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A tuple that can be aligned to any number (not just power of 2) and does not use "pragma pack"
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| #pragma once | |
| #include <type_traits> | |
| #include <tuple> | |
| #include <memory> | |
| template <std::size_t N, class... Types> | |
| struct packed_tuple; | |
| // is_packed_tuple | |
| template <class T> | |
| struct is_packed_tuple : std::false_type { }; | |
| template <std::size_t N, class... Types> | |
| struct is_packed_tuple<packed_tuple<N, Types...>> : std::true_type { }; | |
| template <class T> | |
| inline constexpr bool is_packed_tuple_v = is_packed_tuple<T>::value; | |
| // Concepts | |
| template <class T, class = std::enable_if_t<is_packed_tuple_v<std::decay_t<T>>>> | |
| using packed_tuple_t = T; | |
| // Details | |
| namespace detail | |
| { | |
| // Returns the first appearence of T in packed_tuple | |
| // or sizeof...(Types) if T is not found | |
| template <class T, class L> | |
| struct index_of : std::integral_constant<std::size_t, 0> { }; | |
| template <class T, class L> | |
| inline constexpr std::size_t index_of_v = index_of<T, L>::value; | |
| template <class T, std::size_t N, class First, class... Rest> | |
| struct index_of<T, packed_tuple<N, First, Rest...>> : std::integral_constant< | |
| std::size_t, | |
| std::is_same_v<T, First> ? 0 : index_of_v<T, packed_tuple<N, Rest...>> + 1> { }; | |
| } // namespace detail | |
| // Get value by index argument | |
| template <class Tuple> | |
| inline constexpr decltype(auto) | |
| get(std::in_place_index_t<0>, packed_tuple_t<Tuple>&& tup) noexcept | |
| { return std::forward<Tuple>(tup).get(); } | |
| template <std::size_t I, class Tuple> | |
| inline constexpr decltype(auto) | |
| get(std::in_place_index_t<I>, packed_tuple_t<Tuple>&& tup) noexcept | |
| { return get(std::in_place_index<I - 1>, std::forward<Tuple>(tup).rest_); } | |
| // Get value by type argument | |
| template <class T, class Tuple> | |
| inline constexpr decltype(auto) | |
| get(std::in_place_type_t<T>, packed_tuple_t<Tuple>&& tup) noexcept | |
| { | |
| using I = detail::index_of<T, std::decay_t<Tuple>>; | |
| return get(std::in_place_index<I::value>, std::forward<Tuple>(tup)); | |
| } | |
| // Get value by index template | |
| template <std::size_t I, class Tuple> | |
| inline constexpr decltype(auto) | |
| get(packed_tuple_t<Tuple>&& tup) noexcept | |
| { return get(std::in_place_index<I>, std::forward<Tuple>(tup)); } | |
| // Get value by type template | |
| template <class T, class Tuple> | |
| inline constexpr decltype(auto) | |
| get(packed_tuple_t<Tuple>&& tup) noexcept | |
| { return get(std::in_place_type<T>, std::forward<Tuple>(tup)); } | |
| // This one does not used in specializations below but | |
| // can be used as an empty tuple | |
| template <std::size_t N, class... Types> | |
| struct packed_tuple { }; | |
| // packed_tuple | |
| template <std::size_t N, class First, class... Rest> | |
| struct packed_tuple<N, First, Rest...> : packed_tuple<N, First> { | |
| private: | |
| packed_tuple<N, Rest...> rest_; | |
| template <std::size_t I, class Tuple> | |
| friend constexpr decltype(auto) | |
| get(std::in_place_index_t<I>, Tuple&&) noexcept; | |
| public: | |
| // Constructors | |
| constexpr packed_tuple() = default; | |
| template <class Arg1, class... ArgN, | |
