1 // Copyright 2020 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_CONTAINERS_FIXED_FLAT_SET_H_ 6 #define BASE_CONTAINERS_FIXED_FLAT_SET_H_ 7 8 #include <algorithm> 9 #include <array> 10 #include <functional> 11 #include <type_traits> 12 13 #include "base/check.h" 14 #include "base/containers/flat_set.h" 15 #include "base/containers/flat_tree.h" 16 17 namespace base { 18 19 // fixed_flat_set is a immutable container with a std::set-like interface that 20 // stores its contents in a sorted std::array. 21 // 22 // It is a special case of base::flat_set, and mostly useful as a look-up table. 23 // 24 // Please see //base/containers/README.md for an overview of which container 25 // to select. 26 // 27 // QUICK REFERENCE 28 // 29 // Most of the core functionality is inherited from flat_tree. Please see 30 // flat_tree.h for more details for most of these functions. As a quick 31 // reference, the functions available are: 32 // 33 // Constructors (inputs need to be sorted): 34 // fixed_flat_set(const fixed_flat_set&); 35 // fixed_flat_set(sorted_unique_t, 36 // const container_type& items, 37 // const Compare& compare = Compare()); 38 // 39 // Size management functions: 40 // size_t size() const; 41 // size_t max_size() const; 42 // bool empty() const; 43 // 44 // Iterator functions: 45 // const_iterator begin() const; 46 // const_iterator cbegin() const; 47 // const_iterator end() const; 48 // const_iterator cend() const; 49 // const reverse_iterator rbegin() const; 50 // const_reverse_iterator crbegin() const; 51 // const_reverse_iterator rend() const; 52 // const_reverse_iterator crend() const; 53 // 54 // Comparators (see std::set documentation). 55 // key_compare key_comp() const; 56 // value_compare value_comp() const; 57 // 58 // Search functions: 59 // template <typename K> size_t count(const K&) const; 60 // template <typename K> const_iterator find(const K&) const; 61 // template <typename K> bool contains(const K&) const; 62 // template <typename K> 63 // pair<const_iterator, const_iterator> equal_range(K&) const; 64 // template <typename K> const_iterator lower_bound(const K&) const; 65 // template <typename K> const_iterator upper_bound(const K&) const; 66 // 67 // Non-member operators: 68 // bool operator==(const fixed_flat_set&, const fixed_flat_set&); 69 // bool operator!=(const fixed_flat_set&, const fixed_flat_set&); 70 // bool operator<(const fixed_flat_set&, const fixed_flat_set&); 71 // bool operator>(const fixed_flat_set&, const fixed_flat_set&); 72 // bool operator>=(const fixed_flat_set&, const fixed_flat_set&); 73 // bool operator<=(const fixed_flat_set&, const fixed_flat_set&); 74 // 75 template <class Key, size_t N, class Compare = std::less<>> 76 using fixed_flat_set = base::flat_set<Key, Compare, std::array<const Key, N>>; 77 78 // Utility function to simplify constructing a fixed_flat_set from a fixed list 79 // of keys and values. Requires that the passed in `data` contains unique keys 80 // and be sorted by key. See `MakeFixedFlatSet` for a variant that sorts the 81 // input automatically. 82 // 83 // Example usage: 84 // constexpr auto kSet = base::MakeFixedFlatSet<std::string_view>( 85 // base::sorted_unique, {"bar", "baz", "foo", "qux"}); 86 template <class Key, size_t N, class Compare = std::less<>> 87 consteval fixed_flat_set<Key, N, Compare> MakeFixedFlatSet( 88 sorted_unique_t, 89 std::common_type_t<Key> (&&data)[N], 90 const Compare& comp = Compare()) { 91 CHECK(internal::is_sorted_and_unique(data, comp)); 92 // Specify the value_type explicitly to ensure that the returned array has 93 // immutable keys. 94 return fixed_flat_set<Key, N, Compare>( 95 sorted_unique, internal::ToArray<const Key>(data), comp); 96 } 97 98 // Utility function to simplify constructing a fixed_flat_set from a fixed list 99 // of keys. Requires that the passed in `data` contains unique keys. 100 // 101 // Large inputs will run into compiler limits, e.g. "constexpr evaluation hit 102 // maximum step limit". In that case, use `MakeFixedFlatSet(sorted_unique)`. 103 // 104 // Example usage: 105 // constexpr auto kIntSet = base::MakeFixedFlatSet<int>({1, 2, 3, 4}); 106 // 107 // Data needs not to be sorted: 108 // constexpr auto kStringSet = base::MakeFixedFlatSet<std::string_view>( 109 // {"foo", "bar", "baz", "qux"}); 110 // 111 // Note: Wrapping `Key` in `std::common_type_t` below requires callers to 112 // explicitly specify `Key`, which is desired here. 113 template <class Key, size_t N, class Compare = std::less<>> 114 consteval fixed_flat_set<Key, N, Compare> MakeFixedFlatSet( 115 std::common_type_t<Key> (&&data)[N], 116 const Compare& comp = Compare()) { 117 std::sort(data, data + N, comp); 118 return MakeFixedFlatSet<Key>(sorted_unique, std::move(data), comp); 119 } 120 121 } // namespace base 122 123 #endif // BASE_CONTAINERS_FIXED_FLAT_SET_H_ 124