diff --git a/src/libcore/iter.rs b/src/libcore/iter.rs
index e4d2ab198630a..838480c88895c 100644
--- a/src/libcore/iter.rs
+++ b/src/libcore/iter.rs
@@ -137,7 +137,7 @@ pub trait Iterator {
     ///
     /// ```
     /// let a = [1, 2, 3, 4, 5];
-    /// assert_eq!(a.iter().last().unwrap(), &5);
+    /// assert_eq!(a.iter().last(), Some(&5));
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -155,7 +155,7 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3, 4, 5];
     /// let mut it = a.iter();
-    /// assert_eq!(it.nth(2).unwrap(), &3);
+    /// assert_eq!(it.nth(2), Some(&3));
     /// assert_eq!(it.nth(2), None);
     /// ```
     #[inline]
@@ -178,8 +178,8 @@ pub trait Iterator {
     /// let a = [0];
     /// let b = [1];
     /// let mut it = a.iter().chain(b.iter());
-    /// assert_eq!(it.next().unwrap(), &0);
-    /// assert_eq!(it.next().unwrap(), &1);
+    /// assert_eq!(it.next(), Some(&0));
+    /// assert_eq!(it.next(), Some(&1));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -201,7 +201,7 @@ pub trait Iterator {
     /// let a = [0];
     /// let b = [1];
     /// let mut it = a.iter().zip(b.iter());
-    /// assert_eq!(it.next().unwrap(), (&0, &1));
+    /// assert_eq!(it.next(), Some((&0, &1)));
     /// assert!(it.next().is_none());
     /// ```
     ///
@@ -234,8 +234,8 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2];
     /// let mut it = a.iter().map(|&x| 2 * x);
-    /// assert_eq!(it.next().unwrap(), 2);
-    /// assert_eq!(it.next().unwrap(), 4);
+    /// assert_eq!(it.next(), Some(2));
+    /// assert_eq!(it.next(), Some(4));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -255,7 +255,7 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2];
     /// let mut it = a.iter().filter(|&x| *x > 1);
-    /// assert_eq!(it.next().unwrap(), &2);
+    /// assert_eq!(it.next(), Some(&2));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -275,7 +275,7 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2];
     /// let mut it = a.iter().filter_map(|&x| if x > 1 {Some(2 * x)} else {None});
-    /// assert_eq!(it.next().unwrap(), 4);
+    /// assert_eq!(it.next(), Some(4));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -310,8 +310,8 @@ pub trait Iterator {
     /// ```
     /// let a = [100, 200];
     /// let mut it = a.iter().enumerate();
-    /// assert_eq!(it.next().unwrap(), (0, &100));
-    /// assert_eq!(it.next().unwrap(), (1, &200));
+    /// assert_eq!(it.next(), Some((0, &100)));
+    /// assert_eq!(it.next(), Some((1, &200)));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -329,12 +329,12 @@ pub trait Iterator {
     /// # #![feature(core)]
     /// let xs = [100, 200, 300];
     /// let mut it = xs.iter().cloned().peekable();
-    /// assert_eq!(*it.peek().unwrap(), 100);
-    /// assert_eq!(it.next().unwrap(), 100);
-    /// assert_eq!(it.next().unwrap(), 200);
-    /// assert_eq!(*it.peek().unwrap(), 300);
-    /// assert_eq!(*it.peek().unwrap(), 300);
-    /// assert_eq!(it.next().unwrap(), 300);
+    /// assert_eq!(*it.peek(), Some(100));
+    /// assert_eq!(it.next(), Some(100));
+    /// assert_eq!(it.next(), Some(200));
+    /// assert_eq!(*it.peek(), Some(300));
+    /// assert_eq!(*it.peek(), Some(300));
+    /// assert_eq!(it.next(), Some(300));
     /// assert!(it.peek().is_none());
     /// assert!(it.next().is_none());
     /// ```
@@ -353,9 +353,9 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3, 4, 5];
     /// let mut it = a.iter().skip_while(|&a| *a < 3);
-    /// assert_eq!(it.next().unwrap(), &3);
-    /// assert_eq!(it.next().unwrap(), &4);
-    /// assert_eq!(it.next().unwrap(), &5);
+    /// assert_eq!(it.next(), Some(&3));
+    /// assert_eq!(it.next(), Some(&4));
+    /// assert_eq!(it.next(), Some(&5));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -375,8 +375,8 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3, 4, 5];
     /// let mut it = a.iter().take_while(|&a| *a < 3);
-    /// assert_eq!(it.next().unwrap(), &1);
-    /// assert_eq!(it.next().unwrap(), &2);
