From 919f5afdfddc6c44bf8402044f939ac65a96c29a Mon Sep 17 00:00:00 2001
From: mchlrhw <4028654+mchlrhw@users.noreply.github.com>
Date: Wed, 20 Sep 2017 16:02:10 +0100
Subject: [PATCH] Implement `entry_and_modify`

---
 map.rs | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/map.rs b/map.rs
index 96af227..73263d7 100644
--- a/map.rs
+++ b/map.rs
@@ -2002,6 +2002,41 @@ impl<'a, K, V> Entry<'a, K, V> {
             Vacant(ref entry) => entry.key(),
         }
     }
+
+    /// Provides in-place mutable access to an occupied entry before any
+    /// potential inserts into the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(entry_and_modify)]
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// map.entry("poneyland")
+    ///    .and_modify(|e| { *e += 1 })
+    ///    .or_insert(42);
+    /// assert_eq!(map["poneyland"], 42);
+    ///
+    /// map.entry("poneyland")
+    ///    .and_modify(|e| { *e += 1 })
+    ///    .or_insert(42);
+    /// assert_eq!(map["poneyland"], 43);
+    /// ```
+    #[unstable(feature = "entry_and_modify", issue = "44733")]
+    pub fn and_modify<F>(self, mut f: F) -> Self
+        where F: FnMut(&mut V)
+    {
+        match self {
+            Occupied(mut entry) => {
+                f(entry.get_mut());
+                Occupied(entry)
+            },
+            Vacant(entry) => Vacant(entry),
+        }
+    }
+
 }
 
 impl<'a, K, V: Default> Entry<'a, K, V> {