MapUtil.h | Explore in Territory

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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.
 */

/**
 * MapUtil provides convenience functions to get a value from a map.
 *
 * @refcode folly/docs/examples/folly/MapUtil.cpp
 * @file MapUtil.h
 */

#pragma once

#include <tuple>

#include <folly/Conv.h>
#include <folly/Optional.h>
#include <folly/Range.h>
#include <folly/functional/Invoke.h>

namespace folly {

/**
 * Given a map and a key, return the value corresponding to the key in the map,
 * or a given default value if the key doesn't exist in the map.
 */
template <typename Map, typename Key>
typename Map::mapped_type get_default(const Map& map, const Key& key) { … }
template <
    class Map,
    typename Key = typename Map::key_type,
    typename Value = typename Map::mapped_type,
    typename std::enable_if<!is_invocable_v<Value>>::type* = nullptr>
typename Map::mapped_type get_default(
    const Map& map, const Key& key, Value&& dflt) { … }

/**
 * Give a map and a key, return the value corresponding to the key in the map,
 * or a given default value if the key doesn't exist in the map.
 */
template <
    class Map,
    typename Key = typename Map::key_type,
    typename Func,
    typename = typename std::enable_if<
        is_invocable_r_v<typename Map::mapped_type, Func>>::type>
typename Map::mapped_type get_default(
    const Map& map, const Key& key, Func&& dflt) { … }

/**
 * Given a map and a key, return the value corresponding to the key in the map,
 * or throw an exception of the specified type.
 */
template <
    class E = std::out_of_range,
    class Map,
    typename Key = typename Map::key_type>
const typename Map::mapped_type& get_or_throw(
    const Map& map,
    const Key& key,
    const StringPiece& exceptionStrPrefix = StringPiece()) { … }

template <
    class E = std::out_of_range,
    class Map,
    typename Key = typename Map::key_type>
typename Map::mapped_type& get_or_throw(
    Map& map,
    const Key& key,
    const StringPiece& exceptionStrPrefix = StringPiece()) { … }

/**
 * Given a map and a key, return a Optional<V> if the key exists and None if the
 * key does not exist in the map.
 */
template <
    template <typename> class Optional = folly::Optional,
    class Map,
    typename Key = typename Map::key_type>
Optional<typename Map::mapped_type> get_optional(
    const Map& map, const Key& key) { … }

/**
 * Given a map and a key, return a reference to the value corresponding to the
 * key in the map, or the given default reference if the key doesn't exist in
 * the map.
 */
template <class Map, typename Key = typename Map::key_type>
const typename Map::mapped_type& get_ref_default(
    const Map& map, const Key& key, const typename Map::mapped_type& dflt) { … }

/**
 * Passing a temporary default value returns a dangling reference when it is
 * returned. Lifetime extension is broken by the indirection.
 * The caller must ensure that the default value outlives the reference returned
 * by get_ref_default().
 */
template <class Map, typename Key = typename Map::key_type>
const typename Map::mapped_type& get_ref_default(
    const Map& map, const Key& key, typename Map::mapped_type&& dflt) = delete;

template <class Map, typename Key = typename Map::key_type>
const typename Map::mapped_type& get_ref_default(
    const Map& map,
    const Key& key,
    const typename Map::mapped_type&& dflt) = delete;

/**
 * Given a map and a key, return a reference to the value corresponding to the
 * key in the map, or the given default reference if the key doesn't exist in
 * the map.
 */
template <
    class Map,
    typename Key = typename Map::key_type,
    typename Func,
    typename = typename std::enable_if<
        is_invocable_r_v<const typename Map::mapped_type&, Func>>::type,
    typename = typename std::enable_if<
        std::is_reference<invoke_result_t<Func>>::value>::type>
const typename Map::mapped_type& get_ref_default(
    const Map& map, const Key& key, Func&& dflt) { … }

/**
 * @brief Given a map and a key, return a pointer to the value corresponding to
 * the key in the map, or nullptr if the key doesn't exist in the map.
 */
template <class Map, typename Key = typename Map::key_type>
const auto* get_ptr(const Map& map, const Key& key) { … }

