#pragma once
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#include <type_traits>
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#include <array>
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#include <functional>
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#include <c10/util/TypeList.h>
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#include <c10/util/Array.h>
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namespace c10 { namespace 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 // A == tuple<float, double>
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*/
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template<class Func> struct function_traits {
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static_assert(!std::is_same<Func, Func>::value, "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<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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* Use extract_arg_by_filtered_index to return the i-th argument whose
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* type fulfills a given type trait. The argument itself is perfectly forwarded.
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*
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* Example:
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* std::string arg1 = "Hello";
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* std::string arg2 = "World";
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* std::string&& result = extract_arg_by_filtered_index<is_string, 1>(0, arg1, 2.0, std::move(arg2));
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*
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* Warning: Taking the result by rvalue reference can cause segfaults because ownership will not be passed on
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* from the original reference. The original reference dies after the expression and the resulting
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*/
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namespace detail {
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template<template <class> class Condition, size_t index, class Enable, class... Args> struct extract_arg_by_filtered_index_;
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template<template <class> class Condition, size_t index, class Head, class... Tail>
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struct extract_arg_by_filtered_index_<Condition, index, guts::enable_if_t<!Condition<Head>::value>, Head, Tail...> {
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static auto call(Head&& /*head*/, Tail&&... tail)
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-> decltype(extract_arg_by_filtered_index_<Condition, index, void, Tail...>::call(std::forward<Tail>(tail)...)) {
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return extract_arg_by_filtered_index_<Condition, index, void, Tail...>::call(std::forward<Tail>(tail)...);
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}
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};
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template<template <class> class Condition, size_t index, class Head, class... Tail>
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struct extract_arg_by_filtered_index_<Condition, index, guts::enable_if_t<Condition<Head>::value && index != 0>, Head, Tail...> {
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static auto call(Head&& /*head*/, Tail&&... tail)
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-> decltype(extract_arg_by_filtered_index_<Condition, index-1, void, Tail...>::call(std::forward<Tail>(tail)...)) {
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return extract_arg_by_filtered_index_<Condition, index-1, void, Tail...>::call(std::forward<Tail>(tail)...);
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}
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};
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template<template <class> class Condition, size_t index>
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struct extract_arg_by_filtered_index_<Condition, index, void> {
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static void call() {
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static_assert(index != index, "extract_arg_by_filtered_index out of range.");
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}
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};
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template<template <class> class Condition, size_t index, class Head, class... Tail>
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struct extract_arg_by_filtered_index_<Condition, index, guts::enable_if_t<Condition<Head>::value && index == 0>, Head, Tail...> {
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static auto call(Head&& head, Tail&&... /*tail*/)
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-> decltype(std::forward<Head>(head)) {
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return std::forward<Head>(head);
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}
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};
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}
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template<template <class> class Condition, size_t index, class... Args>
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auto extract_arg_by_filtered_index(Args&&... args)
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-> decltype(detail::extract_arg_by_filtered_index_<Condition, index, void, Args...>::call(std::forward<Args>(args)...)) {
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static_assert(is_type_condition<Condition>::value, "In extract_arg_by_filtered_index, the Condition argument must be a condition type trait, i.e. have a static constexpr bool ::value member.");
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return detail::extract_arg_by_filtered_index_<Condition, index, void, Args...>::call(std::forward<Args>(args)...);
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}
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/**
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* Use filter_map to map a subset of the arguments to values.
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* The subset is defined by type traits, and will be evaluated at compile time.
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* At runtime, it will just loop over the pre-filtered arguments to create an std::array.
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*
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* Example:
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* // in C++14
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* std::array<double, 2> result = filter_map<double, std::is_integral>([] (auto a) {return (double)a;}, 3, "bla", 4);
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* // result == {3.0, 4.0}
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*
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* // same example in C++11
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* struct my_map {
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* template<class T> constexpr double operator()(T a) {
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* return (double)a;
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* }
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* };
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* std::array<double, 2> result = filter_map<double, std::is_integral>(my_map(), 3, "bla", 4);
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* // result == {3.0, 4.0}
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*/
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namespace detail {
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template<class ResultType, size_t num_results> struct filter_map_ {
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template<template <class> class Condition, class Mapper, class... Args, size_t... I>
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static guts::array<ResultType, num_results> call(const Mapper& mapper, guts::index_sequence<I...>, Args&&... args) {
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return guts::array<ResultType, num_results> { mapper(extract_arg_by_filtered_index<Condition, I>(std::forward<Args>(args)...))... };
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}
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};
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template<class ResultType> struct filter_map_<ResultType, 0> {
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template<template <class> class Condition, class Mapper, class... Args, size_t... I>
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static guts::array<ResultType, 0> call(const Mapper& /*mapper*/, guts::index_sequence<I...>, Args&&... /*args*/) {
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return guts::array<ResultType, 0> { };
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}
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};
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}
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template<class ResultType, template <class> class Condition, class Mapper, class... Args> auto filter_map(const Mapper& mapper, Args&&... args)
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-> decltype(detail::filter_map_<ResultType, typelist::count_if<Condition, typelist::typelist<Args...>>::value>::template call<Condition, Mapper, Args...>(mapper, guts::make_index_sequence<typelist::count_if<Condition, typelist::typelist<Args...>>::value>(), std::forward<Args>(args)...)) {
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static_assert(is_type_condition<Condition>::value, "In filter_map<Result, Condition>, the Condition argument must be a condition type trait, i.e. have a static constexpr bool ::value member.");
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static constexpr size_t num_results = typelist::count_if<Condition, typelist::typelist<Args...>>::value;
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return detail::filter_map_<ResultType, num_results>::template call<Condition, Mapper, Args...>(mapper, guts::make_index_sequence<num_results>(), std::forward<Args>(args)...);
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}
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}}
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