FTL: Add SmallMap<K, V, N> (c4b9146f) · Commits · e / os / platform_frameworks_native

include/ftl/InitializerList.h

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		@@ -34,6 +34,14 @@ namespace android::ftl {
		//
		// ... = ftl::init::list<std::string>("abc")()(3u, '?');
		//
		// The following syntax is a shorthand for key-value pairs, where the first argument is the
		// key, and the rest construct the value. The types of the key and value are deduced if the
		// first pair contains exactly two arguments:
		//
		// ... = ftl::init::map<int, std::string>(-1, "abc")(-2)(-3, 3u, '?');
		//
		// ... = ftl::init::map(0, 'a')(1, 'b')(2, 'c');
		//
		// WARNING: The InitializerList returned by an ftl::init::list expression must be consumed
		// immediately, since temporary arguments are destroyed after the full expression. Storing
		// an InitializerList results in dangling references.
		@@ -58,6 +66,29 @@ struct InitializerList<T, std::index_sequence<Sizes...>, Types...> {
		std::tuple<Types...> tuple;
		};

		template <typename K, typename V>
		struct KeyValue {};

		// Shorthand for key-value pairs that assigns the first argument to the key, and the rest to the
		// value. The specialization is on KeyValue rather than std::pair, so that ftl::init::list works
		// with the latter.
		template <typename K, typename V, size_t... Sizes, typename... Types>
		struct InitializerList<KeyValue<K, V>, std::index_sequence<Sizes...>, Types...> {
		// Accumulate the three arguments to std::pair's piecewise constructor.
		template <typename... Args>
		[[nodiscard]] constexpr auto operator()(K&& k, Args&&... args) && -> InitializerList<
		KeyValue<K, V>, std::index_sequence<Sizes..., 3>, Types..., std::piecewise_construct_t,
		std::tuple<K&&>, std::tuple<Args&&...>> {
		return {std::tuple_cat(std::move(tuple),
		std::forward_as_tuple(std::piecewise_construct,
		std::forward_as_tuple(std::forward<K>(k)),
		std::forward_as_tuple(
		std::forward<Args>(args)...)))};
		}

		std::tuple<Types...> tuple;
		};

		namespace init {

		template <typename T, typename... Args>
		@@ -65,5 +96,15 @@ template <typename T, typename... Args>
		return InitializerList<T>{}(std::forward<Args>(args)...);
		}

		template <typename K, typename V, typename... Args>
		[[nodiscard]] constexpr auto map(Args&&... args) {
		return list<KeyValue<K, V>>(std::forward<Args>(args)...);
		}

		template <typename K, typename V>
		[[nodiscard]] constexpr auto map(K&& k, V&& v) {
		return list<KeyValue<K, V>>(std::forward<K>(k), std::forward<V>(v));
		}

		} // namespace init
		} // namespace android::ftl

include/ftl/SmallMap.h

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		/*
		* Copyright 2020 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 <ftl/InitializerList.h>
		#include <ftl/SmallVector.h>

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

		namespace android::ftl {

		// Associative container with unique, unordered keys. Unlike std::unordered_map, key-value pairs are
		// stored in contiguous storage for cache efficiency. The map is allocated statically until its size
		// exceeds N, at which point mappings are relocated to dynamic memory.
		//
		// SmallMap<K, V, 0> unconditionally allocates on the heap.
		//
		// Example usage:
		//
		// ftl::SmallMap<int, std::string, 3> map;
		// assert(map.empty());
		// assert(!map.dynamic());
		//
		// map = ftl::init::map<int, std::string>(123, "abc")(-1)(42, 3u, '?');
		// assert(map.size() == 3u);
		// assert(!map.dynamic());
		//
		// assert(map.contains(123));
		// assert(map.find(42, [](const std::string& s) { return s.size(); }) == 3u);
		//
		// const auto opt = map.find(-1);
		// assert(opt);
		//
		// std::string& ref = *opt;
		// assert(ref.empty());
		// ref = "xyz";
		//
		// assert(map == SmallMap(ftl::init::map(-1, "xyz")(42, "???")(123, "abc")));
		//
		template <typename K, typename V, size_t N>
		class SmallMap final {
		using Map = SmallVector<std::pair<const K, V>, N>;

		public:
		using key_type = K;
		using mapped_type = V;

		using value_type = typename Map::value_type;
		using size_type = typename Map::size_type;
		using difference_type = typename Map::difference_type;

		using reference = typename Map::reference;
		using iterator = typename Map::iterator;

		using const_reference = typename Map::const_reference;
		using const_iterator = typename Map::const_iterator;

		// Creates an empty map.
		SmallMap() = default;

