1 // This is an attempt at an implementation following the ideal
4 // struct BTreeMap<K, V> {
6 // root: Option<Box<Node<K, V, height>>>
9 // struct Node<K, V, height: usize> {
10 // keys: [K; 2 * B - 1],
11 // vals: [V; 2 * B - 1],
12 // edges: [if height > 0 { Box<Node<K, V, height - 1>> } else { () }; 2 * B],
13 // parent: Option<(NonNull<Node<K, V, height + 1>>, u16)>,
18 // Since Rust doesn't actually have dependent types and polymorphic recursion,
19 // we make do with lots of unsafety.
21 // A major goal of this module is to avoid complexity by treating the tree as a generic (if
22 // weirdly shaped) container and avoiding dealing with most of the B-Tree invariants. As such,
23 // this module doesn't care whether the entries are sorted, which nodes can be underfull, or
24 // even what underfull means. However, we do rely on a few invariants:
26 // - Trees must have uniform depth/height. This means that every path down to a leaf from a
27 // given node has exactly the same length.
28 // - A node of length `n` has `n` keys, `n` values, and `n + 1` edges.
29 // This implies that even an empty node has at least one edge.
30 // For a leaf node, "having an edge" only means we can identify a position in the node,
31 // since leaf edges are empty and need no data representation. In an internal node,
32 // an edge both identifies a position and contains a pointer to a child node.
34 use core::marker::PhantomData;
35 use core::mem::{self, MaybeUninit};
36 use core::ptr::{self, NonNull};
37 use core::slice::SliceIndex;
39 use crate::alloc::{Allocator, Layout};
40 use crate::boxed::Box;
43 pub const CAPACITY: usize = 2 * B - 1;
44 pub const MIN_LEN_AFTER_SPLIT: usize = B - 1;
45 const KV_IDX_CENTER: usize = B - 1;
46 const EDGE_IDX_LEFT_OF_CENTER: usize = B - 1;
47 const EDGE_IDX_RIGHT_OF_CENTER: usize = B;
49 /// The underlying representation of leaf nodes and part of the representation of internal nodes.
50 struct LeafNode<K, V> {
51 /// We want to be covariant in `K` and `V`.
52 parent: Option<NonNull<InternalNode<K, V>>>,
54 /// This node's index into the parent node's `edges` array.
55 /// `*node.parent.edges[node.parent_idx]` should be the same thing as `node`.
56 /// This is only guaranteed to be initialized when `parent` is non-null.
57 parent_idx: MaybeUninit<u16>,
59 /// The number of keys and values this node stores.
62 /// The arrays storing the actual data of the node. Only the first `len` elements of each
63 /// array are initialized and valid.
64 keys: [MaybeUninit<K>; CAPACITY],
65 vals: [MaybeUninit<V>; CAPACITY],
68 impl<K, V> LeafNode<K, V> {
69 /// Initializes a new `LeafNode` in-place.
70 unsafe fn init(this: *mut Self) {
71 // As a general policy, we leave fields uninitialized if they can be, as this should
72 // be both slightly faster and easier to track in Valgrind.
74 // parent_idx, keys, and vals are all MaybeUninit
75 ptr::addr_of_mut!((*this).parent).write(None);
76 ptr::addr_of_mut!((*this).len).write(0);
80 /// Creates a new boxed `LeafNode`.
81 fn new<A: Allocator + Clone>(alloc: A) -> Box<Self, A> {
83 let mut leaf = Box::new_uninit_in(alloc);
84 LeafNode::init(leaf.as_mut_ptr());
90 /// The underlying representation of internal nodes. As with `LeafNode`s, these should be hidden
91 /// behind `BoxedNode`s to prevent dropping uninitialized keys and values. Any pointer to an
92 /// `InternalNode` can be directly cast to a pointer to the underlying `LeafNode` portion of the
93 /// node, allowing code to act on leaf and internal nodes generically without having to even check
94 /// which of the two a pointer is pointing at. This property is enabled by the use of `repr(C)`.
96 // gdb_providers.py uses this type name for introspection.
97 struct InternalNode<K, V> {
100 /// The pointers to the children of this node. `len + 1` of these are considered
101 /// initialized and valid, except that near the end, while the tree is held
102 /// through borrow type `Dying`, some of these pointers are dangling.
103 edges: [MaybeUninit<BoxedNode<K, V>>; 2 * B],
106 impl<K, V> InternalNode<K, V> {
107 /// Creates a new boxed `InternalNode`.
110 /// An invariant of internal nodes is that they have at least one
111 /// initialized and valid edge. This function does not set up
113 unsafe fn new<A: Allocator + Clone>(alloc: A) -> Box<Self, A> {
115 let mut node = Box::<Self, _>::new_uninit_in(alloc);
116 // We only need to initialize the data; the edges are MaybeUninit.
117 LeafNode::init(ptr::addr_of_mut!((*node.as_mut_ptr()).data));
123 /// A managed, non-null pointer to a node. This is either an owned pointer to
124 /// `LeafNode<K, V>` or an owned pointer to `InternalNode<K, V>`.
126 /// However, `BoxedNode` contains no information as to which of the two types
127 /// of nodes it actually contains, and, partially due to this lack of information,
128 /// is not a separate type and has no destructor.
129 type BoxedNode<K, V> = NonNull<LeafNode<K, V>>;
131 // N.B. `NodeRef` is always covariant in `K` and `V`, even when the `BorrowType`
132 // is `Mut`. This is technically wrong, but cannot result in any unsafety due to
133 // internal use of `NodeRef` because we stay completely generic over `K` and `V`.
134 // However, whenever a public type wraps `NodeRef`, make sure that it has the
137 /// A reference to a node.
139 /// This type has a number of parameters that controls how it acts:
140 /// - `BorrowType`: A dummy type that describes the kind of borrow and carries a lifetime.
141 /// - When this is `Immut<'a>`, the `NodeRef` acts roughly like `&'a Node`.
142 /// - When this is `ValMut<'a>`, the `NodeRef` acts roughly like `&'a Node`
143 /// with respect to keys and tree structure, but also allows many
144 /// mutable references to values throughout the tree to coexist.
145 /// - When this is `Mut<'a>`, the `NodeRef` acts roughly like `&'a mut Node`,
146 /// although insert methods allow a mutable pointer to a value to coexist.
147 /// - When this is `Owned`, the `NodeRef` acts roughly like `Box<Node>`,
148 /// but does not have a destructor, and must be cleaned up manually.
149 /// - When this is `Dying`, the `NodeRef` still acts roughly like `Box<Node>`,
150 /// but has methods to destroy the tree bit by bit, and ordinary methods,
151 /// while not marked as unsafe to call, can invoke UB if called incorrectly.
152 /// Since any `NodeRef` allows navigating through the tree, `BorrowType`
153 /// effectively applies to the entire tree, not just to the node itself.
154 /// - `K` and `V`: These are the types of keys and values stored in the nodes.
155 /// - `Type`: This can be `Leaf`, `Internal`, or `LeafOrInternal`. When this is
156 /// `Leaf`, the `NodeRef` points to a leaf node, when this is `Internal` the
157 /// `NodeRef` points to an internal node, and when this is `LeafOrInternal` the
158 /// `NodeRef` could be pointing to either type of node.
159 /// `Type` is named `NodeType` when used outside `NodeRef`.
161 /// Both `BorrowType` and `NodeType` restrict what methods we implement, to
162 /// exploit static type safety. There are limitations in the way we can apply
163 /// such restrictions:
164 /// - For each type parameter, we can only define a method either generically
165 /// or for one particular type. For example, we cannot define a method like
166 /// `into_kv` generically for all `BorrowType`, or once for all types that
167 /// carry a lifetime, because we want it to return `&'a` references.
168 /// Therefore, we define it only for the least powerful type `Immut<'a>`.
169 /// - We cannot get implicit coercion from say `Mut<'a>` to `Immut<'a>`.
170 /// Therefore, we have to explicitly call `reborrow` on a more powerful
171 /// `NodeRef` in order to reach a method like `into_kv`.
