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/*
* Copyright 2017 Facebook, Inc.
*
* 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 <folly/Conv.h>
#include <folly/Optional.h>
#include <tuple>
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 <class Map, typename Key = typename Map::key_type>
typename Map::mapped_type get_default(
const Map& map,
const Key& key,
const typename Map::mapped_type& dflt = typename Map::mapped_type()) {
auto pos = map.find(key);
return (pos != map.end() ? pos->second : 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<std::is_convertible<
typename std::result_of<Func()>::type,
typename Map::mapped_type>::value>::type>
typename Map::mapped_type
get_default(const Map& map, const Key& key, Func&& dflt) {
auto pos = map.find(key);
return pos != map.end() ? pos->second : 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 std::string& exceptionStrPrefix = std::string()) {
auto pos = map.find(key);
if (pos != map.end()) {
return pos->second;
}
throw E(folly::to<std::string>(exceptionStrPrefix, key));
}
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 std::string& exceptionStrPrefix = std::string()) {
auto pos = map.find(key);
if (pos != map.end()) {
return pos->second;
}
throw E(folly::to<std::string>(exceptionStrPrefix, key));
}
/**
* 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 <class Map, typename Key = typename Map::key_type>
folly::Optional<typename Map::mapped_type> get_optional(
const Map& map,
const Key& key) {
auto pos = map.find(key);
if (pos != map.end()) {
return folly::Optional<typename Map::mapped_type>(pos->second);
} else {
return folly::none;
}
}
/**
* 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) {
auto pos = map.find(key);
return (pos != map.end() ? pos->second : 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<std::is_convertible<
typename std::result_of<Func()>::type,
const typename Map::mapped_type&>::value>::type,
typename = typename std::enable_if<
std::is_reference<typename std::result_of<Func()>::type>::value>::type>
const typename Map::mapped_type&
get_ref_default(const Map& map, const Key& key, Func&& dflt) {
auto pos = map.find(key);
return (pos != map.end() ? pos->second : dflt());
}
/**
* 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 typename Map::mapped_type* get_ptr(const Map& map, const Key& key) {
auto pos = map.find(key);
return (pos != map.end() ? &pos->second : nullptr);
}
/**
* Non-const overload of the above.
*/
template <class Map, typename Key = typename Map::key_type>
typename Map::mapped_type* get_ptr(Map& map, const Key& key) {
auto pos = map.find(key);
return (pos != map.end() ? &pos->second : nullptr);
}
// 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 {
using type = typename NestedMapType<T, pathLength - 1>::type::mapped_type;
};
template <class T>
struct NestedMapType<T, 1> {
using type = typename T::mapped_type;
};
template <typename... KeysDefault>
struct DefaultType;
template <typename Default>
struct DefaultType<Default> {
using type = Default;
};
template <typename Key, typename... KeysDefault>
struct DefaultType<Key, KeysDefault...> {
using type = typename DefaultType<KeysDefault...>::type;
};
template <class... KeysDefault>
auto extract_default(const KeysDefault&... keysDefault) ->
typename DefaultType<KeysDefault...>::type const& {
return std::get<sizeof...(KeysDefault)-1>(std::tie(keysDefault...));
}
}
/**
* 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* {
auto pos = map.find(key1);
return pos != map.end() ? get_ptr(pos->second, key2, keys...) : nullptr;
}
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* {
auto pos = map.find(key1);
return pos != map.end() ? get_ptr(pos->second, key2, keys...) : nullptr;
}
/**
* 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 {
if (const auto* ptr = get_ptr(map, key1)) {
return get_default(*ptr, key2, keysDefault...);
}
return detail::extract_default(keysDefault...);
}
/**
* 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& {
if (const auto* ptr = get_ptr(map, key1)) {
return get_ref_default(*ptr, key2, keysDefault...);
}
return detail::extract_default(keysDefault...);
}
} // namespace folly