rluvaton commented on code in PR #8785:
URL: https://github.com/apache/arrow-rs/pull/8785#discussion_r2492233804
##########
arrow-array/src/iterator.rs:
##########
@@ -102,6 +102,35 @@ impl<T: ArrayAccessor> Iterator for ArrayIter<T> {
Some(self.current_end - self.current),
)
}
+
+ fn nth(&mut self, n: usize) -> Option<Self::Item> {
+ // Check if we can advance to the desired offset
+ match self.current.checked_add(n) {
+ // Yes, and still within bounds
+ Some(new_current) if new_current < self.current_end => {
+ self.current = new_current;
+ }
+
+ // Either overflow or would exceed current_end
+ _ => {
+ self.current = self.current_end;
+ return None;
+ }
+ }
+
+ self.next()
+ }
+
+ fn last(mut self) -> Option<Self::Item> {
+ self.next_back()
+ }
Review Comment:
The default implementation is doing it in `O(n)` and is not (currently)
taking advantage of it being `DoubleEndedIterator` while we are doing it in
constant time.
this is the default impl:
```rust
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn last(self) -> Option<Self::Item>
where
Self: Sized,
{
#[inline]
fn some<T>(_: Option<T>, x: T) -> Option<T> {
Some(x)
}
self.fold(None, some)
}
```
from [Rust source
code](https://github.com/rust-lang/rust/blob/f15a7f38580ddbdc1a23909dd05cf6cc6d9f3919/library/core/src/iter/traits/iterator.rs#L233-L260)
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