<K, V>,
599 _marker: InvariantLifetime<'id>,
602 impl<'a, K, V> PartialSearchStack<'a, K, V> {
603 /// Creates a new PartialSearchStack from a BTreeMap by initializing the stack with the
604 /// root of the tree.
605 pub fn new(map: &'a mut BTreeMap<K, V>) -> PartialSearchStack<'a, K, V> {
606 let depth = map.depth;
609 next: &mut map.root as *mut _,
611 stack: Vec::with_capacity(depth),
615 /// Breaks up the stack into a `Pusher` and the next `Node`, allowing the given closure
616 /// to interact with, search, and finally push the `Node` onto the stack. The passed in
617 /// closure must be polymorphic on the `'id` lifetime parameter, as this statically
618 /// ensures that only `Handle`s from the correct `Node` can be pushed.
620 /// The reason this works is that the `Pusher` has an `'id` parameter, and will only accept
621 /// handles with the same `'id`. The closure could only get references with that lifetime
622 /// through its arguments or through some other `IdRef` that it has lying around. However,
623 /// no other `IdRef` could possibly work - because the `'id` is held in an invariant
624 /// parameter, it would need to have precisely the correct lifetime, which would mean that
625 /// at least one of the calls to `with` wouldn't be properly polymorphic, wanting a
626 /// specific lifetime instead of the one that `with` chooses to give it.
628 /// See also Haskell's `ST` monad, which uses a similar trick.
629 pub fn with<T, F: for<'id> FnOnce(Pusher<'id, 'a, K, V>,
630 IdRef<'id, Node<K, V>>) -> T>(self, closure: F) -> T {
631 let pusher = Pusher {
634 _marker: InvariantLifetime::new(),
637 inner: unsafe { &mut *self.next },
638 _marker: InvariantLifetime::new(),
641 closure(pusher, node)
645 impl<'id, 'a, K, V> Pusher<'id, 'a, K, V> {
646 /// Pushes the requested child of the stack's current top on top of the stack. If the child
647 /// exists, then a new PartialSearchStack is yielded. Otherwise, a VacantSearchStack is
649 pub fn push(mut self, mut edge: node::Handle<IdRef<'id, Node<K, V>>,
652 -> PartialSearchStack<'a, K, V> {
653 self.stack.push(edge.as_raw());
657 next: edge.edge_mut() as *mut _,
661 /// Converts the PartialSearchStack into a SearchStack.
662 pub fn seal<Type, NodeType>
663 (self, mut handle: node::Handle<IdRef<'id, Node<K, V>>, Type, NodeType>)
664 -> SearchStack<'a, K, V, Type, NodeType> {
668 top: handle.as_raw(),
673 impl<'a, K, V, NodeType> SearchStack<'a, K, V, handle::KV, NodeType> {
674 /// Gets a reference to the value the stack points to.
675 pub fn peek(&self) -> &V {
676 unsafe { self.top.from_raw().into_kv().1 }
679 /// Gets a mutable reference to the value the stack points to.
680 pub fn peek_mut(&mut self) -> &mut V {
681 unsafe { self.top.from_raw_mut().into_kv_mut().1 }
684 /// Converts the stack into a mutable reference to the value it points to, with a lifetime
685 /// tied to the original tree.
686 pub fn into_top(mut self) -> &'a mut V {
688 mem::copy_mut_lifetime(
690 self.top.from_raw_mut().val_mut()
696 impl<'a, K, V> SearchStack<'a, K, V, handle::KV, handle::Leaf> {
697 /// Removes the key and value in the top element of the stack, then handles underflows as
698 /// described in BTree's pop function.
699 fn remove_leaf(mut self) -> V {
700 self.map.length -= 1;
702 // Remove the key-value pair from the leaf that this search stack points to.
703 // Then, note if the leaf is underfull, and promptly forget the leaf and its ptr
704 // to avoid ownership issues.