/**
 * Non-const overload of the above.
 */
template <class Map, typename Key = typename Map::key_type>
auto* get_ptr(Map& map, const Key& key) { … }

/**
 * Same as `get_ptr` but for `find` variants that search for two keys at once.
 */
template <class Map, typename Key = typename Map::key_type>
std::pair<const typename Map::mapped_type*, const typename Map::mapped_type*>
get_ptr2(const Map& map, const Key& key0, const Key& key1) { … }

/**
 * Same as `get_ptr` but for `find` variants that search for two keys at once.
 */
template <class Map, typename Key = typename Map::key_type>
std::pair<typename Map::mapped_type*, typename Map::mapped_type*> get_ptr2(
    Map& map, const Key& key0, const Key& key1) { … }

// TODO: Remove the return type computations when clang 3.5 and gcc 5.1 are
// the minimum supported versions.
namespace detail {
template <
    class T,
    size_t pathLength,
    class = typename std::enable_if<(pathLength > 0)>::type>
struct NestedMapType { … };

NestedMapType<T, 1>;

template <typename... KeysDefault>
struct DefaultType;

DefaultType<Default>;

DefaultType<Key, KeysDefault...>;

template <class... KeysDefault>
auto extract_default(const KeysDefault&... keysDefault) ->
    typename DefaultType<KeysDefault...>::type const& { … }
} // namespace detail

/**
 * Given a map of maps and a path of keys, return a Optional<V> if the nested
 * key exists and None if the nested keys does not exist in the map.
 */
template <class Map, class Key1, class Key2, class... Keys>
auto get_optional(
    const Map& map, const Key1& key1, const Key2& key2, const Keys&... keys)
    -> folly::Optional<
        typename detail::NestedMapType<Map, 2 + sizeof...(Keys)>::type> { … }

/**
 * Given a map of maps and a path of keys, return a pointer to the nested value,
 * or nullptr if the key doesn't exist in the map.
 */
template <class Map, class Key1, class Key2, class... Keys>
auto get_ptr(
    const Map& map, const Key1& key1, const Key2& key2, const Keys&... keys) ->
    typename detail::NestedMapType<Map, 2 + sizeof...(Keys)>::type const* { … }

template <class Map, class Key1, class Key2, class... Keys>
auto get_ptr(Map& map, const Key1& key1, const Key2& key2, const Keys&... keys)
    -> typename detail::NestedMapType<Map, 2 + sizeof...(Keys)>::type* { … }

/**
 * Given a map and a path of keys, return the value corresponding to the nested
 * value, or a given default value if the path doesn't exist in the map.
 * The default value is the last parameter, and is copied when returned.
 */
template <
    class Map,
    class Key1,
    class Key2,
    class... KeysDefault,
    typename = typename std::enable_if<sizeof...(KeysDefault) != 0>::type>
auto get_default(
    const Map& map,
    const Key1& key1,
    const Key2& key2,
    const KeysDefault&... keysDefault) ->
    typename detail::NestedMapType<Map, 1 + sizeof...(KeysDefault)>::type { … }

/**
 * Given a map and a path of keys, return a reference to the value corresponding
 * to the nested value, or the given default reference if the path doesn't exist
 * in the map.
 * The default value is the last parameter, and must be a lvalue reference.
 */
template <
    class Map,
    class Key1,
    class Key2,
    class... KeysDefault,
    typename = typename std::enable_if<sizeof...(KeysDefault) != 0>::type,
    typename = typename std::enable_if<std::is_lvalue_reference<
        typename detail::DefaultType<KeysDefault...>::type>::value>::type>
auto get_ref_default(
    const Map& map,
    const Key1& key1,
    const Key2& key2,
    KeysDefault&&... keysDefault) ->
    typename detail::NestedMapType<Map, 1 + sizeof...(KeysDefault)>::type
    const& { … }
} // namespace folly
folly/folly/container/MapUtil.h
