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/).
21 use core::prelude::v1::*;
23 use core::cmp::Ordering;
25 use core::hash::{Hash, Hasher};
26 use core::iter::{Map, FromIterator};
28 use core::{iter, fmt, mem, usize};
29 use Bound::{self, Included, Excluded, Unbounded};
32 use vec_deque::VecDeque;
34 use self::Continuation::{Continue, Finished};
36 use super::node::ForceResult::{Leaf, Internal};
37 use super::node::TraversalItem::{self, Elem, Edge};
38 use super::node::{Traversal, MutTraversal, MoveTraversal};
39 use super::node::{self, Node, Found, GoDown};
41 /// A map based on a B-Tree.
43 /// B-Trees represent a fundamental compromise between cache-efficiency and actually minimizing
44 /// the amount of work performed in a search. In theory, a binary search tree (BST) is the optimal
45 /// choice for a sorted map, as a perfectly balanced BST performs the theoretical minimum amount of
46 /// comparisons necessary to find an element (log<sub>2</sub>n). However, in practice the way this
47 /// is done is *very* inefficient for modern computer architectures. In particular, every element
48 /// is stored in its own individually heap-allocated node. This means that every single insertion
49 /// triggers a heap-allocation, and every single comparison should be a cache-miss. Since these
50 /// are both notably expensive things to do in practice, we are forced to at very least reconsider
53 /// A B-Tree instead makes each node contain B-1 to 2B-1 elements in a contiguous array. By doing
54 /// this, we reduce the number of allocations by a factor of B, and improve cache efficiency in
55 /// searches. However, this does mean that searches will have to do *more* comparisons on average.
56 /// The precise number of comparisons depends on the node search strategy used. For optimal cache
57 /// efficiency, one could search the nodes linearly. For optimal comparisons, one could search
58 /// the node using binary search. As a compromise, one could also perform a linear search
59 /// that initially only checks every i<sup>th</sup> element for some choice of i.
61 /// Currently, our implementation simply performs naive linear search. This provides excellent
62 /// performance on *small* nodes of elements which are cheap to compare. However in the future we
63 /// would like to further explore choosing the optimal search strategy based on the choice of B,
64 /// and possibly other factors. Using linear search, searching for a random element is expected
65 /// to take O(B log<sub>B</sub>n) comparisons, which is generally worse than a BST. In practice,
66 /// however, performance is excellent.
68 /// It is a logic error for a key to be modified in such a way that the key's ordering relative to
69 /// any other key, as determined by the `Ord` trait, changes while it is in the map. This is
70 /// normally only possible through `Cell`, `RefCell`, global state, I/O, or unsafe code.
72 #[stable(feature = "rust1", since = "1.0.0")]
73 pub struct BTreeMap<K, V> {
80 /// An abstract base over-which all other BTree iterators are built.
83 traversals: VecDeque<T>,
87 /// An iterator over a BTreeMap's entries.
88 #[stable(feature = "rust1", since = "1.0.0")]
89 pub struct Iter<'a, K: 'a, V: 'a> {
90 inner: AbsIter<Traversal<'a, K, V>>
93 /// A mutable iterator over a BTreeMap's entries.
94 #[stable(feature = "rust1", since = "1.0.0")]
95 pub struct IterMut<'a, K: 'a, V: 'a> {
96 inner: AbsIter<MutTraversal<'a, K, V>>
99 /// An owning iterator over a BTreeMap's entries.
100 #[stable(feature = "rust1", since = "1.0.0")]
101 pub struct IntoIter<K, V> {
102 inner: AbsIter<MoveTraversal<K, V>>
105 /// An iterator over a BTreeMap's keys.
106 #[stable(feature = "rust1", since = "1.0.0")]
107 pub struct Keys<'a, K: 'a, V: 'a> {
108 inner: Map<Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a K>
111 /// An iterator over a BTreeMap's values.
112 #[stable(feature = "rust1", since = "1.0.0")]
113 pub struct Values<'a, K: 'a, V: 'a> {
114 inner: Map<Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a V>
117 /// An iterator over a sub-range of BTreeMap's entries.
118 pub struct Range<'a, K: 'a, V: 'a> {
119 inner: AbsIter<Traversal<'a, K, V>>
122 /// A mutable iterator over a sub-range of BTreeMap's entries.
123 pub struct RangeMut<'a, K: 'a, V: 'a> {
124 inner: AbsIter<MutTraversal<'a, K, V>>
127 /// A view into a single entry in a map, which may either be vacant or occupied.
128 #[stable(feature = "rust1", since = "1.0.0")]
129 pub enum Entry<'a, K:'a, V:'a> {
131 #[stable(feature = "rust1", since = "1.0.0")]
132 Vacant(VacantEntry<'a, K, V>),
134 /// An occupied Entry
135 #[stable(feature = "rust1", since = "1.0.0")]
136 Occupied(OccupiedEntry<'a, K, V>),
140 #[stable(feature = "rust1", since = "1.0.0")]
141 pub struct VacantEntry<'a, K:'a, V:'a> {
143 stack: stack::SearchStack<'a, K, V, node::handle::Edge, node::handle::Leaf>,
146 /// An occupied Entry.
147 #[stable(feature = "rust1", since = "1.0.0")]
148 pub struct OccupiedEntry<'a, K:'a, V:'a> {
149 stack: stack::SearchStack<'a, K, V, node::handle::KV, node::handle::LeafOrInternal>,
152 impl<K: Ord, V> BTreeMap<K, V> {
153 /// Makes a new empty BTreeMap with a reasonable choice for B.
154 #[stable(feature = "rust1", since = "1.0.0")]
155 pub fn new() -> BTreeMap<K, V> {
156 //FIXME(Gankro): Tune this as a function of size_of<K/V>?
160 /// Makes a new empty BTreeMap with the given B.
162 /// B cannot be less than 2.
163 pub fn with_b(b: usize) -> BTreeMap<K, V> {
164 assert!(b > 1, "B must be greater than 1");
168 root: Node::make_leaf_root(b),
173 /// Clears the map, removing all values.
178 /// use std::collections::BTreeMap;
180 /// let mut a = BTreeMap::new();
181 /// a.insert(1, "a");
183 /// assert!(a.is_empty());
185 #[stable(feature = "rust1", since = "1.0.0")]
186 pub fn clear(&mut self) {
188 // avoid recursive destructors by manually traversing the tree
189 for _ in mem::replace(self, BTreeMap::with_b(b)) {};
192 // Searching in a B-Tree is pretty straightforward.
