Add Range parameter to BTreeMap::extract_if and BTreeSet::extract_if

This change was requested in the btree_extract_if tracking issue:

rust-lang#70530 (comment)

Author: rs-sac

alloc/src/collections/btree/map.rs

@@ -1151,7 +1151,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
         K: Ord,
         F: FnMut(&K, &mut V) -> bool,
     {
-        self.extract_if(|k, v| !f(k, v)).for_each(drop);
+        self.extract_if(.., |k, v| !f(k, v)).for_each(drop);
     }
 
     /// Moves all elements from `other` into `self`, leaving `other` empty.
@@ -1429,27 +1429,30 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// assert_eq!(odds.keys().copied().collect::<Vec<_>>(), [1, 3, 5, 7]);
     /// ```
     #[unstable(feature = "btree_extract_if", issue = "70530")]
-    pub fn extract_if<F>(&mut self, pred: F) -> ExtractIf<'_, K, V, F, A>
+    pub fn extract_if<F, R>(&mut self, range: R, pred: F) -> ExtractIf<'_, K, V, R, F, A>
     where
         K: Ord,
+        R: RangeBounds<K>,
         F: FnMut(&K, &mut V) -> bool,
     {
-        let (inner, alloc) = self.extract_if_inner();
+        let (inner, alloc) = self.extract_if_inner(range);
         ExtractIf { pred, inner, alloc }
     }
 
-    pub(super) fn extract_if_inner(&mut self) -> (ExtractIfInner<'_, K, V>, A)
+    pub(super) fn extract_if_inner<R>(&mut self, range: R) -> (ExtractIfInner<'_, K, V, R>, A)
     where
         K: Ord,
+        R: RangeBounds<K>,
     {
         if let Some(root) = self.root.as_mut() {
             let (root, dormant_root) = DormantMutRef::new(root);
-            let front = root.borrow_mut().first_leaf_edge();
+            let first = root.borrow_mut().lower_bound(SearchBound::from_range(range.start_bound()));
             (
                 ExtractIfInner {
                     length: &mut self.length,
                     dormant_root: Some(dormant_root),
-                    cur_leaf_edge: Some(front),
+                    cur_leaf_edge: Some(first),
+                    range,
                 },
                 (*self.alloc).clone(),
             )
@@ -1459,6 +1462,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
                     length: &mut self.length,
                     dormant_root: None,
                     cur_leaf_edge: None,
+                    range,
                 },
                 (*self.alloc).clone(),
             )
@@ -1917,18 +1921,19 @@ pub struct ExtractIf<
     'a,
     K,
     V,
+    R,
     F,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + Clone = Global,
 > {
     pred: F,
-    inner: ExtractIfInner<'a, K, V>,
+    inner: ExtractIfInner<'a, K, V, R>,
     /// The BTreeMap will outlive this IntoIter so we don't care about drop order for `alloc`.
     alloc: A,
 }
 
 /// Most of the implementation of ExtractIf are generic over the type
 /// of the predicate, thus also serving for BTreeSet::ExtractIf.
-pub(super) struct ExtractIfInner<'a, K, V> {
+pub(super) struct ExtractIfInner<'a, K, V, R> {
     /// Reference to the length field in the borrowed map, updated live.
     length: &'a mut usize,
     /// Buried reference to the root field in the borrowed map.
@@ -1938,10 +1943,13 @@ pub(super) struct ExtractIfInner<'a, K, V> {
     /// Empty if the map has no root, if iteration went beyond the last leaf edge,
     /// or if a panic occurred in the predicate.
     cur_leaf_edge: Option<Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>>,
+    /// Range over which iteration was requested.  We don't need the left side, but we
+    /// can't extract the right side without requiring K: Clone.
+    range: R,
 }
 
 #[unstable(feature = "btree_extract_if", issue = "70530")]
-impl<K, V, F, A> fmt::Debug for ExtractIf<'_, K, V, F, A>
+impl<K, V, R, F, A> fmt::Debug for ExtractIf<'_, K, V, R, F, A>
 where
     K: fmt::Debug,
     V: fmt::Debug,
@@ -1953,8 +1961,10 @@ where
 }
 
 #[unstable(feature = "btree_extract_if", issue = "70530")]
-impl<K, V, F, A: Allocator + Clone> Iterator for ExtractIf<'_, K, V, F, A>
+impl<K, V, R, F, A: Allocator + Clone> Iterator for ExtractIf<'_, K, V, R, F, A>
 where
+    K: PartialOrd,
+    R: RangeBounds<K>,
     F: FnMut(&K, &mut V) -> bool,
 {
     type Item = (K, V);
@@ -1968,7 +1978,7 @@ where
     }
 }
 
