Implement FlattenOk::rfold

Author: kinto-b

src/flatten_ok.rs

@@ -141,6 +141,17 @@ where
             }
         }
     }
+
+    fn rfold<B, F>(self, init: B, mut f: F) -> B
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> B,
+    {
+        self.iter.rfold(init, |acc, x| match x {
+            Ok(it) => it.into_iter().rfold(acc, |a, o| f(a, Ok(o))),
+            Err(e) => f(acc, Err(e)),
+        })
+    }
 }
 
 impl<I, T, E> Clone for FlattenOk<I, T, E>