194 // Start at the root. Try to find the key in the current node. If we find it, return it.
195 // If it's not in there, follow the edge *before* the smallest key larger than
196 // the search key. If no such key exists (they're *all* smaller), then just take the last
197 // edge in the node. If we're in a leaf and we don't find our key, then it's not
200 /// Returns a reference to the value corresponding to the key.
202 /// The key may be any borrowed form of the map's key type, but the ordering
203 /// on the borrowed form *must* match the ordering on the key type.
208 /// use std::collections::BTreeMap;
210 /// let mut map = BTreeMap::new();
211 /// map.insert(1, "a");
212 /// assert_eq!(map.get(&1), Some(&"a"));
213 /// assert_eq!(map.get(&2), None);
215 #[stable(feature = "rust1", since = "1.0.0")]
216 pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&V> where K: Borrow<Q>, Q: Ord {
217 let mut cur_node = &self.root;
219 match Node::search(cur_node, key) {
220 Found(handle) => return Some(handle.into_kv().1),
221 GoDown(handle) => match handle.force() {
222 Leaf(_) => return None,
223 Internal(internal_handle) => {
224 cur_node = internal_handle.into_edge();
232 /// Returns true if the map contains a value for the specified key.
234 /// The key may be any borrowed form of the map's key type, but the ordering
235 /// on the borrowed form *must* match the ordering on the key type.
240 /// use std::collections::BTreeMap;
242 /// let mut map = BTreeMap::new();
243 /// map.insert(1, "a");
244 /// assert_eq!(map.contains_key(&1), true);
245 /// assert_eq!(map.contains_key(&2), false);
247 #[stable(feature = "rust1", since = "1.0.0")]
248 pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool where K: Borrow<Q>, Q: Ord {
249 self.get(key).is_some()
252 /// Returns a mutable reference to the value corresponding to the key.
254 /// The key may be any borrowed form of the map's key type, but the ordering
255 /// on the borrowed form *must* match the ordering on the key type.
260 /// use std::collections::BTreeMap;
262 /// let mut map = BTreeMap::new();
263 /// map.insert(1, "a");
264 /// if let Some(x) = map.get_mut(&1) {
267 /// assert_eq!(map[&1], "b");
269 // See `get` for implementation notes, this is basically a copy-paste with mut's added
270 #[stable(feature = "rust1", since = "1.0.0")]
271 pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V> where K: Borrow<Q>, Q: Ord {
272 // temp_node is a Borrowck hack for having a mutable value outlive a loop iteration
273 let mut temp_node = &mut self.root;
275 let cur_node = temp_node;
276 match Node::search(cur_node, key) {
277 Found(handle) => return Some(handle.into_kv_mut().1),
278 GoDown(handle) => match handle.force() {
279 Leaf(_) => return None,
280 Internal(internal_handle) => {
281 temp_node = internal_handle.into_edge_mut();
289 // Insertion in a B-Tree is a bit complicated.
291 // First we do the same kind of search described in `find`. But we need to maintain a stack of
292 // all the nodes/edges in our search path. If we find a match for the key we're trying to
293 // insert, just swap the vals and return the old ones. However, when we bottom out in a leaf,
294 // we attempt to insert our key-value pair at the same location we would want to follow another
297 // If the node has room, then this is done in the obvious way by shifting elements. However,
298 // if the node itself is full, we split node into two, and give its median key-value
299 // pair to its parent to insert the new node with. Of course, the parent may also be
300 // full, and insertion can propagate until we reach the root. If we reach the root, and
301 // it is *also* full, then we split the root and place the two nodes under a newly made root.
303 // Note that we subtly deviate from Open Data Structures in our implementation of split.
304 // ODS describes inserting into the node *regardless* of its capacity, and then
305 // splitting *afterwards* if it happens to be overfull. However, this is inefficient.
306 // Instead, we split beforehand, and then insert the key-value pair into the appropriate
307 // result node. This has two consequences:
309 // 1) While ODS produces a left node of size B-1, and a right node of size B,
310 // we may potentially reverse this. However, this shouldn't effect the analysis.
312 // 2) While ODS may potentially return the pair we *just* inserted after
313 // the split, we will never do this. Again, this shouldn't effect the analysis.
315 /// Inserts a key-value pair into the map. If the key already had a value
316 /// present in the map, that value is returned. Otherwise, `None` is returned.
321 /// use std::collections::BTreeMap;
323 /// let mut map = BTreeMap::new();
324 /// assert_eq!(map.insert(37, "a"), None);
325 /// assert_eq!(map.is_empty(), false);
327 /// map.insert(37, "b");
328 /// assert_eq!(map.insert(37, "c"), Some("b"));
329 /// assert_eq!(map[&37], "c");
331 #[stable(feature = "rust1", since = "1.0.0")]
332 pub fn insert(&mut self, mut key: K, mut value: V) -> Option<V> {
333 // This is a stack of rawptrs to nodes paired with indices, respectively
334 // representing the nodes and edges of our search path. We have to store rawptrs
335 // because as far as Rust is concerned, we can mutate aliased data with such a
336 // stack. It is of course correct, but what it doesn't know is that we will only
337 // be popping and using these ptrs one at a time in child-to-parent order. The alternative
338 // to doing this is to take the Nodes from their parents. This actually makes
339 // borrowck *really* happy and everything is pretty smooth. However, this creates
340 // *tons* of pointless writes, and requires us to always walk all the way back to
341 // the root after an insertion, even if we only needed to change a leaf. Therefore,
342 // we accept this potential unsafety and complexity in the name of performance.
344 // Regardless, the actual dangerous logic is completely abstracted away from BTreeMap
345 // by the stack module. All it can do is immutably read nodes, and ask the search stack
346 // to proceed down some edge by index. This makes the search logic we'll be reusing in a
347 // few different methods much neater, and of course drastically improves safety.
