append.rs - source
Description: Source of the Rust file `library/alloc/src/collections/btree/append.rs`.

#
alloc/collections/btree/
append.rs

    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 from the left and the value from the right.
    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        match (a_next, b_next) {
    111            (Some((a_k, _)), Some((_, b_v))) => Some((a_k, b_v)),
    112            (Some(a), None) => Some(a),
    113            (None, Some(b)) => Some(b),
    114            (None, None) => None,
    115        }
    116    }
    117}