705 let (value, mut underflow) = unsafe {
706 let (_, value) = self.top.from_raw_mut().remove_as_leaf();
707 let underflow = self.top.from_raw().node().is_underfull();
712 match self.stack.pop() {
714 // We've reached the root, so no matter what, we're done. We manually
715 // access the root via the tree itself to avoid creating any dangling
717 if self.map.root.is_empty() && !self.map.root.is_leaf() {
718 // We've emptied out the root, so make its only child the new root.
719 // If it's a leaf, we just let it become empty.
721 self.map.root.hoist_lone_child();
725 Some(mut handle) => {
727 // Underflow! Handle it!
729 handle.from_raw_mut().handle_underflow();
730 underflow = handle.from_raw().node().is_underfull();
742 impl<'a, K, V> SearchStack<'a, K, V, handle::KV, handle::LeafOrInternal> {
743 /// Removes the key and value in the top element of the stack, then handles underflows as
744 /// described in BTree's pop function.
745 pub fn remove(self) -> V {
746 // Ensure that the search stack goes to a leaf. This is necessary to perform deletion
747 // in a BTree. Note that this may put the tree in an inconsistent state (further
748 // described in into_leaf's comments), but this is immediately fixed by the
749 // removing the value we want to remove
750 self.into_leaf().remove_leaf()
753 /// Subroutine for removal. Takes a search stack for a key that might terminate at an
754 /// internal node, and mutates the tree and search stack to *make* it a search stack
755 /// for that same key that *does* terminates at a leaf. If the mutation occurs, then this
756 /// leaves the tree in an inconsistent state that must be repaired by the caller by
757 /// removing the entry in question. Specifically the key-value pair and its successor will
759 fn into_leaf(mut self) -> SearchStack<'a, K, V, handle::KV, handle::Leaf> {
761 let mut top_raw = self.top;
762 let mut top = top_raw.from_raw_mut();
764 let key_ptr = top.key_mut() as *mut _;
765 let val_ptr = top.val_mut() as *mut _;
767 // Try to go into the right subtree of the found key to find its successor
769 Leaf(mut leaf_handle) => {
770 // We're a proper leaf stack, nothing to do
774 top: leaf_handle.as_raw()
777 Internal(mut internal_handle) => {
778 let mut right_handle = internal_handle.right_edge();
780 //We're not a proper leaf stack, let's get to work.
781 self.stack.push(right_handle.as_raw());
783 let mut temp_node = right_handle.edge_mut();
785 // Walk into the smallest subtree of this node
786 let node = temp_node;
788 match node.kv_handle(0).force() {
789 Leaf(mut handle) => {
790 // This node is a leaf, do the swap and return
791 mem::swap(handle.key_mut(), &mut *key_ptr);
792 mem::swap(handle.val_mut(), &mut *val_ptr);
799 Internal(kv_handle) => {
800 // This node is internal, go deeper
801 let mut handle = kv_handle.into_left_edge();
802 self.stack.push(handle.as_raw());
803 temp_node = handle.into_edge_mut();
813 impl<'a, K, V> SearchStack<'a, K, V, handle::Edge, handle::Leaf> {
814 /// Inserts the key and value into the top element in the stack, and if that node has to
815 /// split recursively inserts the split contents into the next element stack until
818 /// Assumes that the stack represents a search path from the root to a leaf.
820 /// An &mut V is returned to the inserted value, for callers that want a reference to this.
821 pub fn insert(mut self, key: K, val: V) -> &'a mut V {
823 self.map.length += 1;
825 // Insert the key and value into the leaf at the top of the stack
826 let (mut insertion, inserted_ptr) = self.top.from_raw_mut()
827 .insert_as_leaf(key, val);
832 // The last insertion went off without a hitch, no splits! We can stop
834 return &mut *inserted_ptr;
836 Split(key, val, right) => match self.stack.pop() {
837 // The last insertion triggered a split, so get the next element on the
838 // stack to recursively insert the split node into.
840 // The stack was empty; we've split the root, and need to make a
841 // a new one. This is done in-place because we can't move the
842 // root out of a reference to the tree.
