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#pragma once
#include <type_traits>
#include <array>
#include <functional>
#include <c10/util/TypeList.h>
#include <c10/util/Array.h>
namespace c10 { namespace guts {
/**
* Access information about result type or arguments from a function type.
* Example:
* using A = function_traits<int (float, double)>::return_type // A == int
* using A = function_traits<int (float, double)>::parameter_types::tuple_type // A == tuple<float, double>
*/
template<class Func> struct function_traits {
static_assert(!std::is_same<Func, Func>::value, "In function_traits<Func>, Func must be a plain function type.");
};
template<class Result, class... Args>
struct function_traits<Result (Args...)> {
using func_type = Result (Args...);
using return_type = Result;
using parameter_types = typelist::typelist<Args...>;
static constexpr auto number_of_parameters = sizeof...(Args);
};
/**
* infer_function_traits: creates a `function_traits` type for a simple
* function (pointer) or functor (lambda/struct). Currently does not support
* class methods.
*/
template <typename Functor>
struct infer_function_traits {
using type = function_traits<c10::guts::detail::strip_class_t<decltype(&Functor::operator())>>;
};
template <typename Result, typename... Args>
struct infer_function_traits<Result (*)(Args...)> {
using type = function_traits<Result(Args...)>;
};
template <typename Result, typename... Args>
struct infer_function_traits<Result (Args...)> {
using type = function_traits<Result(Args...)>;
};
template <typename T>
using infer_function_traits_t = typename infer_function_traits<T>::type;
/**
* Use extract_arg_by_filtered_index to return the i-th argument whose
* type fulfills a given type trait. The argument itself is perfectly forwarded.
*
* Example:
* std::string arg1 = "Hello";
* std::string arg2 = "World";
* std::string&& result = extract_arg_by_filtered_index<is_string, 1>(0, arg1, 2.0, std::move(arg2));
*
* Warning: Taking the result by rvalue reference can cause segfaults because ownership will not be passed on
* from the original reference. The original reference dies after the expression and the resulting
*/
namespace detail {
template<template <class> class Condition, size_t index, class Enable, class... Args> struct extract_arg_by_filtered_index_;
template<template <class> class Condition, size_t index, class Head, class... Tail>
struct extract_arg_by_filtered_index_<Condition, index, std::enable_if_t<!Condition<Head>::value>, Head, Tail...> {
static decltype(auto) call(Head&& /*head*/, Tail&&... tail) {
return extract_arg_by_filtered_index_<Condition, index, void, Tail...>::call(std::forward<Tail>(tail)...);
}
};
template<template <class> class Condition, size_t index, class Head, class... Tail>
struct extract_arg_by_filtered_index_<Condition, index, std::enable_if_t<Condition<Head>::value && index != 0>, Head, Tail...> {
static decltype(auto) call(Head&& /*head*/, Tail&&... tail) {
return extract_arg_by_filtered_index_<Condition, index-1, void, Tail...>::call(std::forward<Tail>(tail)...);
}
};
template<template <class> class Condition, size_t index>
struct extract_arg_by_filtered_index_<Condition, index, void> {
static void call() {
static_assert(index != index, "extract_arg_by_filtered_index out of range.");
}
};
template<template <class> class Condition, size_t index, class Head, class... Tail>
struct extract_arg_by_filtered_index_<Condition, index, std::enable_if_t<Condition<Head>::value && index == 0>, Head, Tail...> {
static decltype(auto) call(Head&& head, Tail&&... /*tail*/) {
return std::forward<Head>(head);
}
};
}
template<template <class> class Condition, size_t index, class... Args>
decltype(auto) extract_arg_by_filtered_index(Args&&... args) {
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.");
return detail::extract_arg_by_filtered_index_<Condition, index, void, Args...>::call(std::forward<Args>(args)...);
}
/**
* Use filter_map to map a subset of the arguments to values.
* The subset is defined by type traits, and will be evaluated at compile time.
* At runtime, it will just loop over the pre-filtered arguments to create an std::array.
*
* Example:
* std::array<double, 2> result = filter_map<double, std::is_integral>([] (auto a) {return (double)a;}, 3, "bla", 4);
* // result == {3.0, 4.0}
*/
namespace detail {
template<class ResultType, size_t num_results> struct filter_map_ {
template<template <class> class Condition, class Mapper, class... Args, size_t... INDEX>
static guts::array<ResultType, num_results> call(const Mapper& mapper, std::index_sequence<INDEX...>, Args&&... args) {
return guts::array<ResultType, num_results> { mapper(extract_arg_by_filtered_index<Condition, INDEX>(std::forward<Args>(args)...))... };
}
};
template<class ResultType> struct filter_map_<ResultType, 0> {
template<template <class> class Condition, class Mapper, class... Args, size_t... INDEX>
static guts::array<ResultType, 0> call(const Mapper& /*mapper*/, std::index_sequence<INDEX...>, Args&&... /*args*/) {
return guts::array<ResultType, 0> { };
}
};
}
template<class ResultType, template <class> class Condition, class Mapper, class... Args>
decltype(auto) filter_map(const Mapper& mapper, Args&&... args) {
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.");
static constexpr size_t num_results = typelist::count_if<Condition, typelist::typelist<Args...>>::value;
return detail::filter_map_<ResultType, num_results>::template call<Condition, Mapper, Args...>(mapper, std::make_index_sequence<num_results>(), std::forward<Args>(args)...);
}
/**
* Use tuple_elements to extract a position-indexed subset of elements
* from the argument tuple into a result tuple.
