FTL: Add Optional<T>::transform (a7e22553) · Commits · e / os / platform_frameworks_native

include/ftl/optional.h

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		/*
		* 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 <functional>
		#include <optional>
		#include <type_traits>
		#include <utility>

		namespace android::ftl {

		// Superset of std::optional<T> with monadic operations, as proposed in https://wg21.link/P0798R8.
		//
		// TODO: Remove in C++23.
		//
		template <typename T>
		struct Optional final : std::optional<T> {
		using std::optional<T>::optional;

		using std::optional<T>::has_value;
		using std::optional<T>::value;

		// Returns Optional<U> where F is a function that maps T to U.
		template <typename F>
		constexpr auto transform(F&& f) const& {
		using U = std::remove_cv_t<std::invoke_result_t<F, decltype(value())>>;
		if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), value()));
		return Optional<U>();
		}

		template <typename F>
		constexpr auto transform(F&& f) & {
		using U = std::remove_cv_t<std::invoke_result_t<F, decltype(value())>>;
		if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), value()));
		return Optional<U>();
		}

		template <typename F>
		constexpr auto transform(F&& f) const&& {
		using U = std::invoke_result_t<F, decltype(std::move(value()))>;
		if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), std::move(value())));
		return Optional<U>();
		}

		template <typename F>
		constexpr auto transform(F&& f) && {
		using U = std::invoke_result_t<F, decltype(std::move(value()))>;
		if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), std::move(value())));
		return Optional<U>();
		}
		};

		// Deduction guide.
		template <typename T>
		Optional(T) -> Optional<T>;

		} // namespace android::ftl

libs/ftl/Android.bp

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		@@ -20,6 +20,7 @@ cc_test {
		"fake_guard_test.cpp",
		"flags_test.cpp",
		"future_test.cpp",
		"optional_test.cpp",
		"small_map_test.cpp",
		"small_vector_test.cpp",
		"static_vector_test.cpp",

libs/ftl/optional_test.cpp

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		/*
		* 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/optional.h>
		#include <ftl/static_vector.h>
		#include <ftl/string.h>
		#include <gtest/gtest.h>

		#include <functional>
		#include <numeric>
		#include <utility>

		using namespace std::placeholders;
		using namespace std::string_literals;

		namespace android::test {

		using ftl::Optional;
		using ftl::StaticVector;

		TEST(Optional, Transform) {
		// Empty.
		EXPECT_EQ(std::nullopt, Optional<int>().transform([](int) { return 0; }));

		// By value.
		EXPECT_EQ(0, Optional(0).transform([](int x) { return x; }));
		EXPECT_EQ(100, Optional(99).transform([](int x) { return x + 1; }));
		EXPECT_EQ("0b100"s, Optional(4).transform(std::bind(ftl::to_string<int>, _1, ftl::Radix::kBin)));

		// By reference.
		{
		Optional opt = 'x';
		EXPECT_EQ('z', opt.transform([](char& c) {
		c = 'y';
		return 'z';
		}));

		EXPECT_EQ('y', opt);
		}

		// By rvalue reference.
		{
		std::string out;
		EXPECT_EQ("xyz"s, Optional("abc"s).transform([&out](std::string&& str) {
		out = std::move(str);
		return "xyz"s;
		}));

		EXPECT_EQ(out, "abc"s);
		}

		// Chaining.
		EXPECT_EQ(14u, Optional(StaticVector{"upside"s, "down"s})
		.transform([](StaticVector<std::string, 3>&& v) {
		v.push_back("cake"s);
		return v;
		})
		.transform([](const StaticVector<std::string, 3>& v) {
		return std::accumulate(v.begin(), v.end(), std::string());
		})
		.transform([](const std::string& s) { return s.length(); }));
		}

		} // namespace android::test