843 Node::make_internal_root(&mut self.map.root, self.map.b,
847 return &mut *inserted_ptr;
849 Some(mut handle) => {
850 // The stack wasn't empty, do the insertion and recurse
851 insertion = handle.from_raw_mut()
852 .insert_as_internal(key, val, right);
863 #[stable(feature = "rust1", since = "1.0.0")]
864 impl<K: Ord, V> FromIterator<(K, V)> for BTreeMap<K, V> {
865 fn from_iter<T: IntoIterator<Item=(K, V)>>(iter: T) -> BTreeMap<K, V> {
866 let mut map = BTreeMap::new();
872 #[stable(feature = "rust1", since = "1.0.0")]
873 impl<K: Ord, V> Extend<(K, V)> for BTreeMap<K, V> {
875 fn extend<T: IntoIterator<Item=(K, V)>>(&mut self, iter: T) {
882 #[stable(feature = "extend_ref", since = "1.2.0")]
883 impl<'a, K: Ord + Copy, V: Copy> Extend<(&'a K, &'a V)> for BTreeMap<K, V> {
884 fn extend<I: IntoIterator<Item=(&'a K, &'a V)>>(&mut self, iter: I) {
885 self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
889 #[stable(feature = "rust1", since = "1.0.0")]
890 impl<K: Hash, V: Hash> Hash for BTreeMap<K, V> {
891 fn hash<H: Hasher>(&self, state: &mut H) {
898 #[stable(feature = "rust1", since = "1.0.0")]
899 impl<K: Ord, V> Default for BTreeMap<K, V> {
900 #[stable(feature = "rust1", since = "1.0.0")]
901 fn default() -> BTreeMap<K, V> {
906 #[stable(feature = "rust1", since = "1.0.0")]
907 impl<K: PartialEq, V: PartialEq> PartialEq for BTreeMap<K, V> {
908 fn eq(&self, other: &BTreeMap<K, V>) -> bool {
909 self.len() == other.len() &&
910 self.iter().zip(other).all(|(a, b)| a == b)
914 #[stable(feature = "rust1", since = "1.0.0")]
915 impl<K: Eq, V: Eq> Eq for BTreeMap<K, V> {}
917 #[stable(feature = "rust1", since = "1.0.0")]
918 impl<K: PartialOrd, V: PartialOrd> PartialOrd for BTreeMap<K, V> {
920 fn partial_cmp(&self, other: &BTreeMap<K, V>) -> Option<Ordering> {
921 iter::order::partial_cmp(self.iter(), other.iter())
925 #[stable(feature = "rust1", since = "1.0.0")]
926 impl<K: Ord, V: Ord> Ord for BTreeMap<K, V> {
928 fn cmp(&self, other: &BTreeMap<K, V>) -> Ordering {
929 iter::order::cmp(self.iter(), other.iter())
933 #[stable(feature = "rust1", since = "1.0.0")]
934 impl<K: Debug, V: Debug> Debug for BTreeMap<K, V> {
935 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
936 f.debug_map().entries(self.iter()).finish()
940 #[stable(feature = "rust1", since = "1.0.0")]
941 impl<'a, K: Ord, Q: ?Sized, V> Index<&'a Q> for BTreeMap<K, V>
942 where K: Borrow<Q>, Q: Ord
947 fn index(&self, key: &Q) -> &V {
948 self.get(key).expect("no entry found for key")
952 /// Genericises over how to get the correct type of iterator from the correct type
953 /// of Node ownership.
955 fn traverse(node: N) -> Self;
958 impl<'a, K, V> Traverse<&'a Node<K, V>> for Traversal<'a, K, V> {
959 fn traverse(node: &'a Node<K, V>) -> Traversal<'a, K, V> {
964 impl<'a, K, V> Traverse<&'a mut Node<K, V>> for MutTraversal<'a, K, V> {
965 fn traverse(node: &'a mut Node<K, V>) -> MutTraversal<'a, K, V> {
970 impl<K, V> Traverse<Node<K, V>> for MoveTraversal<K, V> {
971 fn traverse(node: Node<K, V>) -> MoveTraversal<K, V> {
976 /// Represents an operation to perform inside the following iterator methods.
