FTL: Add Expected<T, E>
Extend `base::expected` with `has_error()` and `value_opt()`.
Bug: 185536303
Test: ftl_test
Change-Id: I07d70dc8fe7ebfe2f08626dff51aef0b98430f61
diff --git a/include/ftl/expected.h b/include/ftl/expected.h
new file mode 100644
index 0000000..12b6102
--- /dev/null
+++ b/include/ftl/expected.h
@@ -0,0 +1,65 @@
+/*
+ * Copyright 2024 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 <android-base/expected.h>
+#include <ftl/optional.h>
+
+#include <utility>
+
+namespace android::ftl {
+
+// Superset of base::expected<T, E> with monadic operations.
+//
+// TODO: Extend std::expected<T, E> in C++23.
+//
+template <typename T, typename E>
+struct Expected final : base::expected<T, E> {
+ using Base = base::expected<T, E>;
+ using Base::expected;
+
+ using Base::error;
+ using Base::has_value;
+ using Base::value;
+
+ template <typename P>
+ constexpr bool has_error(P predicate) const {
+ return !has_value() && predicate(error());
+ }
+
+ constexpr Optional<T> value_opt() const& {
+ return has_value() ? Optional(value()) : std::nullopt;
+ }
+
+ constexpr Optional<T> value_opt() && {
+ return has_value() ? Optional(std::move(value())) : std::nullopt;
+ }
+
+ // Delete new for this class. Its base doesn't have a virtual destructor, and
+ // if it got deleted via base class pointer, it would cause undefined
+ // behavior. There's not a good reason to allocate this object on the heap
+ // anyway.
+ static void* operator new(size_t) = delete;
+ static void* operator new[](size_t) = delete;
+};
+
+template <typename E>
+constexpr auto Unexpected(E&& error) {
+ return base::unexpected(std::forward<E>(error));
+}
+
+} // namespace android::ftl