diff options
Diffstat (limited to 'library/alloc/src/collections/btree/map.rs')
| -rw-r--r-- | library/alloc/src/collections/btree/map.rs | 730 |
1 files changed, 728 insertions, 2 deletions
diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs index 1d9c4460e..386cd1a16 100644 --- a/library/alloc/src/collections/btree/map.rs +++ b/library/alloc/src/collections/btree/map.rs @@ -6,7 +6,7 @@ use core::hash::{Hash, Hasher}; use core::iter::{FromIterator, FusedIterator}; use core::marker::PhantomData; use core::mem::{self, ManuallyDrop}; -use core::ops::{Index, RangeBounds}; +use core::ops::{Bound, Index, RangeBounds}; use core::ptr; use crate::alloc::{Allocator, Global}; @@ -15,7 +15,7 @@ use super::borrow::DormantMutRef; use super::dedup_sorted_iter::DedupSortedIter; use super::navigate::{LazyLeafRange, LeafRange}; use super::node::{self, marker, ForceResult::*, Handle, NodeRef, Root}; -use super::search::SearchResult::*; +use super::search::{SearchBound, SearchResult::*}; use super::set_val::SetValZST; mod entry; @@ -2422,6 +2422,732 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> { pub const fn is_empty(&self) -> bool { self.len() == 0 } + + /// Returns a [`Cursor`] pointing at the first element that is above the + /// given bound. + /// + /// If no such element exists then a cursor pointing at the "ghost" + /// non-element is returned. + /// + /// Passing [`Bound::Unbounded`] will return a cursor pointing at the first + /// element of the map. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(btree_cursors)] + /// + /// use std::collections::BTreeMap; + /// use std::ops::Bound; + /// + /// let mut a = BTreeMap::new(); + /// a.insert(1, "a"); + /// a.insert(2, "b"); + /// a.insert(3, "c"); + /// a.insert(4, "c"); + /// let cursor = a.lower_bound(Bound::Excluded(&2)); + /// assert_eq!(cursor.key(), Some(&3)); + /// ``` + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn lower_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V> + where + K: Borrow<Q> + Ord, + Q: Ord, + { + let root_node = match self.root.as_ref() { + None => return Cursor { current: None, root: None }, + Some(root) => root.reborrow(), + }; + let edge = root_node.lower_bound(SearchBound::from_range(bound)); + Cursor { current: edge.next_kv().ok(), root: self.root.as_ref() } + } + + /// Returns a [`CursorMut`] pointing at the first element that is above the + /// given bound. + /// + /// If no such element exists then a cursor pointing at the "ghost" + /// non-element is returned. + /// + /// Passing [`Bound::Unbounded`] will return a cursor pointing at the first + /// element of the map. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(btree_cursors)] + /// + /// use std::collections::BTreeMap; + /// use std::ops::Bound; + /// + /// let mut a = BTreeMap::new(); + /// a.insert(1, "a"); + /// a.insert(2, "b"); + /// a.insert(3, "c"); + /// a.insert(4, "c"); + /// let cursor = a.lower_bound_mut(Bound::Excluded(&2)); + /// assert_eq!(cursor.key(), Some(&3)); + /// ``` + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn lower_bound_mut<Q>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V, A> + where + K: Borrow<Q> + Ord, + Q: Ord, + { + let (root, dormant_root) = DormantMutRef::new(&mut self.root); + let root_node = match root.as_mut() { + None => { + return CursorMut { + current: None, + root: dormant_root, + length: &mut self.length, + alloc: &mut *self.alloc, + }; + } + Some(root) => root.borrow_mut(), + }; + let edge = root_node.lower_bound(SearchBound::from_range(bound)); + CursorMut { + current: edge.next_kv().ok(), + root: dormant_root, + length: &mut self.length, + alloc: &mut *self.alloc, + } + } + + /// Returns a [`Cursor`] pointing at the last element that is below the + /// given bound. + /// + /// If no such element exists then a cursor pointing at the "ghost" + /// non-element is returned. + /// + /// Passing [`Bound::Unbounded`] will return a cursor pointing at the last + /// element of the map. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(btree_cursors)] + /// + /// use std::collections::BTreeMap; + /// use std::ops::Bound; + /// + /// let mut a = BTreeMap::new(); + /// a.insert(1, "a"); + /// a.insert(2, "b"); + /// a.insert(3, "c"); + /// a.insert(4, "c"); + /// let cursor = a.upper_bound(Bound::Excluded(&3)); + /// assert_eq!(cursor.key(), Some(&2)); + /// ``` + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn upper_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V> + where + K: Borrow<Q> + Ord, + Q: Ord, + { + let root_node = match self.root.as_ref() { + None => return Cursor { current: None, root: None }, + Some(root) => root.reborrow(), + }; + let edge = root_node.upper_bound(SearchBound::from_range(bound)); + Cursor { current: edge.next_back_kv().ok(), root: self.root.as_ref() } + } + + /// Returns a [`CursorMut`] pointing at the last element that is below the + /// given bound. + /// + /// If no such element exists then a cursor pointing at the "ghost" + /// non-element is returned. + /// + /// Passing [`Bound::Unbounded`] will return a cursor pointing at the last + /// element of the map. