| // Copyright 2020 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef UTIL_FLAT_MAP_H_ |
| #define UTIL_FLAT_MAP_H_ |
| |
| #include <initializer_list> |
| #include <map> |
| #include <utility> |
| #include <vector> |
| |
| #include "absl/types/optional.h" |
| #include "util/osp_logging.h" |
| |
| namespace openscreen { |
| |
| // For small numbers of elements, a vector is much more efficient than a |
| // map or unordered_map due to not needing hashing. FlatMap allows for |
| // using map-like syntax but is backed by a std::vector, combining all the |
| // performance of a vector with the convenience of a map. |
| // |
| // NOTE: this class allows usage of const char* as Key or Value types, but |
| // it is generally recommended that you use std::string, or absl::string_view |
| // for literals. string_view is similarly efficient to a raw char* pointer, |
| // but gives sizing and equality operators, among other features. |
| template <class Key, class Value> |
| class FlatMap final : public std::vector<std::pair<Key, Value>> { |
| public: |
| FlatMap(std::initializer_list<std::pair<Key, Value>> init_list) |
| : std::vector<std::pair<Key, Value>>(init_list) {} |
| FlatMap() = default; |
| FlatMap(const FlatMap&) = default; |
| FlatMap(FlatMap&&) noexcept = default; |
| FlatMap& operator=(const FlatMap&) = default; |
| FlatMap& operator=(FlatMap&&) = default; |
| ~FlatMap() = default; |
| |
| // Accessors that wrap std::find_if, and return an iterator to the key value |
| // pair. |
| decltype(auto) find(const Key& key) { |
| return std::find_if( |
| this->begin(), this->end(), |
| [key](const std::pair<Key, Value>& pair) { return key == pair.first; }); |
| } |
| |
| decltype(auto) find(const Key& key) const { |
| return const_cast<FlatMap<Key, Value>*>(this)->find(key); |
| } |
| |
| // Remove an entry from the map. Returns an iterator pointing to the new |
| // location of the element that followed the last element erased by the |
| // function call. This is the container end if the operation erased the last |
| // element in the sequence. |
| decltype(auto) erase_key(const Key& key) { |
| auto it = find(key); |
| // This will otherwise segfault on platforms, as it is undefined behavior. |
| OSP_CHECK(it != this->end()) << "failed to erase: element not found"; |
| return static_cast<std::vector<std::pair<Key, Value>>*>(this)->erase(it); |
| } |
| }; |
| |
| } // namespace openscreen |
| |
| #endif // UTIL_FLAT_MAP_H_ |