auto merge of #18468 : jakub-/rust/iter-repeat, r=alexcrichton

Implements a part of RFC 235.

[breaking-change]

src/libcore/iter.rs

@@ -2155,7 +2155,7 @@ type IterateState<'a, T> = (|T|: 'a -> T, Option<T>, bool);
 /// from a given seed value.
 pub type Iterate<'a, T> = Unfold<'a, T, IterateState<'a, T>>;
 
-/// Creates a new iterator that produces an infinite sequence of
+/// Create a new iterator that produces an infinite sequence of
 /// repeated applications of the given function `f`.
 pub fn iterate<'a, T: Clone>(seed: T, f: |T|: 'a -> T) -> Iterate<'a, T> {
     Unfold::new((f, Some(seed), true), |st| {
@@ -2174,6 +2174,11 @@ pub fn iterate<'a, T: Clone>(seed: T, f: |T|: 'a -> T) -> Iterate<'a, T> {
     })
 }
 
+/// Create a new iterator that endlessly repeats the element `elt`.
+pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
+    Repeat::new(elt)
+}
+
 /// Functions for lexicographical ordering of sequences.
 ///
 /// Lexicographical ordering through `<`, `<=`, `>=`, `>` requires

src/libcore/prelude.rs

@@ -39,7 +39,7 @@ pub use ops::{Slice, SliceMut};
 pub use ops::{Fn, FnMut, FnOnce};
 
 // Reexported functions
-pub use iter::range;
+pub use iter::{range, repeat};
 pub use mem::drop;
 
 // Reexported types and traits

src/libcoretest/iter.rs

@@ -846,6 +846,14 @@ fn test_iterate() {
     assert_eq!(it.next(), Some(8u));
 }
 
+#[test]
+fn test_repeat() {
+    let mut it = repeat(42u);
+    assert_eq!(it.next(), Some(42u));
+    assert_eq!(it.next(), Some(42u));
+    assert_eq!(it.next(), Some(42u));
+}
+
 #[bench]
 fn bench_rposition(b: &mut Bencher) {
     let it: Vec<uint> = range(0u, 300).collect();

src/libstd/prelude.rs

@@ -51,7 +51,7 @@
 
 // Reexported functions
 #[doc(no_inline)] pub use from_str::from_str;
-#[doc(no_inline)] pub use iter::range;
+#[doc(no_inline)] pub use iter::{range, repeat};
 #[doc(no_inline)] pub use mem::drop;
 
 // Reexported types and traits