// Copyright 2017 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef V8_BASE_TEMPLATE_UTILS_H_
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#define V8_BASE_TEMPLATE_UTILS_H_
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#include <array>
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#include <memory>
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namespace v8 {
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namespace base {
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namespace detail {
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// make_array_helper statically iteratively creates the index list 0 .. Size-1.
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// A specialization for the base case (first index is 0) finally constructs the
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// array.
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// TODO(clemensh): Use std::index_sequence once we have C++14 support.
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template <class Function, std::size_t... Indexes>
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struct make_array_helper;
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template <class Function, std::size_t... Indexes>
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struct make_array_helper<Function, 0, Indexes...> {
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constexpr static std::array<typename std::result_of<Function(size_t)>::type,
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sizeof...(Indexes) + 1>
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make_array(Function f) {
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return {{f(0), f(Indexes)...}};
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}
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};
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template <class Function, std::size_t FirstIndex, std::size_t... Indexes>
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struct make_array_helper<Function, FirstIndex, Indexes...>
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: make_array_helper<Function, FirstIndex - 1, FirstIndex, Indexes...> {};
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} // namespace detail
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// base::make_array: Create an array of fixed length, initialized by a function.
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// The content of the array is created by calling the function with 0 .. Size-1.
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// Example usage to create the array {0, 2, 4}:
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// std::array<int, 3> arr = base::make_array<3>(
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// [](std::size_t i) { return static_cast<int>(2 * i); });
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// The resulting array will be constexpr if the passed function is constexpr.
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template <std::size_t Size, class Function>
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constexpr std::array<typename std::result_of<Function(size_t)>::type, Size>
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make_array(Function f) {
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static_assert(Size > 0, "Can only create non-empty arrays");
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return detail::make_array_helper<Function, Size - 1>::make_array(f);
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}
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// base::make_unique<T>: Construct an object of type T and wrap it in a
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// std::unique_ptr.
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// Replacement for C++14's std::make_unique.
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template <typename T, typename... Args>
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std::unique_ptr<T> make_unique(Args&&... args) {
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return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
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}
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// Helper to determine how to pass values: Pass scalars and arrays by value,
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// others by const reference (even if it was a non-const ref before; this is
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// disallowed by the style guide anyway).
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// The default is to also remove array extends (int[5] -> int*), but this can be
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// disabled by setting {remove_array_extend} to false.
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template <typename T, bool remove_array_extend = true>
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struct pass_value_or_ref {
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using noref_t = typename std::remove_reference<T>::type;
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using decay_t = typename std::conditional<
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std::is_array<noref_t>::value && !remove_array_extend, noref_t,
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typename std::decay<noref_t>::type>::type;
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using type = typename std::conditional<std::is_scalar<decay_t>::value ||
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std::is_array<decay_t>::value,
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decay_t, const decay_t&>::type;
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};
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// Uses expression SFINAE to detect whether using operator<< would work.
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template <typename T, typename = void>
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struct has_output_operator : std::false_type {};
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template <typename T>
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struct has_output_operator<T, decltype(void(std::declval<std::ostream&>()
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<< std::declval<T>()))>
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: std::true_type {};
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namespace detail {
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template <typename Func, typename T, typename... Ts>
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struct fold_helper {
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static_assert(sizeof...(Ts) == 0, "this is the base case");
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using result_t = typename std::remove_reference<T>::type;
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static constexpr T&& fold(Func func, T&& first) {
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return std::forward<T>(first);
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}
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};
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template <typename Func, typename T1, typename T2, typename... Ts>
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struct fold_helper<Func, T1, T2, Ts...> {
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using folded_t = typename std::result_of<Func(T1, T2)>::type;
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using next_fold_helper = fold_helper<Func, folded_t&&, Ts...>;
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using result_t = typename next_fold_helper::result_t;
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static constexpr result_t fold(Func func, T1&& first, T2&& second,
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Ts&&... more) {
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return next_fold_helper::fold(
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func, func(std::forward<T1>(first), std::forward<T2>(second)),
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std::forward<Ts>(more)...);
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}
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};
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} // namespace detail
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// Fold all arguments from left to right with a given function.
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template <typename Func, typename... Ts>
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constexpr auto fold(Func func, Ts&&... more) ->
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typename detail::fold_helper<Func, Ts...>::result_t {
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return detail::fold_helper<Func, Ts...>::fold(func,
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std::forward<Ts>(more)...);
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}
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// {is_same<Ts...>::value} is true if all Ts are the same, false otherwise.
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template <typename... Ts>
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struct is_same : public std::false_type {};
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template <>
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struct is_same<> : public std::true_type {};
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template <typename T>
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struct is_same<T> : public std::true_type {};
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template <typename T, typename... Ts>
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struct is_same<T, T, Ts...> : public is_same<T, Ts...> {};
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} // namespace base
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} // namespace v8
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#endif // V8_BASE_TEMPLATE_UTILS_H_
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