From 780acda325772b15f12f08f60ca2d4ba558cee51 Mon Sep 17 00:00:00 2001
From: Ulrik Sverdrup <bluss@users.noreply.github.com>
Date: Tue, 25 Oct 2016 15:50:52 +0200
Subject: [PATCH] iter: Implement .fold() for .cloned() and .map()

Implement .fold() specifically for .map() and .cloned() so that any
inner fold improvements are available through map and cloned.
---
 src/libcore/iter/mod.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/libcore/iter/mod.rs b/src/libcore/iter/mod.rs
index 9eeb2608071c..2c3b8864a115 100644
--- a/src/libcore/iter/mod.rs
+++ b/src/libcore/iter/mod.rs
@@ -399,6 +399,12 @@ impl<'a, I, T: 'a> Iterator for Cloned<I>
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.it.size_hint()
     }
+
+    fn fold<Acc, F>(self, init: Acc, mut f: F) -> Acc
+        where F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.it.fold(init, move |acc, elt| f(acc, elt.clone()))
+    }
 }
 
 #[stable(feature = "iter_cloned", since = "1.1.0")]
@@ -939,6 +945,13 @@ impl<B, I: Iterator, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B {
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.iter.size_hint()
     }
+
+    fn fold<Acc, G>(self, init: Acc, mut g: G) -> Acc
+        where G: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter.fold(init, move |acc, elt| g(acc, f(elt)))
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]