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(btree_cursors)] + /// + /// use std::collections::BTreeMap; + /// use std::ops::Bound; + /// + /// let mut a = BTreeMap::new(); + /// a.insert(1, "a"); + /// a.insert(2, "b"); + /// a.insert(3, "c"); + /// a.insert(4, "c"); + /// let cursor = a.upper_bound_mut(Bound::Excluded(&3)); + /// assert_eq!(cursor.key(), Some(&2)); + /// ``` + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn upper_bound_mut<Q>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V, A> + where + K: Borrow<Q> + Ord, + Q: Ord, + { + let (root, dormant_root) = DormantMutRef::new(&mut self.root); + let root_node = match root.as_mut() { + None => { + return CursorMut { + current: None, + root: dormant_root, + length: &mut self.length, + alloc: &mut *self.alloc, + }; + } + Some(root) => root.borrow_mut(), + }; + let edge = root_node.upper_bound(SearchBound::from_range(bound)); + CursorMut { + current: edge.next_back_kv().ok(), + root: dormant_root, + length: &mut self.length, + alloc: &mut *self.alloc, + } + } +} + +/// A cursor over a `BTreeMap`. +/// +/// A `Cursor` is like an iterator, except that it can freely seek back-and-forth. +/// +/// Cursors always point to an element in the tree, and index in a logically circular way. +/// To accommodate this, there is a "ghost" non-element that yields `None` between the last and +/// first elements of the tree. +/// +/// A `Cursor` is created with the [`BTreeMap::lower_bound`] and [`BTreeMap::upper_bound`] methods. +#[unstable(feature = "btree_cursors", issue = "107540")] +pub struct Cursor<'a, K: 'a, V: 'a> { + current: Option<Handle<NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>, marker::KV>>, + root: Option<&'a node::Root<K, V>>, +} + +#[unstable(feature = "btree_cursors", issue = "107540")] +impl<K, V> Clone for Cursor<'_, K, V> { + fn clone(&self) -> Self { + let Cursor { current, root } = *self; + Cursor { current, root } + } +} + +#[unstable(feature = "btree_cursors", issue = "107540")] +impl<K: Debug, V: Debug> Debug for Cursor<'_, K, V> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("Cursor").field(&self.key_value()).finish() + } +} + +/// A cursor over a `BTreeMap` with editing operations. +/// +/// A `Cursor` is like an iterator, except that it can freely seek back-and-forth, and can +/// safely mutate the tree during iteration. This is because the lifetime of its yielded +/// references is tied to its own lifetime, instead of just the underlying tree. This means +/// cursors cannot yield multiple elements at once. +/// +/// Cursors always point to an element in the tree, and index in a logically circular way. +/// To accommodate this, there is a "ghost" non-element that yields `None` between the last and +/// first elements of the tree. +/// +/// A `Cursor` is created with the [`BTreeMap::lower_bound_mut`] and [`BTreeMap::upper_bound_mut`] +/// methods. +#[unstable(feature = "btree_cursors", issue = "107540")] +pub struct CursorMut< + 'a, + K: 'a, + V: 'a, + #[unstable(feature = "allocator_api", issue = "32838")] A = Global, +> { + current: Option<Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV>>, + root: DormantMutRef<'a, Option<node::Root<K, V>>>, + length: &'a mut usize, + alloc: &'a mut A, +} + +#[unstable(feature = "btree_cursors", issue = "107540")] +impl<K: Debug, V: Debug, A> Debug for CursorMut<'_, K, V, A> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("CursorMut").field(&self.key_value()).finish() + } +} + +impl<'a, K, V> Cursor<'a, K, V> { + /// Moves the cursor to the next element of the `BTreeMap`. + /// + /// If the cursor is pointing to the "ghost" non-element then this will move it to + /// the first element of the `BTreeMap`. If it is pointing to the last + /// element of the `BTreeMap` then this will move it to the "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn move_next(&mut self) { + match self.current.take() { + None => { + self.current = self.root.and_then(|root| { + root.reborrow().first_leaf_edge().forget_node_type().right_kv().ok() + }); + } + Some(current) => { + self.current = current.next_leaf_edge().next_kv().ok(); + } + } + } + + /// Moves the cursor to the previous element of the `BTreeMap`. + /// + /// If the cursor is pointing to the "ghost" non-element then this will move it to + /// the last element of the `BTreeMap`. If it is pointing to the first + /// element of the `BTreeMap` then this will move it to the "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn move_prev(&mut self) { + match