Rollup merge of rust-lang#34688 - GuillaumeGomez:double_ended_iterator, r=steveklabnik

Improve DoubleEndedIterator examples

Fixes rust-lang#34065.

r? @steveklabnik

Author: Manishearth

src/libcore/iter/traits.rs

@@ -371,13 +371,16 @@ pub trait Extend<A> {
 /// Basic usage:
 ///
 /// ```
-/// let numbers = vec![1, 2, 3];
+/// let numbers = vec![1, 2, 3, 4, 5, 6];
 ///
 /// let mut iter = numbers.iter();
 ///
 /// assert_eq!(Some(&1), iter.next());
-/// assert_eq!(Some(&3), iter.next_back());
-/// assert_eq!(Some(&2), iter.next_back());
+/// assert_eq!(Some(&6), iter.next_back());
+/// assert_eq!(Some(&5), iter.next_back());
+/// assert_eq!(Some(&2), iter.next());
+/// assert_eq!(Some(&3), iter.next());
+/// assert_eq!(Some(&4), iter.next());
 /// assert_eq!(None, iter.next());
 /// assert_eq!(None, iter.next_back());
 /// ```
@@ -395,13 +398,16 @@ pub trait DoubleEndedIterator: Iterator {
     /// Basic usage:
     ///
     /// ```
-    /// let numbers = vec![1, 2, 3];
+    /// let numbers = vec![1, 2, 3, 4, 5, 6];
     ///
     /// let mut iter = numbers.iter();
     ///
     /// assert_eq!(Some(&1), iter.next());
-    /// assert_eq!(Some(&3), iter.next_back());
-    /// assert_eq!(Some(&2), iter.next_back());
+    /// assert_eq!(Some(&6), iter.next_back());
+    /// assert_eq!(Some(&5), iter.next_back());
+    /// assert_eq!(Some(&2), iter.next());
+    /// assert_eq!(Some(&3), iter.next());
+    /// assert_eq!(Some(&4), iter.next());
     /// assert_eq!(None, iter.next());
     /// assert_eq!(None, iter.next_back());
     /// ```