*
* Example:
* std::tuple<int, const char*, double> t = std::make_tuple(0, "HEY", 2.0);
* std::tuple<int, double> result = tuple_elements(t, std::index_sequence<0, 2>());
*/
template <class Tuple, size_t... ns>
constexpr auto tuple_elements(Tuple t, std::index_sequence<ns...>) {
return std::tuple<std::tuple_element_t<ns, Tuple>...>(std::get<ns>(t)...);
}
/**
* Use tuple_take to extract the first n elements from the argument tuple
* into a result tuple.
*
* Example:
* std::tuple<int, const char*, double> t = std::make_tuple(0, "HEY", 2.0);
* std::tuple<int, const char*> result = tuple_take<decltype(t), 2>(t);
*/
template <class Tuple, size_t n>
constexpr auto tuple_take(Tuple t) {
return tuple_elements(t, std::make_index_sequence<n>{});
}
/**
* Use tuple_map to run a mapping function over a tuple to get a new tuple.
*
* Example 1:
* auto result = tuple_map(std::tuple<int32_t, int32_t, int32_t>(3, 4, 5), [] (int32_t a) -> int16_t {return a+1;});
* // result == std::tuple<int16_t, int16_t, int16_t>(4, 5, 6)
*
* Example 2:
* struct Mapper {
* std::string operator()(int32_t a) const {
* return std::to_string(a);
* }
* int64_t operator()(const std::string& a) const {
* return atoi(a.c_str());
* }
* };
* auto result = tuple_map(std::tuple<int32_t, std::string>(3, "4"), Mapper());
* // result == std::tuple<std::string, int64_t>("3", 4)
*
* Example 3:
* struct A final {
* int32_t func() {
* return 5;
* }
* };
* struct B final {
* std::string func() {
* return "5";
* }
* };
* auto result = tuple_map(std::make_tuple(A(), B()), [] (auto a) { return a.func(); });
* // result == std::tuple<int32_t, std::string>(5, "5");
*/
namespace detail {
template<class Mapper, class... Args, size_t... Indices>
auto tuple_map(std::tuple<Args...>&& tuple, const Mapper& mapper, std::index_sequence<Indices...>) {
return std::tuple<decltype(mapper(std::forward<Args>(std::get<Indices>(tuple))))...>(
mapper(std::forward<Args>(std::get<Indices>(tuple)))...
);
}
}
template<class Mapper, class... Args>
auto tuple_map(std::tuple<Args...>&& tuple, const Mapper& mapper) {
return detail::tuple_map(std::move(tuple), mapper, std::index_sequence_for<Args...>());
}
/**
* tuple_concat concatenates several tuples into one.
*/
namespace detail {
// extract_tuple_element_by_index is a helper that takes a list of tuples and extracts the i-th element
// in a flattened view of the tuples.
// Example: extract_tuple_element_by_index<3>(tuple(2,3), tuple(4,5), tuple(6,7)) == 5.
template<size_t index, class HeadTuple, class... TailTuples, std::enable_if_t<index < std::tuple_size<HeadTuple>::value, int> = 0>
decltype(auto) extract_tuple_element_by_index(HeadTuple&& head_tuple, TailTuples&&... tail_tuples) {
// TODO if constexpr instead of enable_if
return std::get<index>(std::forward<HeadTuple>(head_tuple));
}
template<size_t index, class HeadTuple, class... TailTuples, std::enable_if_t<index >= std::tuple_size<HeadTuple>::value, int> = 0>
decltype(auto) extract_tuple_element_by_index(HeadTuple&& head_tuple, TailTuples&&... tail_tuples) {
// TODO if constexpr instead of enable_if
return extract_tuple_element_by_index<index - std::tuple_size<HeadTuple>::value, TailTuples...>(std::forward<TailTuples>(tail_tuples)...);
}
static_assert(
std::is_same<
int&&,
decltype(extract_tuple_element_by_index<2>(std::tuple<int32_t>(2), std::tuple<int32_t&&, int32_t>(std::declval<int32_t>(), 3)))
>::value,
"extract_tuple_element_by_index should return rvalue references if the tuple contains them. It should not move them into a value"
);
template<class ConcatenatedTuple, class... Tuples, size_t... ElementIndices>
auto tuple_concat(Tuples&&... tuples, std::index_sequence<ElementIndices...>) {
return ConcatenatedTuple(extract_tuple_element_by_index<ElementIndices>(std::forward<Tuples>(tuples)...)...);
}
}
template<class... Tuples>
auto tuple_concat(Tuples&&... tuples) {
using flattened_types = guts::typelist::concat_t<guts::typelist::from_tuple_t<Tuples>...>;
using concatenated_tuple = guts::typelist::to_tuple_t<flattened_types>;
constexpr size_t num_elements = guts::typelist::size<flattened_types>::value;
return detail::tuple_concat<concatenated_tuple, Tuples...>(std::forward<Tuples>(tuples)..., std::make_index_sequence<num_elements>());
}
}}
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