173 /// All methods on `NodeRef` that return some kind of reference, either:
174 /// - Take `self` by value, and return the lifetime carried by `BorrowType`.
175 /// Sometimes, to invoke such a method, we need to call `reborrow_mut`.
176 /// - Take `self` by reference, and (implicitly) return that reference's
177 /// lifetime, instead of the lifetime carried by `BorrowType`. That way,
178 /// the borrow checker guarantees that the `NodeRef` remains borrowed as long
179 /// as the returned reference is used.
180 /// The methods supporting insert bend this rule by returning a raw pointer,
181 /// i.e., a reference without any lifetime.
182 pub struct NodeRef<BorrowType, K, V, Type> {
183 /// The number of levels that the node and the level of leaves are apart, a
184 /// constant of the node that cannot be entirely described by `Type`, and that
185 /// the node itself does not store. We only need to store the height of the root
186 /// node, and derive every other node's height from it.
187 /// Must be zero if `Type` is `Leaf` and non-zero if `Type` is `Internal`.
189 /// The pointer to the leaf or internal node. The definition of `InternalNode`
190 /// ensures that the pointer is valid either way.
191 node: NonNull<LeafNode<K, V>>,
192 _marker: PhantomData<(BorrowType, Type)>,
195 /// The root node of an owned tree.
197 /// Note that this does not have a destructor, and must be cleaned up manually.
198 pub type Root<K, V> = NodeRef<marker::Owned, K, V, marker::LeafOrInternal>;
200 impl<'a, K: 'a, V: 'a, Type> Copy for NodeRef<marker::Immut<'a>, K, V, Type> {}
201 impl<'a, K: 'a, V: 'a, Type> Clone for NodeRef<marker::Immut<'a>, K, V, Type> {
202 fn clone(&self) -> Self {
207 unsafe impl<BorrowType, K: Sync, V: Sync, Type> Sync for NodeRef<BorrowType, K, V, Type> {}
209 unsafe impl<K: Sync, V: Sync, Type> Send for NodeRef<marker::Immut<'_>, K, V, Type> {}
210 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Mut<'_>, K, V, Type> {}
211 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::ValMut<'_>, K, V, Type> {}
212 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Owned, K, V, Type> {}
213 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Dying, K, V, Type> {}
215 impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
216 pub fn new_leaf<A: Allocator + Clone>(alloc: A) -> Self {
217 Self::from_new_leaf(LeafNode::new(alloc))
220 fn from_new_leaf<A: Allocator + Clone>(leaf: Box<LeafNode<K, V>, A>) -> Self {
221 NodeRef { height: 0, node: NonNull::from(Box::leak(leaf)), _marker: PhantomData }
225 impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
226 fn new_internal<A: Allocator + Clone>(child: Root<K, V>, alloc: A) -> Self {
227 let mut new_node = unsafe { InternalNode::new(alloc) };
228 new_node.edges[0].write(child.node);
229 unsafe { NodeRef::from_new_internal(new_node, child.height + 1) }
233 /// `height` must not be zero.
234 unsafe fn from_new_internal<A: Allocator + Clone>(
235 internal: Box<InternalNode<K, V>, A>,
238 debug_assert!(height > 0);
239 let node = NonNull::from(Box::leak(internal)).cast();
240 let mut this = NodeRef { height, node, _marker: PhantomData };
241 this.borrow_mut().correct_all_childrens_parent_links();
246 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
247 /// Unpack a node reference that was packed as `NodeRef::parent`.
248 fn from_internal(node: NonNull<InternalNode<K, V>>, height: usize) -> Self {
249 debug_assert!(height > 0);
250 NodeRef { height, node: node.cast(), _marker: PhantomData }
254 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
255 /// Exposes the data of an internal node.
257 /// Returns a raw ptr to avoid invalidating other references to this node.
258 fn as_internal_ptr(this: &Self) -> *mut InternalNode<K, V> {
259 // SAFETY: the static node type is `Internal`.
260 this.node.as_ptr() as *mut InternalNode<K, V>
264 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
265 /// Borrows exclusive access to the data of an internal node.
266 fn as_internal_mut(&mut self) -> &mut InternalNode<K, V> {
267 let ptr = Self::as_internal_ptr(self);
272 impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
273 /// Finds the length of the node. This is the number of keys or values.
274 /// The number of edges is `len() + 1`.
275 /// Note that, despite being safe, calling this function can have the side effect
276 /// of invalidating mutable references that unsafe code has created.
277 pub fn len(&self) -> usize {
278 // Crucially, we only access the `len` field here. If BorrowType is marker::ValMut,
279 // there might be outstanding mutable references to values that we must not invalidate.
280 unsafe { usize::from((*Self::as_leaf_ptr(self)).len) }
283 /// Returns the number of levels that the node and leaves are apart. Zero
284 /// height means the node is a leaf itself. If you picture trees with the
285 /// root on top, the number says at which elevation the node appears.
286 /// If you picture trees with leaves on top, the number says how high
287 /// the tree extends above the node.
288 pub fn height(&self) -> usize {
292 /// Temporarily takes out another, immutable reference to the same node.
293 pub fn reborrow(&self) -> NodeRef<marker::Immut<'_>, K, V, Type> {
294 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
297 /// Exposes the leaf portion of any leaf or internal node.
299 /// Returns a raw ptr to avoid invalidating other references to this node.
300 fn as_leaf_ptr(this: &Self) -> *mut LeafNode<K, V> {
301 // The node must be valid for at least the LeafNode portion.
302 // This is not a reference in the NodeRef type because we don't know if
303 // it should be unique or shared.
308 impl<BorrowType: marker::BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
309 /// Finds the parent of the current node. Returns `Ok(handle)` if the current
310 /// node actually has a parent, where `handle` points to the edge of the parent
311 /// that points to the current node. Returns `Err(self)` if the current node has
312 /// no parent, giving back the original `NodeRef`.
314 /// The method name assumes you picture trees with the root node on top.
316 /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
317 /// both, upon success, do nothing.
320 ) -> Result<Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>, Self> {
322 assert!(BorrowType::TRAVERSAL_PERMIT);
325 // We need to use raw pointers to nodes because, if BorrowType is marker::ValMut,
326 // there might be outstanding mutable references to values that we must not invalidate.
327 let leaf_ptr: *const _ = Self::as_leaf_ptr(&self);
328 unsafe { (*leaf_ptr).parent }
330 .map(|parent| Handle {
331 node: NodeRef::from_internal(*parent, self.height + 1),
332 idx: unsafe { usize::from((*leaf_ptr).parent_idx.assume_init()) },
333 _marker: PhantomData,
338 pub fn first_edge(self) -> Handle<Self, marker::Edge> {
339 unsafe { Handle::new_edge(self, 0) }
342 pub fn last_edge(self) -> Handle<Self, marker::Edge> {
343 let len = self.len();
344 unsafe { Handle::new_edge(self, len) }
347 /// Note that `self` must be nonempty.
348 pub fn first_kv(self) -> Handle<Self, marker::KV> {
349 let len = self.len();
351 unsafe { Handle::new_kv(self, 0) }
354 /// Note that `self` must be nonempty.
355 pub fn last_kv(self) -> Handle<Self, marker::KV> {
356 let len = self.len();
358 unsafe { Handle::new_kv(self, len - 1) }
362 impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
363 /// Could be a public implementation of PartialEq, but only used in this module.
364 fn eq(&self, other: &Self) -> bool {
365 let Self { node, height, _marker } = self;
366 if node.eq(&other.node) {
367 debug_assert_eq!(*height, other.height);
375 impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
376 /// Exposes the leaf portion of any leaf or internal node in an immutable tree.
377 fn into_leaf(self) -> &'a LeafNode<K, V> {
378 let ptr = Self::as_leaf_ptr(&self);
379 // SAFETY: there can be no mutable references into this tree borrowed as `Immut`.
383 /// Borrows a view into the keys stored in the node.
