From bcc901260ce5b2b0a832ca68464f069b6d56a63c Mon Sep 17 00:00:00 2001
From: Chloe Ross <orangesnowfox@gmail.com>
Date: Fri, 18 Sep 2020 21:05:24 -0700
Subject: [PATCH] add `slice::replace`

---
 library/core/src/slice/mod.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index fd98f60c3ddc6..362c2e2cf378d 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -3059,6 +3059,30 @@ impl<T> [T] {
 
         left
     }
+
+    /// Moves `value` into `self[index]`, returning the old value.
+    ///
+    /// Neither value is dropped.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` is out of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(slice_replace)]
+    ///
+    /// let mut v = [1, 2, 3];
+    /// let r = v.replace(1, 20);
+    ///
+    /// assert_eq!(v, [1, 20, 3]);
+    /// assert_eq!(r, 2);
+    /// ```
+    #[unstable(feature = "slice_replace", reason = "new API", issue = "none")]
+    pub fn replace(&mut self, index: usize, value: T) -> T {
+        mem::replace(&mut self[index], value)
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]