diff options
Diffstat (limited to 'src/liballoc/vec.rs')
| -rw-r--r-- | src/liballoc/vec.rs | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs index cd62c3e0524..073d3ab5937 100644 --- a/src/liballoc/vec.rs +++ b/src/liballoc/vec.rs @@ -937,8 +937,8 @@ impl<T> Vec<T> { /// Retains only the elements specified by the predicate. /// /// In other words, remove all elements `e` such that `f(&e)` returns `false`. - /// This method operates in place and preserves the order of the retained - /// elements. + /// This method operates in place, visiting each element exactly once in the + /// original order, and preserves the order of the retained elements. /// /// # Examples /// @@ -947,6 +947,16 @@ impl<T> Vec<T> { /// vec.retain(|&x| x%2 == 0); /// assert_eq!(vec, [2, 4]); /// ``` + /// + /// The exact order may be useful for tracking external state, like an index. + /// + /// ``` + /// let mut vec = vec![1, 2, 3, 4, 5]; + /// let keep = [false, true, true, false, true]; + /// let mut i = 0; + /// vec.retain(|_| (keep[i], i += 1).0); + /// assert_eq!(vec, [2, 3, 5]); + /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn retain<F>(&mut self, mut f: F) where F: FnMut(&T) -> bool |