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// 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 <functional>
#include <iosfwd>
#include <tuple>
#include <type_traits>
#include <utility>
namespace v8 {
namespace base {
namespace detail {
template <typename Function, std::size_t... Indexes>
constexpr inline auto make_array_helper(Function f,
std::index_sequence<Indexes...>)
-> std::array<decltype(f(0)), sizeof...(Indexes)> {
return {{f(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 auto make_array(Function f) {
return detail::make_array_helper(f, std::make_index_sequence<Size>{});
}
// 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 TStream = std::ostream, typename = void>
struct has_output_operator : std::false_type {};
template <typename T, typename TStream>
struct has_output_operator<
T, TStream, decltype(void(std::declval<TStream&>() << std::declval<T>()))>
: std::true_type {};
// Turn std::tuple<A...> into std::tuple<A..., T>.
template <class Tuple, class T>
using append_tuple_type = decltype(std::tuple_cat(
std::declval<Tuple>(), std::declval<std::tuple<T>>()));
// Turn std::tuple<A...> into std::tuple<T, A...>.
template <class T, class Tuple>
using prepend_tuple_type = decltype(std::tuple_cat(
std::declval<std::tuple<T>>(), std::declval<Tuple>()));
namespace detail {
template <size_t N, typename Tuple>
constexpr bool NIsNotGreaterThanTupleSize =
N <= std::tuple_size_v<std::decay_t<Tuple>>;
template <size_t N, typename T, size_t... Ints>
constexpr auto tuple_slice_impl(const T& tpl, std::index_sequence<Ints...>) {
return std::tuple{std::get<N + Ints>(tpl)...};
}
template <typename Tuple, typename Function, size_t... Index>
constexpr auto tuple_for_each_impl(const Tuple& tpl, Function&& function,
std::index_sequence<Index...>) {
(function(std::get<Index>(tpl)), ...);
}
template <typename Tuple, typename Function, size_t... Index>
constexpr auto tuple_for_each_with_index_impl(const Tuple& tpl,
Function&& function,
std::index_sequence<Index...>) {
(function(std::get<Index>(tpl), std::integral_constant<size_t, Index>()),
...);
}
} // namespace detail
// Get the first N elements from a tuple.
template <size_t N, typename Tuple>
constexpr auto tuple_head(Tuple&& tpl) {
constexpr size_t total_size = std::tuple_size_v<std::decay_t<Tuple>>;
static_assert(N <= total_size);
return detail::tuple_slice_impl<0>(std::forward<Tuple>(tpl),
std::make_index_sequence<N>());
}
// Drop the first N elements from a tuple.
template <
size_t N, typename Tuple,
// If the user accidentally passes in an N that is larger than the tuple
// size, the unsigned subtraction will create a giant index sequence and
// crash the compiler. To avoid this and fail early, disable this function
// for invalid N.
typename = std::enable_if_t<detail::NIsNotGreaterThanTupleSize<N, Tuple>>>
constexpr auto tuple_drop(Tuple&& tpl) {
constexpr size_t total_size = std::tuple_size_v<std::decay_t<Tuple>>;
static_assert(N <= total_size);
return detail::tuple_slice_impl<N>(
std::forward<Tuple>(tpl), std::make_index_sequence<total_size - N>());
}
// Calls `function(v)` for each `v` in the tuple.
template <typename Tuple, typename Function>
constexpr void tuple_for_each(Tuple&& tpl, Function&& function) {
detail::tuple_for_each_impl(
std::forward<Tuple>(tpl), function,
std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>());
}
// Calls `function(v, i)` for each `v` in the tuple, with index `i`. The index
// `i` is passed as an std::integral_constant<size_t>, rather than a raw size_t,
// to allow it to be used
template <typename Tuple, typename Function>
constexpr void tuple_for_each_with_index(Tuple&& tpl, Function&& function) {
detail::tuple_for_each_with_index_impl(
std::forward<Tuple>(tpl), function,
std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>());
}
#ifdef __clang__
template <size_t N, typename... Ts>
using nth_type = __type_pack_element<N, Ts...>;
#else
template <size_t N, typename... Ts>
struct nth_type;
template <typename T, typename... Ts>
struct nth_type<0, T, Ts...> {
using type = T;
};
template <size_t N, typename T, typename... Ts>
struct nth_type<N, T, Ts...> : public nth_type<N - 1, Ts...> {};
#endif
template <size_t N, typename... T>
using nth_type_t = typename nth_type<N, T...>::type;
// Find SearchT in Ts. SearchT must be present at most once in Ts, and returns
// sizeof...(Ts) if not found.
template <typename SearchT, typename... Ts>
struct index_of_type;
// Not found / empty list.
template <typename SearchT>
struct index_of_type<SearchT> : public std::integral_constant<size_t, 0> {};
// SearchT found at head of list.
template <typename SearchT, typename... Ts>
struct index_of_type<SearchT, SearchT, Ts...>
: public std::integral_constant<size_t, 0> {
// SearchT is not allowed to be anywhere else in the list.
static_assert(index_of_type<SearchT, Ts...>::value == sizeof...(Ts));
};
// Recursion, SearchT not found at head of list.
template <typename SearchT, typename T, typename... Ts>
struct index_of_type<SearchT, T, Ts...>
: public std::integral_constant<size_t,
1 + index_of_type<SearchT, Ts...>::value> {
};
template <typename SearchT, typename... Ts>
constexpr size_t index_of_type_v = index_of_type<SearchT, Ts...>::value;
} // namespace base
} // namespace v8
#endif // V8_BASE_TEMPLATE_UTILS_H_
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