From e015e9da717bf501ab4752b2ea045d899f804a42 Mon Sep 17 00:00:00 2001 From: The8472 Date: Sat, 24 Jul 2021 17:42:20 +0200 Subject: implement fold() on array::IntoIter to improve flatten().collect() perf ``` # old test vec::bench_flat_map_collect ... bench: 2,244,024 ns/iter (+/- 18,903) # new test vec::bench_flat_map_collect ... bench: 172,863 ns/iter (+/- 2,141) ``` --- library/core/src/array/iter.rs | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'library/core/src/array') diff --git a/library/core/src/array/iter.rs b/library/core/src/array/iter.rs index 61ab1b1faff..004d1736b0f 100644 --- a/library/core/src/array/iter.rs +++ b/library/core/src/array/iter.rs @@ -123,6 +123,22 @@ impl Iterator for IntoIter { (len, Some(len)) } + #[inline] + fn fold(mut self, init: Acc, mut fold: Fold) -> Acc + where + Fold: FnMut(Acc, Self::Item) -> Acc, + { + let data = &mut self.data; + (&mut self.alive) + .try_fold::<_, _, Result<_, !>>(init, |acc, idx| { + // SAFETY: idx is obtained by folding over the `alive` range, which implies the + // value is currently considered alive but as the range is being consumed each value + // we read here will only be read once and then considered dead. + Ok(fold(acc, unsafe { data.get_unchecked(idx).assume_init_read() })) + }) + .unwrap() + } + fn count(self) -> usize { self.len() } -- cgit 1.4.1-3-g733a5