Auto merge of #35856 - phimuemue:master, r=brson

[rust.git] / src / libcore / iter / iterator.rs

diff --git a/src/libcore/iter/iterator.rs b/src/libcore/iter/iterator.rs
index ea97c87efbb410fad9c24a4aed79cf75f5eba764..6b616f8018156bf8e5e217d46de70b4223d109e8 100644 (file)
--- a/src/libcore/iter/iterator.rs
+++ b/src/libcore/iter/iterator.rs
@@ -1657,6 +1657,32 @@ fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
             .map(|(_, x)| x)
     }
 
+    /// Returns the element that gives the maximum value with respect to the
+    /// specified comparison function.
+    ///
+    /// Returns the rightmost element if the comparison determines two elements
+    /// to be equally maximum.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(iter_max_by)]
+    /// let a = [-3_i32, 0, 1, 5, -10];
+    /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5);
+    /// ```
+    #[inline]
+    #[unstable(feature = "iter_max_by", issue="36105")]
+    fn max_by<F>(self, mut compare: F) -> Option<Self::Item>
+        where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,
+    {
+        select_fold1(self,
+                     |_| (),
+                     // switch to y even if it is only equal, to preserve
+                     // stability.
+                     |_, x, _, y| Ordering::Greater != compare(x, y))
+            .map(|(_, x)| x)
+    }
+
     /// Returns the element that gives the minimum value from the
     /// specified function.
     ///
@@ -1681,6 +1707,33 @@ fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
             .map(|(_, x)| x)
     }
 
+    /// Returns the element that gives the minimum value with respect to the
+    /// specified comparison function.
+    ///
+    /// Returns the latest element if the comparison determines two elements
+    /// to be equally minimum.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(iter_min_by)]
+    /// let a = [-3_i32, 0, 1, 5, -10];
+    /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10);
+    /// ```
+    #[inline]
+    #[unstable(feature = "iter_min_by", issue="36105")]
+    fn min_by<F>(self, mut compare: F) -> Option<Self::Item>
+        where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,
+    {
+        select_fold1(self,
+                     |_| (),
+                     // switch to y even if it is strictly smaller, to
+                     // preserve stability.
+                     |_, x, _, y| Ordering::Greater == compare(x, y))
+            .map(|(_, x)| x)
+    }
+
+
     /// Reverses an iterator's direction.
     ///
     /// Usually, iterators iterate from left to right. After using `rev()`,