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