Merge pull request #421 from cuviper/pop_if

Add map and set `pop_if`, similar to Rust 1.86's `Vec::pop_if`

Author: cuviper

src/map.rs

@@ -1136,6 +1136,36 @@ impl<K, V, S> IndexMap<K, V, S> {
         self.core.pop()
     }
 
+    /// Removes and returns the last key-value pair from a map if the predicate
+    /// returns `true`, or [`None`] if the predicate returns false or the map
+    /// is empty (the predicate will not be called in that case).
+    ///
+    /// This preserves the order of the remaining elements.
+    ///
+    /// Computes in **O(1)** time (average).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use indexmap::IndexMap;
+    ///
+    /// let init = [(1, 'a'), (2, 'b'), (3, 'c'), (4, 'd')];
+    /// let mut map = IndexMap::from(init);
+    /// let pred = |key: &i32, _value: &mut char| *key % 2 == 0;
+    ///
+    /// assert_eq!(map.pop_if(pred), Some((4, 'd')));
+    /// assert_eq!(map.as_slice(), &init[..3]);
+    /// assert_eq!(map.pop_if(pred), None);
+    /// ```
+    pub fn pop_if(&mut self, predicate: impl FnOnce(&K, &mut V) -> bool) -> Option<(K, V)> {
+        let (last_key, last_value) = self.last_mut()?;
+        if predicate(last_key, last_value) {
+            self.core.pop()
+        } else {
+            None
+        }
+    }
+
     /// Scan through each key-value pair in the map and keep those where the
     /// closure `keep` returns `true`.
     ///

src/set.rs

@@ -904,6 +904,35 @@ impl<T, S> IndexSet<T, S> {
         self.map.pop().map(|(x, ())| x)
     }
 
+    /// Removes and returns the last value from a set if the predicate
+    /// returns `true`, or [`None`] if the predicate returns false or the set
+    /// is empty (the predicate will not be called in that case).
+    ///
+    /// This preserves the order of the remaining elements.
+    ///
+    /// Computes in **O(1)** time (average).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use indexmap::IndexSet;
+    ///
+    /// let mut set = IndexSet::from([1, 2, 3, 4]);
+    /// let pred = |x: &i32| *x % 2 == 0;
+    ///
+    /// assert_eq!(set.pop_if(pred), Some(4));
+    /// assert_eq!(set.as_slice(), &[1, 2, 3]);
+    /// assert_eq!(set.pop_if(pred), None);
+    /// ```
+    pub fn pop_if(&mut self, predicate: impl FnOnce(&T) -> bool) -> Option<T> {
+        let last = self.last()?;
+        if predicate(last) {
+            self.pop()
+        } else {
+            None
+        }
+    }
+
     /// Scan through each value in the set and keep those where the
     /// closure `keep` returns `true`.
     ///