384 pub fn keys(&self) -> &[K] {
385 let leaf = self.into_leaf();
387 MaybeUninit::slice_assume_init_ref(leaf.keys.get_unchecked(..usize::from(leaf.len)))
392 impl<K, V> NodeRef<marker::Dying, K, V, marker::LeafOrInternal> {
393 /// Similar to `ascend`, gets a reference to a node's parent node, but also
394 /// deallocates the current node in the process. This is unsafe because the
395 /// current node will still be accessible despite being deallocated.
396 pub unsafe fn deallocate_and_ascend<A: Allocator + Clone>(
399 ) -> Option<Handle<NodeRef<marker::Dying, K, V, marker::Internal>, marker::Edge>> {
400 let height = self.height;
401 let node = self.node;
402 let ret = self.ascend().ok();
407 Layout::new::<InternalNode<K, V>>()
409 Layout::new::<LeafNode<K, V>>()
417 impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
418 /// Temporarily takes out another mutable reference to the same node. Beware, as
419 /// this method is very dangerous, doubly so since it might not immediately appear
422 /// Because mutable pointers can roam anywhere around the tree, the returned
423 /// pointer can easily be used to make the original pointer dangling, out of
424 /// bounds, or invalid under stacked borrow rules.
425 // FIXME(@gereeter) consider adding yet another type parameter to `NodeRef`
426 // that restricts the use of navigation methods on reborrowed pointers,
427 // preventing this unsafety.
428 unsafe fn reborrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
429 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
432 /// Borrows exclusive access to the leaf portion of a leaf or internal node.
433 fn as_leaf_mut(&mut self) -> &mut LeafNode<K, V> {
434 let ptr = Self::as_leaf_ptr(self);
435 // SAFETY: we have exclusive access to the entire node.
439 /// Offers exclusive access to the leaf portion of a leaf or internal node.
440 fn into_leaf_mut(mut self) -> &'a mut LeafNode<K, V> {
441 let ptr = Self::as_leaf_ptr(&mut self);
442 // SAFETY: we have exclusive access to the entire node.
446 /// Returns a dormant copy of this node with its lifetime erased which can
447 /// be reawakened later.
448 pub fn dormant(&self) -> NodeRef<marker::DormantMut, K, V, Type> {
449 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
453 impl<K, V, Type> NodeRef<marker::DormantMut, K, V, Type> {
454 /// Revert to the unique borrow initially captured.
458 /// The reborrow must have ended, i.e., the reference returned by `new` and
459 /// all pointers and references derived from it, must not be used anymore.
460 pub unsafe fn awaken<'a>(self) -> NodeRef<marker::Mut<'a>, K, V, Type> {
461 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
465 impl<K, V, Type> NodeRef<marker::Dying, K, V, Type> {
466 /// Borrows exclusive access to the leaf portion of a dying leaf or internal node.
467 fn as_leaf_dying(&mut self) -> &mut LeafNode<K, V> {
468 let ptr = Self::as_leaf_ptr(self);
469 // SAFETY: we have exclusive access to the entire node.
474 impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
475 /// Borrows exclusive access to an element of the key storage area.
478 /// `index` is in bounds of 0..CAPACITY
479 unsafe fn key_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
481 I: SliceIndex<[MaybeUninit<K>], Output = Output>,
483 // SAFETY: the caller will not be able to call further methods on self
484 // until the key slice reference is dropped, as we have unique access
485 // for the lifetime of the borrow.
486 unsafe { self.as_leaf_mut().keys.as_mut_slice().get_unchecked_mut(index) }
489 /// Borrows exclusive access to an element or slice of the node's value storage area.
492 /// `index` is in bounds of 0..CAPACITY
493 unsafe fn val_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
495 I: SliceIndex<[MaybeUninit<V>], Output = Output>,
497 // SAFETY: the caller will not be able to call further methods on self
498 // until the value slice reference is dropped, as we have unique access
499 // for the lifetime of the borrow.
500 unsafe { self.as_leaf_mut().vals.as_mut_slice().get_unchecked_mut(index) }
504 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
505 /// Borrows exclusive access to an element or slice of the node's storage area for edge contents.
508 /// `index` is in bounds of 0..CAPACITY + 1
509 unsafe fn edge_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
511 I: SliceIndex<[MaybeUninit<BoxedNode<K, V>>], Output = Output>,
513 // SAFETY: the caller will not be able to call further methods on self
514 // until the edge slice reference is dropped, as we have unique access
515 // for the lifetime of the borrow.
516 unsafe { self.as_internal_mut().edges.as_mut_slice().get_unchecked_mut(index) }
520 impl<'a, K, V, Type> NodeRef<marker::ValMut<'a>, K, V, Type> {
522 /// - The node has more than `idx` initialized elements.
523 unsafe fn into_key_val_mut_at(mut self, idx: usize) -> (&'a K, &'a mut V) {
524 // We only create a reference to the one element we are interested in,
525 // to avoid aliasing with outstanding references to other elements,
526 // in particular, those returned to the caller in earlier iterations.
527 let leaf = Self::as_leaf_ptr(&mut self);
528 let keys = unsafe { ptr::addr_of!((*leaf).keys) };
529 let vals = unsafe { ptr::addr_of_mut!((*leaf).vals) };
530 // We must coerce to unsized array pointers because of Rust issue #74679.
531 let keys: *const [_] = keys;
532 let vals: *mut [_] = vals;
533 let key = unsafe { (&*keys.get_unchecked(idx)).assume_init_ref() };
534 let val = unsafe { (&mut *vals.get_unchecked_mut(idx)).assume_init_mut() };
539 impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
540 /// Borrows exclusive access to the length of the node.
541 pub fn len_mut(&mut self) -> &mut u16 {
542 &mut self.as_leaf_mut().len
546 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
548 /// Every item returned by `range` is a valid edge index for the node.
549 unsafe fn correct_childrens_parent_links<R: Iterator<Item = usize>>(&mut self, range: R) {
551 debug_assert!(i <= self.len());
552 unsafe { Handle::new_edge(self.reborrow_mut(), i) }.correct_parent_link();
556 fn correct_all_childrens_parent_links(&mut self) {
557 let len = self.len();
558 unsafe { self.correct_childrens_parent_links(0..=len) };
562 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
563 /// Sets the node's link to its parent edge,
564 /// without invalidating other references to the node.
565 fn set_parent_link(&mut self, parent: NonNull<InternalNode<K, V>>, parent_idx: usize) {
566 let leaf = Self::as_leaf_ptr(self);
567 unsafe { (*leaf).parent = Some(parent) };
568 unsafe { (*leaf).parent_idx.write(parent_idx as u16) };
572 impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
573 /// Clears the root's link to its parent edge.
574 fn clear_parent_link(&mut self) {
575 let mut root_node = self.borrow_mut();
576 let leaf = root_node.as_leaf_mut();
581 impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
582 /// Returns a new owned tree, with its own root node that is initially empty.
583 pub fn new<A: Allocator + Clone>(alloc: A) -> Self {
584 NodeRef::new_leaf(alloc).forget_type()
587 /// Adds a new internal node with a single edge pointing to the previous root node,
588 /// make that new node the root node, and return it. This increases the height by 1
589 /// and is the opposite of `pop_internal_level`.
590 pub fn push_internal_level<A: Allocator + Clone>(
593 ) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
594 super::mem::take_mut(self, |old_root| NodeRef::new_internal(old_root, alloc).forget_type());
596 // `self.borrow_mut()`, except that we just forgot we're internal now:
597 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
600 /// Removes the internal root node, using its first child as the new root node.
601 /// As it is intended only to be called when the root node has only one child,
602 /// no cleanup is done on any of the keys, values and other children.
603 /// This decreases the height by 1 and is the opposite of `push_internal_level`.
605 /// Requires exclusive access to the `NodeRef` object but not to the root node;
606 /// it will not invalidate other handles or references to the root node.
608 /// Panics if there is no internal level, i.e., if the root node is a leaf.
609 pub fn pop_internal_level<A: Allocator + Clone>(&mut self, alloc: A) {
610 assert!(self.height > 0);
614 // SAFETY: we asserted to be internal.
