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Implement RFC 771: std::iter::once
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@ -3030,6 +3030,100 @@ pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
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Repeat{element: elt}
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}
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/// An iterator that yields nothing.
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#[unstable(feature="iter_empty", reason = "new addition")]
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pub struct Empty<T>(marker::PhantomData<T>);
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#[unstable(feature="iter_empty", reason = "new addition")]
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impl<T> Iterator for Empty<T> {
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type Item = T;
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fn next(&mut self) -> Option<T> {
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None
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}
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fn size_hint(&self) -> (usize, Option<usize>){
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(0, Some(0))
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}
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}
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#[unstable(feature="iter_empty", reason = "new addition")]
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impl<T> DoubleEndedIterator for Empty<T> {
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fn next_back(&mut self) -> Option<T> {
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None
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}
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}
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#[unstable(feature="iter_empty", reason = "new addition")]
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impl<T> ExactSizeIterator for Empty<T> {
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fn len(&self) -> usize {
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0
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}
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}
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// not #[derive] because that adds a Clone bound on T,
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// which isn't necessary.
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#[unstable(feature="iter_empty", reason = "new addition")]
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impl<T> Clone for Empty<T> {
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fn clone(&self) -> Empty<T> {
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Empty(marker::PhantomData)
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}
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}
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// not #[derive] because that adds a Default bound on T,
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// which isn't necessary.
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#[unstable(feature="iter_empty", reason = "new addition")]
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impl<T> Default for Empty<T> {
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fn default() -> Empty<T> {
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Empty(marker::PhantomData)
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}
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}
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/// Creates an iterator that yields nothing.
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#[unstable(feature="iter_empty", reason = "new addition")]
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pub fn empty<T>() -> Empty<T> {
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Empty(marker::PhantomData)
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}
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/// An iterator that yields an element exactly once.
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#[unstable(feature="iter_once", reason = "new addition")]
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pub struct Once<T> {
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inner: ::option::IntoIter<T>
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}
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#[unstable(feature="iter_once", reason = "new addition")]
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impl<T> Iterator for Once<T> {
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type Item = T;
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fn next(&mut self) -> Option<T> {
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self.inner.next()
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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self.inner.size_hint()
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}
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}
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#[unstable(feature="iter_once", reason = "new addition")]
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impl<T> DoubleEndedIterator for Once<T> {
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fn next_back(&mut self) -> Option<T> {
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self.inner.next_back()
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}
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}
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#[unstable(feature="iter_once", reason = "new addition")]
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impl<T> ExactSizeIterator for Once<T> {
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fn len(&self) -> usize {
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self.inner.len()
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}
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}
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/// Creates an iterator that yields an element exactly once.
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#[unstable(feature="iter_once", reason = "new addition")]
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pub fn once<T>(value: T) -> Once<T> {
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Once { inner: Some(value).into_iter() }
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}
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/// Functions for lexicographical ordering of sequences.
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///
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/// Lexicographical ordering through `<`, `<=`, `>=`, `>` requires
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@ -1096,6 +1096,19 @@ fn test_fuse_count() {
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// Can't check len now because count consumes.
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}
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#[test]
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fn test_once() {
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let mut it = once(42);
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assert_eq!(it.next(), Some(42));
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assert_eq!(it.next(), None);
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}
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#[test]
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fn test_empty() {
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let mut it = empty::<i32>();
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assert_eq!(it.next(), None);
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}
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#[bench]
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fn bench_rposition(b: &mut Bencher) {
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let it: Vec<usize> = (0..300).collect();
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@ -25,6 +25,8 @@
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#![feature(slice_patterns)]
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#![feature(float_from_str_radix)]
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#![feature(cell_extras)]
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#![feature(iter_empty)]
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#![feature(iter_once)]
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extern crate core;
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extern crate test;
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