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/libs/ftl/Android.bp b/libs/ftl/Android.bp
index df0b271..8e57152 100644
--- a/libs/ftl/Android.bp
+++ b/libs/ftl/Android.bp
@@ -22,6 +22,7 @@
"flags_test.cpp",
"future_test.cpp",
"match_test.cpp",
+ "mixins_test.cpp",
"non_null_test.cpp",
"optional_test.cpp",
"shared_mutex_test.cpp",
diff --git a/libs/ftl/mixins_test.cpp b/libs/ftl/mixins_test.cpp
new file mode 100644
index 0000000..2c9f9df
--- /dev/null
+++ b/libs/ftl/mixins_test.cpp
@@ -0,0 +1,185 @@
+/*
+ * 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.
+ */
+
+#include <ftl/mixins.h>
+#include <gtest/gtest.h>
+
+#include <chrono>
+#include <functional>
+#include <type_traits>
+#include <utility>
+
+namespace android::test {
+namespace {
+
+// Keep in sync with example usage in header file.
+
+struct Id : ftl::Constructible<Id, std::int32_t>, ftl::Equatable<Id> {
+ using Constructible::Constructible;
+};
+
+static_assert(!std::is_default_constructible_v<Id>);
+
+struct Color : ftl::DefaultConstructible<Color, std::uint8_t>,
+ ftl::Equatable<Color>,
+ ftl::Orderable<Color> {
+ using DefaultConstructible::DefaultConstructible;
+};
+
+static_assert(Color() == Color(0u));
+static_assert(ftl::to_underlying(Color(-1)) == 255u);
+static_assert(Color(1u) < Color(2u));
+
+struct Sequence : ftl::DefaultConstructible<Sequence, std::int8_t, -1>,
+ ftl::Equatable<Sequence>,
+ ftl::Orderable<Sequence>,
+ ftl::Incrementable<Sequence> {
+ using DefaultConstructible::DefaultConstructible;
+};
+
+static_assert(Sequence() == Sequence(-1));
+
+struct Timeout : ftl::DefaultConstructible<Timeout, std::chrono::seconds, 10>,
+ ftl::Equatable<Timeout>,
+ ftl::Addable<Timeout> {
+ using DefaultConstructible::DefaultConstructible;
+};
+
+using namespace std::chrono_literals;
+static_assert(Timeout() + Timeout(5s) == Timeout(15s));
+
+// Construction.
+constexpr Id kId{1234};
+constexpr Sequence kSequence;
+
+// Underlying value.
+static_assert(ftl::to_underlying(Id(-42)) == -42);
+static_assert(ftl::to_underlying(kSequence) == -1);
+
+// Casting.
+static_assert(static_cast<std::int32_t>(Id(-1)) == -1);
+static_assert(static_cast<std::int8_t>(kSequence) == -1);
+
+static_assert(!std::is_convertible_v<std::int32_t, Id>);
+static_assert(!std::is_convertible_v<Id, std::int32_t>);
+
+// Equality.
+static_assert(kId == Id(1234));
+static_assert(kId != Id(123));
+static_assert(kSequence == Sequence(-1));
+
+// Ordering.
+static_assert(Sequence(1) < Sequence(2));
+static_assert(Sequence(2) > Sequence(1));
+static_assert(Sequence(3) <= Sequence(4));
+static_assert(Sequence(4) >= Sequence(3));
+static_assert(Sequence(5) <= Sequence(5));
+static_assert(Sequence(6) >= Sequence(6));
+
+// Incrementing.
+template <typename Op, typename T, typename... Ts>
+constexpr auto mutable_op(Op op, T lhs, Ts... rhs) {
+ const T result = op(lhs, rhs...);
+ return std::make_pair(lhs, result);
+}
+
+static_assert(mutable_op([](auto& lhs) { return ++lhs; }, Sequence()) ==
+ std::make_pair(Sequence(0), Sequence(0)));
+
+static_assert(mutable_op([](auto& lhs) { return lhs++; }, Sequence()) ==
+ std::make_pair(Sequence(0), Sequence(-1)));
+
+// Addition.