615 let internal_self = unsafe { self.borrow_mut().cast_to_internal_unchecked() };
616 // SAFETY: we borrowed `self` exclusively and its borrow type is exclusive.
617 let internal_node = unsafe { &mut *NodeRef::as_internal_ptr(&internal_self) };
618 // SAFETY: the first edge is always initialized.
619 self.node = unsafe { internal_node.edges[0].assume_init_read() };
621 self.clear_parent_link();
624 alloc.deallocate(top.cast(), Layout::new::<InternalNode<K, V>>());
629 impl<K, V, Type> NodeRef<marker::Owned, K, V, Type> {
630 /// Mutably borrows the owned root node. Unlike `reborrow_mut`, this is safe
631 /// because the return value cannot be used to destroy the root, and there
632 /// cannot be other references to the tree.
633 pub fn borrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
634 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
637 /// Slightly mutably borrows the owned root node.
638 pub fn borrow_valmut(&mut self) -> NodeRef<marker::ValMut<'_>, K, V, Type> {
639 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
642 /// Irreversibly transitions to a reference that permits traversal and offers
643 /// destructive methods and little else.
644 pub fn into_dying(self) -> NodeRef<marker::Dying, K, V, Type> {
645 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
649 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
650 /// Adds a key-value pair to the end of the node, and returns
651 /// the mutable reference of the inserted value.
652 pub fn push(&mut self, key: K, val: V) -> &mut V {
653 let len = self.len_mut();
654 let idx = usize::from(*len);
655 assert!(idx < CAPACITY);
658 self.key_area_mut(idx).write(key);
659 self.val_area_mut(idx).write(val)
664 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
665 /// Adds a key-value pair, and an edge to go to the right of that pair,
666 /// to the end of the node.
667 pub fn push(&mut self, key: K, val: V, edge: Root<K, V>) {
668 assert!(edge.height == self.height - 1);
670 let len = self.len_mut();
671 let idx = usize::from(*len);
672 assert!(idx < CAPACITY);
675 self.key_area_mut(idx).write(key);
676 self.val_area_mut(idx).write(val);
677 self.edge_area_mut(idx + 1).write(edge.node);
678 Handle::new_edge(self.reborrow_mut(), idx + 1).correct_parent_link();
683 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Leaf> {
684 /// Removes any static information asserting that this node is a `Leaf` node.
685 pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
686 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
690 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
691 /// Removes any static information asserting that this node is an `Internal` node.
692 pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
693 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
697 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
698 /// Checks whether a node is an `Internal` node or a `Leaf` node.
702 NodeRef<BorrowType, K, V, marker::Leaf>,
703 NodeRef<BorrowType, K, V, marker::Internal>,
705 if self.height == 0 {
706 ForceResult::Leaf(NodeRef {
709 _marker: PhantomData,
712 ForceResult::Internal(NodeRef {
715 _marker: PhantomData,
721 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
722 /// Unsafely asserts to the compiler the static information that this node is a `Leaf`.
723 unsafe fn cast_to_leaf_unchecked(self) -> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
724 debug_assert!(self.height == 0);
725 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
728 /// Unsafely asserts to the compiler the static information that this node is an `Internal`.
729 unsafe fn cast_to_internal_unchecked(self) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
730 debug_assert!(self.height > 0);
731 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
735 /// A reference to a specific key-value pair or edge within a node. The `Node` parameter
736 /// must be a `NodeRef`, while the `Type` can either be `KV` (signifying a handle on a key-value
737 /// pair) or `Edge` (signifying a handle on an edge).
739 /// Note that even `Leaf` nodes can have `Edge` handles. Instead of representing a pointer to
740 /// a child node, these represent the spaces where child pointers would go between the key-value
741 /// pairs. For example, in a node with length 2, there would be 3 possible edge locations - one
742 /// to the left of the node, one between the two pairs, and one at the right of the node.
743 pub struct Handle<Node, Type> {
746 _marker: PhantomData<Type>,
749 impl<Node: Copy, Type> Copy for Handle<Node, Type> {}
750 // We don't need the full generality of `#[derive(Clone)]`, as the only time `Node` will be
751 // `Clone`able is when it is an immutable reference and therefore `Copy`.
752 impl<Node: Copy, Type> Clone for Handle<Node, Type> {
753 fn clone(&self) -> Self {
758 impl<Node, Type> Handle<Node, Type> {
759 /// Retrieves the node that contains the edge or key-value pair this handle points to.
760 pub fn into_node(self) -> Node {
764 /// Returns the position of this handle in the node.
765 pub fn idx(&self) -> usize {
770 impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV> {
771 /// Creates a new handle to a key-value pair in `node`.
772 /// Unsafe because the caller must ensure that `idx < node.len()`.
773 pub unsafe fn new_kv(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
774 debug_assert!(idx < node.len());
776 Handle { node, idx, _marker: PhantomData }
779 pub fn left_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
780 unsafe { Handle::new_edge(self.node, self.idx) }
783 pub fn right_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
784 unsafe { Handle::new_edge(self.node, self.idx + 1) }
788 impl<BorrowType, K, V, NodeType, HandleType> PartialEq
789 for Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
791 fn eq(&self, other: &Self) -> bool {
792 let Self { node, idx, _marker } = self;
793 node.eq(&other.node) && *idx == other.idx
797 impl<BorrowType, K, V, NodeType, HandleType>
798 Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
800 /// Temporarily takes out another immutable handle on the same location.
801 pub fn reborrow(&self) -> Handle<NodeRef<marker::Immut<'_>, K, V, NodeType>, HandleType> {
802 // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
803 Handle { node: self.node.reborrow(), idx: self.idx, _marker: PhantomData }
807 impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
808 /// Temporarily takes out another mutable handle on the same location. Beware, as
809 /// this method is very dangerous, doubly so since it might not immediately appear
812 /// For details, see `NodeRef::reborrow_mut`.
813 pub unsafe fn reborrow_mut(
815 ) -> Handle<NodeRef<marker::Mut<'_>, K, V, NodeType>, HandleType> {
816 // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
817 Handle { node: unsafe { self.node.reborrow_mut() }, idx: self.idx, _marker: PhantomData }
820 /// Returns a dormant copy of this handle which can be reawakened later.
822 /// See `DormantMutRef` for more details.
823 pub fn dormant(&self) -> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
824 Handle { node: self.node.dormant(), idx: self.idx, _marker: PhantomData }
828 impl<K, V, NodeType, HandleType> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
829 /// Revert to the unique borrow initially captured.
833 /// The reborrow must have ended, i.e., the reference returned by `new` and
834 /// all pointers and references derived from it, must not be used anymore.
835 pub unsafe fn awaken<'a>(self) -> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
836 Handle { node: unsafe { self.node.awaken() }, idx: self.idx, _marker: PhantomData }
840 impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
841 /// Creates a new handle to an edge in `node`.
842 /// Unsafe because the caller must ensure that `idx <= node.len()`.
843 pub unsafe fn new_edge(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
844 debug_assert!(idx <= node.len());
846 Handle { node, idx, _marker: PhantomData }
849 pub fn left_kv(self) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
851 Ok(unsafe { Handle::new_kv(self.node, self.idx - 1) })
857 pub fn right_kv(self) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
858 if self.idx < self.node.len() {
859 Ok(unsafe { Handle::new_kv(self.node, self.idx) })
866 pub enum LeftOrRight<T> {
871 /// Given an edge index where we want to insert into a node filled to capacity,
872 /// computes a sensible KV index of a split point and where to perform the insertion.
873 /// The goal of the split point is for its key and value to end up in a parent node;
874 /// the keys, values and edges to the left of the split point become the left child;
875 /// the keys, values and edges to the right of the split point become the right child.
876 fn splitpoint(edge_idx: usize) -> (usize, LeftOrRight<usize>) {
877 debug_assert!(edge_idx <= CAPACITY);
878 // Rust issue #74834 tries to explain these symmetric rules.