348 let mut stack = stack::PartialSearchStack::new(self);
351 let result = stack.with(move |pusher, node| {
352 // Same basic logic as found in `find`, but with PartialSearchStack mediating the
353 // actual nodes for us
354 match Node::search(node, &key) {
355 Found(mut handle) => {
356 // Perfect match, swap the values and return the old one
357 mem::swap(handle.val_mut(), &mut value);
358 Finished(Some(value))
361 // We need to keep searching, try to get the search stack
362 // to go down further
363 match handle.force() {
364 Leaf(leaf_handle) => {
365 // We've reached a leaf, perform the insertion here
366 pusher.seal(leaf_handle).insert(key, value);
369 Internal(internal_handle) => {
370 // We've found the subtree to insert this key/value pair in,
372 Continue((pusher.push(internal_handle), key, value))
379 Finished(ret) => return ret,
380 Continue((new_stack, renewed_key, renewed_val)) => {
389 // Deletion is the most complicated operation for a B-Tree.
391 // First we do the same kind of search described in
392 // `find`. But we need to maintain a stack of all the nodes/edges in our search path.
393 // If we don't find the key, then we just return `None` and do nothing. If we do find the
394 // key, we perform two operations: remove the item, and then possibly handle underflow.
396 // # removing the item
397 // If the node is a leaf, we just remove the item, and shift
398 // any items after it back to fill the hole.
400 // If the node is an internal node, we *swap* the item with the smallest item in
401 // in its right subtree (which must reside in a leaf), and then revert to the leaf
404 // # handling underflow
405 // After removing an item, there may be too few items in the node. We want nodes
406 // to be mostly full for efficiency, although we make an exception for the root, which
407 // may have as few as one item. If this is the case, we may first try to steal
408 // an item from our left or right neighbour.
410 // To steal from the left (right) neighbour,
411 // we take the largest (smallest) item and child from it. We then swap the taken item
412 // with the item in their mutual parent that separates them, and then insert the
413 // parent's item and the taken child into the first (last) index of the underflowed node.
415 // However, stealing has the possibility of underflowing our neighbour. If this is the
416 // case, we instead *merge* with our neighbour. This of course reduces the number of
417 // children in the parent. Therefore, we also steal the item that separates the now
418 // merged nodes, and insert it into the merged node.
420 // Merging may cause the parent to underflow. If this is the case, then we must repeat
421 // the underflow handling process on the parent. If merging merges the last two children
422 // of the root, then we replace the root with the merged node.
424 /// Removes a key from the map, returning the value at the key if the key
425 /// was previously in the map.
427 /// The key may be any borrowed form of the map's key type, but the ordering
428 /// on the borrowed form *must* match the ordering on the key type.
433 /// use std::collections::BTreeMap;
435 /// let mut map = BTreeMap::new();
436 /// map.insert(1, "a");
437 /// assert_eq!(map.remove(&1), Some("a"));
438 /// assert_eq!(map.remove(&1), None);
440 #[stable(feature = "rust1", since = "1.0.0")]
441 pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V> where K: Borrow<Q>, Q: Ord {
442 // See `swap` for a more thorough description of the stuff going on in here
443 let mut stack = stack::PartialSearchStack::new(self);
445 let result = stack.with(move |pusher, node| {
446 match Node::search(node, key) {
448 // Perfect match. Terminate the stack here, and remove the entry
449 Finished(Some(pusher.seal(handle).remove()))
452 // We need to keep searching, try to go down the next edge
453 match handle.force() {
454 // We're at a leaf; the key isn't in here
455 Leaf(_) => Finished(None),
456 Internal(internal_handle) => Continue(pusher.push(internal_handle))
462 Finished(ret) => return ret,
463 Continue(new_stack) => stack = new_stack
469 #[stable(feature = "rust1", since = "1.0.0")]
470 impl<K, V> IntoIterator for BTreeMap<K, V> {
472 type IntoIter = IntoIter<K, V>;
474 /// Gets an owning iterator over the entries of the map.
479 /// use std::collections::BTreeMap;
481 /// let mut map = BTreeMap::new();
482 /// map.insert(1, "a");
483 /// map.insert(2, "b");
484 /// map.insert(3, "c");
486 /// for (key, value) in map.into_iter() {
487 /// println!("{}: {}", key, value);
490 fn into_iter(self) -> IntoIter<K, V> {
491 let len = self.len();
492 let mut lca = VecDeque::new();
493 lca.push_back(Traverse::traverse(self.root));
503 #[stable(feature = "rust1", since = "1.0.0")]
504 impl<'a, K, V> IntoIterator for &'a BTreeMap<K, V> {
505 type Item = (&'a K, &'a V);
506 type IntoIter = Iter<'a, K, V>;
508 fn into_iter(self) -> Iter<'a, K, V> {
513 #[stable(feature = "rust1", since = "1.0.0")]
514 impl<'a, K, V> IntoIterator for &'a mut BTreeMap<K, V> {
515 type Item = (&'a K, &'a mut V);
516 type IntoIter = IterMut<'a, K, V>;
518 fn into_iter(mut self) -> IterMut<'a, K, V> {
523 /// A helper enum useful for deciding whether to continue a loop since we can't
524 /// return from a closure
525 enum Continuation<A, B> {
530 /// The stack module provides a safe interface for constructing and manipulating a stack of ptrs
531 /// to nodes. By using this module much better safety guarantees can be made, and more search
532 /// boilerplate gets cut out.
535 use core::prelude::v1::*;
538 use core::ops::{Deref, DerefMut};
540 use super::super::node::{self, Node, Fit, Split, Internal, Leaf};
541 use super::super::node::handle;
544 struct InvariantLifetime<'id>(
545 marker::PhantomData<::core::cell::Cell<&'id ()>>);
547 impl<'id> InvariantLifetime<'id> {
548 fn new() -> InvariantLifetime<'id> {
549 InvariantLifetime(marker::PhantomData)
553 /// A generic mutable reference, identical to `&mut` except for the fact that its lifetime
554 /// parameter is invariant. This means that wherever an `IdRef` is expected, only an `IdRef`
555 /// with the exact requested lifetime can be used. This is in contrast to normal references,
556 /// where `&'static` can be used in any function expecting any lifetime reference.
557 pub struct IdRef<'id, T: 'id> {
559 _marker: InvariantLifetime<'id>,
562 impl<'id, T> Deref for IdRef<'id, T> {
565 fn deref(&self) -> &T {
570 impl<'id, T> DerefMut for IdRef<'id, T> {
571 fn deref_mut(&mut self) -> &mut T {
576 type StackItem<K, V> = node::Handle<*mut Node<K, V>, handle::Edge, handle::Internal>;
577 type Stack<K, V> = Vec<StackItem<K, V>>;
579 /// A `PartialSearchStack` handles the construction of a search stack.
