FTL: Standardize style
Adopt STL-flavored Google style for internal and libbase consistency.
Add README.
Bug: 160012986
Test: ftl_test
Change-Id: I1056f6fa890d68717386d634c398bb2faa46775c
diff --git a/include/ftl/small_map.h b/include/ftl/small_map.h
new file mode 100644
index 0000000..d058369
--- /dev/null
+++ b/include/ftl/small_map.h
@@ -0,0 +1,205 @@
+/*
+ * 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/initializer_list.h>
+#include <ftl/small_vector.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, std::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, std::size_t... Sizes, typename... Types>
+ SmallMap(InitializerList<U, std::index_sequence<Sizes...>, Types...>&& list)
+ : map_(std::move(list)) {
+ // TODO: Enforce unique keys.
+ }
+
+ size_type max_size() const { return map_.max_size(); }
+ size_type size() const { return map_.size(); }
+ bool empty() const { return map_.empty(); }
+
+ // Returns whether the map is backed by static or dynamic storage.
+ bool dynamic() const { return map_.dynamic(); }
+
+ iterator begin() { return map_.begin(); }
+ const_iterator begin() const { return cbegin(); }
+ const_iterator cbegin() const { return map_.cbegin(); }
+
+ iterator end() { return map_.end(); }
+ const_iterator end() const { return cend(); }
+ const_iterator cend() const { return map_.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 map_;
+};
+
+// Deduction guide for in-place constructor.
+template <typename K, typename V, std::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, std::size_t N, typename Q, typename W, std::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, std::size_t N, typename Q, typename W, std::size_t M>
+inline bool operator!=(const SmallMap<K, V, N>& lhs, const SmallMap<Q, W, M>& rhs) {
+ return !(lhs == rhs);
+}
+
+} // namespace android::ftl