880 0..EDGE_IDX_LEFT_OF_CENTER => (KV_IDX_CENTER - 1, LeftOrRight::Left(edge_idx)),
881 EDGE_IDX_LEFT_OF_CENTER => (KV_IDX_CENTER, LeftOrRight::Left(edge_idx)),
882 EDGE_IDX_RIGHT_OF_CENTER => (KV_IDX_CENTER, LeftOrRight::Right(0)),
883 _ => (KV_IDX_CENTER + 1, LeftOrRight::Right(edge_idx - (KV_IDX_CENTER + 1 + 1))),
887 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
888 /// Inserts a new key-value pair between the key-value pairs to the right and left of
889 /// this edge. This method assumes that there is enough space in the node for the new
891 unsafe fn insert_fit(
895 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
896 debug_assert!(self.node.len() < CAPACITY);
897 let new_len = self.node.len() + 1;
900 slice_insert(self.node.key_area_mut(..new_len), self.idx, key);
901 slice_insert(self.node.val_area_mut(..new_len), self.idx, val);
902 *self.node.len_mut() = new_len as u16;
904 Handle::new_kv(self.node, self.idx)
909 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
910 /// Inserts a new key-value pair between the key-value pairs to the right and left of
911 /// this edge. This method splits the node if there isn't enough room.
913 /// Returns a dormant handle to the inserted node which can be reawakened
914 /// once splitting is complete.
915 fn insert<A: Allocator + Clone>(
921 Option<SplitResult<'a, K, V, marker::Leaf>>,
922 Handle<NodeRef<marker::DormantMut, K, V, marker::Leaf>, marker::KV>,
924 if self.node.len() < CAPACITY {
925 // SAFETY: There is enough space in the node for insertion.
926 let handle = unsafe { self.insert_fit(key, val) };
927 (None, handle.dormant())
929 let (middle_kv_idx, insertion) = splitpoint(self.idx);
930 let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
931 let mut result = middle.split(alloc);
932 let insertion_edge = match insertion {
933 LeftOrRight::Left(insert_idx) => unsafe {
934 Handle::new_edge(result.left.reborrow_mut(), insert_idx)
936 LeftOrRight::Right(insert_idx) => unsafe {
937 Handle::new_edge(result.right.borrow_mut(), insert_idx)
940 // SAFETY: We just split the node, so there is enough space for
942 let handle = unsafe { insertion_edge.insert_fit(key, val).dormant() };
943 (Some(result), handle)
948 impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
949 /// Fixes the parent pointer and index in the child node that this edge
950 /// links to. This is useful when the ordering of edges has been changed,
951 fn correct_parent_link(self) {
952 // Create backpointer without invalidating other references to the node.
953 let ptr = unsafe { NonNull::new_unchecked(NodeRef::as_internal_ptr(&self.node)) };
955 let mut child = self.descend();
956 child.set_parent_link(ptr, idx);
960 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
961 /// Inserts a new key-value pair and an edge that will go to the right of that new pair
962 /// between this edge and the key-value pair to the right of this edge. This method assumes
963 /// that there is enough space in the node for the new pair to fit.
964 fn insert_fit(&mut self, key: K, val: V, edge: Root<K, V>) {
965 debug_assert!(self.node.len() < CAPACITY);
966 debug_assert!(edge.height == self.node.height - 1);
967 let new_len = self.node.len() + 1;
970 slice_insert(self.node.key_area_mut(..new_len), self.idx, key);
971 slice_insert(self.node.val_area_mut(..new_len), self.idx, val);
972 slice_insert(self.node.edge_area_mut(..new_len + 1), self.idx + 1, edge.node);
973 *self.node.len_mut() = new_len as u16;
975 self.node.correct_childrens_parent_links(self.idx + 1..new_len + 1);
979 /// Inserts a new key-value pair and an edge that will go to the right of that new pair
980 /// between this edge and the key-value pair to the right of this edge. This method splits
981 /// the node if there isn't enough room.
982 fn insert<A: Allocator + Clone>(
988 ) -> Option<SplitResult<'a, K, V, marker::Internal>> {
989 assert!(edge.height == self.node.height - 1);
991 if self.node.len() < CAPACITY {
992 self.insert_fit(key, val, edge);
995 let (middle_kv_idx, insertion) = splitpoint(self.idx);
996 let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
997 let mut result = middle.split(alloc);
998 let mut insertion_edge = match insertion {
999 LeftOrRight::Left(insert_idx) => unsafe {
1000 Handle::new_edge(result.left.reborrow_mut(), insert_idx)
1002 LeftOrRight::Right(insert_idx) => unsafe {
1003 Handle::new_edge(result.right.borrow_mut(), insert_idx)
1006 insertion_edge.insert_fit(key, val, edge);
1012 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
1013 /// Inserts a new key-value pair between the key-value pairs to the right and left of
1014 /// this edge. This method splits the node if there isn't enough room, and tries to
1015 /// insert the split off portion into the parent node recursively, until the root is reached.
1017 /// If the returned result is some `SplitResult`, the `left` field will be the root node.
1018 /// The returned pointer points to the inserted value, which in the case of `SplitResult`
1019 /// is in the `left` or `right` tree.
1020 pub fn insert_recursing<A: Allocator + Clone>(
1025 split_root: impl FnOnce(SplitResult<'a, K, V, marker::LeafOrInternal>),
1026 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
1027 let (mut split, handle) = match self.insert(key, value, alloc.clone()) {
1028 // SAFETY: we have finished splitting and can now re-awaken the
1029 // handle to the inserted element.
1030 (None, handle) => return unsafe { handle.awaken() },
1031 (Some(split), handle) => (split.forget_node_type(), handle),
1035 split = match split.left.ascend() {
1037 match parent.insert(split.kv.0, split.kv.1, split.right, alloc.clone()) {
1038 // SAFETY: we have finished splitting and can now re-awaken the
1039 // handle to the inserted element.
1040 None => return unsafe { handle.awaken() },
1041 Some(split) => split.forget_node_type(),
1045 split_root(SplitResult { left: root, ..split });
1046 // SAFETY: we have finished splitting and can now re-awaken the
1047 // handle to the inserted element.
1048 return unsafe { handle.awaken() };
1055 impl<BorrowType: marker::BorrowType, K, V>
1056 Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>
1058 /// Finds the node pointed to by this edge.
1060 /// The method name assumes you picture trees with the root node on top.
1062 /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
1063 /// both, upon success, do nothing.
1064 pub fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
1066 assert!(BorrowType::TRAVERSAL_PERMIT);
1069 // We need to use raw pointers to nodes because, if BorrowType is
1070 // marker::ValMut, there might be outstanding mutable references to
1071 // values that we must not invalidate. There's no worry accessing the
1072 // height field because that value is copied. Beware that, once the
1073 // node pointer is dereferenced, we access the edges array with a
1074 // reference (Rust issue #73987) and invalidate any other references
1075 // to or inside the array, should any be around.
1076 let parent_ptr = NodeRef::as_internal_ptr(&self.node);
1077 let node = unsafe { (*parent_ptr).edges.get_unchecked(self.idx).assume_init_read() };
1078 NodeRef { node, height: self.node.height - 1, _marker: PhantomData }
1082 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Immut<'a>, K, V, NodeType>, marker::KV> {
1083 pub fn into_kv(self) -> (&'a K, &'a V) {
1084 debug_assert!(self.idx < self.node.len());
1085 let leaf = self.node.into_leaf();
1086 let k = unsafe { leaf.keys.get_unchecked(self.idx).assume_init_ref() };
1087 let v = unsafe { leaf.vals.get_unchecked(self.idx).assume_init_ref() };
1092 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1093 pub fn key_mut(&mut self) -> &mut K {
1094 unsafe { self.node.key_area_mut(self.idx).assume_init_mut() }
1097 pub fn into_val_mut(self) -> &'a mut V {
1098 debug_assert!(self.idx < self.node.len());
1099 let leaf = self.node.into_leaf_mut();
1100 unsafe { leaf.vals.get_unchecked_mut(self.idx).assume_init_mut() }
1103 pub fn into_kv_valmut(self) -> (&'a K, &'a mut V) {
1104 debug_assert!(self.idx < self.node.len());
1105 let leaf = self.node.into_leaf_mut();
1106 let k = unsafe { leaf.keys.get_unchecked(self.idx).assume_init_ref() };
1107 let v = unsafe { leaf.vals.get_unchecked_mut(self.idx).assume_init_mut() };
1112 impl<'a, K, V, NodeType> Handle<NodeRef<marker::ValMut<'a>, K, V, NodeType>, marker::KV> {
1113 pub fn into_kv_valmut(self) -> (&'a K, &'a mut V) {
1114 unsafe { self.node.into_key_val_mut_at(self.idx) }
1118 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1119 pub fn kv_mut(&mut self) -> (&mut K, &mut V) {
1120 debug_assert!(self.idx < self.node.len());
1121 // We cannot call separate key and value methods, because calling the second one
1122 // invalidates the reference returned by the first.