977 /// This is necessary to use in `next` because we want to modify `self.traversals` inside
978 /// a match that borrows it. Similarly in `next_back`. Instead, we use this enum to note
979 /// what we want to do, and do it after the match.
984 impl<K, V, E, T> Iterator for AbsIter<T> where
985 T: DoubleEndedIterator<Item=TraversalItem<K, V, E>> + Traverse<E>,
989 // Our iterator represents a queue of all ancestors of elements we have
990 // yet to yield, from smallest to largest. Note that the design of these
991 // iterators permits an *arbitrary* initial pair of min and max, making
992 // these arbitrary sub-range iterators.
993 fn next(&mut self) -> Option<(K, V)> {
995 // We want the smallest element, so try to get the back of the queue
996 let op = match self.traversals.back_mut() {
998 // The queue wasn't empty, so continue along the node in its head
999 Some(iter) => match iter.next() {
1000 // The head is empty, so Pop it off and continue the process
1002 // The head yielded an edge, so make that the new head
1003 Some(Edge(next)) => Push(Traverse::traverse(next)),
1004 // The head yielded an entry, so yield that
1012 // Handle any operation as necessary, without a conflicting borrow of the queue
1014 Push(item) => { self.traversals.push_back(item); },
1015 Pop => { self.traversals.pop_back(); },
1020 fn size_hint(&self) -> (usize, Option<usize>) {
1021 (self.size, Some(self.size))
1025 impl<K, V, E, T> DoubleEndedIterator for AbsIter<T> where
1026 T: DoubleEndedIterator<Item=TraversalItem<K, V, E>> + Traverse<E>,
1028 // next_back is totally symmetric to next
1030 fn next_back(&mut self) -> Option<(K, V)> {
1032 let op = match self.traversals.front_mut() {
1033 None => return None,
1034 Some(iter) => match iter.next_back() {
1036 Some(Edge(next)) => Push(Traverse::traverse(next)),
1045 Push(item) => { self.traversals.push_front(item); },
1046 Pop => { self.traversals.pop_front(); }
1052 impl<'a, K, V> Clone for Iter<'a, K, V> {
1053 fn clone(&self) -> Iter<'a, K, V> { Iter { inner: self.inner.clone() } }
1055 #[stable(feature = "rust1", since = "1.0.0")]
1056 impl<'a, K, V> Iterator for Iter<'a, K, V> {
1057 type Item = (&'a K, &'a V);
1059 fn next(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next() }
1060 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1062 #[stable(feature = "rust1", since = "1.0.0")]
1063 impl<'a, K, V> DoubleEndedIterator for Iter<'a, K, V> {
1064 fn next_back(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next_back() }
1066 #[stable(feature = "rust1", since = "1.0.0")]
1067 impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {}
1069 #[stable(feature = "rust1", since = "1.0.0")]
1070 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
1071 type Item = (&'a K, &'a mut V);
1073 fn next(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next() }
1074 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1076 #[stable(feature = "rust1", since = "1.0.0")]
1077 impl<'a, K, V> DoubleEndedIterator for IterMut<'a, K, V> {
1078 fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next_back() }
1080 #[stable(feature = "rust1", since = "1.0.0")]
1081 impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {}
1083 #[stable(feature = "rust1", since = "1.0.0")]
1084 impl<K, V> Iterator for IntoIter<K, V> {
1087 fn next(&mut self) -> Option<(K, V)> { self.inner.next() }
1088 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1090 #[stable(feature = "rust1", since = "1.0.0")]
1091 impl<K, V> DoubleEndedIterator for IntoIter<K, V> {
1092 fn next_back(&mut self) -> Option<(K, V)> { self.inner.next_back() }
1094 #[stable(feature = "rust1", since = "1.0.0")]
1095 impl<K, V> ExactSizeIterator for IntoIter<K, V> {}
1097 impl<'a, K, V> Clone for Keys<'a, K, V> {
1098 fn clone(&self) -> Keys<'a, K, V> { Keys { inner: self.inner.clone() } }
1100 #[stable(feature = "rust1", since = "1.0.0")]
1101 impl<'a, K, V> Iterator for Keys<'a, K, V> {
