1/*
2 * Copyright 2016-present Facebook, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16#pragma once
17
18#include <array>
19#include <type_traits>
20#include <utility>
21
22#include <folly/CPortability.h>
23#include <folly/Traits.h>
24#include <folly/Utility.h>
25
26namespace folly {
27
28namespace array_detail {
29template <typename>
30struct is_ref_wrapper : std::false_type {};
31template <typename T>
32struct is_ref_wrapper<std::reference_wrapper<T>> : std::true_type {};
33
34template <typename T>
35using not_ref_wrapper =
36 folly::Negation<is_ref_wrapper<typename std::decay<T>::type>>;
37
38template <typename D, typename...>
39struct return_type_helper {
40 using type = D;
41};
42template <typename... TList>
43struct return_type_helper<void, TList...> {
44 static_assert(
45 folly::Conjunction<not_ref_wrapper<TList>...>::value,
46 "TList cannot contain reference_wrappers when D is void");
47 using type = typename std::common_type<TList...>::type;
48};
49
50template <typename D, typename... TList>
51using return_type = std::
52 array<typename return_type_helper<D, TList...>::type, sizeof...(TList)>;
53} // namespace array_detail
54
55template <typename D = void, typename... TList>
56constexpr array_detail::return_type<D, TList...> make_array(TList&&... t) {
57 using value_type =
58 typename array_detail::return_type_helper<D, TList...>::type;
59 return {{static_cast<value_type>(std::forward<TList>(t))...}};
60}
61
62namespace array_detail {
63template <typename MakeItem, std::size_t... Index>
64FOLLY_ALWAYS_INLINE FOLLY_ATTR_VISIBILITY_HIDDEN constexpr auto make_array_with(
65 MakeItem const& make,
66 index_sequence<Index...>) {
67 return std::array<decltype(make(0)), sizeof...(Index)>{{make(Index)...}};
68}
69} // namespace array_detail
70
71// make_array_with
72//
73// Constructs a std::array<..., Size> with elements m(i) for i in [0, Size).
74template <std::size_t Size, typename MakeItem>
75constexpr auto make_array_with(MakeItem const& make) {
76 return array_detail::make_array_with(make, make_index_sequence<Size>{});
77}
78
79} // namespace folly
80