1124 let leaf = self.node.as_leaf_mut();
1125 let key = leaf.keys.get_unchecked_mut(self.idx).assume_init_mut();
1126 let val = leaf.vals.get_unchecked_mut(self.idx).assume_init_mut();
1131 /// Replaces the key and value that the KV handle refers to.
1132 pub fn replace_kv(&mut self, k: K, v: V) -> (K, V) {
1133 let (key, val) = self.kv_mut();
1134 (mem::replace(key, k), mem::replace(val, v))
1138 impl<K, V, NodeType> Handle<NodeRef<marker::Dying, K, V, NodeType>, marker::KV> {
1139 /// Extracts the key and value that the KV handle refers to.
1141 /// The node that the handle refers to must not yet have been deallocated.
1142 pub unsafe fn into_key_val(mut self) -> (K, V) {
1143 debug_assert!(self.idx < self.node.len());
1144 let leaf = self.node.as_leaf_dying();
1146 let key = leaf.keys.get_unchecked_mut(self.idx).assume_init_read();
1147 let val = leaf.vals.get_unchecked_mut(self.idx).assume_init_read();
1152 /// Drops the key and value that the KV handle refers to.
1154 /// The node that the handle refers to must not yet have been deallocated.
1156 pub unsafe fn drop_key_val(mut self) {
1157 debug_assert!(self.idx < self.node.len());
1158 let leaf = self.node.as_leaf_dying();
1160 leaf.keys.get_unchecked_mut(self.idx).assume_init_drop();
1161 leaf.vals.get_unchecked_mut(self.idx).assume_init_drop();
1166 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1167 /// Helps implementations of `split` for a particular `NodeType`,
1168 /// by taking care of leaf data.
1169 fn split_leaf_data(&mut self, new_node: &mut LeafNode<K, V>) -> (K, V) {
1170 debug_assert!(self.idx < self.node.len());
1171 let old_len = self.node.len();
1172 let new_len = old_len - self.idx - 1;
1173 new_node.len = new_len as u16;
1175 let k = self.node.key_area_mut(self.idx).assume_init_read();
1176 let v = self.node.val_area_mut(self.idx).assume_init_read();
1179 self.node.key_area_mut(self.idx + 1..old_len),
1180 &mut new_node.keys[..new_len],
1183 self.node.val_area_mut(self.idx + 1..old_len),
1184 &mut new_node.vals[..new_len],
1187 *self.node.len_mut() = self.idx as u16;
1193 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
1194 /// Splits the underlying node into three parts:
1196 /// - The node is truncated to only contain the key-value pairs to the left of
1198 /// - The key and value pointed to by this handle are extracted.
1199 /// - All the key-value pairs to the right of this handle are put into a newly
1201 pub fn split<A: Allocator + Clone>(mut self, alloc: A) -> SplitResult<'a, K, V, marker::Leaf> {
1202 let mut new_node = LeafNode::new(alloc);
1204 let kv = self.split_leaf_data(&mut new_node);
1206 let right = NodeRef::from_new_leaf(new_node);
1207 SplitResult { left: self.node, kv, right }
1210 /// Removes the key-value pair pointed to by this handle and returns it, along with the edge
1211 /// that the key-value pair collapsed into.
1214 ) -> ((K, V), Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>) {
1215 let old_len = self.node.len();
1217 let k = slice_remove(self.node.key_area_mut(..old_len), self.idx);
1218 let v = slice_remove(self.node.val_area_mut(..old_len), self.idx);
1219 *self.node.len_mut() = (old_len - 1) as u16;
1220 ((k, v), self.left_edge())
1225 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
1226 /// Splits the underlying node into three parts:
1228 /// - The node is truncated to only contain the edges and key-value pairs to the
1229 /// left of this handle.
1230 /// - The key and value pointed to by this handle are extracted.
1231 /// - All the edges and key-value pairs to the right of this handle are put into
1232 /// a newly allocated node.
1233 pub fn split<A: Allocator + Clone>(
1236 ) -> SplitResult<'a, K, V, marker::Internal> {
1237 let old_len = self.node.len();
1239 let mut new_node = InternalNode::new(alloc);
1240 let kv = self.split_leaf_data(&mut new_node.data);
1241 let new_len = usize::from(new_node.data.len);
1243 self.node.edge_area_mut(self.idx + 1..old_len + 1),
1244 &mut new_node.edges[..new_len + 1],
1247 let height = self.node.height;
1248 let right = NodeRef::from_new_internal(new_node, height);
1250 SplitResult { left: self.node, kv, right }
1255 /// Represents a session for evaluating and performing a balancing operation
1256 /// around an internal key-value pair.
1257 pub struct BalancingContext<'a, K, V> {
1258 parent: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV>,
1259 left_child: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1260 right_child: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1263 impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
1264 pub fn consider_for_balancing(self) -> BalancingContext<'a, K, V> {
1265 let self1 = unsafe { ptr::read(&self) };
1266 let self2 = unsafe { ptr::read(&self) };
1269 left_child: self1.left_edge().descend(),
1270 right_child: self2.right_edge().descend(),
1275 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1276 /// Chooses a balancing context involving the node as a child, thus between
1277 /// the KV immediately to the left or to the right in the parent node.
1278 /// Returns an `Err` if there is no parent.
1279 /// Panics if the parent is empty.
1281 /// Prefers the left side, to be optimal if the given node is somehow
1282 /// underfull, meaning here only that it has fewer elements than its left
1283 /// sibling and than its right sibling, if they exist. In that case,
1284 /// merging with the left sibling is faster, since we only need to move
1285 /// the node's N elements, instead of shifting them to the right and moving
1286 /// more than N elements in front. Stealing from the left sibling is also
1287 /// typically faster, since we only need to shift the node's N elements to
1288 /// the right, instead of shifting at least N of the sibling's elements to
1290 pub fn choose_parent_kv(self) -> Result<LeftOrRight<BalancingContext<'a, K, V>>, Self> {
1291 match unsafe { ptr::read(&self) }.ascend() {
1292 Ok(parent_edge) => match parent_edge.left_kv() {
1293 Ok(left_parent_kv) => Ok(LeftOrRight::Left(BalancingContext {
1294 parent: unsafe { ptr::read(&left_parent_kv) },
1295 left_child: left_parent_kv.left_edge().descend(),
1298 Err(parent_edge) => match parent_edge.right_kv() {
1299 Ok(right_parent_kv) => Ok(LeftOrRight::Right(BalancingContext {
1300 parent: unsafe { ptr::read(&right_parent_kv) },
1302 right_child: right_parent_kv.right_edge().descend(),
1304 Err(_) => unreachable!("empty internal node"),
1307 Err(root) => Err(root),
1312 impl<'a, K, V> BalancingContext<'a, K, V> {
1313 pub fn left_child_len(&self) -> usize {
1314 self.left_child.len()
1317 pub fn right_child_len(&self) -> usize {
1318 self.right_child.len()
1321 pub fn into_left_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1325 pub fn into_right_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1329 /// Returns whether merging is possible, i.e., whether there is enough room
1330 /// in a node to combine the central KV with both adjacent child nodes.
1331 pub fn can_merge(&self) -> bool {
1332 self.left_child.len() + 1 + self.right_child.len() <= CAPACITY
1336 impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
1337 /// Performs a merge and lets a closure decide what to return.