580 pub struct PartialSearchStack<'a, K:'a, V:'a> {
581 map: &'a mut BTreeMap<K, V>,
583 next: *mut Node<K, V>,
586 /// A `SearchStack` represents a full path to an element or an edge of interest. It provides
587 /// methods depending on the type of what the path points to for removing an element, inserting
588 /// a new element, and manipulating to element at the top of the stack.
589 pub struct SearchStack<'a, K:'a, V:'a, Type, NodeType> {
590 map: &'a mut BTreeMap<K, V>,
592 top: node::Handle<*mut Node<K, V>, Type, NodeType>,
595 /// A `PartialSearchStack` that doesn't hold a a reference to the next node, and is just
596 /// just waiting for a `Handle` to that next node to be pushed. See `PartialSearchStack::with`
597 /// for more details.
598 pub struct Pusher<'id, 'a, K:'a, V:'a> {
599 map: &'a mut BTreeMap<K, V>,
601 _marker: InvariantLifetime<'id>,
604 impl<'a, K, V> PartialSearchStack<'a, K, V> {
605 /// Creates a new PartialSearchStack from a BTreeMap by initializing the stack with the
606 /// root of the tree.
607 pub fn new(map: &'a mut BTreeMap<K, V>) -> PartialSearchStack<'a, K, V> {
608 let depth = map.depth;
611 next: &mut map.root as *mut _,
613 stack: Vec::with_capacity(depth),
617 /// Breaks up the stack into a `Pusher` and the next `Node`, allowing the given closure
618 /// to interact with, search, and finally push the `Node` onto the stack. The passed in
619 /// closure must be polymorphic on the `'id` lifetime parameter, as this statically
620 /// ensures that only `Handle`s from the correct `Node` can be pushed.
622 /// The reason this works is that the `Pusher` has an `'id` parameter, and will only accept
623 /// handles with the same `'id`. The closure could only get references with that lifetime
624 /// through its arguments or through some other `IdRef` that it has lying around. However,
625 /// no other `IdRef` could possibly work - because the `'id` is held in an invariant
626 /// parameter, it would need to have precisely the correct lifetime, which would mean that
627 /// at least one of the calls to `with` wouldn't be properly polymorphic, wanting a
628 /// specific lifetime instead of the one that `with` chooses to give it.
630 /// See also Haskell's `ST` monad, which uses a similar trick.
631 pub fn with<T, F: for<'id> FnOnce(Pusher<'id, 'a, K, V>,
632 IdRef<'id, Node<K, V>>) -> T>(self, closure: F) -> T {
633 let pusher = Pusher {
636 _marker: InvariantLifetime::new(),
639 inner: unsafe { &mut *self.next },
640 _marker: InvariantLifetime::new(),
643 closure(pusher, node)
647 impl<'id, 'a, K, V> Pusher<'id, 'a, K, V> {
648 /// Pushes the requested child of the stack's current top on top of the stack. If the child
649 /// exists, then a new PartialSearchStack is yielded. Otherwise, a VacantSearchStack is
651 pub fn push(mut self, mut edge: node::Handle<IdRef<'id, Node<K, V>>,
654 -> PartialSearchStack<'a, K, V> {
655 self.stack.push(edge.as_raw());
659 next: edge.edge_mut() as *mut _,
663 /// Converts the PartialSearchStack into a SearchStack.
664 pub fn seal<Type, NodeType>
665 (self, mut handle: node::Handle<IdRef<'id, Node<K, V>>, Type, NodeType>)
666 -> SearchStack<'a, K, V, Type, NodeType> {
670 top: handle.as_raw(),
675 impl<'a, K, V, NodeType> SearchStack<'a, K, V, handle::KV, NodeType> {
676 /// Gets a reference to the value the stack points to.
677 pub fn peek(&self) -> &V {
678 unsafe { self.top.from_raw().into_kv().1 }
681 /// Gets a mutable reference to the value the stack points to.
682 pub fn peek_mut(&mut self) -> &mut V {
683 unsafe { self.top.from_raw_mut().into_kv_mut().1 }
686 /// Converts the stack into a mutable reference to the value it points to, with a lifetime
687 /// tied to the original tree.
688 pub fn into_top(mut self) -> &'a mut V {
690 &mut *(self.top.from_raw_mut().val_mut() as *mut V)
695 impl<'a, K, V> SearchStack<'a, K, V, handle::KV, handle::Leaf> {
696 /// Removes the key and value in the top element of the stack, then handles underflows as
697 /// described in BTree's pop function.
698 fn remove_leaf(mut self) -> V {
699 self.map.length -= 1;
701 // Remove the key-value pair from the leaf that this search stack points to.
702 // Then, note if the leaf is underfull, and promptly forget the leaf and its ptr
703 // to avoid ownership issues.
704 let (value, mut underflow) = unsafe {
705 let (_, value) = self.top.from_raw_mut().remove_as_leaf();
706 let underflow = self.top.from_raw().node().is_underfull();
711 match self.stack.pop() {
713 // We've reached the root, so no matter what, we're done. We manually
714 // access the root via the tree itself to avoid creating any dangling
716 if self.map.root.is_empty() && !self.map.root.is_leaf() {
717 // We've emptied out the root, so make its only child the new root.
718 // If it's a leaf, we just let it become empty.
720 self.map.root.hoist_lone_child();
724 Some(mut handle) => {
726 // Underflow! Handle it!
728 handle.from_raw_mut().handle_underflow();
729 underflow = handle.from_raw().node().is_underfull();
741 impl<'a, K, V> SearchStack<'a, K, V, handle::KV, handle::LeafOrInternal> {
742 /// Removes the key and value in the top element of the stack, then handles underflows as
743 /// described in BTree's pop function.
744 pub fn remove(self) -> V {
745 // Ensure that the search stack goes to a leaf. This is necessary to perform deletion
746 // in a BTree. Note that this may put the tree in an inconsistent state (further
747 // described in into_leaf's comments), but this is immediately fixed by the
748 // removing the value we want to remove
749 self.into_leaf().remove_leaf()
752 /// Subroutine for removal. Takes a search stack for a key that might terminate at an
753 /// internal node, and mutates the tree and search stack to *make* it a search stack
754 /// for that same key that *does* terminates at a leaf. If the mutation occurs, then this
755 /// leaves the tree in an inconsistent state that must be repaired by the caller by
756 /// removing the entry in question. Specifically the key-value pair and its successor will
758 fn into_leaf(mut self) -> SearchStack<'a, K, V, handle::KV, handle::Leaf> {
760 let mut top_raw = self.top;
761 let mut top = top_raw.from_raw_mut();
763 let key_ptr = top.key_mut() as *mut _;
764 let val_ptr = top.val_mut() as *mut _;
766 // Try to go into the right subtree of the found key to find its successor
768 Leaf(mut leaf_handle) => {
769 // We're a proper leaf stack, nothing to do
773 top: leaf_handle.as_raw()
776 Internal(mut internal_handle) => {
777 let mut right_handle = internal_handle.right_edge();
779 //We're not a proper leaf stack, let's get to work.
