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//
// Copyright (c) 2016-2017 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_VARIANT_HPP
#define BOOST_BEAST_DETAIL_VARIANT_HPP
#include <boost/beast/core/detail/type_traits.hpp>
#include <boost/assert.hpp>
#include <cstddef>
#include <tuple>
#include <type_traits>
namespace boost {
namespace beast {
namespace detail {
// This simple variant gets the job done without
// causing too much trouble with template depth:
//
// * Always allows an empty state I==0
// * emplace() and get() support 1-based indexes only
// * Basic exception guarantee
// * Max 255 types
//
template<class... TN>
class variant
{
typename std::aligned_storage<
max_sizeof<TN...>(),
max_alignof<TN...>()
>::type buf_;
unsigned char i_ = 0;
template<std::size_t I>
using type = typename std::tuple_element<
I , std::tuple<TN...>>::type;
template<std::size_t I>
using C = std::integral_constant<std::size_t, I>;
public:
variant() = default;
~variant()
{
if(i_)
destroy(C<0>{});
}
// 0 = empty
unsigned char
index() const
{
return i_;
}
// moved-from object becomes empty
variant(variant&& other)
{
i_ = other.move(&buf_, C<0>{});
}
variant(variant const& other)
{
i_ = other.copy(&buf_, C<0>{});
}
// moved-from object becomes empty
variant& operator=(variant&& other)
{
if(i_ != 0)
destroy(C<0>{});
i_ = other.move(&buf_, C<0>{});
return *this;
}
variant& operator=(variant const& other)
{
if(i_ != 0)
destroy(C<0>{});
i_ = other.copy(&buf_, C<0>{});
return *this;
}
template<std::size_t I, class... Args>
void
emplace(Args&&... args)
{
if(i_ != 0)
destroy(C<0>{});
new(&buf_) type<I-1>(
std::forward<Args>(args)...);
i_ = I;
}
template<std::size_t I>
type<I-1>&
get()
{
BOOST_ASSERT(i_ == I);
return *reinterpret_cast<
type<I-1>*>(&buf_);
}
template<std::size_t I>
type<I-1> const&
get() const
{
BOOST_ASSERT(i_ == I);
return *reinterpret_cast<
type<I-1> const*>(&buf_);
}
void
reset()
{
if(i_ == 0)
return;
destroy(C<0>{});
}
private:
void
destroy(C<sizeof...(TN)>)
{
return;
}
template<std::size_t I>
void
destroy(C<I>)
{
if(i_ == I+1)
{
using T = type<I>;
get<I+1>().~T();
i_ = 0;
return;
}
destroy(C<I+1>{});
}
unsigned char
move(void*, C<sizeof...(TN)>)
{
return 0;
}
template<std::size_t I>
unsigned char
move(void* dest, C<I>)
{
if(i_ == I+1)
{
using T = type<I>;
new(dest) T{std::move(get<I+1>())};
get<I+1>().~T();
i_ = 0;
return I+1;
}
return move(dest, C<I+1>{});
}
unsigned char
copy(void*, C<sizeof...(TN)>) const
{
return 0;
}
template<std::size_t I>
unsigned char
copy(void* dest, C<I>) const
{
if(i_ == I+1)
{
using T = type<I>;
auto const& t = get<I+1>();
new(dest) T{t};
return I+1;
}
return copy(dest, C<I+1>{});
}
};
} // detail
} // beast
} // boost
#endif
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