aligned_union.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2019 Tobias Hienzsch
 
#ifndef TETL_TYPE_TRAITS_ALIGNED_UNION_HPP
#define TETL_TYPE_TRAITS_ALIGNED_UNION_HPP
 
#include <etl/_cstddef/size_t.hpp>
 
namespace etl {
 
namespace detail {
template <typename T>
[[nodiscard]] constexpr auto vmax(T val) -> T
{
    return val;
}
 
template <typename T0, typename T1, typename... Ts>
[[nodiscard]] constexpr auto vmax(T0 val1, T1 val2, Ts... vs) -> T0
{
    return (val1 > val2) ? vmax(val1, vs...) : vmax(val2, vs...);
}
} // namespace detail
 
/// \brief Provides the nested type type, which is a trivial standard-layout
/// type of a size and alignment suitable for use as uninitialized storage for
/// an object of any of the types listed in Types.
///
/// The size of the storage is at least Len. aligned_union also determines the
/// strictest (largest) alignment requirement among all Types and makes it
/// available as the constant alignment_value. If sizeof...(Types) == 0 or if
/// any of the types in Types is not a complete object type, the behavior is undefined.
///
/// It is implementation-defined whether any extended alignment is supported. The
/// behavior of a program that adds specializations for aligned_union is
/// undefined.
///
/// \ingroup type_traits
template <size_t Len, typename... Types>
struct aligned_union {
    static constexpr size_t alignment_value = detail::vmax(alignof(Types)...);
 
    struct type {
        alignas(alignment_value) char storage[detail::vmax(Len, sizeof(Types)...)];
    };
};
 
/// \relates aligned_union
/// \ingroup type_traits
template <size_t Len, typename... Types>
using aligned_union_t = typename aligned_union<Len, Types...>::type;
 
} // namespace etl
 
#endif // TETL_TYPE_TRAITS_ALIGNED_UNION_HPP