+    /// assert_eq!(it.next(), Some(&1));
+    /// assert_eq!(it.next(), Some(&2));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -395,8 +395,8 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3, 4, 5];
     /// let mut it = a.iter().skip(3);
-    /// assert_eq!(it.next().unwrap(), &4);
-    /// assert_eq!(it.next().unwrap(), &5);
+    /// assert_eq!(it.next(), Some(&4));
+    /// assert_eq!(it.next(), Some(&5));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -413,9 +413,9 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3, 4, 5];
     /// let mut it = a.iter().take(3);
-    /// assert_eq!(it.next().unwrap(), &1);
-    /// assert_eq!(it.next().unwrap(), &2);
-    /// assert_eq!(it.next().unwrap(), &3);
+    /// assert_eq!(it.next(), Some(&1));
+    /// assert_eq!(it.next(), Some(&2));
+    /// assert_eq!(it.next(), Some(&3));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -437,11 +437,11 @@ pub trait Iterator {
     ///   *fac = *fac * x;
     ///   Some(*fac)
     /// });
-    /// assert_eq!(it.next().unwrap(), 1);
-    /// assert_eq!(it.next().unwrap(), 2);
-    /// assert_eq!(it.next().unwrap(), 6);
-    /// assert_eq!(it.next().unwrap(), 24);
-    /// assert_eq!(it.next().unwrap(), 120);
+    /// assert_eq!(it.next(), Some(1));
+    /// assert_eq!(it.next(), Some(2));
+    /// assert_eq!(it.next(), Some(6));
+    /// assert_eq!(it.next(), Some(24));
+    /// assert_eq!(it.next(), Some(120));
     /// assert!(it.next().is_none());
     /// ```
     #[inline]
@@ -680,7 +680,7 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3, 4, 5];
     /// let mut it = a.iter();
-    /// assert_eq!(it.find(|&x| *x == 3).unwrap(), &3);
+    /// assert_eq!(it.find(|&x| *x == 3), Some(&3));
     /// assert_eq!(it.collect::<Vec<_>>(), [&4, &5]);
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -715,7 +715,7 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3, 4, 5];
     /// let mut it = a.iter();
-    /// assert_eq!(it.position(|x| *x == 3).unwrap(), 2);
+    /// assert_eq!(it.position(|x| *x == 3), Some(2));
     /// assert_eq!(it.collect::<Vec<_>>(), [&4, &5]);
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -743,7 +743,7 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 2, 4, 5];
     /// let mut it = a.iter();
-    /// assert_eq!(it.rposition(|x| *x == 2).unwrap(), 2);
+    /// assert_eq!(it.rposition(|x| *x == 2), Some(2));
     /// assert_eq!(it.collect::<Vec<_>>(), [&1, &2]);
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -773,7 +773,7 @@ pub trait Iterator {
     ///
     /// ```
     /// let a = [1, 2, 3, 4, 5];
-    /// assert_eq!(a.iter().max().unwrap(), &5);
+    /// assert_eq!(a.iter().max(), Some(&5));
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -796,7 +796,7 @@ pub trait Iterator {
     ///
     /// ```
     /// let a = [1, 2, 3, 4, 5];
-    /// assert_eq!(a.iter().min().unwrap(), &1);
+    /// assert_eq!(a.iter().min(), Some(&1));
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -900,7 +900,7 @@ pub trait Iterator {
     /// # #![feature(core)]
     ///
     /// let a = [-3_i32, 0, 1, 5, -10];
-    /// assert_eq!(*a.iter().max_by(|x| x.abs()).unwrap(), -10);
+    /// assert_eq!(*a.iter().max_by(|x| x.abs()), Some(-10));
     /// ```
     #[inline]
     #[unstable(feature = "core",
@@ -929,7 +929,7 @@ pub trait Iterator {
     /// # #![feature(core)]
     ///
     /// let a = [-3_i32, 0, 1, 5, -10];
-    /// assert_eq!(*a.iter().min_by(|x| x.abs()).unwrap(), 0);
+    /// assert_eq!(*a.iter().min_by(|x| x.abs()), Some(0));
     /// ```
     #[inline]
     #[unstable(feature = "core",
@@ -1025,9 +1025,9 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2];
     /// let mut it = a.iter().cycle();
-    /// assert_eq!(it.next().unwrap(), &1);
-    /// assert_eq!(it.next().unwrap(), &2);
-    /// assert_eq!(it.next().unwrap(), &1);
+    /// assert_eq!(it.next(), Some(&1));
+    /// assert_eq!(it.next(), Some(&2));
+    /// assert_eq!(it.next(), Some(&1));
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]