self.current.take() { + None => { + self.current = self.root.and_then(|root| { + root.reborrow().last_leaf_edge().forget_node_type().left_kv().ok() + }); + } + Some(current) => { + self.current = current.next_back_leaf_edge().next_back_kv().ok(); + } + } + } + + /// Returns a reference to the key of the element that the cursor is + /// currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn key(&self) -> Option<&'a K> { + self.current.as_ref().map(|current| current.into_kv().0) + } + + /// Returns a reference to the value of the element that the cursor is + /// currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn value(&self) -> Option<&'a V> { + self.current.as_ref().map(|current| current.into_kv().1) + } + + /// Returns a reference to the key and value of the element that the cursor + /// is currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn key_value(&self) -> Option<(&'a K, &'a V)> { + self.current.as_ref().map(|current| current.into_kv()) + } + + /// Returns a reference to the next element. + /// + /// If the cursor is pointing to the "ghost" non-element then this returns + /// the first element of the `BTreeMap`. If it is pointing to the last + /// element of the `BTreeMap` then this returns `None`. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn peek_next(&self) -> Option<(&'a K, &'a V)> { + let mut next = self.clone(); + next.move_next(); + next.current.as_ref().map(|current| current.into_kv()) + } + + /// Returns a reference to the previous element. + /// + /// If the cursor is pointing to the "ghost" non-element then this returns + /// the last element of the `BTreeMap`. If it is pointing to the first + /// element of the `BTreeMap` then this returns `None`. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn peek_prev(&self) -> Option<(&'a K, &'a V)> { + let mut prev = self.clone(); + prev.move_prev(); + prev.current.as_ref().map(|current| current.into_kv()) + } +} + +impl<'a, K, V, A> CursorMut<'a, K, V, A> { + /// Moves the cursor to the next element of the `BTreeMap`. + /// + /// If the cursor is pointing to the "ghost" non-element then this will move it to + /// the first element of the `BTreeMap`. If it is pointing to the last + /// element of the `BTreeMap` then this will move it to the "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn move_next(&mut self) { + match self.current.take() { + None => { + // SAFETY: The previous borrow of root has ended. + self.current = unsafe { self.root.reborrow() }.as_mut().and_then(|root| { + root.borrow_mut().first_leaf_edge().forget_node_type().right_kv().ok() + }); + } + Some(current) => { + self.current = current.next_leaf_edge().next_kv().ok(); + } + } + } + + /// Moves the cursor to the previous element of the `BTreeMap`. + /// + /// If the cursor is pointing to the "ghost" non-element then this will move it to + /// the last element of the `BTreeMap`. If it is pointing to the first + /// element of the `BTreeMap` then this will move it to the "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn move_prev(&mut self) { + match self.current.take() { + None => { + // SAFETY: The previous borrow of root has ended. + self.current = unsafe { self.root.reborrow() }.as_mut().and_then(|root| { + root.borrow_mut().last_leaf_edge().forget_node_type().left_kv().ok() + }); + } + Some(current) => { + self.current = current.next_back_leaf_edge().next_back_kv().ok(); + } + } + } + + /// Returns a reference to the key of the element that the cursor is + /// currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn key(&self) -> Option<&K> { + self.current.as_ref().map(|current| current.reborrow().into_kv().0) + } + + /// Returns a reference to the value of the element that the cursor is + /// currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn value(&self) -> Option<&V> { + self.current.as_ref().map(|current| current.reborrow().into_kv().1) + } + + /// Returns a reference to the key and value of the element that the cursor + /// is currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn key_value(&self) -> Option<(&K, &V)> { + self.current.as_ref().map(|current| current.reborrow().into_kv()) + } + + /// Returns a mutable reference to the value of the element that the cursor + /// is currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn value_mut(&mut self) -> Option<&mut V> { + self.current.as_mut().map(|current| current.kv_mut().1) + } + + /// Returns a reference to the key and mutable reference to the value of the + /// element that the cursor is currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn key_value_mut(&mut self) -> Option<(&K, &mut V)> { + self.current.as_mut().map(|current| { + let (k, v) = current.kv_mut(); + (&*k, v) + }) + } + + /// Returns a mutable reference to the of the element that the cursor is + /// currently pointing to. + /// + /// This returns `None` if the cursor is currently pointing to the + /// "ghost" non-element. + /// + /// # Safety + /// + /// This can be used to modify the key, but you must ensure that the + /// `BTreeMap` invariants are maintained. Specifically: + /// + /// * The key must remain unique within the tree. + /// * The key must remain in sorted order with regards to other elements in + /// the tree. