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boost/beast/core/detail/type_traits.hpp

//
// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/boostorg/beast
//

#ifndef BOOST_BEAST_DETAIL_TYPE_TRAITS_HPP
#define BOOST_BEAST_DETAIL_TYPE_TRAITS_HPP

#include <boost/type_traits/make_void.hpp>
#include <type_traits>
#include <new>

namespace boost {
namespace beast {
namespace detail {

template<class U>
std::size_t constexpr
max_sizeof()
{
    return sizeof(U);
}

template<class U0, class U1, class... Us>
std::size_t constexpr
max_sizeof()
{
    return
        max_sizeof<U0>() > max_sizeof<U1, Us...>() ?
        max_sizeof<U0>() : max_sizeof<U1, Us...>();
}

template<class U>
std::size_t constexpr
max_alignof()
{
    return alignof(U);
}

template<class U0, class U1, class... Us>
std::size_t constexpr
max_alignof()
{
    return
        max_alignof<U0>() > max_alignof<U1, Us...>() ?
        max_alignof<U0>() : max_alignof<U1, Us...>();
}

// (since C++17)
template<class... Ts>
using make_void = boost::make_void<Ts...>;
template<class... Ts>
using void_t = boost::void_t<Ts...>;

// (since C++11) missing from g++4.8
template<std::size_t Len, class... Ts>
struct aligned_union
{
    static
    std::size_t constexpr alignment_value =
        max_alignof<Ts...>();

    using type = typename std::aligned_storage<
        (Len > max_sizeof<Ts...>()) ? Len : (max_sizeof<Ts...>()),
            alignment_value>::type;
};

template<std::size_t Len, class... Ts>
using aligned_union_t =
    typename aligned_union<Len, Ts...>::type;

//------------------------------------------------------------------------------

// for span
template<class T, class E, class = void>
struct is_contiguous_container: std::false_type {};

template<class T, class E>
struct is_contiguous_container<T, E, void_t<
    decltype(
        std::declval<std::size_t&>() = std::declval<T const&>().size(),
        std::declval<E*&>() = std::declval<T&>().data()),
    typename std::enable_if<
        std::is_same<
            typename std::remove_cv<E>::type,
            typename std::remove_cv<
                typename std::remove_pointer<
                    decltype(std::declval<T&>().data())
                >::type
            >::type
        >::value
    >::type>>: std::true_type
{};

template <class T, class U>
T launder_cast(U* u)
{
#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606
    return std::launder(reinterpret_cast<T>(u));
#elif defined(BOOST_GCC) && BOOST_GCC_VERSION > 80000
    return __builtin_launder(reinterpret_cast<T>(u));
#else
    return reinterpret_cast<T>(u);
#endif
}

} // detail
} // beast
} // boost

#endif