+
+// `Addable` implies `Incrementable`.
+static_assert(mutable_op([](auto& lhs) { return ++lhs; }, Timeout()) ==
+ std::make_pair(Timeout(11s), Timeout(11s)));
+
+static_assert(mutable_op([](auto& lhs) { return lhs++; }, Timeout()) ==
+ std::make_pair(Timeout(11s), Timeout(10s)));
+
+static_assert(Timeout(5s) + Timeout(6s) == Timeout(11s));
+
+static_assert(mutable_op([](auto& lhs, const auto& rhs) { return lhs += rhs; }, Timeout(7s),
+ Timeout(8s)) == std::make_pair(Timeout(15s), Timeout(15s)));
+
+// Type safety.
+
+namespace traits {
+
+template <typename, typename = void>
+struct is_incrementable : std::false_type {};
+
+template <typename T>
+struct is_incrementable<T, std::void_t<decltype(++std::declval<T&>())>> : std::true_type {};
+
+template <typename T>
+constexpr bool is_incrementable_v = is_incrementable<T>{};
+
+template <typename, typename, typename, typename = void>
+struct has_binary_op : std::false_type {};
+
+template <typename Op, typename T, typename U>
+struct has_binary_op<Op, T, U, std::void_t<decltype(Op{}(std::declval<T&>(), std::declval<U&>()))>>
+ : std::true_type {};
+
+template <typename T, typename U>
+constexpr bool is_equatable_v =
+ has_binary_op<std::equal_to<void>, T, U>{} && has_binary_op<std::not_equal_to<void>, T, U>{};
+
+template <typename T, typename U>
+constexpr bool is_orderable_v =
+ has_binary_op<std::less<void>, T, U>{} && has_binary_op<std::less_equal<void>, T, U>{} &&
+ has_binary_op<std::greater<void>, T, U>{} && has_binary_op<std::greater_equal<void>, T, U>{};
+
+template <typename T, typename U>
+constexpr bool is_addable_v = has_binary_op<std::plus<void>, T, U>{};
+
+} // namespace traits
+
+struct Real : ftl::Constructible<Real, float> {
+ using Constructible::Constructible;
+};
+
+static_assert(traits::is_equatable_v<Id, Id>);
+static_assert(!traits::is_equatable_v<Real, Real>);
+static_assert(!traits::is_equatable_v<Id, Color>);
+static_assert(!traits::is_equatable_v<Sequence, Id>);
+static_assert(!traits::is_equatable_v<Id, std::int32_t>);
+static_assert(!traits::is_equatable_v<std::chrono::seconds, Timeout>);
+
+static_assert(traits::is_orderable_v<Color, Color>);
+static_assert(!traits::is_orderable_v<Id, Id>);
+static_assert(!traits::is_orderable_v<Real, Real>);
+static_assert(!traits::is_orderable_v<Color, Sequence>);
+static_assert(!traits::is_orderable_v<Color, std::uint8_t>);
+static_assert(!traits::is_orderable_v<std::chrono::seconds, Timeout>);
+
+static_assert(traits::is_incrementable_v<Sequence>);
+static_assert(traits::is_incrementable_v<Timeout>);
+static_assert(!traits::is_incrementable_v<Id>);
+static_assert(!traits::is_incrementable_v<Color>);
+static_assert(!traits::is_incrementable_v<Real>);
+
+static_assert(traits::is_addable_v<Timeout, Timeout>);
+static_assert(!traits::is_addable_v<Id, Id>);
+static_assert(!traits::is_addable_v<Real, Real>);
+static_assert(!traits::is_addable_v<Sequence, Sequence>);
+static_assert(!traits::is_addable_v<Timeout, Sequence>);
+static_assert(!traits::is_addable_v<Color, Timeout>);
+
+} // namespace
+} // namespace android::test