1104 fn next(&mut self) -> Option<(&'a K)> { self.inner.next() }
1105 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1107 #[stable(feature = "rust1", since = "1.0.0")]
1108 impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V> {
1109 fn next_back(&mut self) -> Option<(&'a K)> { self.inner.next_back() }
1111 #[stable(feature = "rust1", since = "1.0.0")]
1112 impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {}
1115 impl<'a, K, V> Clone for Values<'a, K, V> {
1116 fn clone(&self) -> Values<'a, K, V> { Values { inner: self.inner.clone() } }
1118 #[stable(feature = "rust1", since = "1.0.0")]
1119 impl<'a, K, V> Iterator for Values<'a, K, V> {
1122 fn next(&mut self) -> Option<(&'a V)> { self.inner.next() }
1123 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1125 #[stable(feature = "rust1", since = "1.0.0")]
1126 impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V> {
1127 fn next_back(&mut self) -> Option<(&'a V)> { self.inner.next_back() }
1129 #[stable(feature = "rust1", since = "1.0.0")]
1130 impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {}
1132 impl<'a, K, V> Clone for Range<'a, K, V> {
1133 fn clone(&self) -> Range<'a, K, V> { Range { inner: self.inner.clone() } }
1135 impl<'a, K, V> Iterator for Range<'a, K, V> {
1136 type Item = (&'a K, &'a V);
1138 fn next(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next() }
1140 impl<'a, K, V> DoubleEndedIterator for Range<'a, K, V> {
1141 fn next_back(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next_back() }
1144 impl<'a, K, V> Iterator for RangeMut<'a, K, V> {
1145 type Item = (&'a K, &'a mut V);
1147 fn next(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next() }
1149 impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V> {
1150 fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next_back() }
1153 impl<'a, K: Ord, V> Entry<'a, K, V> {
1154 #[unstable(feature = "entry",
1155 reason = "will soon be replaced by or_insert")]
1156 #[deprecated(since = "1.0",
1157 reason = "replaced with more ergonomic `or_insert` and `or_insert_with`")]
1158 /// Returns a mutable reference to the entry if occupied, or the VacantEntry if vacant
1159 pub fn get(self) -> Result<&'a mut V, VacantEntry<'a, K, V>> {
1161 Occupied(entry) => Ok(entry.into_mut()),
1162 Vacant(entry) => Err(entry),
1166 #[stable(feature = "rust1", since = "1.0.0")]
1167 /// Ensures a value is in the entry by inserting the default if empty, and returns
1168 /// a mutable reference to the value in the entry.
1169 pub fn or_insert(self, default: V) -> &'a mut V {
1171 Occupied(entry) => entry.into_mut(),
1172 Vacant(entry) => entry.insert(default),
1176 #[stable(feature = "rust1", since = "1.0.0")]
1177 /// Ensures a value is in the entry by inserting the result of the default function if empty,
1178 /// and returns a mutable reference to the value in the entry.
1179 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
1181 Occupied(entry) => entry.into_mut(),
1182 Vacant(entry) => entry.insert(default()),
1187 impl<'a, K: Ord, V> VacantEntry<'a, K, V> {
1188 /// Sets the value of the entry with the VacantEntry's key,
1189 /// and returns a mutable reference to it.
1190 #[stable(feature = "rust1", since = "1.0.0")]
1191 pub fn insert(self, value: V) -> &'a mut V {
1192 self.stack.insert(self.key, value)
1196 impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
1197 /// Gets a reference to the value in the entry.
1198 #[stable(feature = "rust1", since = "1.0.0")]
1199 pub fn get(&self) -> &V {
1203 /// Gets a mutable reference to the value in the entry.
1204 #[stable(feature = "rust1", since = "1.0.0")]
1205 pub fn get_mut(&mut self) -> &mut V {
1206 self.stack.peek_mut()
1209 /// Converts the entry into a mutable reference to its value.
1210 #[stable(feature = "rust1", since = "1.0.0")]
1211 pub fn into_mut(self) -> &'a mut V {
1212 self.stack.into_top()
1215 /// Sets the value of the entry with the OccupiedEntry's key,
1216 /// and returns the entry's old value.
