FTL: Add std::variant matcher
Bug: 185536303
Test: ftl_test
Change-Id: Id6357fa04ffe0c17b17c99b49b5a5262d68925bf
diff --git a/include/ftl/details/match.h b/include/ftl/details/match.h
new file mode 100644
index 0000000..51b99d2
--- /dev/null
+++ b/include/ftl/details/match.h
@@ -0,0 +1,59 @@
+/*
+ * 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 <type_traits>
+#include <variant>
+
+namespace android::ftl::details {
+
+template <typename... Ms>
+struct Matcher : Ms... {
+ using Ms::operator()...;
+};
+
+// Deduction guide.
+template <typename... Ms>
+Matcher(Ms...) -> Matcher<Ms...>;
+
+template <typename Matcher, typename... Ts>
+constexpr bool is_exhaustive_match_v = (std::is_invocable_v<Matcher, Ts> && ...);
+
+template <typename...>
+struct Match;
+
+template <typename T, typename U, typename... Ts>
+struct Match<T, U, Ts...> {
+ template <typename Variant, typename Matcher>
+ static decltype(auto) match(Variant& variant, const Matcher& matcher) {
+ if (auto* const ptr = std::get_if<T>(&variant)) {
+ return matcher(*ptr);
+ } else {
+ return Match<U, Ts...>::match(variant, matcher);
+ }
+ }
+};
+
+template <typename T>
+struct Match<T> {
+ template <typename Variant, typename Matcher>
+ static decltype(auto) match(Variant& variant, const Matcher& matcher) {
+ return matcher(std::get<T>(variant));
+ }
+};
+
+} // namespace android::ftl::details