From aa2fee237c42efe197d287138ac34b487b210628 Mon Sep 17 00:00:00 2001
From: Owen Leung <owen.leung2@gmail.com>
Date: Tue, 10 Oct 2023 21:40:15 +0800
Subject: [PATCH 1/3] Implement custom fold for while some

Implement custom fold for while some
---
 benches/bench1.rs   | 19 +++++++++++++++++++
 src/adaptors/mod.rs | 11 +++++++++++
 2 files changed, 30 insertions(+)

diff --git a/benches/bench1.rs b/benches/bench1.rs
index fbcaa05a7..46d7953e4 100644
--- a/benches/bench1.rs
+++ b/benches/bench1.rs
@@ -448,6 +448,24 @@ fn group_by_lazy_2(c: &mut Criterion) {
     });
 }
 
+fn while_some(c: &mut Criterion) {
+    c.bench_function("while_some", |b| {
+        b.iter(|| {
+            let data = black_box(
+                (0..)
+                    .fuse()
+                    .map(|i| std::char::from_digit(i, 16))
+                    .while_some(),
+            );
+            let result: String = data.fold(String::new(), |acc, ch| acc + &ch.to_string());
+            assert_eq!(
+                result.chars().collect::<Vec<_>>(),
+                "0123456789abcdef".chars().collect::<Vec<_>>()
+            );
+        });
+    });
+}
+
 fn slice_chunks(c: &mut Criterion) {
     let data = vec![0; 1024];
 
@@ -884,5 +902,6 @@ criterion_group!(
     permutations_range,
     permutations_slice,
     with_position_fold,
+    while_some,
 );
 criterion_main!(benches);
diff --git a/src/adaptors/mod.rs b/src/adaptors/mod.rs
index 90cf46eed..6ee2adc5f 100644
--- a/src/adaptors/mod.rs
+++ b/src/adaptors/mod.rs
@@ -581,6 +581,17 @@ where
     fn size_hint(&self) -> (usize, Option<usize>) {
         (0, self.iter.size_hint().1)
     }
+
+    fn fold<B, F>(self, acc: B, f: F) -> B
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> B,
+    {
+        self.iter
+            .take_while(|opt| opt.is_some())
+            .map(|item| item.unwrap())
+            .fold(acc, f)
+    }
 }
 
 /// An iterator to iterate through all combinations in a `Clone`-able iterator that produces tuples

From 147915b8d6151513db7790dd8eca955151d5ba8d Mon Sep 17 00:00:00 2001
From: Owen Leung <owen.leung2@gmail.com>
Date: Wed, 11 Oct 2023 22:13:26 +0800
Subject: [PATCH 2/3] Revise benchmark & use try_fold for fold

---
 benches/bench1.rs   | 11 ++++++-----
 src/adaptors/mod.rs | 12 +++++++-----
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/benches/bench1.rs b/benches/bench1.rs
index 46d7953e4..664191ab4 100644
--- a/benches/bench1.rs
+++ b/benches/bench1.rs
@@ -457,11 +457,12 @@ fn while_some(c: &mut Criterion) {
                     .map(|i| std::char::from_digit(i, 16))
                     .while_some(),
             );
-            let result: String = data.fold(String::new(), |acc, ch| acc + &ch.to_string());
-            assert_eq!(
-                result.chars().collect::<Vec<_>>(),
-                "0123456789abcdef".chars().collect::<Vec<_>>()
-            );
+            // let result: String = data.fold(String::new(), |acc, ch| acc + &ch.to_string());
+            let result = data.fold(String::new(), |mut acc, ch| {
+                acc.push(ch);
+                acc
+            });
+            assert_eq!(result.as_str(), "0123456789abcdef");
         });
     });
 }
diff --git a/src/adaptors/mod.rs b/src/adaptors/mod.rs
index 6ee2adc5f..c5a0bfccb 100644
--- a/src/adaptors/mod.rs
+++ b/src/adaptors/mod.rs
@@ -582,15 +582,17 @@ where
         (0, self.iter.size_hint().1)
     }
 
-    fn fold<B, F>(self, acc: B, f: F) -> B
+    fn fold<B, F>(mut self, acc: B, mut f: F) -> B
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> B,
     {
-        self.iter
-            .take_while(|opt| opt.is_some())
-            .map(|item| item.unwrap())
-            .fold(acc, f)
+        let res = self.iter.try_fold(acc, |acc, item| match item {
+            Some(item) => Ok(f(acc, item)),
+            None => Err(acc),
+        });
+        let (Err(res) | Ok(res)) = res;
+        res
     }
 }
 

From 2a592401266a9be227461fac244947e26a7f661b Mon Sep 17 00:00:00 2001
From: Owen Leung <owen.leung2@gmail.com>
Date: Wed, 11 Oct 2023 22:27:34 +0800
Subject: [PATCH 3/3] fix failing msrv test

---
 src/adaptors/mod.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/adaptors/mod.rs b/src/adaptors/mod.rs
index c5a0bfccb..18c864ad1 100644
--- a/src/adaptors/mod.rs
+++ b/src/adaptors/mod.rs
@@ -591,7 +591,10 @@ where
             Some(item) => Ok(f(acc, item)),
             None => Err(acc),
         });
-        let (Err(res) | Ok(res)) = res;
+        let res = match res {
+            Ok(val) => val,
+            Err(val) => val,
+        };
         res
     }
 }