1217 #[stable(feature = "rust1", since = "1.0.0")]
1218 pub fn insert(&mut self, mut value: V) -> V {
1219 mem::swap(self.stack.peek_mut(), &mut value);
1223 /// Takes the value of the entry out of the map, and returns it.
1224 #[stable(feature = "rust1", since = "1.0.0")]
1225 pub fn remove(self) -> V {
1230 impl<K, V> BTreeMap<K, V> {
1231 /// Gets an iterator over the entries of the map.
1236 /// use std::collections::BTreeMap;
1238 /// let mut map = BTreeMap::new();
1239 /// map.insert(1, "a");
1240 /// map.insert(2, "b");
1241 /// map.insert(3, "c");
1243 /// for (key, value) in map.iter() {
1244 /// println!("{}: {}", key, value);
1247 /// let (first_key, first_value) = map.iter().next().unwrap();
1248 /// assert_eq!((*first_key, *first_value), (1, "a"));
1250 #[stable(feature = "rust1", since = "1.0.0")]
1251 pub fn iter(&self) -> Iter<K, V> {
1252 let len = self.len();
1253 // NB. The initial capacity for ringbuf is large enough to avoid reallocs in many cases.
1254 let mut lca = VecDeque::new();
1255 lca.push_back(Traverse::traverse(&self.root));
1264 /// Gets a mutable iterator over the entries of the map.
1269 /// use std::collections::BTreeMap;
1271 /// let mut map = BTreeMap::new();
1272 /// map.insert("a", 1);
1273 /// map.insert("b", 2);
1274 /// map.insert("c", 3);
1276 /// // add 10 to the value if the key isn't "a"
1277 /// for (key, value) in map.iter_mut() {
1278 /// if key != &"a" {
1283 #[stable(feature = "rust1", since = "1.0.0")]
1284 pub fn iter_mut(&mut self) -> IterMut<K, V> {
1285 let len = self.len();
1286 let mut lca = VecDeque::new();
1287 lca.push_back(Traverse::traverse(&mut self.root));
1296 /// Gets an iterator over the keys of the map.
1301 /// use std::collections::BTreeMap;
1303 /// let mut a = BTreeMap::new();
1304 /// a.insert(1, "a");
1305 /// a.insert(2, "b");
1307 /// let keys: Vec<_> = a.keys().cloned().collect();
1308 /// assert_eq!(keys, [1, 2]);
1310 #[stable(feature = "rust1", since = "1.0.0")]
1311 pub fn keys<'a>(&'a self) -> Keys<'a, K, V> {
1312 fn first<A, B>((a, _): (A, B)) -> A { a }
1313 let first: fn((&'a K, &'a V)) -> &'a K = first; // coerce to fn pointer
1315 Keys { inner: self.iter().map(first) }
1318 /// Gets an iterator over the values of the map.
1323 /// use std::collections::BTreeMap;
1325 /// let mut a = BTreeMap::new();
1326 /// a.insert(1, "a");
1327 /// a.insert(2, "b");
1329 /// let values: Vec<&str> = a.values().cloned().collect();
1330 /// assert_eq!(values, ["a", "b"]);
1332 #[stable(feature = "rust1", since = "1.0.0")]
1333 pub fn values<'a>(&'a self) -> Values<'a, K, V> {
1334 fn second<A, B>((_, b): (A, B)) -> B { b }
1335 let second: fn((&'a K, &'a V)) -> &'a V = second; // coerce to fn pointer
1337 Values { inner: self.iter().map(second) }
1340 /// Returns the number of elements in the map.
1345 /// use std::collections::BTreeMap;
1347 /// let mut a = BTreeMap::new();
1348 /// assert_eq!(a.len(), 0);
1349 /// a.insert(1, "a");
1350 /// assert_eq!(a.len(), 1);
1352 #[stable(feature = "rust1", since = "1.0.0")]
1353 pub fn len(&self) -> usize { self.length }
1355 /// Returns true if the map contains no elements.
