alloc/collections/btree/
append.rs

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1use core::alloc::Allocator;
2use core::iter::FusedIterator;
3
4use super::merge_iter::MergeIterInner;
5use super::node::{self, Root};
6
7impl<K, V> Root<K, V> {
8    /// Appends all key-value pairs from the union of two ascending iterators,
9    /// incrementing a `length` variable along the way. The latter makes it
10    /// easier for the caller to avoid a leak when a drop handler panicks.
11    ///
12    /// If both iterators produce the same key, this method drops the pair from
13    /// the left iterator and appends the pair from the right iterator.
14    ///
15    /// If you want the tree to end up in a strictly ascending order, like for
16    /// a `BTreeMap`, both iterators should produce keys in strictly ascending
17    /// order, each greater than all keys in the tree, including any keys
18    /// already in the tree upon entry.
19    pub(super) fn append_from_sorted_iters<I, A: Allocator + Clone>(
20        &mut self,
21        left: I,
22        right: I,
23        length: &mut usize,
24        alloc: A,
25    ) where
26        K: Ord,
27        I: Iterator<Item = (K, V)> + FusedIterator,
28    {
29        // We prepare to merge `left` and `right` into a sorted sequence in linear time.
30        let iter = MergeIter(MergeIterInner::new(left, right));
31
32        // Meanwhile, we build a tree from the sorted sequence in linear time.
33        self.bulk_push(iter, length, alloc)
34    }
35
36    /// Pushes all key-value pairs to the end of the tree, incrementing a
37    /// `length` variable along the way. The latter makes it easier for the
38    /// caller to avoid a leak when the iterator panicks.
39    pub(super) fn bulk_push<I, A: Allocator + Clone>(
40        &mut self,
41        iter: I,
42        length: &mut usize,
43        alloc: A,
44    ) where
45        I: Iterator<Item = (K, V)>,
46    {
47        let mut cur_node = self.borrow_mut().last_leaf_edge().into_node();
48        // Iterate through all key-value pairs, pushing them into nodes at the right level.
49        for (key, value) in iter {
50            // Try to push key-value pair into the current leaf node.
51            if cur_node.len() < node::CAPACITY {
52                cur_node.push(key, value);
53            } else {
54                // No space left, go up and push there.
55                let mut open_node;
56                let mut test_node = cur_node.forget_type();
57                loop {
58                    match test_node.ascend() {
59                        Ok(parent) => {
60                            let parent = parent.into_node();
61                            if parent.len() < node::CAPACITY {
62                                // Found a node with space left, push here.
63                                open_node = parent;
64                                break;
65                            } else {
66                                // Go up again.
67                                test_node = parent.forget_type();
68                            }
69                        }
70                        Err(_) => {
71                            // We are at the top, create a new root node and push there.
72                            open_node = self.push_internal_level(alloc.clone());
73                            break;
74                        }
75                    }
76                }
77
78                // Push key-value pair and new right subtree.
79                let tree_height = open_node.height() - 1;
80                let mut right_tree = Root::new(alloc.clone());
81                for _ in 0..tree_height {
82                    right_tree.push_internal_level(alloc.clone());
83                }
84                open_node.push(key, value, right_tree);
85
86                // Go down to the rightmost leaf again.
87                cur_node = open_node.forget_type().last_leaf_edge().into_node();
88            }
89
90            // Increment length every iteration, to make sure the map drops
91            // the appended elements even if advancing the iterator panicks.
92            *length += 1;
93        }
94        self.fix_right_border_of_plentiful();
95    }
96}
97
98// An iterator for merging two sorted sequences into one
99struct MergeIter<K, V, I: Iterator<Item = (K, V)>>(MergeIterInner<I>);
100
101impl<K: Ord, V, I> Iterator for MergeIter<K, V, I>
102where
103    I: Iterator<Item = (K, V)> + FusedIterator,
104{
105    type Item = (K, V);
106
107    /// If two keys are equal, returns the key-value pair from the right source.
108    fn next(&mut self) -> Option<(K, V)> {
109        let (a_next, b_next) = self.0.nexts(|a: &(K, V), b: &(K, V)| K::cmp(&a.0, &b.0));
110        b_next.or(a_next)
111    }
112}
alloc/collections/btree/append.rs

alloc/collections/btree/
append.rs