-impl<'a, K, V> ExtractIfInner<'a, K, V> {
+impl<'a, K, V, R> ExtractIfInner<'a, K, V, R> {
     /// Allow Debug implementations to predict the next element.
     pub(super) fn peek(&self) -> Option<(&K, &V)> {
         let edge = self.cur_leaf_edge.as_ref()?;
@@ -1978,10 +1988,22 @@ impl<'a, K, V> ExtractIfInner<'a, K, V> {
     /// Implementation of a typical `ExtractIf::next` method, given the predicate.
     pub(super) fn next<F, A: Allocator + Clone>(&mut self, pred: &mut F, alloc: A) -> Option<(K, V)>
     where
+        K: PartialOrd,
+        R: RangeBounds<K>,
         F: FnMut(&K, &mut V) -> bool,
     {
         while let Ok(mut kv) = self.cur_leaf_edge.take()?.next_kv() {
             let (k, v) = kv.kv_mut();
+
+            // On creation, we navigated directly to the left bound, so we need only check the
+            // right bound here to decide whether to stop.
+            match self.range.end_bound() {
+                Bound::Included(ref end) if (*k).le(end) => (),
+                Bound::Excluded(ref end) if (*k).lt(end) => (),
+                Bound::Unbounded => (),
+                _ => return None,
+            }
+
             if pred(k, v) {
                 *self.length -= 1;
                 let (kv, pos) = kv.remove_kv_tracking(
@@ -2013,7 +2035,13 @@ impl<'a, K, V> ExtractIfInner<'a, K, V> {
 }
 
 #[unstable(feature = "btree_extract_if", issue = "70530")]
-impl<K, V, F> FusedIterator for ExtractIf<'_, K, V, F> where F: FnMut(&K, &mut V) -> bool {}
+impl<K, V, R, F> FusedIterator for ExtractIf<'_, K, V, R, F>
+where
+    K: PartialOrd,
+    R: RangeBounds<K>,
+    F: FnMut(&K, &mut V) -> bool,
+{
+}
 
 #[stable(feature = "btree_range", since = "1.17.0")]
 impl<'a, K, V> Iterator for Range<'a, K, V> {

alloc/src/collections/btree/set.rs

@@ -1109,7 +1109,7 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
         T: Ord,
         F: FnMut(&T) -> bool,
     {
-        self.extract_if(|v| !f(v)).for_each(drop);
+        self.extract_if(.., |v| !f(v)).for_each(drop);
     }
 
     /// Moves all elements from `other` into `self`, leaving `other` empty.
@@ -1214,12 +1214,13 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// assert_eq!(odds.into_iter().collect::<Vec<_>>(), vec![1, 3, 5, 7]);
     /// ```
     #[unstable(feature = "btree_extract_if", issue = "70530")]
-    pub fn extract_if<'a, F>(&'a mut self, pred: F) -> ExtractIf<'a, T, F, A>
+    pub fn extract_if<'a, F, R>(&'a mut self, range: R, pred: F) -> ExtractIf<'a, T, R, F, A>
     where
         T: Ord,
+        R: RangeBounds<T>,
         F: 'a + FnMut(&T) -> bool,
     {
-        let (inner, alloc) = self.map.extract_if_inner();
+        let (inner, alloc) = self.map.extract_if_inner(range);
         ExtractIf { pred, inner, alloc }
     }
 
@@ -1554,17 +1555,18 @@ impl<'a, T, A: Allocator + Clone> IntoIterator for &'a BTreeSet<T, A> {
 pub struct ExtractIf<
     'a,
     T,
+    R,
     F,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator + Clone = Global,
 > {
     pred: F,
-    inner: super::map::ExtractIfInner<'a, T, SetValZST>,
+    inner: super::map::ExtractIfInner<'a, T, SetValZST, R>,
     /// The BTreeMap will outlive this IntoIter so we don't care about drop order for `alloc`.
     alloc: A,
 }
 
 #[unstable(feature = "btree_extract_if", issue = "70530")]
-impl<T, F, A> fmt::Debug for ExtractIf<'_, T, F, A>
+impl<T, R, F, A> fmt::Debug for ExtractIf<'_, T, R, F, A>
 where
     T: fmt::Debug,
     A: Allocator + Clone,
@@ -1577,8 +1579,10 @@ where
 }
 
 #[unstable(feature = "btree_extract_if", issue = "70530")]
-impl<'a, T, F, A: Allocator + Clone> Iterator for ExtractIf<'_, T, F, A>
+impl<'a, T, R, F, A: Allocator + Clone> Iterator for ExtractIf<'_, T, R, F, A>
 where
+    T: PartialOrd,
+    R: RangeBounds<T>,
     F: 'a + FnMut(&T) -> bool,
 {
     type Item = T;
@@ -1595,7 +1599,13 @@ where
 }
 
 #[unstable(feature = "btree_extract_if", issue = "70530")]
-impl<T, F, A: Allocator + Clone> FusedIterator for ExtractIf<'_, T, F, A> where F: FnMut(&T) -> bool {}
+impl<T, R, F, A: Allocator + Clone> FusedIterator for ExtractIf<'_, T, R, F, A>
+where
+    T: PartialOrd,
+    R: RangeBounds<T>,
+    F: FnMut(&T) -> bool,
+{
+}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord, A: Allocator + Clone> Extend<T> for BTreeSet<T, A> {