		// Constructs at most N key-value pairs in place by forwarding per-pair constructor arguments.
		// The template arguments K, V, and N are inferred using the deduction guide defined below.
		// The syntax for listing pairs is as follows:
		//
		// ftl::SmallMap map = ftl::init::map<int, std::string>(123, "abc")(-1)(42, 3u, '?');
		//
		// static_assert(std::is_same_v<decltype(map), ftl::SmallMap<int, std::string, 3>>);
		// assert(map.size() == 3u);
		// assert(map.contains(-1) && map.find(-1)->get().empty());
		// assert(map.contains(42) && map.find(42)->get() == "???");
		// assert(map.contains(123) && map.find(123)->get() == "abc");
		//
		// The types of the key and value are deduced if the first pair contains exactly two arguments:
		//
		// ftl::SmallMap map = ftl::init::map(0, 'a')(1, 'b')(2, 'c');
		// static_assert(std::is_same_v<decltype(map), ftl::SmallMap<int, char, 3>>);
		//
		template <typename U, size_t... Sizes, typename... Types>
		SmallMap(InitializerList<U, std::index_sequence<Sizes...>, Types...>&& init)
		: mMap(std::move(init)) {
		// TODO: Enforce unique keys.
		}

		size_type max_size() const { return mMap.max_size(); }
		size_type size() const { return mMap.size(); }
		bool empty() const { return mMap.empty(); }

		// Returns whether the map is backed by static or dynamic storage.
		bool dynamic() const { return mMap.dynamic(); }

		iterator begin() { return mMap.begin(); }
		const_iterator begin() const { return cbegin(); }
		const_iterator cbegin() const { return mMap.cbegin(); }

		iterator end() { return mMap.end(); }
		const_iterator end() const { return cend(); }
		const_iterator cend() const { return mMap.cend(); }

		// Returns whether a mapping exists for the given key.
		bool contains(const key_type& key) const {
		return find(key, [](const mapped_type&) {});
		}

		// Returns a reference to the value for the given key, or std::nullopt if the key was not found.
		//
		// ftl::SmallMap map = ftl::init::map('a', 'A')('b', 'B')('c', 'C');
		//
		// const auto opt = map.find('c');
		// assert(opt == 'C');
		//
		// char d = 'd';
		// const auto ref = map.find('d').value_or(std::ref(d));
		// ref.get() = 'D';
		// assert(d == 'D');
		//
		auto find(const key_type& key) const
		-> std::optional<std::reference_wrapper<const mapped_type>> {
		return find(key, [](const mapped_type& v) { return std::cref(v); });
		}

		auto find(const key_type& key) -> std::optional<std::reference_wrapper<mapped_type>> {
		return find(key, [](mapped_type& v) { return std::ref(v); });
		}

		// Returns the result R of a unary operation F on (a constant or mutable reference to) the value
		// for the given key, or std::nullopt if the key was not found. If F has a return type of void,
		// then the Boolean result indicates whether the key was found.
		//
		// ftl::SmallMap map = ftl::init::map('a', 'x')('b', 'y')('c', 'z');
		//
		// assert(map.find('c', [](char c) { return std::toupper(c); }) == 'Z');
		// assert(map.find('c', [](char& c) { c = std::toupper(c); }));
		//
		template <typename F, typename R = std::invoke_result_t<F, const mapped_type&>>
		auto find(const key_type& key, F f) const
		-> std::conditional_t<std::is_void_v<R>, bool, std::optional<R>> {
		for (auto& [k, v] : *this) {
		if (k == key) {
		if constexpr (std::is_void_v<R>) {
		f(v);
		return true;
		} else {
		return f(v);
		}
		}
		}

		return {};
		}

		template <typename F>
		auto find(const key_type& key, F f) {
		return std::as_const(*this).find(key, [&f](const mapped_type& v) {
		return f(const_cast<mapped_type&>(v));
		});
		}

		private:
		Map mMap;
		};

		// Deduction guide for in-place constructor.
		template <typename K, typename V, size_t... Sizes, typename... Types>
		SmallMap(InitializerList<KeyValue<K, V>, std::index_sequence<Sizes...>, Types...>&&)
		-> SmallMap<K, V, sizeof...(Sizes)>;

		// Returns whether the key-value pairs of two maps are equal.
		template <typename K, typename V, size_t N, typename Q, typename W, size_t M>
		bool operator==(const SmallMap<K, V, N>& lhs, const SmallMap<Q, W, M>& rhs) {
		if (lhs.size() != rhs.size()) return false;

		for (const auto& [k, v] : lhs) {
		const auto& lv = v;
		if (!rhs.find(k, [&lv](const auto& rv) { return lv == rv; }).value_or(false)) {
		return false;
		}
		}

		return true;
		}

		// TODO: Remove in C++20.
		template <typename K, typename V, size_t N, typename Q, typename W, size_t M>
		inline bool operator!=(const SmallMap<K, V, N>& lhs, const SmallMap<Q, W, M>& rhs) {
		return !(lhs == rhs);
		}

