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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/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
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