Implement custom fold for WhileSome

benches/bench1.rs

@@ -448,6 +448,25 @@ 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());
+            let result = data.fold(String::new(), |mut acc, ch| {
+                acc.push(ch);
+                acc
+            });
+            assert_eq!(result.as_str(), "0123456789abcdef");
+        });
+    });
+}
+
 fn slice_chunks(c: &mut Criterion) {
     let data = vec![0; 1024];
 
@@ -884,5 +903,6 @@ criterion_group!(
     permutations_range,
     permutations_slice,
     with_position_fold,
+    while_some,
 );
 criterion_main!(benches);

src/adaptors/mod.rs

@@ -581,6 +581,22 @@ where
     fn size_hint(&self) -> (usize, Option<usize>) {
         (0, self.iter.size_hint().1)
     }
+
+    fn fold<B, F>(mut self, acc: B, mut f: F) -> B
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> B,
+    {
+        let res = self.iter.try_fold(acc, |acc, item| match item {
+            Some(item) => Ok(f(acc, item)),
+            None => Err(acc),
+        });
+        let res = match res {
+            Ok(val) => val,
+            Err(val) => val,
+        };
+        res
+    }
 }
 
 /// An iterator to iterate through all combinations in a `Clone`-able iterator that produces tuples