auto merge of #6177 : gifnksm/rust/iter-chain, r=thestinger

`T: Iterator<A>` and `U: Iterator<A>` should be able to `chain` whether `T` and `U` are same or not.

Author: bors

src/libcore/iterator.rs

@@ -29,7 +29,7 @@ pub trait Iterator<A> {
 ///
 /// In the future these will be default methods instead of a utility trait.
 pub trait IteratorUtil<A> {
-    fn chain(self, other: Self) -> ChainIterator<Self>;
+    fn chain<U: Iterator<A>>(self, other: U) -> ChainIterator<Self, U>;
     fn zip<B, U: Iterator<B>>(self, other: U) -> ZipIterator<Self, U>;
     // FIXME: #5898: should be called map
     fn transform<'r, B>(self, f: &'r fn(A) -> B) -> MapIterator<'r, A, B, Self>;
@@ -50,7 +50,7 @@ pub trait IteratorUtil<A> {
 /// In the future these will be default methods instead of a utility trait.
 impl<A, T: Iterator<A>> IteratorUtil<A> for T {
     #[inline(always)]
-    fn chain(self, other: T) -> ChainIterator<T> {
+    fn chain<U: Iterator<A>>(self, other: U) -> ChainIterator<T, U> {
         ChainIterator{a: self, b: other, flag: false}
     }
 
@@ -115,13 +115,13 @@ impl<A, T: Iterator<A>> IteratorUtil<A> for T {
     }
 }
 
-pub struct ChainIterator<T> {
+pub struct ChainIterator<T, U> {
     priv a: T,
-    priv b: T,
+    priv b: U,
     priv flag: bool
 }
 
-impl<A, T: Iterator<A>> Iterator<A> for ChainIterator<T> {
+impl<A, T: Iterator<A>, U: Iterator<A>> Iterator<A> for ChainIterator<T, U> {
     #[inline]
     fn next(&mut self) -> Option<A> {
         if self.flag {
@@ -385,7 +385,7 @@ mod tests {
     #[test]
     fn test_iterator_chain() {
         let xs = [0u, 1, 2, 3, 4, 5];
-        let ys = [30, 40, 50, 60];
+        let ys = [30u, 40, 50, 60];
         let expected = [0, 1, 2, 3, 4, 5, 30, 40, 50, 60];
         let mut it = xs.iter().chain(ys.iter());
         let mut i = 0;
@@ -394,6 +394,15 @@ mod tests {
             i += 1;
         }
         assert_eq!(i, expected.len());
+
+        let ys = Counter::new(30u, 10).take(4);
+        let mut it = xs.iter().transform(|&x| x).chain(ys);
+        let mut i = 0;
+        for it.advance |x: uint| {
+            assert_eq!(x, expected[i]);
+            i += 1;
+        }
+        assert_eq!(i, expected.len());
     }
 
     #[test]