225 lines
6.9 KiB
C++
225 lines
6.9 KiB
C++
#pragma once
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#include <c10/util/TypeList.h>
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#include <type_traits>
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namespace c10::guts {
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/**
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* Access information about result type or arguments from a function type.
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* Example:
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* using A = function_traits<int (float, double)>::return_type // A == int
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* using A = function_traits<int (float, double)>::parameter_types::tuple_type
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* // A == tuple<float, double>
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*/
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template <class Func>
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struct function_traits {
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static_assert(
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!std::is_same_v<Func, Func>,
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"In function_traits<Func>, Func must be a plain function type.");
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};
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template <class Result, class... Args>
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struct function_traits<Result(Args...)> {
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using func_type = Result(Args...);
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using return_type = Result;
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using parameter_types = typelist::typelist<Args...>;
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static constexpr auto number_of_parameters = sizeof...(Args);
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};
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/**
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* infer_function_traits: creates a `function_traits` type for a simple
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* function (pointer) or functor (lambda/struct). Currently does not support
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* class methods.
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*/
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template <typename Functor>
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struct infer_function_traits {
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using type = function_traits<
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c10::guts::detail::strip_class_t<decltype(&Functor::operator())>>;
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};
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template <typename Result, typename... Args>
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struct infer_function_traits<Result (*)(Args...)> {
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using type = function_traits<Result(Args...)>;
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};
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template <typename Result, typename... Args>
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struct infer_function_traits<Result(Args...)> {
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using type = function_traits<Result(Args...)>;
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};
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template <typename T>
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using infer_function_traits_t = typename infer_function_traits<T>::type;
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/**
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* make_function_traits: creates a `function_traits` type given a Return type
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* and a typelist of Argument types
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*
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* Example:
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* bool f(int, int);
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*
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* infer_function_traits_t<f> == make_function_traits_t<bool,
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* typelist::typelist<int, int>>
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*/
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template <typename Result, typename ArgList>
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struct make_function_traits {
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static_assert(
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false_t<ArgList>::value,
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"In guts::make_function_traits<Result, TypeList>, the ArgList argument must be typelist<...>.");
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};
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template <typename Result, typename... Args>
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struct make_function_traits<Result, typelist::typelist<Args...>> {
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using type = function_traits<Result(Args...)>;
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};
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template <typename Result, typename ArgList>
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using make_function_traits_t =
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typename make_function_traits<Result, ArgList>::type;
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/**
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* make_offset_index_sequence<Start, N>
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* Like make_index_sequence<N>, but starting from Start instead of 0.
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*
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* Example:
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* make_offset_index_sequence<10, 3> == std::index_sequence<10, 11, 12>
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*/
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template <size_t Start, size_t N, size_t... Is>
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struct make_offset_index_sequence_impl
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: make_offset_index_sequence_impl<Start, N - 1, Start + N - 1, Is...> {
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static_assert(
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static_cast<int>(Start) >= 0,
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"make_offset_index_sequence: Start < 0");
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static_assert(static_cast<int>(N) >= 0, "make_offset_index_sequence: N < 0");
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};
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template <size_t Start, size_t... Is>
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struct make_offset_index_sequence_impl<Start, 0, Is...> {
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typedef std::index_sequence<Is...> type;
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};
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template <size_t Start, size_t N>
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using make_offset_index_sequence =
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typename make_offset_index_sequence_impl<Start, N>::type;
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/**
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* Use tuple_elements to extract a position-indexed subset of elements
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* from the argument tuple into a result tuple.
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*
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* Example:
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* std::tuple<int, const char*, double> t = std::make_tuple(0, "HEY", 2.0);
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* std::tuple<int, double> result = tuple_elements(t, std::index_sequence<0,
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* 2>());
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*/
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template <class Tuple, size_t... Is>
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constexpr auto tuple_elements(Tuple t, std::index_sequence<Is...>) {
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return std::tuple<std::tuple_element_t<Is, Tuple>...>(std::get<Is>(t)...);
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}
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/**
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* Use tuple_take to extract the first or last n elements from the argument
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* tuple into a result tuple.
