V8 API Reference, 7.2.502.16 (for Deno 0.2.4)
template-utils.h
1 // Copyright 2017 the V8 project authors. All rights reserved.
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 V8_BASE_TEMPLATE_UTILS_H_
6 #define V8_BASE_TEMPLATE_UTILS_H_
7 
8 #include <array>
9 #include <memory>
10 
11 namespace v8 {
12 namespace base {
13 
14 namespace detail {
15 
16 // make_array_helper statically iteratively creates the index list 0 .. Size-1.
17 // A specialization for the base case (first index is 0) finally constructs the
18 // array.
19 // TODO(clemensh): Use std::index_sequence once we have C++14 support.
20 template <class Function, std::size_t... Indexes>
22 
23 template <class Function, std::size_t... Indexes>
24 struct make_array_helper<Function, 0, Indexes...> {
25  constexpr static std::array<typename std::result_of<Function(size_t)>::type,
26  sizeof...(Indexes) + 1>
27  make_array(Function f) {
28  return {{f(0), f(Indexes)...}};
29  }
30 };
31 
32 template <class Function, std::size_t FirstIndex, std::size_t... Indexes>
33 struct make_array_helper<Function, FirstIndex, Indexes...>
34  : make_array_helper<Function, FirstIndex - 1, FirstIndex, Indexes...> {};
35 
36 } // namespace detail
37 
38 // base::make_array: Create an array of fixed length, initialized by a function.
39 // The content of the array is created by calling the function with 0 .. Size-1.
40 // Example usage to create the array {0, 2, 4}:
41 // std::array<int, 3> arr = base::make_array<3>(
42 // [](std::size_t i) { return static_cast<int>(2 * i); });
43 // The resulting array will be constexpr if the passed function is constexpr.
44 template <std::size_t Size, class Function>
45 constexpr std::array<typename std::result_of<Function(size_t)>::type, Size>
46 make_array(Function f) {
47  static_assert(Size > 0, "Can only create non-empty arrays");
49 }
50 
51 // base::make_unique<T>: Construct an object of type T and wrap it in a
52 // std::unique_ptr.
53 // Replacement for C++14's std::make_unique.
54 template <typename T, typename... Args>
55 std::unique_ptr<T> make_unique(Args&&... args) {
56  return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
57 }
58 
59 // Helper to determine how to pass values: Pass scalars and arrays by value,
60 // others by const reference (even if it was a non-const ref before; this is
61 // disallowed by the style guide anyway).
62 // The default is to also remove array extends (int[5] -> int*), but this can be
63 // disabled by setting {remove_array_extend} to false.
64 template <typename T, bool remove_array_extend = true>
66  using noref_t = typename std::remove_reference<T>::type;
67  using decay_t = typename std::conditional<
68  std::is_array<noref_t>::value && !remove_array_extend, noref_t,
69  typename std::decay<noref_t>::type>::type;
70  using type = typename std::conditional<std::is_scalar<decay_t>::value ||
71  std::is_array<decay_t>::value,
72  decay_t, const decay_t&>::type;
73 };
74 
75 // Uses expression SFINAE to detect whether using operator<< would work.
76 template <typename T, typename = void>
77 struct has_output_operator : std::false_type {};
78 template <typename T>
79 struct has_output_operator<T, decltype(void(std::declval<std::ostream&>()
80  << std::declval<T>()))>
81  : std::true_type {};
82 
83 namespace detail {
84 
85 template <typename Func, typename T, typename... Ts>
86 struct fold_helper {
87  static_assert(sizeof...(Ts) == 0, "this is the base case");
88  using result_t = typename std::remove_reference<T>::type;
89  static constexpr T&& fold(Func func, T&& first) {
90  return std::forward<T>(first);
91  }
92 };
93 
94 template <typename Func, typename T1, typename T2, typename... Ts>
95 struct fold_helper<Func, T1, T2, Ts...> {
96  using folded_t = typename std::result_of<Func(T1, T2)>::type;
97  using next_fold_helper = fold_helper<Func, folded_t&&, Ts...>;
98  using result_t = typename next_fold_helper::result_t;
99  static constexpr result_t fold(Func func, T1&& first, T2&& second,
100  Ts&&... more) {
101  return next_fold_helper::fold(
102  func, func(std::forward<T1>(first), std::forward<T2>(second)),
103  std::forward<Ts>(more)...);
104  }
105 };
106 
107 } // namespace detail
108 
109 // Fold all arguments from left to right with a given function.
110 template <typename Func, typename... Ts>
111 constexpr auto fold(Func func, Ts&&... more) ->
112  typename detail::fold_helper<Func, Ts...>::result_t {
114  std::forward<Ts>(more)...);
115 }
116 
117 // {is_same<Ts...>::value} is true if all Ts are the same, false otherwise.
118 template <typename... Ts>
119 struct is_same : public std::false_type {};
120 template <>
121 struct is_same<> : public std::true_type {};
122 template <typename T>
123 struct is_same<T> : public std::true_type {};
124 template <typename T, typename... Ts>
125 struct is_same<T, T, Ts...> : public is_same<T, Ts...> {};
126 
127 } // namespace base
128 } // namespace v8
129 
130 #endif // V8_BASE_TEMPLATE_UTILS_H_
STL namespace.
Definition: libplatform.h:13