feat: add lazy scan planning iterators

example/demo_example.cc

@@ -79,16 +79,26 @@ int main(int argc, char** argv) {
   }
 
   auto scan = std::move(scan_result.value());
-  auto plan_result = scan->PlanFiles();
+  auto plan_result = scan->PlanFilesIterator();
   if (!plan_result.has_value()) {
     std::cerr << "Failed to plan files: " << plan_result.error().message << std::endl;
     return 1;
   }
 
   std::cout << "Scan tasks: " << std::endl;
   auto scan_tasks = std::move(plan_result.value());
-  for (const auto& scan_task : scan_tasks) {
-    std::cout << " - " << scan_task->data_file()->file_path << std::endl;
+  while (true) {
+    auto task_result = scan_tasks->Next();
+    if (!task_result.has_value()) {
+      std::cerr << "Failed to plan next file: " << task_result.error().message
+                << std::endl;
+      return 1;
+    }
+    if (!task_result.value().has_value()) {
+      break;
+    }
+    std::cout << " - " << task_result.value().value()->data_file()->file_path
+              << std::endl;
   }
 
   return 0;

src/iceberg/file_scan_task_iterator.h

@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#pragma once
+
+/// \file iceberg/file_scan_task_iterator.h
+/// \brief Define the owning iterator type for file scan tasks.
+
+#include <memory>
+
+#include "iceberg/util/iterator.h"
+
+namespace iceberg {
+
+class FileScanTask;
+
+using FileScanTaskIterator = std::unique_ptr<Iterator<std::shared_ptr<FileScanTask>>>;
+
+}  // namespace iceberg