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Rollup merge of #87679 - ssomers:btree_comments, r=joshtriplett

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BTree: refine some comments
This commit is contained in:
Manish Goregaokar 2021-10-03 23:13:16 -07:00 committed by GitHub
commit 0f9e960241
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3 changed files with 8 additions and 10 deletions
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10
library/alloc/src/collections/btree/map.rs
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@ -19,16 +19,16 @@ mod entry;
pub use entry::{Entry, OccupiedEntry, OccupiedError, VacantEntry};
use Entry::*;
/// Minimum number of elements in nodes that are not a root.
/// Minimum number of elements in a node that is not a root.
/// We might temporarily have fewer elements during methods.
pub(super) const MIN_LEN: usize = node::MIN_LEN_AFTER_SPLIT;
// A tree in a `BTreeMap` is a tree in the `node` module with additional invariants:
// - Keys must appear in ascending order (according to the key's type).
// - If the root node is internal, it must contain at least 1 element.
// - Every non-leaf node contains at least 1 element (has at least 2 children).
// - Every non-root node contains at least MIN_LEN elements.
//
// An empty map may be represented both by the absence of a root node or by a
// An empty map is represented either by the absence of a root node or by a
// root node that is an empty leaf.
/// A map based on a [B-Tree].
@ -1735,8 +1735,8 @@ impl<'a, K: 'a, V: 'a> DrainFilterInner<'a, K, V> {
pub(super) fn size_hint(&self) -> (usize, Option<usize>) {
// In most of the btree iterators, `self.length` is the number of elements
// yet to be visited. Here, it includes elements that were visited and that
// the predicate decided not to drain. Making this upper bound more accurate
// requires maintaining an extra field and is not worth while.
// the predicate decided not to drain. Making this upper bound more tight
// during iteration would require an extra field.
(0, Some(*self.length))
}
}

6
library/alloc/src/collections/btree/navigate.rs
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@ -440,8 +440,7 @@ impl<K, V> Handle<NodeRef<marker::Dying, K, V, marker::Leaf>, marker::Edge> {
/// - The given edge must not have been previously returned by counterpart
/// `deallocating_next_back`.
/// - The returned KV handle is only valid to access the key and value,
/// and only valid until the next call to this method or counterpart
/// `deallocating_next_back`.
/// and only valid until the next call to a `deallocating_` method.
unsafe fn deallocating_next(
self,
) -> Option<(Self, Handle<NodeRef<marker::Dying, K, V, marker::LeafOrInternal>, marker::KV>)>
@ -470,8 +469,7 @@ impl<K, V> Handle<NodeRef<marker::Dying, K, V, marker::Leaf>, marker::Edge> {
/// - The given edge must not have been previously returned by counterpart
/// `deallocating_next`.
/// - The returned KV handle is only valid to access the key and value,
/// and only valid until the next call to this method or counterpart
/// `deallocating_next`.
/// and only valid until the next call to a `deallocating_` method.
unsafe fn deallocating_next_back(
self,
) -> Option<(Self, Handle<NodeRef<marker::Dying, K, V, marker::LeafOrInternal>, marker::KV>)>

2
library/alloc/src/collections/btree/node.rs
View File

@ -574,7 +574,7 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
/// no cleanup is done on any of the keys, values and other children.
/// This decreases the height by 1 and is the opposite of `push_internal_level`.
///
/// Requires exclusive access to the `Root` object but not to the root node;
/// Requires exclusive access to the `NodeRef` object but not to the root node;
/// it will not invalidate other handles or references to the root node.
///
/// Panics if there is no internal level, i.e., if the root node is a leaf.