FTL: Add Optional<T>::and_then
Bug: 185536303
Test: ftl_test
Change-Id: Ic907a662a2090ad1363bd329e7d758b2acef55ad
diff --git a/include/ftl/details/optional.h b/include/ftl/details/optional.h
new file mode 100644
index 0000000..bff7c1e
--- /dev/null
+++ b/include/ftl/details/optional.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright 2022 The Android Open Source Project
+ *
+ * Licensed 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
+
+#include <functional>
+#include <optional>
+
+#include <ftl/details/type_traits.h>
+
+namespace android::ftl {
+
+template <typename>
+struct Optional;
+
+namespace details {
+
+template <typename>
+struct is_optional : std::false_type {};
+
+template <typename T>
+struct is_optional<std::optional<T>> : std::true_type {};
+
+template <typename T>
+struct is_optional<Optional<T>> : std::true_type {};
+
+template <typename F, typename T>
+struct transform_result {
+ using type = Optional<std::remove_cv_t<std::invoke_result_t<F, T>>>;
+};
+
+template <typename F, typename T>
+using transform_result_t = typename transform_result<F, T>::type;
+
+template <typename F, typename T>
+struct and_then_result {
+ using type = remove_cvref_t<std::invoke_result_t<F, T>>;
+ static_assert(is_optional<type>{}, "and_then function must return an optional");
+};
+
+template <typename F, typename T>
+using and_then_result_t = typename and_then_result<F, T>::type;
+
+} // namespace details
+} // namespace android::ftl