1360 /// use std::collections::BTreeMap;
1362 /// let mut a = BTreeMap::new();
1363 /// assert!(a.is_empty());
1364 /// a.insert(1, "a");
1365 /// assert!(!a.is_empty());
1367 #[stable(feature = "rust1", since = "1.0.0")]
1368 pub fn is_empty(&self) -> bool { self.len() == 0 }
1371 macro_rules! range_impl {
1372 ($root:expr, $min:expr, $max:expr, $as_slices_internal:ident, $iter:ident, $Range:ident,
1373 $edges:ident, [$($mutability:ident)*]) => (
1375 // A deque that encodes two search paths containing (left-to-right):
1376 // a series of truncated-from-the-left iterators, the LCA's doubly-truncated iterator,
1377 // and a series of truncated-from-the-right iterators.
1378 let mut traversals = VecDeque::new();
1379 let (root, min, max) = ($root, $min, $max);
1381 let mut leftmost = None;
1382 let mut rightmost = None;
1384 match (&min, &max) {
1385 (&Unbounded, &Unbounded) => {
1386 traversals.push_back(Traverse::traverse(root))
1388 (&Unbounded, &Included(_)) | (&Unbounded, &Excluded(_)) => {
1389 rightmost = Some(root);
1391 (&Included(_), &Unbounded) | (&Excluded(_), &Unbounded) => {
1392 leftmost = Some(root);
1394 (&Included(min_key), &Included(max_key))
1395 | (&Included(min_key), &Excluded(max_key))
1396 | (&Excluded(min_key), &Included(max_key))
1397 | (&Excluded(min_key), &Excluded(max_key)) => {
1398 // lca represents the Lowest Common Ancestor, above which we never
1399 // walk, since everything else is outside the range to iterate.
1400 // ___________________
1401 // |__0_|_80_|_85_|_90_| (root)
1405 // ___________________
1406 // |__5_|_15_|_30_|_73_|
1410 // ___________________
1411 // |_33_|_58_|_63_|_68_| lca for the range [41, 65]
1412 // | |\___|___/| | iterator at traversals[2]
1417 let mut is_leaf = root.is_leaf();
1418 let mut lca = root.$as_slices_internal();
1420 let slice = lca.slice_from(min_key).slice_to(max_key);
1421 if let [ref $($mutability)* edge] = slice.edges {
1422 // Follow the only edge that leads the node that covers the range.
1423 is_leaf = edge.is_leaf();
1424 lca = edge.$as_slices_internal();
1426 let mut iter = slice.$iter();
1431 // Only change the state of nodes with edges.
1432 leftmost = iter.next_edge_item();
1433 rightmost = iter.next_edge_item_back();
1435 traversals.push_back(iter);
1441 // Keep narrowing the range by going down.
1442 // ___________________
1443 // |_38_|_43_|_48_|_53_|
1444 // | |____|____|____/ iterator at traversals[1]
1447 // ___________________
1448 // |_39_|_40_|_41_|_42_| (leaf, the last leftmost)
1449 // \_________| iterator at traversals[0]
1451 Included(key) | Excluded(key) =>
1452 while let Some(left) = leftmost {
1453 let is_leaf = left.is_leaf();
1454 let mut iter = left.$as_slices_internal().slice_from(key).$iter();
1455 leftmost = if is_leaf {
1458 // Only change the state of nodes with edges.
1459 iter.next_edge_item()
1461 traversals.push_back(iter);
1465 // If the leftmost iterator starts with an element, then it was an exact match.
1466 if let (Excluded(_), Some(leftmost_iter)) = (min, traversals.back_mut()) {
1467 // Drop this excluded element. `next_kv_item` has no effect when
1468 // the next item is an edge.
1469 leftmost_iter.next_kv_item();
1472 // The code for the right side is similar.