780 self.stack.push(right_handle.as_raw());
782 let mut temp_node = right_handle.edge_mut();
784 // Walk into the smallest subtree of this node
785 let node = temp_node;
787 match node.kv_handle(0).force() {
788 Leaf(mut handle) => {
789 // This node is a leaf, do the swap and return
790 mem::swap(handle.key_mut(), &mut *key_ptr);
791 mem::swap(handle.val_mut(), &mut *val_ptr);
798 Internal(kv_handle) => {
799 // This node is internal, go deeper
800 let mut handle = kv_handle.into_left_edge();
801 self.stack.push(handle.as_raw());
802 temp_node = handle.into_edge_mut();
812 impl<'a, K, V> SearchStack<'a, K, V, handle::Edge, handle::Leaf> {
813 /// Inserts the key and value into the top element in the stack, and if that node has to
814 /// split recursively inserts the split contents into the next element stack until
817 /// Assumes that the stack represents a search path from the root to a leaf.
819 /// An &mut V is returned to the inserted value, for callers that want a reference to this.
820 pub fn insert(mut self, key: K, val: V) -> &'a mut V {
822 self.map.length += 1;
824 // Insert the key and value into the leaf at the top of the stack
825 let (mut insertion, inserted_ptr) = self.top.from_raw_mut()
826 .insert_as_leaf(key, val);
831 // The last insertion went off without a hitch, no splits! We can stop
833 return &mut *inserted_ptr;
835 Split(key, val, right) => match self.stack.pop() {
836 // The last insertion triggered a split, so get the next element on the
837 // stack to recursively insert the split node into.
839 // The stack was empty; we've split the root, and need to make a
840 // a new one. This is done in-place because we can't move the
841 // root out of a reference to the tree.
842 Node::make_internal_root(&mut self.map.root, self.map.b,
846 return &mut *inserted_ptr;
848 Some(mut handle) => {
849 // The stack wasn't empty, do the insertion and recurse
850 insertion = handle.from_raw_mut()
851 .insert_as_internal(key, val, right);
862 #[stable(feature = "rust1", since = "1.0.0")]
863 impl<K: Ord, V> FromIterator<(K, V)> for BTreeMap<K, V> {
864 fn from_iter<T: IntoIterator<Item=(K, V)>>(iter: T) -> BTreeMap<K, V> {
865 let mut map = BTreeMap::new();
871 #[stable(feature = "rust1", since = "1.0.0")]
872 impl<K: Ord, V> Extend<(K, V)> for BTreeMap<K, V> {
874 fn extend<T: IntoIterator<Item=(K, V)>>(&mut self, iter: T) {
881 #[stable(feature = "extend_ref", since = "1.2.0")]
882 impl<'a, K: Ord + Copy, V: Copy> Extend<(&'a K, &'a V)> for BTreeMap<K, V> {
883 fn extend<I: IntoIterator<Item=(&'a K, &'a V)>>(&mut self, iter: I) {
884 self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
888 #[stable(feature = "rust1", since = "1.0.0")]
889 impl<K: Hash, V: Hash> Hash for BTreeMap<K, V> {
890 fn hash<H: Hasher>(&self, state: &mut H) {
897 #[stable(feature = "rust1", since = "1.0.0")]
898 impl<K: Ord, V> Default for BTreeMap<K, V> {
899 #[stable(feature = "rust1", since = "1.0.0")]
900 fn default() -> BTreeMap<K, V> {
905 #[stable(feature = "rust1", since = "1.0.0")]
906 impl<K: PartialEq, V: PartialEq> PartialEq for BTreeMap<K, V> {
907 fn eq(&self, other: &BTreeMap<K, V>) -> bool {
908 self.len() == other.len() &&
909 self.iter().zip(other).all(|(a, b)| a == b)
913 #[stable(feature = "rust1", since = "1.0.0")]
914 impl<K: Eq, V: Eq> Eq for BTreeMap<K, V> {}
916 #[stable(feature = "rust1", since = "1.0.0")]
917 impl<K: PartialOrd, V: PartialOrd> PartialOrd for BTreeMap<K, V> {
919 fn partial_cmp(&self, other: &BTreeMap<K, V>) -> Option<Ordering> {
920 iter::order::partial_cmp(self.iter(), other.iter())
924 #[stable(feature = "rust1", since = "1.0.0")]
925 impl<K: Ord, V: Ord> Ord for BTreeMap<K, V> {
927 fn cmp(&self, other: &BTreeMap<K, V>) -> Ordering {
928 iter::order::cmp(self.iter(), other.iter())
932 #[stable(feature = "rust1", since = "1.0.0")]
933 impl<K: Debug, V: Debug> Debug for BTreeMap<K, V> {
934 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
935 f.debug_map().entries(self.iter()).finish()
939 #[stable(feature = "rust1", since = "1.0.0")]
940 impl<'a, K: Ord, Q: ?Sized, V> Index<&'a Q> for BTreeMap<K, V>
941 where K: Borrow<Q>, Q: Ord
946 fn index(&self, key: &Q) -> &V {
947 self.get(key).expect("no entry found for key")
951 /// Genericises over how to get the correct type of iterator from the correct type
952 /// of Node ownership.
954 fn traverse(node: N) -> Self;
957 impl<'a, K, V> Traverse<&'a Node<K, V>> for Traversal<'a, K, V> {
958 fn traverse(node: &'a Node<K, V>) -> Traversal<'a, K, V> {
963 impl<'a, K, V> Traverse<&'a mut Node<K, V>> for MutTraversal<'a, K, V> {
964 fn traverse(node: &'a mut Node<K, V>) -> MutTraversal<'a, K, V> {
969 impl<K, V> Traverse<Node<K, V>> for MoveTraversal<K, V> {
970 fn traverse(node: Node<K, V>) -> MoveTraversal<K, V> {
975 /// Represents an operation to perform inside the following iterator methods.