		} // namespace android::ftl

libs/ftl/Android.bp

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		@@ -5,6 +5,7 @@ cc_test {
		address: true,
		},
		srcs: [
		"SmallMap_test.cpp",
		"SmallVector_test.cpp",
		"StaticVector_test.cpp",
		],

libs/ftl/SmallMap_test.cpp

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+131 −0

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		/*
		* Copyright 2020 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/SmallMap.h>
		#include <gtest/gtest.h>

		#include <cctype>

		namespace android::test {

		using ftl::SmallMap;

		// Keep in sync with example usage in header file.
		TEST(SmallMap, Example) {
		ftl::SmallMap<int, std::string, 3> map;
		EXPECT_TRUE(map.empty());
		EXPECT_FALSE(map.dynamic());

		map = ftl::init::map<int, std::string>(123, "abc")(-1)(42, 3u, '?');
		EXPECT_EQ(map.size(), 3u);
		EXPECT_FALSE(map.dynamic());

		EXPECT_TRUE(map.contains(123));

		EXPECT_EQ(map.find(42, [](const std::string& s) { return s.size(); }), 3u);

		const auto opt = map.find(-1);
		ASSERT_TRUE(opt);

		std::string& ref = *opt;
		EXPECT_TRUE(ref.empty());
		ref = "xyz";

		EXPECT_EQ(map, SmallMap(ftl::init::map(-1, "xyz")(42, "???")(123, "abc")));
		}

		TEST(SmallMap, Construct) {
		{
		// Default constructor.
		SmallMap<int, std::string, 2> map;

		EXPECT_TRUE(map.empty());
		EXPECT_FALSE(map.dynamic());
		}
		{
		// In-place constructor with same types.
		SmallMap<int, std::string, 5> map =
		ftl::init::map<int, std::string>(123, "abc")(456, "def")(789, "ghi");

		EXPECT_EQ(map.size(), 3u);
		EXPECT_EQ(map.max_size(), 5u);
		EXPECT_FALSE(map.dynamic());

		EXPECT_EQ(map, SmallMap(ftl::init::map(123, "abc")(456, "def")(789, "ghi")));
		}
		{
		// In-place constructor with different types.
		SmallMap<int, std::string, 5> map =
		ftl::init::map<int, std::string>(123, "abc")(-1)(42, 3u, '?');

		EXPECT_EQ(map.size(), 3u);
		EXPECT_EQ(map.max_size(), 5u);
		EXPECT_FALSE(map.dynamic());

		EXPECT_EQ(map, SmallMap(ftl::init::map(42, "???")(123, "abc")(-1, "\0\0\0")));
		}
		{
		// In-place constructor with implicit size.
		SmallMap map = ftl::init::map<int, std::string>(123, "abc")(-1)(42, 3u, '?');

		static_assert(std::is_same_v<decltype(map), SmallMap<int, std::string, 3>>);
		EXPECT_EQ(map.size(), 3u);
		EXPECT_EQ(map.max_size(), 3u);
		EXPECT_FALSE(map.dynamic());

		EXPECT_EQ(map, SmallMap(ftl::init::map(-1, "\0\0\0")(42, "???")(123, "abc")));
		}
		}

		TEST(SmallMap, Find) {
		{
		// Constant reference.
		const ftl::SmallMap map = ftl::init::map('a', 'A')('b', 'B')('c', 'C');

		const auto opt = map.find('b');
		EXPECT_EQ(opt, 'B');

		const char d = 'D';
		const auto ref = map.find('d').value_or(std::cref(d));
		EXPECT_EQ(ref.get(), 'D');
		}
		{
		// Mutable reference.
		ftl::SmallMap map = ftl::init::map('a', 'A')('b', 'B')('c', 'C');

		const auto opt = map.find('c');
		EXPECT_EQ(opt, 'C');

		char d = 'd';
		const auto ref = map.find('d').value_or(std::ref(d));
		ref.get() = 'D';
		EXPECT_EQ(d, 'D');
		}
		{
		// Constant unary operation.
		const ftl::SmallMap map = ftl::init::map('a', 'x')('b', 'y')('c', 'z');
		EXPECT_EQ(map.find('c', [](char c) { return std::toupper(c); }), 'Z');
		}
		{
		// Mutable unary operation.
		ftl::SmallMap map = ftl::init::map('a', 'x')('b', 'y')('c', 'z');
		EXPECT_TRUE(map.find('c', [](char& c) { c = std::toupper(c); }));

		EXPECT_EQ(map, SmallMap(ftl::init::map('c', 'Z')('b', 'y')('a', 'x')));
		}
		}

		} // namespace android::test