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#pragma once
using size_t = decltype(alignof(char));
namespace type_traits {
template< class T > struct remove_cv { typedef T type; };
template< class T > struct remove_cv<const T> { typedef T type; };
template< class T > struct remove_cv<volatile T> { typedef T type; };
template< class T > struct remove_cv<const volatile T> { typedef T type; };
template< class T > using remove_cv_t = typename remove_cv<T>::type;
template< class T > struct remove_reference { typedef T type; };
template< class T > struct remove_reference<T&> { typedef T type; };
template< class T > struct remove_reference<T&&> { typedef T type; };
template< class T > using remove_reference_t = typename remove_reference<T>::type;
template< class T >
struct remove_cvref {
using type = remove_cv_t<remove_reference_t<T>>;
};
template< class T > using remove_cvref_t = typename remove_cvref<T>::type;
namespace detail {
template <class T> struct type_identity { using type = T; };
template <class T>
auto try_add_lvalue_reference(int)->type_identity<T&>;
template <class T>
auto try_add_lvalue_reference(...)->type_identity<T>;
template <class T>
auto try_add_rvalue_reference(int)->type_identity<T&&>;
template <class T>
auto try_add_rvalue_reference(...)->type_identity<T>;
} // type_traits::detail
template <class T> struct add_lvalue_reference : decltype(detail::try_add_lvalue_reference<T>(0)) {};
template< class T > using add_lvalue_reference_t = typename add_lvalue_reference<T>::type;
template <class T> struct add_rvalue_reference : decltype(detail::try_add_rvalue_reference<T>(0)) {};
template< class T > using add_rvalue_reference_t = typename add_rvalue_reference<T>::type;
template <typename T, typename U> inline constexpr bool is_same_v = false;
template <typename T> inline constexpr bool is_same_v<T, T> = true;
template <typename T> inline constexpr bool is_void_v = is_same_v<remove_cv_t<T>, void>;
} // type_traits
template<class T> type_traits::add_rvalue_reference_t<T> declval() noexcept;
template <typename T>
inline constexpr T maxv(const T& a, const T& b) {
return (b < a) ? a : b;
}
template <typename T>
inline constexpr T minv(const T& a, const T& b) {
return (a < b) ? a : b;
}
template <typename T>
inline constexpr T clampv(const T& v, const T& lo, const T& hi) {
return minv(maxv(v, lo), hi);
}
template <typename T>
inline constexpr const T& select_ref(bool pred, const T& t, const T& f) {
return pred ? t : f;
}
template <typename First, typename... Rest>
inline constexpr size_t max_size_of = maxv(sizeof(First), max_size_of<Rest...>);
template <typename T>
inline constexpr size_t max_size_of<T> = sizeof(T);
template <typename First, typename... Rest>
inline constexpr size_t max_align_of = maxv(alignof(First), max_align_of<Rest...>);
template <typename T>
inline constexpr size_t max_align_of<T> = alignof(T);
namespace detail {
template <typename... Ts>
struct b1_index_of_impl {
template <typename...>
struct idx {
static constexpr size_t value = 0;
};
template <typename T, typename First, typename... Rest>
struct idx <T, First, Rest...> {
static constexpr size_t value = []() {
if constexpr (type_traits::is_same_v<T, First>) {
return sizeof...(Ts) - sizeof...(Rest);
}
return idx<T, Rest...>::value;
}();
};
};
} // detail
template <typename T, typename First, typename... Rest>
inline constexpr int base1_index_of =
detail::b1_index_of_impl<First, Rest...>::template idx<T, First, Rest...>::value;
/*
Requirements: Every type is trivially-copyable and is not an array type
Can be initialized to an empty state as if by using
std::variant<std::monostate, First, Rest...>
*/
template <typename First, typename... Rest>
struct tagged_union {
// Requirements: The return type of Visitor is default-constructible (or void)
// Returns a value-initialized object when in an empty or invalid state
template<typename Visitor>
inline constexpr auto visit(Visitor vis) {
return visit_impl<Visitor, First, Rest...>(vis);
}
template<typename Visitor>
inline constexpr auto visit(Visitor vis) const {
return visit_impl<Visitor, First, Rest...>(vis);
}
template<typename T>
static constexpr int id = base1_index_of<T, First, Rest...>;
int tag = 0;
struct storage_t {
alignas(max_align_of<First, Rest...>) char bytes[max_size_of<First, Rest...>];
template <typename T>
inline constexpr T& as() {
static_assert(id<T> != 0, "tagged_union can not hold T");
return reinterpret_cast<T&>(bytes);
}
template <typename T>
inline constexpr const T& as() const {
static_assert(id<T> != 0, "tagged_union can not hold T");
return reinterpret_cast<const T&>(bytes);
}
} storage;
constexpr tagged_union() noexcept = default;
template<typename T>
inline constexpr tagged_union(const T& val) noexcept {
tag = id<T>;
storage.template as<T>() = val;
}
template<typename T>
inline constexpr tagged_union& operator=(const T& val) noexcept {
tag = id<T>;
storage.template as<T>() = val;
return *this;
}
private:
template<typename Visitor, typename T1, typename... TRest>
inline constexpr auto visit_impl(Visitor vis) const {
if (tag == id<T1>) {
return vis(storage.template as<T1>());
}
if constexpr (sizeof...(TRest) > 0) {
return visit_impl<Visitor, TRest...>(vis);
}
else {
using ReturnType = decltype(vis(declval<First&>()));
if constexpr (!type_traits::is_void_v<ReturnType>) return ReturnType{};
}
}
template<typename Visitor, typename T1, typename... TRest>
inline constexpr auto visit_impl(Visitor vis) {
if (tag == id<T1>) {
return vis(storage.template as<T1>());
}
if constexpr (sizeof...(TRest) > 0) {
return visit_impl<Visitor, TRest...>(vis);
}
else {
using ReturnType = decltype(vis(declval<First&>()));
if constexpr (!type_traits::is_void_v<ReturnType>) return ReturnType{};
}
}
};
template<class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
template<class... Ts> overloaded(Ts...)->overloaded<Ts...>;
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