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub unsafe fn key_mut_unchecked(&mut self) -> Option<&mut K> { + self.current.as_mut().map(|current| current.kv_mut().0) + } + + /// Returns a reference to the key and value of the next element. + /// + /// If the cursor is pointing to the "ghost" non-element then this returns + /// the first element of the `BTreeMap`. If it is pointing to the last + /// element of the `BTreeMap` then this returns `None`. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn peek_next(&mut self) -> Option<(&K, &mut V)> { + let (k, v) = match self.current { + None => { + // SAFETY: The previous borrow of root has ended. + unsafe { self.root.reborrow() } + .as_mut()? + .borrow_mut() + .first_leaf_edge() + .next_kv() + .ok()? + .into_kv_valmut() + } + // SAFETY: We're not using this to mutate the tree. + Some(ref mut current) => { + unsafe { current.reborrow_mut() }.next_leaf_edge().next_kv().ok()?.into_kv_valmut() + } + }; + Some((k, v)) + } + + /// Returns a reference to the key and value of the previous element. + /// + /// If the cursor is pointing to the "ghost" non-element then this returns + /// the last element of the `BTreeMap`. If it is pointing to the first + /// element of the `BTreeMap` then this returns `None`. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn peek_prev(&mut self) -> Option<(&K, &mut V)> { + let (k, v) = match self.current.as_mut() { + None => { + // SAFETY: The previous borrow of root has ended. + unsafe { self.root.reborrow() } + .as_mut()? + .borrow_mut() + .first_leaf_edge() + .next_kv() + .ok()? + .into_kv_valmut() + } + Some(current) => { + // SAFETY: We're not using this to mutate the tree. + unsafe { current.reborrow_mut() } + .next_back_leaf_edge() + .next_back_kv() + .ok()? + .into_kv_valmut() + } + }; + Some((k, v)) + } + + /// Returns a read-only cursor pointing to the current element. + /// + /// The lifetime of the returned `Cursor` is bound to that of the + /// `CursorMut`, which means it cannot outlive the `CursorMut` and that the + /// `CursorMut` is frozen for the lifetime of the `Cursor`. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn as_cursor(&self) -> Cursor<'_, K, V> { + Cursor { + // SAFETY: The tree is immutable while the cursor exists. + root: unsafe { self.root.reborrow_shared().as_ref() }, + current: self.current.as_ref().map(|current| current.reborrow()), + } + } +} + +// Now the tree editing operations +impl<'a, K: Ord, V, A: Allocator + Clone> CursorMut<'a, K, V, A> { + /// Inserts a new element into the `BTreeMap` after the current one. + /// + /// If the cursor is pointing at the "ghost" non-element then the new element is + /// inserted at the front of the `BTreeMap`. + /// + /// # Safety + /// + /// You must ensure that the `BTreeMap` invariants are maintained. + /// Specifically: + /// + /// * The key of the newly inserted element must be unique in the tree. + /// * All keys in the tree must remain in sorted order. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub unsafe fn insert_after_unchecked(&mut self, key: K, value: V) { + let edge = match self.current.take() { + None => { + // SAFETY: We have no other reference to the tree. + match unsafe { self.root.reborrow() } { + root @ None => { + // Tree is empty, allocate a new root. + let mut node = NodeRef::new_leaf(self.alloc.clone()); + node.borrow_mut().push(key, value); + *root = Some(node.forget_type()); + *self.length += 1; + return; + } + Some(root) => root.borrow_mut().first_leaf_edge(), + } + } + Some(current) => current.next_leaf_edge(), + }; + + let handle = edge.insert_recursing(key, value, self.alloc.clone(), |ins| { + drop(ins.left); + // SAFETY: The handle to the newly inserted value is always on a + // leaf node, so adding a new root node doesn't invalidate it. + let root = unsafe { self.root.reborrow().as_mut().unwrap() }; + root.push_internal_level(self.alloc.clone()).push(ins.kv.0, ins.kv.1, ins.right) + }); + self.current = handle.left_edge().next_back_kv().ok(); + *self.length += 1; + } + + /// Inserts a new element into the `BTreeMap` before the current one. + /// + /// If the cursor is pointing at the "ghost" non-element then the new element is + /// inserted at the end of the `BTreeMap`. + /// + /// # Safety + /// + /// You must ensure that the `BTreeMap` invariants are maintained. + /// Specifically: + /// + /// * The key of the newly inserted element must be unique in the tree. + /// * All keys in the tree must remain in sorted order. