From 4a8ddac99e1edfb219e11c3ea2d6c43ccecb29ab Mon Sep 17 00:00:00 2001 From: Josh Stone Date: Wed, 21 Jun 2017 13:22:27 -0700 Subject: Use `fold` to implement `Iterator::for_each` The benefit of using internal iteration is shown in new benchmarks: test iter::bench_for_each_chain_fold ... bench: 635,110 ns/iter (+/- 5,135) test iter::bench_for_each_chain_loop ... bench: 2,249,983 ns/iter (+/- 42,001) test iter::bench_for_each_chain_ref_fold ... bench: 2,248,061 ns/iter (+/- 51,940) --- src/libcore/benches/iter.rs | 47 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) (limited to 'src/libcore/benches') diff --git a/src/libcore/benches/iter.rs b/src/libcore/benches/iter.rs index 93d38a5bc83..5b06229c21f 100644 --- a/src/libcore/benches/iter.rs +++ b/src/libcore/benches/iter.rs @@ -99,3 +99,50 @@ fn bench_zip_add(b: &mut Bencher) { add_zip(&source, &mut dst) }); } + +/// `Iterator::for_each` implemented as a plain loop. +fn for_each_loop(iter: I, mut f: F) where + I: Iterator, F: FnMut(I::Item) +{ + for item in iter { + f(item); + } +} + +/// `Iterator::for_each` implemented with `fold` for internal iteration. +/// (except when `by_ref()` effectively disables that optimization.) +fn for_each_fold(iter: I, mut f: F) where + I: Iterator, F: FnMut(I::Item) +{ + iter.fold((), move |(), item| f(item)); +} + +#[bench] +fn bench_for_each_chain_loop(b: &mut Bencher) { + b.iter(|| { + let mut acc = 0; + let iter = (0i64..1000000).chain(0..1000000).map(black_box); + for_each_loop(iter, |x| acc += x); + acc + }); +} + +#[bench] +fn bench_for_each_chain_fold(b: &mut Bencher) { + b.iter(|| { + let mut acc = 0; + let iter = (0i64..1000000).chain(0..1000000).map(black_box); + for_each_fold(iter, |x| acc += x); + acc + }); +} + +#[bench] +fn bench_for_each_chain_ref_fold(b: &mut Bencher) { + b.iter(|| { + let mut acc = 0; + let mut iter = (0i64..1000000).chain(0..1000000).map(black_box); + for_each_fold(iter.by_ref(), |x| acc += x); + acc + }); +} -- cgit 1.4.1-3-g733a5