976 /// This is necessary to use in `next` because we want to modify `self.traversals` inside
977 /// a match that borrows it. Similarly in `next_back`. Instead, we use this enum to note
978 /// what we want to do, and do it after the match.
983 impl<K, V, E, T> Iterator for AbsIter<T> where
984 T: DoubleEndedIterator<Item=TraversalItem<K, V, E>> + Traverse<E>,
988 // Our iterator represents a queue of all ancestors of elements we have
989 // yet to yield, from smallest to largest. Note that the design of these
990 // iterators permits an *arbitrary* initial pair of min and max, making
991 // these arbitrary sub-range iterators.
992 fn next(&mut self) -> Option<(K, V)> {
994 // We want the smallest element, so try to get the back of the queue
995 let op = match self.traversals.back_mut() {
997 // The queue wasn't empty, so continue along the node in its head
998 Some(iter) => match iter.next() {
999 // The head is empty, so Pop it off and continue the process
1001 // The head yielded an edge, so make that the new head
1002 Some(Edge(next)) => Push(Traverse::traverse(next)),
1003 // The head yielded an entry, so yield that
1011 // Handle any operation as necessary, without a conflicting borrow of the queue
1013 Push(item) => { self.traversals.push_back(item); },
1014 Pop => { self.traversals.pop_back(); },
1019 fn size_hint(&self) -> (usize, Option<usize>) {
1020 (self.size, Some(self.size))
1024 impl<K, V, E, T> DoubleEndedIterator for AbsIter<T> where
1025 T: DoubleEndedIterator<Item=TraversalItem<K, V, E>> + Traverse<E>,
1027 // next_back is totally symmetric to next
1029 fn next_back(&mut self) -> Option<(K, V)> {
1031 let op = match self.traversals.front_mut() {
1032 None => return None,
1033 Some(iter) => match iter.next_back() {
1035 Some(Edge(next)) => Push(Traverse::traverse(next)),
1044 Push(item) => { self.traversals.push_front(item); },
1045 Pop => { self.traversals.pop_front(); }
1051 impl<'a, K, V> Clone for Iter<'a, K, V> {
1052 fn clone(&self) -> Iter<'a, K, V> { Iter { inner: self.inner.clone() } }
1054 #[stable(feature = "rust1", since = "1.0.0")]
1055 impl<'a, K, V> Iterator for Iter<'a, K, V> {
1056 type Item = (&'a K, &'a V);
1058 fn next(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next() }
1059 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1061 #[stable(feature = "rust1", since = "1.0.0")]
1062 impl<'a, K, V> DoubleEndedIterator for Iter<'a, K, V> {
1063 fn next_back(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next_back() }
1065 #[stable(feature = "rust1", since = "1.0.0")]
1066 impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {}
1068 #[stable(feature = "rust1", since = "1.0.0")]
1069 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
1070 type Item = (&'a K, &'a mut V);
1072 fn next(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next() }
1073 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1075 #[stable(feature = "rust1", since = "1.0.0")]
1076 impl<'a, K, V> DoubleEndedIterator for IterMut<'a, K, V> {
1077 fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next_back() }
1079 #[stable(feature = "rust1", since = "1.0.0")]
1080 impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {}
1082 #[stable(feature = "rust1", since = "1.0.0")]
1083 impl<K, V> Iterator for IntoIter<K, V> {
1086 fn next(&mut self) -> Option<(K, V)> { self.inner.next() }
1087 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1089 #[stable(feature = "rust1", since = "1.0.0")]
1090 impl<K, V> DoubleEndedIterator for IntoIter<K, V> {
1091 fn next_back(&mut self) -> Option<(K, V)> { self.inner.next_back() }
1093 #[stable(feature = "rust1", since = "1.0.0")]
1094 impl<K, V> ExactSizeIterator for IntoIter<K, V> {}
1096 impl<'a, K, V> Clone for Keys<'a, K, V> {
1097 fn clone(&self) -> Keys<'a, K, V> { Keys { inner: self.inner.clone() } }
1099 #[stable(feature = "rust1", since = "1.0.0")]
1100 impl<'a, K, V> Iterator for Keys<'a, K, V> {
1103 fn next(&mut self) -> Option<(&'a K)> { self.inner.next() }
1104 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1106 #[stable(feature = "rust1", since = "1.0.0")]
1107 impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V> {
1108 fn next_back(&mut self) -> Option<(&'a K)> { self.inner.next_back() }
1110 #[stable(feature = "rust1", since = "1.0.0")]
1111 impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {}
1114 impl<'a, K, V> Clone for Values<'a, K, V> {
1115 fn clone(&self) -> Values<'a, K, V> { Values { inner: self.inner.clone() } }
1117 #[stable(feature = "rust1", since = "1.0.0")]
1118 impl<'a, K, V> Iterator for Values<'a, K, V> {
1121 fn next(&mut self) -> Option<(&'a V)> { self.inner.next() }
1122 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1124 #[stable(feature = "rust1", since = "1.0.0")]
1125 impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V> {
1126 fn next_back(&mut self) -> Option<(&'a V)> { self.inner.next_back() }
1128 #[stable(feature = "rust1", since = "1.0.0")]
1129 impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {}
1131 impl<'a, K, V> Clone for Range<'a, K, V> {
1132 fn clone(&self) -> Range<'a, K, V> { Range { inner: self.inner.clone() } }
1134 impl<'a, K, V> Iterator for Range<'a, K, V> {
1135 type Item = (&'a K, &'a V);
1137 fn next(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next() }
1139 impl<'a, K, V> DoubleEndedIterator for Range<'a, K, V> {
1140 fn next_back(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next_back() }
1143 impl<'a, K, V> Iterator for RangeMut<'a, K, V> {
1144 type Item = (&'a K, &'a mut V);
1146 fn next(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next() }
1148 impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V> {
1149 fn next_back(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next_back() }
1152 impl<'a, K: Ord, V> Entry<'a, K, V> {
1153 #[unstable(feature = "entry",
1154 reason = "will soon be replaced by or_insert")]
1155 #[deprecated(since = "1.0",
1156 reason = "replaced with more ergonomic `or_insert` and `or_insert_with`")]
1157 /// Returns a mutable reference to the entry if occupied, or the VacantEntry if vacant
1158 pub fn get(self) -> Result<&'a mut V, VacantEntry<'a, K, V>> {
1160 Occupied(entry) => Ok(entry.into_mut()),
1161 Vacant(entry) => Err(entry),
1165 #[stable(feature = "rust1", since = "1.0.0")]
1166 /// Ensures a value is in the entry by inserting the default if empty, and returns
1167 /// a mutable reference to the value in the entry.