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub unsafe fn insert_before_unchecked(&mut self, key: K, value: V) { + let edge = match self.current.take() { + None => { + // SAFETY: We have no other reference to the tree. + match unsafe { self.root.reborrow() } { + root @ None => { + // Tree is empty, allocate a new root. + let mut node = NodeRef::new_leaf(self.alloc.clone()); + node.borrow_mut().push(key, value); + *root = Some(node.forget_type()); + *self.length += 1; + return; + } + Some(root) => root.borrow_mut().last_leaf_edge(), + } + } + Some(current) => current.next_back_leaf_edge(), + }; + + let handle = edge.insert_recursing(key, value, self.alloc.clone(), |ins| { + drop(ins.left); + // SAFETY: The handle to the newly inserted value is always on a + // leaf node, so adding a new root node doesn't invalidate it. + let root = unsafe { self.root.reborrow().as_mut().unwrap() }; + root.push_internal_level(self.alloc.clone()).push(ins.kv.0, ins.kv.1, ins.right) + }); + self.current = handle.right_edge().next_kv().ok(); + *self.length += 1; + } + + /// Inserts a new element into the `BTreeMap` after the current one. + /// + /// If the cursor is pointing at the "ghost" non-element then the new element is + /// inserted at the front of the `BTreeMap`. + /// + /// # Panics + /// + /// This function panics if: + /// - the given key compares less than or equal to the current element (if + /// any). + /// - the given key compares greater than or equal to the next element (if + /// any). + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn insert_after(&mut self, key: K, value: V) { + if let Some(current) = self.key() { + if &key <= current { + panic!("key must be ordered above the current element"); + } + } + if let Some((next, _)) = self.peek_prev() { + if &key >= next { + panic!("key must be ordered below the next element"); + } + } + unsafe { + self.insert_after_unchecked(key, value); + } + } + + /// Inserts a new element into the `BTreeMap` before the current one. + /// + /// If the cursor is pointing at the "ghost" non-element then the new element is + /// inserted at the end of the `BTreeMap`. + /// + /// # Panics + /// + /// This function panics if: + /// - the given key compares greater than or equal to the current element + /// (if any). + /// - the given key compares less than or equal to the previous element (if + /// any). + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn insert_before(&mut self, key: K, value: V) { + if let Some(current) = self.key() { + if &key >= current { + panic!("key must be ordered below the current element"); + } + } + if let Some((prev, _)) = self.peek_prev() { + if &key <= prev { + panic!("key must be ordered above the previous element"); + } + } + unsafe { + self.insert_before_unchecked(key, value); + } + } + + /// Removes the current element from the `BTreeMap`. + /// + /// The element that was removed is returned, and the cursor is + /// moved to point to the next element in the `BTreeMap`. + /// + /// If the cursor is currently pointing to the "ghost" non-element then no element + /// is removed and `None` is returned. The cursor is not moved in this case. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn remove_current(&mut self) -> Option<(K, V)> { + let current = self.current.take()?; + let mut emptied_internal_root = false; + let (kv, pos) = + current.remove_kv_tracking(|| emptied_internal_root = true, self.alloc.clone()); + self.current = pos.next_kv().ok(); + *self.length -= 1; + if emptied_internal_root { + // SAFETY: This is safe since current does not point within the now + // empty root node. + let root = unsafe { self.root.reborrow().as_mut().unwrap() }; + root.pop_internal_level(self.alloc.clone()); + } + Some(kv) + } + + /// Removes the current element from the `BTreeMap`. + /// + /// The element that was removed is returned, and the cursor is + /// moved to point to the previous element in the `BTreeMap`. + /// + /// If the cursor is currently pointing to the "ghost" non-element then no element + /// is removed and `None` is returned. The cursor is not moved in this case. + #[unstable(feature = "btree_cursors", issue = "107540")] + pub fn remove_current_and_move_back(&mut self) -> Option<(K, V)> { + let current = self.current.take()?; + let mut emptied_internal_root = false; + let (kv, pos) = + current.remove_kv_tracking(|| emptied_internal_root = true, self.alloc.clone()); + self.current = pos.next_back_kv().ok(); + *self.length -= 1; + if emptied_internal_root { + // SAFETY: This is safe since current does not point within the now + // empty root node. + let root = unsafe { self.root.reborrow().as_mut().unwrap() }; + root.pop_internal_level(self.alloc.clone()); + } + Some(kv) + } } #[cfg(test)] |