From eebb54cefe4d0062d08d0c7430f5b04894bd0704 Mon Sep 17 00:00:00 2001
From: Josh Stone <cuviper@gmail.com>
Date: Mon, 22 Feb 2021 17:37:51 -0800
Subject: [PATCH] add Entry::or_insert_with_key like Rust 1.50

---
 src/map/core.rs | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/map/core.rs b/src/map/core.rs
index 1c261a51..aaa3768a 100644
--- a/src/map/core.rs
+++ b/src/map/core.rs
@@ -470,6 +470,24 @@ impl<'a, K, V> Entry<'a, K, V> {
         }
     }
 
+    /// Inserts the result of the `call` function with a reference to the entry's key if it is
+    /// vacant, and returns a mutable reference to the new value. Otherwise a mutable reference to
+    /// an already existent value is returned.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    pub fn or_insert_with_key<F>(self, call: F) -> &'a mut V
+    where
+        F: FnOnce(&K) -> V,
+    {
+        match self {
+            Entry::Occupied(entry) => entry.into_mut(),
+            Entry::Vacant(entry) => {
+                let value = call(&entry.key);
+                entry.insert(value)
+            }
+        }
+    }
+
     /// Gets a reference to the entry's key, either within the map if occupied,
     /// or else the new key that was used to find the entry.
     pub fn key(&self) -> &K {