From 20d8478864333b2633509c530b66d52ffef91fbb Mon Sep 17 00:00:00 2001
From: Lzu Tao <taolzu@gmail.com>
Date: Mon, 18 Jan 2021 03:02:47 +0000
Subject: [PATCH 1/2] Fix intersperse_fold
---
library/core/src/iter/adapters/intersperse.rs | 5 ++--
library/core/tests/iter.rs | 29 +++++++++++++++++++
2 files changed, 31 insertions(+), 3 deletions(-)
diff --git a/library/core/src/iter/adapters/intersperse.rs b/library/core/src/iter/adapters/intersperse.rs
index 1d01e9b5fb7dc..2143509d71dc7 100644
--- a/library/core/src/iter/adapters/intersperse.rs
+++ b/library/core/src/iter/adapters/intersperse.rs
@@ -160,7 +160,7 @@ where
}
fn intersperse_fold<I, B, F, G>(
- mut iter: Peekable<I>,
+ mut iter: I,
init: B,
mut f: F,
mut separator: G,
@@ -173,8 +173,7 @@ where
{
let mut accum = init;
- // Use `peek()` first to avoid calling `next()` on an empty iterator.
- if !needs_sep || iter.peek().is_some() {
+ if !needs_sep {
if let Some(x) = iter.next() {
accum = f(accum, x);
}
diff --git a/library/core/tests/iter.rs b/library/core/tests/iter.rs
index bc5421bfb5f8f..fa259e68a4370 100644
--- a/library/core/tests/iter.rs
+++ b/library/core/tests/iter.rs
@@ -3562,6 +3562,35 @@ fn test_intersperse_size_hint() {
assert_eq!([].iter().intersperse(&()).size_hint(), (0, Some(0)));
}
+#[test]
+fn test_intersperse_fold() {
+ let v = (1..4).intersperse(9).fold(Vec::new(), |mut acc, x| {
+ acc.push(x);
+ acc
+ });
+ assert_eq!(v.as_slice(), [1, 9, 2, 9, 3]);
+
+ let mut iter = (1..4).intersperse(9);
+ assert_eq!(iter.next(), Some(1));
+ let v = iter.fold(Vec::new(), |mut acc, x| {
+ acc.push(x);
+ acc
+ });
+ assert_eq!(v.as_slice(), [9, 2, 9, 3]);
+}
+
+#[test]
+fn test_intersperse_collect_string() {
+ let contents = vec![1, 2, 3];
+
+ let contents_string = contents
+ .into_iter()
+ .map(|id| id.to_string())
+ .intersperse(", ".to_owned())
+ .collect::<String>();
+ assert_eq!(contents_string, "1, 2, 3");
+}
+
#[test]
fn test_fold_specialization_intersperse() {
let mut iter = (1..2).intersperse(0);
From 9272d53c5a73198436f429a1a70e5d60afa995a7 Mon Sep 17 00:00:00 2001
From: Mara Bos <m-ou.se@m-ou.se>
Date: Tue, 19 Jan 2021 12:17:58 +0000
Subject: [PATCH 2/2] Stop `fold` at first None when iterator yield
---
library/core/src/iter/adapters/intersperse.rs | 2 ++
library/core/tests/iter.rs | 12 ++++++++++++
2 files changed, 14 insertions(+)
diff --git a/library/core/src/iter/adapters/intersperse.rs b/library/core/src/iter/adapters/intersperse.rs
index 2143509d71dc7..b1170f32ba161 100644
--- a/library/core/src/iter/adapters/intersperse.rs
+++ b/library/core/src/iter/adapters/intersperse.rs
@@ -176,6 +176,8 @@ where
if !needs_sep {
if let Some(x) = iter.next() {
accum = f(accum, x);
+ } else {
+ return accum;
}
}
diff --git a/library/core/tests/iter.rs b/library/core/tests/iter.rs
index fa259e68a4370..78b4d1acaf5cd 100644
--- a/library/core/tests/iter.rs
+++ b/library/core/tests/iter.rs
@@ -3577,6 +3577,18 @@ fn test_intersperse_fold() {
acc
});
assert_eq!(v.as_slice(), [9, 2, 9, 3]);
+
+ struct NoneAtStart(i32); // Produces: None, Some(2), Some(3), None, ...
+ impl Iterator for NoneAtStart {
+ type Item = i32;
+ fn next(&mut self) -> Option<i32> {
+ self.0 += 1;
+ Some(self.0).filter(|i| i % 3 != 1)
+ }
+ }
+
+ let v = NoneAtStart(0).intersperse(1000).fold(0, |a, b| a + b);
+ assert_eq!(v, 0);
}
#[test]