Focus as an iterator-like.

Author: bodil

CHANGELOG.md

@@ -9,6 +9,13 @@ Versioning](http://semver.org/spec/v2.0.0.html).
 ## [Unreleased]
 
 ### Added
+- `Vector` now has `Focus` and `FocusMut` APIs for caching index lookups,
+  yielding huge performance gains when performing multiple adjacent index
+  lookups.  `Vector::iter` has been reimplemented using this API, and is now
+  much simpler and about twice as fast as a result, and `Vector::iter_mut` now
+  runs nearly an order of magnitude faster. Likewise, `Vector::sort` and
+  `Vector::retain` are now using `FocusMut` and run considerably faster as a
+  result.
 - `Vector::set` now returns the replaced value.
 
 ### Changed

benches/vector.rs

@@ -5,13 +5,25 @@
 #![feature(test)]
 
 extern crate im;
+extern crate rand;
 extern crate test;
 
+use im::iter::unfold_mut;
+use rand::distributions::{Distribution, Standard};
+use rand::Rng;
 use std::iter::FromIterator;
 use test::Bencher;
 
 use im::vector::Vector;
 
+fn rando<A>() -> impl Iterator<Item = A>
+where
+    Standard: Distribution<A>,
+{
+    let rng = rand::thread_rng();
+    unfold_mut(rng, |rng| Some(rng.gen()))
+}
+
 // fn vector_push_front(b: &mut Bencher, count: usize) {
 //     b.iter(|| {
 //         let mut l = Vector::new();
@@ -306,6 +318,123 @@ fn vector_append_100000(b: &mut Bencher) {
     vector_append(b, 100_000)
 }
 
+fn vector_iter(b: &mut Bencher, count: usize) {
+    let vec: Vector<i32> = rando().take(count).collect();
+    b.iter(|| {
+        let it = vec.iter();
+        for _ in it {}
+    })
+}
+
+#[bench]
+fn vector_iter_10(b: &mut Bencher) {
+    vector_iter(b, 10)
+}
+
+#[bench]
+fn vector_iter_100(b: &mut Bencher) {
+    vector_iter(b, 100)
+}
+
+#[bench]
+fn vector_iter_1000(b: &mut Bencher) {
+    vector_iter(b, 1000)
+}
+
+#[bench]
+fn vector_iter_100000(b: &mut Bencher) {
+    vector_iter(b, 100_000)
+}
+
+fn vector_get_seq(b: &mut Bencher, count: usize) {
+    let vec: Vector<i32> = rando().take(count).collect();
+    b.iter(|| {
+        for i in 0..count {
+            let _ = vec.get(i);
+        }
+    })
+}
+
+#[bench]
+fn vector_get_seq_10(b: &mut Bencher) {
+    vector_get_seq(b, 10)
+}
+
+#[bench]
+fn vector_get_seq_100(b: &mut Bencher) {
+    vector_get_seq(b, 100)
+}
+
+#[bench]
+fn vector_get_seq_1000(b: &mut Bencher) {
+    vector_get_seq(b, 1000)
+}
+
+#[bench]
+fn vector_get_seq_100000(b: &mut Bencher) {
+    vector_get_seq(b, 100_000)
+}
+
+fn vector_get_seq_focus(b: &mut Bencher, count: usize) {
+    let vec: Vector<i32> = rando().take(count).collect();
+    let mut focus = vec.focus();
+    b.iter(|| {
+        for i in 0..count {
+            let _ = focus.get(i);
+        }
+    })
+}
+
+#[bench]
+fn vector_get_seq_focus_10(b: &mut Bencher) {
+    vector_get_seq_focus(b, 10)
+}
+
+#[bench]
+fn vector_get_seq_focus_100(b: &mut Bencher) {
+    vector_get_seq_focus(b, 100)
+}
+
+#[bench]
+fn vector_get_seq_focus_1000(b: &mut Bencher) {
+    vector_get_seq_focus(b, 1000)
+}
+
+#[bench]
+fn vector_get_seq_focus_100000(b: &mut Bencher) {
+    vector_get_seq_focus(b, 100_000)
+}
+
+fn vector_get_seq_focus_mut(b: &mut Bencher, count: usize) {
+    let mut vec: Vector<i32> = rando().take(count).collect();
+    let mut focus = vec.focus_mut();
+    b.iter(|| {
+        for i in 0..count {
+            let _ = focus.get(i);
+        }
+    })
+}
+
+#[bench]
+fn vector_get_seq_focus_mut_10(b: &mut Bencher) {
+    vector_get_seq_focus_mut(b, 10)
+}
+
+#[bench]
+fn vector_get_seq_focus_mut_100(b: &mut Bencher) {
+    vector_get_seq_focus_mut(b, 100)
+}
+
+#[bench]
+fn vector_get_seq_focus_mut_1000(b: &mut Bencher) {
+    vector_get_seq_focus_mut(b, 1000)
+}
+
+#[bench]
+fn vector_get_seq_focus_mut_100000(b: &mut Bencher) {
+    vector_get_seq_focus_mut(b, 100_000)
+}
+
 // fn vector_extend(b: &mut Bencher, count: usize) {
 //     let vec = Vec::from_iter(0..count);
 //     b.iter(|| {

proptest-regressions/vector/mod.txt

@@ -0,0 +1,7 @@
+# Seeds for failure cases proptest has generated in the past. It is
+# automatically read and these particular cases re-run before any
+# novel cases are generated.
+#
+# It is recommended to check this file in to source control so that
+# everyone who runs the test benefits from these saved cases.
+xs 781088174 2402437932 46071810 3445483747 # shrinks to ref vec = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]