From 7c827ae9325400f05ec6703f86171c43497d02c5 Mon Sep 17 00:00:00 2001
From: Philippe-Cholet <phcholet@orange.fr>
Date: Wed, 8 Nov 2023 12:09:17 +0100
Subject: [PATCH 1/2] `Interleave::fold`

---
 src/adaptors/mod.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/src/adaptors/mod.rs b/src/adaptors/mod.rs
index 08d91e397..36ff1cde6 100644
--- a/src/adaptors/mod.rs
+++ b/src/adaptors/mod.rs
@@ -76,6 +76,30 @@ where
     fn size_hint(&self) -> (usize, Option<usize>) {
         size_hint::add(self.a.size_hint(), self.b.size_hint())
     }
+
+    fn fold<B, F>(self, mut init: B, mut f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        let Self { mut a, mut b, flag } = self;
+        if flag {
+            match b.next() {
+                Some(y) => init = f(init, y),
+                None => return a.fold(init, f),
+            }
+        }
+        let res = a.try_fold(init, |mut acc, x| {
+            acc = f(acc, x);
+            match b.next() {
+                Some(y) => Ok(f(acc, y)),
+                None => Err(acc),
+            }
+        });
+        match res {
+            Ok(acc) => b.fold(acc, f),
+            Err(acc) => a.fold(acc, f),
+        }
+    }
 }
 
 impl<I, J> FusedIterator for Interleave<I, J>

From a4e74863c2b4e1a07edaa36aa389da4319766424 Mon Sep 17 00:00:00 2001
From: Philippe-Cholet <phcholet@orange.fr>
Date: Wed, 8 Nov 2023 12:10:10 +0100
Subject: [PATCH 2/2] `InterleaveShortest::fold`

---
 src/adaptors/mod.rs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/src/adaptors/mod.rs b/src/adaptors/mod.rs
index 36ff1cde6..a2bfb92ea 100644
--- a/src/adaptors/mod.rs
+++ b/src/adaptors/mod.rs
@@ -195,6 +195,34 @@ where
         };
         (lower, upper)
     }
+
+    fn fold<B, F>(self, mut init: B, mut f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        let Self {
+            mut it0,
+            mut it1,
+            phase,
+        } = self;
+        if phase {
+            match it1.next() {
+                Some(y) => init = f(init, y),
+                None => return init,
+            }
+        }
+        let res = it0.try_fold(init, |mut acc, x| {
+            acc = f(acc, x);
+            match it1.next() {
+                Some(y) => Ok(f(acc, y)),
+                None => Err(acc),
+            }
+        });
+        match res {
+            Ok(val) => val,
+            Err(val) => val,
+        }
+    }
 }
 
 impl<I, J> FusedIterator for InterleaveShortest<I, J>