1340 NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
1341 NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1350 let Handle { node: mut parent_node, idx: parent_idx, _marker } = self.parent;
1351 let old_parent_len = parent_node.len();
1352 let mut left_node = self.left_child;
1353 let old_left_len = left_node.len();
1354 let mut right_node = self.right_child;
1355 let right_len = right_node.len();
1356 let new_left_len = old_left_len + 1 + right_len;
1358 assert!(new_left_len <= CAPACITY);
1361 *left_node.len_mut() = new_left_len as u16;
1363 let parent_key = slice_remove(parent_node.key_area_mut(..old_parent_len), parent_idx);
1364 left_node.key_area_mut(old_left_len).write(parent_key);
1366 right_node.key_area_mut(..right_len),
1367 left_node.key_area_mut(old_left_len + 1..new_left_len),
1370 let parent_val = slice_remove(parent_node.val_area_mut(..old_parent_len), parent_idx);
1371 left_node.val_area_mut(old_left_len).write(parent_val);
1373 right_node.val_area_mut(..right_len),
1374 left_node.val_area_mut(old_left_len + 1..new_left_len),
1377 slice_remove(&mut parent_node.edge_area_mut(..old_parent_len + 1), parent_idx + 1);
1378 parent_node.correct_childrens_parent_links(parent_idx + 1..old_parent_len);
1379 *parent_node.len_mut() -= 1;
1381 if parent_node.height > 1 {
1382 // SAFETY: the height of the nodes being merged is one below the height
1383 // of the node of this edge, thus above zero, so they are internal.
1384 let mut left_node = left_node.reborrow_mut().cast_to_internal_unchecked();
1385 let mut right_node = right_node.cast_to_internal_unchecked();
1387 right_node.edge_area_mut(..right_len + 1),
1388 left_node.edge_area_mut(old_left_len + 1..new_left_len + 1),
1391 left_node.correct_childrens_parent_links(old_left_len + 1..new_left_len + 1);
1393 alloc.deallocate(right_node.node.cast(), Layout::new::<InternalNode<K, V>>());
1395 alloc.deallocate(right_node.node.cast(), Layout::new::<LeafNode<K, V>>());
1398 result(parent_node, left_node)
1401 /// Merges the parent's key-value pair and both adjacent child nodes into
1402 /// the left child node and returns the shrunk parent node.
1404 /// Panics unless we `.can_merge()`.
1405 pub fn merge_tracking_parent<A: Allocator + Clone>(
1408 ) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
1409 self.do_merge(|parent, _child| parent, alloc)
1412 /// Merges the parent's key-value pair and both adjacent child nodes into
1413 /// the left child node and returns that child node.
1415 /// Panics unless we `.can_merge()`.
1416 pub fn merge_tracking_child<A: Allocator + Clone>(
1419 ) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1420 self.do_merge(|_parent, child| child, alloc)
1423 /// Merges the parent's key-value pair and both adjacent child nodes into
1424 /// the left child node and returns the edge handle in that child node
1425 /// where the tracked child edge ended up,
1427 /// Panics unless we `.can_merge()`.
1428 pub fn merge_tracking_child_edge<A: Allocator + Clone>(
1430 track_edge_idx: LeftOrRight<usize>,
1432 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1433 let old_left_len = self.left_child.len();
1434 let right_len = self.right_child.len();
1435 assert!(match track_edge_idx {
1436 LeftOrRight::Left(idx) => idx <= old_left_len,
1437 LeftOrRight::Right(idx) => idx <= right_len,
1439 let child = self.merge_tracking_child(alloc);
1440 let new_idx = match track_edge_idx {
1441 LeftOrRight::Left(idx) => idx,
1442 LeftOrRight::Right(idx) => old_left_len + 1 + idx,
1444 unsafe { Handle::new_edge(child, new_idx) }
1447 /// Removes a key-value pair from the left child and places it in the key-value storage
1448 /// of the parent, while pushing the old parent key-value pair into the right child.
1449 /// Returns a handle to the edge in the right child corresponding to where the original
1450 /// edge specified by `track_right_edge_idx` ended up.
1453 track_right_edge_idx: usize,
1454 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1455 self.bulk_steal_left(1);
1456 unsafe { Handle::new_edge(self.right_child, 1 + track_right_edge_idx) }
1459 /// Removes a key-value pair from the right child and places it in the key-value storage
1460 /// of the parent, while pushing the old parent key-value pair onto the left child.
1461 /// Returns a handle to the edge in the left child specified by `track_left_edge_idx`,
1462 /// which didn't move.
1465 track_left_edge_idx: usize,
1466 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1467 self.bulk_steal_right(1);
1468 unsafe { Handle::new_edge(self.left_child, track_left_edge_idx) }
1471 /// This does stealing similar to `steal_left` but steals multiple elements at once.
1472 pub fn bulk_steal_left(&mut self, count: usize) {
1475 let left_node = &mut self.left_child;
1476 let old_left_len = left_node.len();
1477 let right_node = &mut self.right_child;
1478 let old_right_len = right_node.len();
1480 // Make sure that we may steal safely.
1481 assert!(old_right_len + count <= CAPACITY);
1482 assert!(old_left_len >= count);
1484 let new_left_len = old_left_len - count;
1485 let new_right_len = old_right_len + count;
1486 *left_node.len_mut() = new_left_len as u16;
1487 *right_node.len_mut() = new_right_len as u16;
1491 // Make room for stolen elements in the right child.
1492 slice_shr(right_node.key_area_mut(..new_right_len), count);
1493 slice_shr(right_node.val_area_mut(..new_right_len), count);
1495 // Move elements from the left child to the right one.
1497 left_node.key_area_mut(new_left_len + 1..old_left_len),
1498 right_node.key_area_mut(..count - 1),
1501 left_node.val_area_mut(new_left_len + 1..old_left_len),
1502 right_node.val_area_mut(..count - 1),
1505 // Move the left-most stolen pair to the parent.
1506 let k = left_node.key_area_mut(new_left_len).assume_init_read();
1507 let v = left_node.val_area_mut(new_left_len).assume_init_read();
1508 let (k, v) = self.parent.replace_kv(k, v);
1510 // Move parent's key-value pair to the right child.
1511 right_node.key_area_mut(count - 1).write(k);
1512 right_node.val_area_mut(count - 1).write(v);
1515 match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) {
1516 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1517 // Make room for stolen edges.
1518 slice_shr(right.edge_area_mut(..new_right_len + 1), count);
1522 left.edge_area_mut(new_left_len + 1..old_left_len + 1),
1523 right.edge_area_mut(..count),
1526 right.correct_childrens_parent_links(0..new_right_len + 1);
1528 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1529 _ => unreachable!(),
1534 /// The symmetric clone of `bulk_steal_left`.
1535 pub fn bulk_steal_right(&mut self, count: usize) {
1538 let left_node = &mut self.left_child;
1539 let old_left_len = left_node.len();
1540 let right_node = &mut self.right_child;
1541 let old_right_len = right_node.len();
1543 // Make sure that we may steal safely.
1544 assert!(old_left_len + count <= CAPACITY);
1545 assert!(old_right_len >= count);
1547 let new_left_len = old_left_len + count;
1548 let new_right_len = old_right_len - count;
1549 *left_node.len_mut() = new_left_len as u16;
1550 *right_node.len_mut() = new_right_len as u16;
1554 // Move the right-most stolen pair to the parent.
1555 let k = right_node.key_area_mut(count - 1).assume_init_read();
1556 let v = right_node.val_area_mut(count - 1).assume_init_read();
1557 let (k, v) = self.parent.replace_kv(k, v);
1559 // Move parent's key-value pair to the left child.
1560 left_node.key_area_mut(old_left_len).write(k);
1561 left_node.val_area_mut(old_left_len).write(v);
1563 // Move elements from the right child to the left one.
1565 right_node.key_area_mut(..count - 1),
1566 left_node.key_area_mut(old_left_len + 1..new_left_len),
1569 right_node.val_area_mut(..count - 1),
1570 left_node.val_area_mut(old_left_len + 1..new_left_len),
1573 // Fill gap where stolen elements used to be.
