FTL: Add mixins for type-safe wrappers
For now, allow mixing in construction, default construction, equality,
ordering, incrementing, and addition.
Bug: 185536303
Test: ftl_test
Change-Id: I9017e124656ba0e7f13f378814c5b1c19a36655b
diff --git a/include/ftl/details/mixins.h b/include/ftl/details/mixins.h
new file mode 100644
index 0000000..9ab9e08
--- /dev/null
+++ b/include/ftl/details/mixins.h
@@ -0,0 +1,30 @@
+/*
+ * 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
+
+namespace android::ftl::details {
+
+template <typename Self, template <typename> class>
+class Mixin {
+ protected:
+ constexpr Self& self() { return *static_cast<Self*>(this); }
+ constexpr const Self& self() const { return *static_cast<const Self*>(this); }
+
+ constexpr auto& mut() { return self().value_; }
+};
+
+} // namespace android::ftl::details