1168 pub fn or_insert(self, default: V) -> &'a mut V {
1170 Occupied(entry) => entry.into_mut(),
1171 Vacant(entry) => entry.insert(default),
1175 #[stable(feature = "rust1", since = "1.0.0")]
1176 /// Ensures a value is in the entry by inserting the result of the default function if empty,
1177 /// and returns a mutable reference to the value in the entry.
1178 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
1180 Occupied(entry) => entry.into_mut(),
1181 Vacant(entry) => entry.insert(default()),
1186 impl<'a, K: Ord, V> VacantEntry<'a, K, V> {
1187 /// Sets the value of the entry with the VacantEntry's key,
1188 /// and returns a mutable reference to it.
1189 #[stable(feature = "rust1", since = "1.0.0")]
1190 pub fn insert(self, value: V) -> &'a mut V {
1191 self.stack.insert(self.key, value)
1195 impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
1196 /// Gets a reference to the value in the entry.
1197 #[stable(feature = "rust1", since = "1.0.0")]
1198 pub fn get(&self) -> &V {
1202 /// Gets a mutable reference to the value in the entry.
1203 #[stable(feature = "rust1", since = "1.0.0")]
1204 pub fn get_mut(&mut self) -> &mut V {
1205 self.stack.peek_mut()
1208 /// Converts the entry into a mutable reference to its value.
1209 #[stable(feature = "rust1", since = "1.0.0")]
1210 pub fn into_mut(self) -> &'a mut V {
1211 self.stack.into_top()
1214 /// Sets the value of the entry with the OccupiedEntry's key,
1215 /// and returns the entry's old value.
1216 #[stable(feature = "rust1", since = "1.0.0")]
1217 pub fn insert(&mut self, mut value: V) -> V {
1218 mem::swap(self.stack.peek_mut(), &mut value);
1222 /// Takes the value of the entry out of the map, and returns it.
1223 #[stable(feature = "rust1", since = "1.0.0")]
1224 pub fn remove(self) -> V {
1229 impl<K, V> BTreeMap<K, V> {
1230 /// Gets an iterator over the entries of the map.
1235 /// use std::collections::BTreeMap;
1237 /// let mut map = BTreeMap::new();
1238 /// map.insert(1, "a");
1239 /// map.insert(2, "b");
1240 /// map.insert(3, "c");
1242 /// for (key, value) in map.iter() {
1243 /// println!("{}: {}", key, value);
1246 /// let (first_key, first_value) = map.iter().next().unwrap();
1247 /// assert_eq!((*first_key, *first_value), (1, "a"));
1249 #[stable(feature = "rust1", since = "1.0.0")]
1250 pub fn iter(&self) -> Iter<K, V> {
1251 let len = self.len();
1252 // NB. The initial capacity for ringbuf is large enough to avoid reallocs in many cases.
1253 let mut lca = VecDeque::new();
1254 lca.push_back(Traverse::traverse(&self.root));
1263 /// Gets a mutable iterator over the entries of the map.
1268 /// use std::collections::BTreeMap;
1270 /// let mut map = BTreeMap::new();
1271 /// map.insert("a", 1);
1272 /// map.insert("b", 2);
1273 /// map.insert("c", 3);
1275 /// // add 10 to the value if the key isn't "a"
1276 /// for (key, value) in map.iter_mut() {
1277 /// if key != &"a" {
1282 #[stable(feature = "rust1", since = "1.0.0")]
1283 pub fn iter_mut(&mut self) -> IterMut<K, V> {
1284 let len = self.len();
1285 let mut lca = VecDeque::new();
1286 lca.push_back(Traverse::traverse(&mut self.root));
1295 /// Gets an iterator over the keys of the map.
1300 /// use std::collections::BTreeMap;
1302 /// let mut a = BTreeMap::new();
1303 /// a.insert(1, "a");
1304 /// a.insert(2, "b");
1306 /// let keys: Vec<_> = a.keys().cloned().collect();
1307 /// assert_eq!(keys, [1, 2]);
1309 #[stable(feature = "rust1", since = "1.0.0")]
1310 pub fn keys<'a>(&'a self) -> Keys<'a, K, V> {
1311 fn first<A, B>((a, _): (A, B)) -> A { a }
1312 let first: fn((&'a K, &'a V)) -> &'a K = first; // coerce to fn pointer
1314 Keys { inner: self.iter().map(first) }
1317 /// Gets an iterator over the values of the map.
1322 /// use std::collections::BTreeMap;
1324 /// let mut a = BTreeMap::new();
1325 /// a.insert(1, "a");
1326 /// a.insert(2, "b");
1328 /// let values: Vec<&str> = a.values().cloned().collect();
1329 /// assert_eq!(values, ["a", "b"]);
1331 #[stable(feature = "rust1", since = "1.0.0")]
1332 pub fn values<'a>(&'a self) -> Values<'a, K, V> {
1333 fn second<A, B>((_, b): (A, B)) -> B { b }
1334 let second: fn((&'a K, &'a V)) -> &'a V = second; // coerce to fn pointer
1336 Values { inner: self.iter().map(second) }
1339 /// Returns the number of elements in the map.
1344 /// use std::collections::BTreeMap;
1346 /// let mut a = BTreeMap::new();
1347 /// assert_eq!(a.len(), 0);
1348 /// a.insert(1, "a");
1349 /// assert_eq!(a.len(), 1);
1351 #[stable(feature = "rust1", since = "1.0.0")]
1352 pub fn len(&self) -> usize { self.length }
1354 /// Returns true if the map contains no elements.
1359 /// use std::collections::BTreeMap;
1361 /// let mut a = BTreeMap::new();
1362 /// assert!(a.is_empty());
1363 /// a.insert(1, "a");
1364 /// assert!(!a.is_empty());
1366 #[stable(feature = "rust1", since = "1.0.0")]
1367 pub fn is_empty(&self) -> bool { self.len() == 0 }
1370 macro_rules! range_impl {
1371 ($root:expr, $min:expr, $max:expr, $as_slices_internal:ident, $iter:ident, $Range:ident,
1372 $edges:ident, [$($mutability:ident)*]) => (
1374 // A deque that encodes two search paths containing (left-to-right):
1375 // a series of truncated-from-the-left iterators, the LCA's doubly-truncated iterator,
1376 // and a series of truncated-from-the-right iterators.
