aligned_storage.hpp

/**
 * \file aligned_storage.hpp
 *
 * \brief This header defines a utility type for aligned storage
 *
 * \author Matthew Rodusek (matthew.rodusek@gmail.com)
 */
#ifndef BIT_STL_UTILITIES_ALIGNED_STORAGE_HPP
#define BIT_STL_UTILITIES_ALIGNED_STORAGE_HPP

#include "../traits/composition/conjunction.hpp"
#include "../traits/composition/size_constant.hpp"

#include <cstddef> // std::size_t, std::max_align_t

namespace bit {
  namespace stl {
    namespace detail {
      template<std::size_t Max, std::size_t...Sizes>
      struct aligned_storage_max;

      template<std::size_t Max, std::size_t Size0, std::size_t...Sizes>
      struct aligned_storage_max<Max,Size0,Sizes...>
        : aligned_storage_max<(Max > Size0 ? Max : Size0),Sizes...>{};

      template<std::size_t Max>
      struct aligned_storage_max<Max> : size_constant<Max>{};
    } // namespace detail

    constexpr auto max_align = alignof(std::max_align_t);

    ///////////////////////////////////////////////////////////////////////////
    /// \brief Provides the nested type type, which is a PODType suitable for
    ///        use as uninitialized storage for any object whose size is at
    ///        most Len and whose alignment requirement is a divisor of Align.
    ///
    /// The default value of Align is the most stringent (the largest)
    /// alignment requirement for any object whose size is at most Len.
    /// If the default value is not used, Align must be the value of
    ///  alignof(T) for some type T, or the behavior is undefined.
    ///
    /// The behavior is undefined if Len == 0.
    ///
    /// \tparam Len the length of the storage
    /// \tparam Align the alignment of the storage
    //////////////////////////////////////////////////////////////////////////
    template<std::size_t Len, std::size_t Align = max_align>
    struct aligned_storage
    {
      union type
      {
        char data[Len];
        alignas(Align) struct dummy{} dummy;
      };
    };

    /// \brief Type-alias for extracting aligned_storage::type
    template<std::size_t Len, std::size_t Align = max_align>
    using aligned_storage_t = typename aligned_storage<Len,Align>::type;

    /// \brief Type-alias for creating aligned_storage large enough and suitably
    ///        aligned for all specified Types...
    ///
    /// \tparam Types the types to ensure alignment and size of
    template<typename...Types>
    using aligned_storage_for = aligned_storage_t<detail::aligned_storage_max<sizeof(Types)...>::value,
                                                  detail::aligned_storage_max<alignof(Types)...>::value>;

  } // namespace stl
} // namespace bit

#endif /* BIT_STL_UTILITIES_ALIGNED_STORAGE_HPP */