From a3d18bc95b1639cf3cb967165f7104e2c79893f5 Mon Sep 17 00:00:00 2001
From: Kevin Ballard <kevin@sb.org>
Date: Sat, 3 Aug 2013 15:41:29 -0700
Subject: Make Zip iterator short-circuit

Python's zip() short-circuits by not even querying its right-hand
iterator if the left-hand one is done. Match that behavior here by not
calling .next() on the right iterator if the left one returns None.
---
 src/libstd/iterator.rs | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

(limited to 'src/libstd/iterator.rs')

diff --git a/src/libstd/iterator.rs b/src/libstd/iterator.rs
index 841b6134410..3b4c31349c9 100644
--- a/src/libstd/iterator.rs
+++ b/src/libstd/iterator.rs
@@ -929,9 +929,12 @@ pub struct Zip<T, U> {
 impl<A, B, T: Iterator<A>, U: Iterator<B>> Iterator<(A, B)> for Zip<T, U> {
     #[inline]
     fn next(&mut self) -> Option<(A, B)> {
-        match (self.a.next(), self.b.next()) {
-            (Some(x), Some(y)) => Some((x, y)),
-            _ => None
+        match self.a.next() {
+            None => None,
+            Some(x) => match self.b.next() {
+                None => None,
+                Some(y) => Some((x, y))
+            }
         }
     }
 
@@ -962,9 +965,12 @@ RandomAccessIterator<(A, B)> for Zip<T, U> {
 
     #[inline]
     fn idx(&self, index: uint) -> Option<(A, B)> {
-        match (self.a.idx(index), self.b.idx(index)) {
-            (Some(x), Some(y)) => Some((x, y)),
-            _ => None
+        match self.a.idx(index) {
+            None => None,
+            Some(x) => match self.b.idx(index) {
+                None => None,
+                Some(y) => Some((x, y))
+            }
         }
     }
 }
-- 
cgit 1.4.1-3-g733a5