1377 let mut traversals = VecDeque::new();
1378 let (root, min, max) = ($root, $min, $max);
1380 let mut leftmost = None;
1381 let mut rightmost = None;
1383 match (&min, &max) {
1384 (&Unbounded, &Unbounded) => {
1385 traversals.push_back(Traverse::traverse(root))
1387 (&Unbounded, &Included(_)) | (&Unbounded, &Excluded(_)) => {
1388 rightmost = Some(root);
1390 (&Included(_), &Unbounded) | (&Excluded(_), &Unbounded) => {
1391 leftmost = Some(root);
1393 (&Included(min_key), &Included(max_key))
1394 | (&Included(min_key), &Excluded(max_key))
1395 | (&Excluded(min_key), &Included(max_key))
1396 | (&Excluded(min_key), &Excluded(max_key)) => {
1397 // lca represents the Lowest Common Ancestor, above which we never
1398 // walk, since everything else is outside the range to iterate.
1399 // ___________________
1400 // |__0_|_80_|_85_|_90_| (root)
1404 // ___________________
1405 // |__5_|_15_|_30_|_73_|
1409 // ___________________
1410 // |_33_|_58_|_63_|_68_| lca for the range [41, 65]
1411 // | |\___|___/| | iterator at traversals[2]
1416 let mut is_leaf = root.is_leaf();
1417 let mut lca = root.$as_slices_internal();
1419 let slice = lca.slice_from(min_key).slice_to(max_key);
1420 if let [ref $($mutability)* edge] = slice.edges {
1421 // Follow the only edge that leads the node that covers the range.
1422 is_leaf = edge.is_leaf();
1423 lca = edge.$as_slices_internal();
1425 let mut iter = slice.$iter();
1430 // Only change the state of nodes with edges.
1431 leftmost = iter.next_edge_item();
1432 rightmost = iter.next_edge_item_back();
1434 traversals.push_back(iter);
1440 // Keep narrowing the range by going down.
1441 // ___________________
1442 // |_38_|_43_|_48_|_53_|
1443 // | |____|____|____/ iterator at traversals[1]
1446 // ___________________
1447 // |_39_|_40_|_41_|_42_| (leaf, the last leftmost)
1448 // \_________| iterator at traversals[0]
1450 Included(key) | Excluded(key) =>
1451 while let Some(left) = leftmost {
1452 let is_leaf = left.is_leaf();
1453 let mut iter = left.$as_slices_internal().slice_from(key).$iter();
1454 leftmost = if is_leaf {
1457 // Only change the state of nodes with edges.
1458 iter.next_edge_item()
1460 traversals.push_back(iter);
1464 // If the leftmost iterator starts with an element, then it was an exact match.
1465 if let (Excluded(_), Some(leftmost_iter)) = (min, traversals.back_mut()) {
1466 // Drop this excluded element. `next_kv_item` has no effect when
1467 // the next item is an edge.
1468 leftmost_iter.next_kv_item();
1471 // The code for the right side is similar.
1473 Included(key) | Excluded(key) =>
1474 while let Some(right) = rightmost {
1475 let is_leaf = right.is_leaf();
1476 let mut iter = right.$as_slices_internal().slice_to(key).$iter();
1477 rightmost = if is_leaf {
1480 iter.next_edge_item_back()
1482 traversals.push_front(iter);
1486 if let (Excluded(_), Some(rightmost_iter)) = (max, traversals.front_mut()) {
1487 rightmost_iter.next_kv_item_back();
1492 traversals: traversals,
1493 size: usize::MAX, // unused
1500 impl<K: Ord, V> BTreeMap<K, V> {
1501 /// Constructs a double-ended iterator over a sub-range of elements in the map, starting
1502 /// at min, and ending at max. If min is `Unbounded`, then it will be treated as "negative
1503 /// infinity", and if max is `Unbounded`, then it will be treated as "positive infinity".
1504 /// Thus range(Unbounded, Unbounded) will yield the whole collection.
1509 /// #![feature(btree_range, collections_bound)]
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(btree_range, collections_bound)]
1539 /// use std::collections::BTreeMap;
1540 /// use std::collections::Bound::{Included, Excluded};
1542 /// let mut map: BTreeMap<&str, i32> = ["Alice", "Bob", "Carol", "Cheryl"].iter()
1543 /// .map(|&s| (s, 0))
1545 /// for (_, balance) in map.range_mut(Included(&"B"), Excluded(&"Cheryl")) {
1546 /// *balance += 100;
1548 /// for (name, balance) in &map {
1549 /// println!("{} => {}", name, balance);
1552 #[unstable(feature = "btree_range",
1553 reason = "matches collection reform specification, waiting for dust to settle")]
1554 pub fn range_mut<'a>(&'a mut self, min: Bound<&K>, max: Bound<&K>) -> RangeMut<'a, K, V> {
1555 range_impl!(&mut self.root, min, max, as_slices_internal_mut, iter_mut, RangeMut,
1559 /// Gets the given key's corresponding entry in the map for in-place manipulation.
1564 /// use std::collections::BTreeMap;
1566 /// let mut count: BTreeMap<&str, usize> = BTreeMap::new();
1568 /// // count the number of occurrences of letters in the vec
1569 /// for x in vec!["a","b","a","c","a","b"] {
1570 /// *count.entry(x).or_insert(0) += 1;
1573 /// assert_eq!(count["a"], 3);
1575 #[stable(feature = "rust1", since = "1.0.0")]
1576 pub fn entry(&mut self, mut key: K) -> Entry<K, V> {
1577 // same basic logic of `swap` and `pop`, blended together
1578 let mut stack = stack::PartialSearchStack::new(self);
1580 let result = stack.with(move |pusher, node| {
1581 match Node::search(node, &key) {
1584 Finished(Occupied(OccupiedEntry {
1585 stack: pusher.seal(handle)
1589 match handle.force() {
1590 Leaf(leaf_handle) => {
1591 Finished(Vacant(VacantEntry {
1592 stack: pusher.seal(leaf_handle),
1596 Internal(internal_handle) => {
1598 pusher.push(internal_handle),
1607 Finished(finished) => return finished,
1608 Continue((new_stack, renewed_key)) => {