Indicate the anonymous lifetime of the GroupBy and GroupByMut

Author: Kerollmops

library/core/src/slice/mod.rs

@@ -1233,7 +1233,7 @@ impl<T> [T] {
     /// ```
     #[unstable(feature = "slice_group_by", issue = "none")]
     #[inline]
-    pub fn group_by<F>(&self, pred: F) -> GroupBy<T, F>
+    pub fn group_by<F>(&self, pred: F) -> GroupBy<'_, T, F>
     where F: FnMut(&T, &T) -> bool
     {
         GroupBy::new(self, pred)
@@ -1262,7 +1262,7 @@ impl<T> [T] {
     /// ```
     #[unstable(feature = "slice_group_by", issue = "none")]
     #[inline]
-    pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<T, F>
+    pub fn group_by_mut<F>(&mut self, pred: F) -> GroupByMut<'_, T, F>
     where F: FnMut(&T, &T) -> bool
     {
         GroupByMut::new(self, pred)