BTreeMap: admit the existence of leaf edges in comments

Author: ssomers

library/alloc/src/collections/btree/node.rs

@@ -9,11 +9,8 @@
 // struct Node<K, V, height: usize> {
 //     keys: [K; 2 * B - 1],
 //     vals: [V; 2 * B - 1],
-//     edges: if height > 0 {
-//         [Box<Node<K, V, height - 1>>; 2 * B]
-//     } else { () },
-//     parent: Option<NonNull<Node<K, V, height + 1>>>,
-//     parent_idx: u16,
+//     edges: [if height > 0 { Box<Node<K, V, height - 1>> } else { () }; 2 * B],
+//     parent: Option<(NonNull<Node<K, V, height + 1>>, u16)>,
 //     len: u16,
 // }
 // ```
@@ -28,8 +25,8 @@
 //
 // - Trees must have uniform depth/height. This means that every path down to a leaf from a
 //   given node has exactly the same length.
-// - A node of length `n` has `n` keys, `n` values, and (in an internal node) `n + 1` edges.
-//   This implies that even an empty internal node has at least one edge.
+// - A node of length `n` has `n` keys, `n` values, and `n + 1` edges.
+//   This implies that even an empty node has at least one edge.
 
 use core::cmp::Ordering;
 use core::marker::PhantomData;
@@ -298,9 +295,8 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
 }
 
 impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
-    /// Finds the length of the node. This is the number of keys or values. In an
-    /// internal node, the number of edges is `len() + 1`.
-    /// For any node, the number of possible edge handles is also `len() + 1`.
+    /// Finds the length of the node. This is the number of keys or values.
+    /// The number of edges is `len() + 1`.
     /// Note that, despite being safe, calling this function can have the side effect
     /// of invalidating mutable references that unsafe code has created.
     pub fn len(&self) -> usize {
@@ -321,9 +317,6 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
     }
 
     /// Exposes the leaf portion of any leaf or internal node.
-    /// If the node is a leaf, this function simply opens up its data.
-    /// If the node is an internal node, so not a leaf, it does have all the data a leaf has
-    /// (header, keys and values), and this function exposes that.
     ///
     /// Returns a raw ptr to avoid invalidating other references to this node,
     /// which is possible when BorrowType is marker::ValMut.
@@ -471,9 +464,6 @@ impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
     }
 
     /// Exposes the leaf portion of any leaf or internal node for writing.
-    /// If the node is a leaf, this function simply opens up its data.
-    /// If the node is an internal node, so not a leaf, it does have all the data a leaf has
-    /// (header, keys and values), and this function exposes that.
     ///
     /// We don't need to return a raw ptr because we have unique access to the entire node.
     fn as_leaf_mut(&mut self) -> &'a mut LeafNode<K, V> {
@@ -679,9 +669,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
 }
 
 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
-    /// Removes a key/value pair from the end of this node and returns the pair.
-    /// If this is an internal node, also removes the edge that was to the right
-    /// of that pair and returns the orphaned node that this edge owned.
+    /// Removes a key/value pair from the end of the node and returns the pair.
+    /// Also removes the edge that was to the right of that pair and, if the node
+    /// is internal, returns the orphaned subtree that this edge owned.
     fn pop(&mut self) -> (K, V, Option<Root<K, V>>) {
         debug_assert!(self.len() > 0);
 
@@ -705,9 +695,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
         }
     }
 
-    /// Removes a key/value pair from the beginning of this node and returns the pair.
-    /// If this is an internal node, also removes the edge that was to the left
-    /// of that pair and returns the orphaned node that this edge owned.
+    /// Removes a key/value pair from the beginning of the node and returns the pair.
+    /// Also removes the edge that was to the left of that pair and, if the node is
+    /// internal, returns the orphaned subtree that this edge owned.
     fn pop_front(&mut self) -> (K, V, Option<Root<K, V>>) {
         debug_assert!(self.len() > 0);