FTL: Add Expected<T, E> (9bb429aa) · Commits · e / os / android_frameworks_native

include/ftl/expected.h

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		/*
		* 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

libs/ftl/Android.bp

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		@@ -10,11 +10,15 @@ package {
		cc_test {
		name: "ftl_test",
		test_suites: ["device-tests"],
		header_libs: [
		"libbase_headers",
		],
		srcs: [
		"algorithm_test.cpp",
		"cast_test.cpp",
		"concat_test.cpp",
		"enum_test.cpp",
		"expected_test.cpp",
		"fake_guard_test.cpp",
		"flags_test.cpp",
		"function_test.cpp",

libs/ftl/expected_test.cpp

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		/*
		* 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.
		*/

		#include <ftl/expected.h>
		#include <gtest/gtest.h>

		#include <string>
		#include <system_error>

		namespace android::test {

		using IntExp = ftl::Expected<int, std::errc>;
		using StringExp = ftl::Expected<std::string, std::errc>;

		using namespace std::string_literals;

		TEST(Expected, Construct) {
		// Default value.
		EXPECT_TRUE(IntExp().has_value());
		EXPECT_EQ(IntExp(), IntExp(0));

		EXPECT_TRUE(StringExp().has_value());
		EXPECT_EQ(StringExp(), StringExp(""));

		// Value.
		ASSERT_TRUE(IntExp(42).has_value());
		EXPECT_EQ(42, IntExp(42).value());

		ASSERT_TRUE(StringExp("test").has_value());
		EXPECT_EQ("test"s, StringExp("test").value());

		// Error.
		const auto exp = StringExp(ftl::Unexpected(std::errc::invalid_argument));
		ASSERT_FALSE(exp.has_value());
		EXPECT_EQ(std::errc::invalid_argument, exp.error());
		}

		TEST(Expected, HasError) {
		EXPECT_FALSE(IntExp(123).has_error([](auto) { return true; }));
		EXPECT_FALSE(IntExp(ftl::Unexpected(std::errc::io_error)).has_error([](auto) { return false; }));

		EXPECT_TRUE(StringExp(ftl::Unexpected(std::errc::permission_denied)).has_error([](auto e) {
		return e == std::errc::permission_denied;
		}));
		}

		TEST(Expected, ValueOpt) {
		EXPECT_EQ(ftl::Optional(-1), IntExp(-1).value_opt());
		EXPECT_EQ(std::nullopt, IntExp(ftl::Unexpected(std::errc::broken_pipe)).value_opt());

		{
		const StringExp exp("foo"s);
		EXPECT_EQ(ftl::Optional('f'),
		exp.value_opt().transform([](const auto& s) { return s.front(); }));
		EXPECT_EQ("foo"s, exp.value());
		}
		{
		StringExp exp("foobar"s);
		EXPECT_EQ(ftl::Optional(6), std::move(exp).value_opt().transform(&std::string::length));
		EXPECT_TRUE(exp.value().empty());
		}
		}

		} // namespace android::test