PutBackN::fold

Author: Philippe-Cholet

Diff for: src/put_back_n_impl.rs

@@ -59,4 +59,12 @@ impl<I: Iterator> Iterator for PutBackN<I> {
     fn size_hint(&self) -> (usize, Option<usize>) {
         size_hint::add_scalar(self.iter.size_hint(), self.top.len())
     }
+
+    fn fold<B, F>(self, mut init: B, mut f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        init = self.top.into_iter().rfold(init, &mut f);
+        self.iter.fold(init, f)
+    }
 }