1474 Included(key) | Excluded(key) =>
1475 while let Some(right) = rightmost {
1476 let is_leaf = right.is_leaf();
1477 let mut iter = right.$as_slices_internal().slice_to(key).$iter();
1478 rightmost = if is_leaf {
1481 iter.next_edge_item_back()
1483 traversals.push_front(iter);
1487 if let (Excluded(_), Some(rightmost_iter)) = (max, traversals.front_mut()) {
1488 rightmost_iter.next_kv_item_back();
1493 traversals: traversals,
1494 size: usize::MAX, // unused
1501 impl<K: Ord, V> BTreeMap<K, V> {
1502 /// Constructs a double-ended iterator over a sub-range of elements in the map, starting
1503 /// at min, and ending at max. If min is `Unbounded`, then it will be treated as "negative
1504 /// infinity", and if max is `Unbounded`, then it will be treated as "positive infinity".
1505 /// Thus range(Unbounded, Unbounded) will yield the whole collection.
1510 /// # #![feature(collections)]
1511 /// use std::collections::BTreeMap;
1512 /// use std::collections::Bound::{Included, Unbounded};
1514 /// let mut map = BTreeMap::new();
1515 /// map.insert(3, "a");
1516 /// map.insert(5, "b");
1517 /// map.insert(8, "c");
1518 /// for (&key, &value) in map.range(Included(&4), Included(&8)) {
1519 /// println!("{}: {}", key, value);
1521 /// assert_eq!(Some((&5, &"b")), map.range(Included(&4), Unbounded).next());
1523 #[unstable(feature = "btree_range",
1524 reason = "matches collection reform specification, waiting for dust to settle")]
1525 pub fn range<'a>(&'a self, min: Bound<&K>, max: Bound<&K>) -> Range<'a, K, V> {
1526 range_impl!(&self.root, min, max, as_slices_internal, iter, Range, edges, [])
1529 /// Constructs a mutable double-ended iterator over a sub-range of elements in the map, starting
1530 /// at min, and ending at max. If min is `Unbounded`, then it will be treated as "negative
1531 /// infinity", and if max is `Unbounded`, then it will be treated as "positive infinity".
1532 /// Thus range(Unbounded, Unbounded) will yield the whole collection.
1537 /// # #![feature(collections)]
1538 /// use std::collections::BTreeMap;
1539 /// use std::collections::Bound::{Included, Excluded};
1541 /// let mut map: BTreeMap<&str, i32> = ["Alice", "Bob", "Carol", "Cheryl"].iter()
1542 /// .map(|&s| (s, 0))
1544 /// for (_, balance) in map.range_mut(Included(&"B"), Excluded(&"Cheryl")) {
1545 /// *balance += 100;
1547 /// for (name, balance) in &map {
1548 /// println!("{} => {}", name, balance);
1551 #[unstable(feature = "btree_range",
1552 reason = "matches collection reform specification, waiting for dust to settle")]
1553 pub fn range_mut<'a>(&'a mut self, min: Bound<&K>, max: Bound<&K>) -> RangeMut<'a, K, V> {
1554 range_impl!(&mut self.root, min, max, as_slices_internal_mut, iter_mut, RangeMut,
1558 /// Gets the given key's corresponding entry in the map for in-place manipulation.
1563 /// use std::collections::BTreeMap;
1565 /// let mut count: BTreeMap<&str, usize> = BTreeMap::new();
1567 /// // count the number of occurrences of letters in the vec
1568 /// for x in vec!["a","b","a","c","a","b"] {
1569 /// *count.entry(x).or_insert(0) += 1;
1572 /// assert_eq!(count["a"], 3);
1574 #[stable(feature = "rust1", since = "1.0.0")]
1575 pub fn entry(&mut self, mut key: K) -> Entry<K, V> {
1576 // same basic logic of `swap` and `pop`, blended together
1577 let mut stack = stack::PartialSearchStack::new(self);
1579 let result = stack.with(move |pusher, node| {
1580 match Node::search(node, &key) {
1583 Finished(Occupied(OccupiedEntry {
1584 stack: pusher.seal(handle)
1588 match handle.force() {
1589 Leaf(leaf_handle) => {
1590 Finished(Vacant(VacantEntry {
1591 stack: pusher.seal(leaf_handle),
1595 Internal(internal_handle) => {
1597 pusher.push(internal_handle),
1606 Finished(finished) => return finished,
1607 Continue((new_stack, renewed_key)) => {