auto merge of #11479 : khodzha/rust/peekable_empty, r=brson

to fix https://github.com/mozilla/rust/issues/11218

src/libstd/iter.rs

@@ -1,4 +1,4 @@
-// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -1362,6 +1362,12 @@ impl<'a, A, T: Iterator<A>> Peekable<A, T> {
             None => None,
         }
     }
+
+    /// Check whether peekable iterator is empty or not.
+    #[inline]
+    pub fn is_empty(&mut self) -> bool {
+        self.peek().is_some()
+    }
 }
 
 /// An iterator which rejects elements while `predicate` is true
@@ -2923,4 +2929,12 @@ mod tests {
         ys.mut_iter().reverse_();
         assert_eq!(ys, [5, 4, 3, 2, 1]);
     }
+
+    fn test_peekable_is_empty() {
+        let a = [1];
+        let mut it = a.iter().peekable();
+        assert!( !it.is_empty() );
+        it.next();
+        assert!( it.is_empty() );
+    }
 }