btree: avoid forcing the allocator to be a reference

Author: RalfJung

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

@@ -15,12 +15,12 @@ impl<K, V> Root<K, V> {
     /// a `BTreeMap`, both iterators should produce keys in strictly ascending
     /// order, each greater than all keys in the tree, including any keys
     /// already in the tree upon entry.
-    pub fn append_from_sorted_iters<I, A: Allocator>(
+    pub fn append_from_sorted_iters<I, A: Allocator + Clone>(
         &mut self,
         left: I,
         right: I,
         length: &mut usize,
-        alloc: &A,
+        alloc: A,
     ) where
         K: Ord,
         I: Iterator<Item = (K, V)> + FusedIterator,
@@ -35,7 +35,7 @@ impl<K, V> Root<K, V> {
     /// Pushes all key-value pairs to the end of the tree, incrementing a
     /// `length` variable along the way. The latter makes it easier for the
     /// caller to avoid a leak when the iterator panicks.
-    pub fn bulk_push<I, A: Allocator>(&mut self, iter: I, length: &mut usize, alloc: &A)
+    pub fn bulk_push<I, A: Allocator + Clone>(&mut self, iter: I, length: &mut usize, alloc: A)
     where
         I: Iterator<Item = (K, V)>,
     {
@@ -64,17 +64,17 @@ impl<K, V> Root<K, V> {
                         }
                         Err(_) => {
                             // We are at the top, create a new root node and push there.
-                            open_node = self.push_internal_level(alloc);
+                            open_node = self.push_internal_level(alloc.clone());
                             break;
                         }
                     }
                 }
 
                 // Push key-value pair and new right subtree.
                 let tree_height = open_node.height() - 1;
-                let mut right_tree = Root::new(alloc);
+                let mut right_tree = Root::new(alloc.clone());
                 for _ in 0..tree_height {
-                    right_tree.push_internal_level(alloc);
+                    right_tree.push_internal_level(alloc.clone());
                 }
                 open_node.push(key, value, right_tree);
 

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

@@ -7,9 +7,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
     /// sibling. If successful but at the cost of shrinking the parent node,
     /// returns that shrunk parent node. Returns an `Err` if the node is
     /// an empty root.
-    fn fix_node_through_parent<A: Allocator>(
+    fn fix_node_through_parent<A: Allocator + Clone>(
         self,
-        alloc: &A,
+        alloc: A,
     ) -> Result<Option<NodeRef<marker::Mut<'a>, K, V, marker::Internal>>, Self> {
         let len = self.len();
         if len >= MIN_LEN {
@@ -54,9 +54,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
     ///
     /// This method does not expect ancestors to already be underfull upon entry
     /// and panics if it encounters an empty ancestor.
-    pub fn fix_node_and_affected_ancestors<A: Allocator>(mut self, alloc: &A) -> bool {
+    pub fn fix_node_and_affected_ancestors<A: Allocator + Clone>(mut self, alloc: A) -> bool {
         loop {
-            match self.fix_node_through_parent(alloc) {
+            match self.fix_node_through_parent(alloc.clone()) {
                 Ok(Some(parent)) => self = parent.forget_type(),
                 Ok(None) => return true,
                 Err(_) => return false,
@@ -67,28 +67,28 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
 
 impl<K, V> Root<K, V> {
     /// Removes empty levels on the top, but keeps an empty leaf if the entire tree is empty.
-    pub fn fix_top<A: Allocator>(&mut self, alloc: &A) {
+    pub fn fix_top<A: Allocator + Clone>(&mut self, alloc: A) {
         while self.height() > 0 && self.len() == 0 {
-            self.pop_internal_level(alloc);
+            self.pop_internal_level(alloc.clone());
         }
     }
 
     /// Stocks up or merge away any underfull nodes on the right border of the
     /// tree. The other nodes, those that are not the root nor a rightmost edge,
     /// must already have at least MIN_LEN elements.
-    pub fn fix_right_border<A: Allocator>(&mut self, alloc: &A) {
-        self.fix_top(alloc);
+    pub fn fix_right_border<A: Allocator + Clone>(&mut self, alloc: A) {
+        self.fix_top(alloc.clone());
         if self.len() > 0 {
-            self.borrow_mut().last_kv().fix_right_border_of_right_edge(alloc);
+            self.borrow_mut().last_kv().fix_right_border_of_right_edge(alloc.clone());
             self.fix_top(alloc);
         }
     }
 
     /// The symmetric clone of `fix_right_border`.
-    pub fn fix_left_border<A: Allocator>(&mut self, alloc: &A) {
-        self.fix_top(alloc);
+    pub fn fix_left_border<A: Allocator + Clone>(&mut self, alloc: A) {
+        self.fix_top(alloc.clone());
         if self.len() > 0 {
-            self.borrow_mut().first_kv().fix_left_border_of_left_edge(alloc);
+            self.borrow_mut().first_kv().fix_left_border_of_left_edge(alloc.clone());
             self.fix_top(alloc);
         }
     }
@@ -115,16 +115,16 @@ impl<K, V> Root<K, V> {
 }
 
 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV> {
-    fn fix_left_border_of_left_edge<A: Allocator>(mut self, alloc: &A) {
+    fn fix_left_border_of_left_edge<A: Allocator + Clone>(mut self, alloc: A) {
         while let Internal(internal_kv) = self.force() {
-            self = internal_kv.fix_left_child(alloc).first_kv();
+            self = internal_kv.fix_left_child(alloc.clone()).first_kv();
             debug_assert!(self.reborrow().into_node().len() > MIN_LEN);
         }
     }
 
-    fn fix_right_border_of_right_edge<A: Allocator>(mut self, alloc: &A) {
+    fn fix_right_border_of_right_edge<A: Allocator + Clone>(mut self, alloc: A) {
         while let Internal(internal_kv) = self.force() {
-            self = internal_kv.fix_right_child(alloc).last_kv();
+            self = internal_kv.fix_right_child(alloc.clone()).last_kv();
             debug_assert!(self.reborrow().into_node().len() > MIN_LEN);
         }
     }
@@ -135,9 +135,9 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
     /// provisions an extra element to allow merging its children in turn
     /// without becoming underfull.
     /// Returns the left child.
-    fn fix_left_child<A: Allocator>(
+    fn fix_left_child<A: Allocator + Clone>(
         self,
-        alloc: &A,
+        alloc: A,
     ) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
         let mut internal_kv = self.consider_for_balancing();
         let left_len = internal_kv.left_child_len();
@@ -158,9 +158,9 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
     /// provisions an extra element to allow merging its children in turn
     /// without becoming underfull.
     /// Returns wherever the right child ended up.
-    fn fix_right_child<A: Allocator>(
+    fn fix_right_child<A: Allocator + Clone>(
         self,
-        alloc: &A,
+        alloc: A,
     ) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
         let mut internal_kv = self.consider_for_balancing();
         let right_len = internal_kv.right_child_len();