diff options
| -rw-r--r-- | src/libcore/iter/traits/double_ended.rs | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/src/libcore/iter/traits/double_ended.rs b/src/libcore/iter/traits/double_ended.rs index cceb373d552..f6329c6c593 100644 --- a/src/libcore/iter/traits/double_ended.rs +++ b/src/libcore/iter/traits/double_ended.rs @@ -63,6 +63,32 @@ pub trait DoubleEndedIterator: Iterator { /// assert_eq!(None, iter.next()); /// assert_eq!(None, iter.next_back()); /// ``` + /// + /// # Remarks + /// + /// The elements yielded by `DoubleEndedIterator`'s methods may differ from + /// the ones yielded by `Iterator`'s methods: + /// + /// ``` + /// let vec = vec![(1, 'a'), (1, 'b'), (1, 'c'), (2, 'a'), (2, 'b')]; + /// let uniq_by_fst_comp = || { + /// let mut seen = std::collections::HashSet::new(); + /// vec.iter().copied().filter(move |x| seen.insert(x.0)) + /// }; + /// + /// assert_eq!(uniq_by_fst_comp().last(), Some((2, 'a'))); + /// assert_eq!(uniq_by_fst_comp().next_back(), Some((2, 'b'))); + /// + /// assert_eq!( + /// uniq_by_fst_comp().fold(vec![], |mut v, x| {v.push(x); v}), + /// vec![(1, 'a'), (2, 'a')] + /// ); + /// assert_eq!( + /// uniq_by_fst_comp().rfold(vec![], |mut v, x| {v.push(x); v}), + /// vec![(2, 'b'), (1, 'c')] + /// ); + /// ``` + /// #[stable(feature = "rust1", since = "1.0.0")] fn next_back(&mut self) -> Option<Self::Item>; |