| class = std::enable_if_t<std::is_constructible_v<First, Arg1>> | |
| > | |
| constexpr packed_tuple(Arg1&& arg1, ArgN&&... argn) | |
| noexcept ( | |
| std::is_nothrow_constructible_v<packed_tuple<N, First>, Arg1> and | |
| std::is_nothrow_constructible_v<packed_tuple<N, Rest...>, ArgN...> | |
| ) | |
| : packed_tuple<N, First>(std::forward<Arg1>(arg1)) | |
| , rest_(std::forward<ArgN>(argn)...) | |
| { } | |
| }; | |
| template <std::size_t N, class T> | |
| struct packed_tuple<N, T> { | |
| private: | |
| // Aligned storage | |
| unsigned char storage_[(sizeof(T) + N - 1) / N * N]; | |
| public: | |
| // Default constructor | |
| template <class... Args, | |
| class = std::enable_if_t<std::is_constructible_v<T, Args...>> | |
| > | |
| constexpr packed_tuple(Args&&... args) | |
| noexcept (std::is_nothrow_constructible_v<T, Args...>) | |
| { ::new (storage_) T(std::forward<Args>(args)...); } | |
| // Copy constructor | |
| constexpr packed_tuple(const packed_tuple& rhs) | |
| noexcept (std::is_nothrow_copy_constructible_v<T>) | |
| { ::new (storage_) T(rhs.get()); } | |
| // Move constructor | |
| constexpr packed_tuple(packed_tuple&& rhs) | |
| noexcept (std::is_nothrow_move_constructible_v<T>) | |
| { ::new (storage_) T(std::move(rhs).get()); } | |
| // Destructor | |
| ~packed_tuple() | |
| noexcept (std::is_nothrow_destructible_v<T>) | |
| { | |
| if constexpr (not std::is_trivially_destructible_v<T>) | |
| std::destroy_at((T*)storage_); | |
| } | |
| // Copy assignment | |
| packed_tuple& operator=(const packed_tuple& rhs) | |
| noexcept (std::is_nothrow_copy_assignable_v<T>) | |
| { return (this->get() = rhs.get(), *this); } | |
| // Move assignment | |
| packed_tuple& operator=(packed_tuple&& rhs) | |
| noexcept (std::is_nothrow_move_assignable_v<T>) | |
| { return (this->get() = std::move(rhs).get(), *this); } | |
| // Getters | |
| const T& get() const & noexcept | |
| { return *(const T*)storage_; } | |
| T& get() & noexcept | |
| { return *(T*)storage_; } | |
| const T&& get() const && noexcept | |
| { return std::move(*(const T*)storage_); } | |
| T&& get() && noexcept | |
| { return std::move(*(T*)storage_); } | |
| }; | |
| // Size of packed_tuple (structured binding) | |
| template <std::size_t N, class... Types> | |
| struct std::tuple_size<packed_tuple<N, Types...>> | |
| : std::integral_constant<std::size_t, sizeof...(Types)> | |
| { }; | |
| // Element type (structured binding) | |
| template <std::size_t I, std::size_t N, class... Types> | |
| struct std::tuple_element<I, packed_tuple<N, Types...>> | |
| : std::tuple_element<I, std::tuple<Types...>> | |
| { }; |
Tests:
static_assert(sizeof(packed_tuple<1, char, int>) == 5);
static_assert(sizeof(packed_tuple<1, int, char>) == 5);
static_assert(sizeof(packed_tuple<2, char, int>) == 6);
static_assert(sizeof(packed_tuple<2, int, char>) == 6);
static_assert(sizeof(packed_tuple<3, char, int>) == 9);
static_assert(sizeof(packed_tuple<3, int, char>) == 9);
static_assert(sizeof(packed_tuple<4, char, int>) == 8);
static_assert(sizeof(packed_tuple<4, int, char>) == 8);
static_assert(sizeof(packed_tuple<1, double, char, int>) == 13);
static_assert(sizeof(packed_tuple<2, double, char, int>) == 14);
static_assert(sizeof(packed_tuple<3, double, char, int>) == 18);
static_assert(sizeof(packed_tuple<4, double, char, int>) == 16);
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Example. Create tuple that is aligned to
short