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*
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* Example:
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* std::tuple<int, const char*, double> t = std::make_tuple(0, "HEY", 2.0);
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* std::tuple<int, const char*> first_two = tuple_take<decltype(t), 2>(t);
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* std::tuple<const char*, double> last_two = tuple_take<decltype(t), -2>(t);
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*/
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template <class Tuple, int N, class Enable = void>
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struct TupleTake {};
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template <class Tuple, int N>
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struct TupleTake<Tuple, N, std::enable_if_t<N >= 0, void>> {
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static auto call(Tuple t) {
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constexpr size_t size = std::tuple_size<Tuple>();
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static_assert(N <= size, "tuple_take: N > size");
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return tuple_elements(t, std::make_index_sequence<N>{});
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}
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};
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template <class Tuple, int N>
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struct TupleTake < Tuple,
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N, std::enable_if_t<N<0, void>> {
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static auto call(Tuple t) {
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constexpr size_t size = std::tuple_size<Tuple>();
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static_assert(-N <= size, "tuple_take: -N > size");
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return tuple_elements(t, make_offset_index_sequence<size + N, -N>{});
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}
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};
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template <class Tuple, int N>
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auto tuple_take(Tuple t) {
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return TupleTake<Tuple, N>::call(t);
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}
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/**
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* Use tuple_slice to extract a contiguous subtuple from the argument.
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*
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* Example:
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* std::tuple<int, const char*, double, bool> t = std::make_tuple(0,
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* "HEY", 2.0, false); std::tuple<int, const char*> middle_two =
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* tuple_slice<decltype(t), 1, 2>(t);
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*/
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template <class Tuple, size_t Start, size_t N>
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constexpr auto tuple_slice(Tuple t) {
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constexpr size_t size = std::tuple_size<Tuple>();
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static_assert(Start + N <= size, "tuple_slice: Start + N > size");
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return tuple_elements(t, make_offset_index_sequence<Start, N>{});
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}
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/**
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* Use tuple_map to run a mapping function over a tuple to get a new tuple.
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*
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* Example 1:
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* auto result = tuple_map(std::tuple<int32_t, int32_t, int32_t>(3, 4, 5), []
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* (int32_t a) -> int16_t {return a+1;});
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* // result == std::tuple<int16_t, int16_t, int16_t>(4, 5, 6)
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*
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* Example 2:
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* struct Mapper {
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* std::string operator()(int32_t a) const {
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* return std::to_string(a);
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* }
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* int64_t operator()(const std::string& a) const {
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* return atoi(a.c_str());
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* }
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* };
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* auto result = tuple_map(std::tuple<int32_t, std::string>(3, "4"),
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* Mapper());
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* // result == std::tuple<std::string, int64_t>("3", 4)
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*
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* Example 3:
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* struct A final {
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* int32_t func() {
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* return 5;
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* }
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* };
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* struct B final {
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* std::string func() {
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* return "5";
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* }
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* };
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* auto result = tuple_map(std::make_tuple(A(), B()), [] (auto a) { return
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* a.func(); });
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* // result == std::tuple<int32_t, std::string>(5, "5");
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*/
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namespace detail {
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template <class Mapper, class... Args, size_t... Indices>
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auto tuple_map(
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// NOLINTNEXTLINE(cppcoreguidelines-rvalue-reference-param-not-moved)
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std::tuple<Args...>&& tuple,
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const Mapper& mapper,
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std::index_sequence<Indices...>) {
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return std::tuple<decltype(mapper(std::forward<Args>(std::get<Indices>(
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tuple))))...>(mapper(std::forward<Args>(std::get<Indices>(tuple)))...);
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}
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} // namespace detail
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template <class Mapper, class... Args>
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auto tuple_map(std::tuple<Args...>&& tuple, const Mapper& mapper) {
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return detail::tuple_map(
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std::move(tuple), mapper, std::index_sequence_for<Args...>());
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}
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} // namespace c10::guts
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