1574 slice_shl(right_node.key_area_mut(..old_right_len), count);
1575 slice_shl(right_node.val_area_mut(..old_right_len), count);
1578 match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) {
1579 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1582 right.edge_area_mut(..count),
1583 left.edge_area_mut(old_left_len + 1..new_left_len + 1),
1586 // Fill gap where stolen edges used to be.
1587 slice_shl(right.edge_area_mut(..old_right_len + 1), count);
1589 left.correct_childrens_parent_links(old_left_len + 1..new_left_len + 1);
1590 right.correct_childrens_parent_links(0..new_right_len + 1);
1592 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1593 _ => unreachable!(),
1599 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
1600 pub fn forget_node_type(
1602 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
1603 unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
1607 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge> {
1608 pub fn forget_node_type(
1610 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
1611 unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
1615 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::KV> {
1616 pub fn forget_node_type(
1618 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV> {
1619 unsafe { Handle::new_kv(self.node.forget_type(), self.idx) }
1623 impl<BorrowType, K, V, Type> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, Type> {
1624 /// Checks whether the underlying node is an `Internal` node or a `Leaf` node.
1628 Handle<NodeRef<BorrowType, K, V, marker::Leaf>, Type>,
1629 Handle<NodeRef<BorrowType, K, V, marker::Internal>, Type>,
1631 match self.node.force() {
1632 ForceResult::Leaf(node) => {
1633 ForceResult::Leaf(Handle { node, idx: self.idx, _marker: PhantomData })
1635 ForceResult::Internal(node) => {
1636 ForceResult::Internal(Handle { node, idx: self.idx, _marker: PhantomData })
1642 impl<'a, K, V, Type> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, Type> {
1643 /// Unsafely asserts to the compiler the static information that the handle's node is a `Leaf`.
1644 pub unsafe fn cast_to_leaf_unchecked(
1646 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, Type> {
1647 let node = unsafe { self.node.cast_to_leaf_unchecked() };
1648 Handle { node, idx: self.idx, _marker: PhantomData }
1652 impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1653 /// Move the suffix after `self` from one node to another one. `right` must be empty.
1654 /// The first edge of `right` remains unchanged.
1657 right: &mut NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1660 let new_left_len = self.idx;
1661 let mut left_node = self.reborrow_mut().into_node();
1662 let old_left_len = left_node.len();
1664 let new_right_len = old_left_len - new_left_len;
1665 let mut right_node = right.reborrow_mut();
1667 assert!(right_node.len() == 0);
1668 assert!(left_node.height == right_node.height);
1670 if new_right_len > 0 {
1671 *left_node.len_mut() = new_left_len as u16;
1672 *right_node.len_mut() = new_right_len as u16;
1675 left_node.key_area_mut(new_left_len..old_left_len),
1676 right_node.key_area_mut(..new_right_len),
1679 left_node.val_area_mut(new_left_len..old_left_len),
1680 right_node.val_area_mut(..new_right_len),
1682 match (left_node.force(), right_node.force()) {
1683 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1685 left.edge_area_mut(new_left_len + 1..old_left_len + 1),
1686 right.edge_area_mut(1..new_right_len + 1),
1688 right.correct_childrens_parent_links(1..new_right_len + 1);
1690 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1691 _ => unreachable!(),
1698 pub enum ForceResult<Leaf, Internal> {
1703 /// Result of insertion, when a node needed to expand beyond its capacity.
1704 pub struct SplitResult<'a, K, V, NodeType> {
1705 // Altered node in existing tree with elements and edges that belong to the left of `kv`.
1706 pub left: NodeRef<marker::Mut<'a>, K, V, NodeType>,
1707 // Some key and value that existed before and were split off, to be inserted elsewhere.
1709 // Owned, unattached, new node with elements and edges that belong to the right of `kv`.
1710 pub right: NodeRef<marker::Owned, K, V, NodeType>,
1713 impl<'a, K, V> SplitResult<'a, K, V, marker::Leaf> {
1714 pub fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
1715 SplitResult { left: self.left.forget_type(), kv: self.kv, right: self.right.forget_type() }
1719 impl<'a, K, V> SplitResult<'a, K, V, marker::Internal> {
1720 pub fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
1721 SplitResult { left: self.left.forget_type(), kv: self.kv, right: self.right.forget_type() }
1726 use core::marker::PhantomData;
1729 pub enum Internal {}
1730 pub enum LeafOrInternal {}
1734 pub enum DormantMut {}
1735 pub struct Immut<'a>(PhantomData<&'a ()>);
1736 pub struct Mut<'a>(PhantomData<&'a mut ()>);
1737 pub struct ValMut<'a>(PhantomData<&'a mut ()>);
1739 pub trait BorrowType {
1740 /// If node references of this borrow type allow traversing to other
1741 /// nodes in the tree, this constant is set to `true`. It can be used
1742 /// for a compile-time assertion.
1743 const TRAVERSAL_PERMIT: bool = true;
1745 impl BorrowType for Owned {
1746 /// Reject traversal, because it isn't needed. Instead traversal
1747 /// happens using the result of `borrow_mut`.
1748 /// By disabling traversal, and only creating new references to roots,
1749 /// we know that every reference of the `Owned` type is to a root node.
1750 const TRAVERSAL_PERMIT: bool = false;
1752 impl BorrowType for Dying {}
1753 impl<'a> BorrowType for Immut<'a> {}
1754 impl<'a> BorrowType for Mut<'a> {}
1755 impl<'a> BorrowType for ValMut<'a> {}
1756 impl BorrowType for DormantMut {}
1762 /// Inserts a value into a slice of initialized elements followed by one uninitialized element.
1765 /// The slice has more than `idx` elements.
1766 unsafe fn slice_insert<T>(slice: &mut [MaybeUninit<T>], idx: usize, val: T) {
1768 let len = slice.len();
1769 debug_assert!(len > idx);
1770 let slice_ptr = slice.as_mut_ptr();
1772 ptr::copy(slice_ptr.add(idx), slice_ptr.add(idx + 1), len - idx - 1);
1774 (*slice_ptr.add(idx)).write(val);
1778 /// Removes and returns a value from a slice of all initialized elements, leaving behind one
1779 /// trailing uninitialized element.
1782 /// The slice has more than `idx` elements.
1783 unsafe fn slice_remove<T>(slice: &mut [MaybeUninit<T>], idx: usize) -> T {
1785 let len = slice.len();
1786 debug_assert!(idx < len);
1787 let slice_ptr = slice.as_mut_ptr();
1788 let ret = (*slice_ptr.add(idx)).assume_init_read();
1789 ptr::copy(slice_ptr.add(idx + 1), slice_ptr.add(idx), len - idx - 1);
1794 /// Shifts the elements in a slice `distance` positions to the left.
1797 /// The slice has at least `distance` elements.
1798 unsafe fn slice_shl<T>(slice: &mut [MaybeUninit<T>], distance: usize) {
1800 let slice_ptr = slice.as_mut_ptr();
1801 ptr::copy(slice_ptr.add(distance), slice_ptr, slice.len() - distance);
1805 /// Shifts the elements in a slice `distance` positions to the right.
1808 /// The slice has at least `distance` elements.
1809 unsafe fn slice_shr<T>(slice: &mut [MaybeUninit<T>], distance: usize) {
1811 let slice_ptr = slice.as_mut_ptr();
1812 ptr::copy(slice_ptr, slice_ptr.add(distance), slice.len() - distance);
1816 /// Moves all values from a slice of initialized elements to a slice
1817 /// of uninitialized elements, leaving behind `src` as all uninitialized.
1818 /// Works like `dst.copy_from_slice(src)` but does not require `T` to be `Copy`.
1819 fn move_to_slice<T>(src: &mut [MaybeUninit<T>], dst: &mut [MaybeUninit<T>]) {
1820 assert!(src.len() == dst.len());
1822 ptr::copy_nonoverlapping(src.as_ptr(), dst.as_mut_ptr(), src.len());