Revise benchmark & use try_fold for fold

Author: Owen-CH-Leung

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");
         });
     });
 }

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
     }
 }