variant.hpp

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// Copyright 2016-2018 by Martin Moene
//
// https://github.com/martinmoene/variant-lite
//
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#pragma once

#ifndef NONSTD_VARIANT_LITE_HPP
#define NONSTD_VARIANT_LITE_HPP

#define variant_lite_MAJOR  1
#define variant_lite_MINOR  1
#define variant_lite_PATCH  0

#define variant_lite_VERSION  variant_STRINGIFY(variant_lite_MAJOR) "." variant_STRINGIFY(variant_lite_MINOR) "." variant_STRINGIFY(variant_lite_PATCH)

#define variant_STRINGIFY(  x )  variant_STRINGIFY_( x )
#define variant_STRINGIFY_( x )  #x

// variant-lite configuration:

#define variant_VARIANT_DEFAULT  0
#define variant_VARIANT_NONSTD   1
#define variant_VARIANT_STD      2

#if !defined( variant_CONFIG_SELECT_VARIANT )
# define variant_CONFIG_SELECT_VARIANT  ( variant_HAVE_STD_VARIANT ? variant_VARIANT_STD : variant_VARIANT_NONSTD )
#endif

#ifndef  variant_CONFIG_OMIT_VARIANT_SIZE_V_MACRO
# define variant_CONFIG_OMIT_VARIANT_SIZE_V_MACRO  0
#endif

#ifndef  variant_CONFIG_OMIT_VARIANT_ALTERNATIVE_T_MACRO
# define variant_CONFIG_OMIT_VARIANT_ALTERNATIVE_T_MACRO  0
#endif

// Control presence of exception handling (try and auto discover):

#ifndef variant_CONFIG_NO_EXCEPTIONS
# if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)
#  define variant_CONFIG_NO_EXCEPTIONS  0
# else
#  define variant_CONFIG_NO_EXCEPTIONS  1
# endif
#endif

// C++ language version detection (C++20 is speculative):
// Note: VC14.0/1900 (VS2015) lacks too much from C++14.

#ifndef   variant_CPLUSPLUS
# if defined(_MSVC_LANG ) && !defined(__clang__)
#  define variant_CPLUSPLUS  (_MSC_VER == 1900 ? 201103L : _MSVC_LANG )
# else
#  define variant_CPLUSPLUS  __cplusplus
# endif
#endif

#define variant_CPP98_OR_GREATER  ( variant_CPLUSPLUS >= 199711L )
#define variant_CPP11_OR_GREATER  ( variant_CPLUSPLUS >= 201103L )
#define variant_CPP11_OR_GREATER_ ( variant_CPLUSPLUS >= 201103L )
#define variant_CPP14_OR_GREATER  ( variant_CPLUSPLUS >= 201402L )
#define variant_CPP17_OR_GREATER  ( variant_CPLUSPLUS >= 201703L )
#define variant_CPP20_OR_GREATER  ( variant_CPLUSPLUS >= 202000L )

// Use C++17 std::variant if available and requested:

#if variant_CPP17_OR_GREATER && defined(__has_include )
# if __has_include( <variant> )
#  define variant_HAVE_STD_VARIANT  1
# else
#  define variant_HAVE_STD_VARIANT  0
# endif
#else
# define  variant_HAVE_STD_VARIANT  0
#endif

#define  variant_USES_STD_VARIANT  ( (variant_CONFIG_SELECT_VARIANT == variant_VARIANT_STD) || ((variant_CONFIG_SELECT_VARIANT == variant_VARIANT_DEFAULT) && variant_HAVE_STD_VARIANT) )

//
// in_place: code duplicated in any-lite, expected-lite, optional-lite, value-ptr-lite, variant-lite:
//

#ifndef nonstd_lite_HAVE_IN_PLACE_TYPES
#define nonstd_lite_HAVE_IN_PLACE_TYPES  1

// C++17 std::in_place in <utility>:

#if variant_CPP17_OR_GREATER

#include <utility>

namespace nonstd {

using std::in_place;
using std::in_place_type;
using std::in_place_index;
using std::in_place_t;
using std::in_place_type_t;
using std::in_place_index_t;

#define nonstd_lite_in_place_t(      T)  std::in_place_t
#define nonstd_lite_in_place_type_t( T)  std::in_place_type_t<T>
#define nonstd_lite_in_place_index_t(K)  std::in_place_index_t<K>

#define nonstd_lite_in_place(      T)    std::in_place_t{}
#define nonstd_lite_in_place_type( T)    std::in_place_type_t<T>{}
#define nonstd_lite_in_place_index(K)    std::in_place_index_t<K>{}

} // namespace nonstd

#else // variant_CPP17_OR_GREATER

#include <cstddef>

namespace nonstd {
namespace detail {

template< class T >
struct in_place_type_tag {};

template< std::size_t K >
struct in_place_index_tag {};

} // namespace detail

struct in_place_t {};

template< class T >
inline in_place_t in_place( detail::in_place_type_tag<T> = detail::in_place_type_tag<T>() )
{
    return in_place_t();
}

template< std::size_t K >
inline in_place_t in_place( detail::in_place_index_tag<K> = detail::in_place_index_tag<K>() )
{
    return in_place_t();
}

template< class T >
inline in_place_t in_place_type( detail::in_place_type_tag<T> = detail::in_place_type_tag<T>() )
{
    return in_place_t();
}

template< std::size_t K >
inline in_place_t in_place_index( detail::in_place_index_tag<K> = detail::in_place_index_tag<K>() )
{
    return in_place_t();
}

// mimic templated typedef:

#define nonstd_lite_in_place_t(      T)  nonstd::in_place_t(&)( nonstd::detail::in_place_type_tag<T>  )
#define nonstd_lite_in_place_type_t( T)  nonstd::in_place_t(&)( nonstd::detail::in_place_type_tag<T>  )
#define nonstd_lite_in_place_index_t(K)  nonstd::in_place_t(&)( nonstd::detail::in_place_index_tag<K> )

#define nonstd_lite_in_place(      T)    nonstd::in_place_type<T>
#define nonstd_lite_in_place_type( T)    nonstd::in_place_type<T>
#define nonstd_lite_in_place_index(K)    nonstd::in_place_index<K>

} // namespace nonstd

#endif // variant_CPP17_OR_GREATER
#endif // nonstd_lite_HAVE_IN_PLACE_TYPES

//
// Use C++17 std::variant:
//

#if variant_USES_STD_VARIANT

#include <functional>   // std::hash<>
#include <variant>

#if ! variant_CONFIG_OMIT_VARIANT_SIZE_V_MACRO
# define variant_size_V(T)  nonstd::variant_size<T>::value
#endif

#if ! variant_CONFIG_OMIT_VARIANT_ALTERNATIVE_T_MACRO
# define variant_alternative_T(K,T)  typename nonstd::variant_alternative<K,T >::type
#endif

namespace nonstd {

    using std::variant;
    using std::monostate;
    using std::bad_variant_access;
    using std::variant_size;
    using std::variant_size_v;
    using std::variant_alternative;
    using std::variant_alternative_t;
    using std::hash;

    using std::visit;
    using std::holds_alternative;
    using std::get;
    using std::get_if;
    using std::operator==;
    using std::operator!=;
    using std::operator<;
    using std::operator<=;
    using std::operator>;
    using std::operator>=;
    using std::swap;

    constexpr auto variant_npos = std::variant_npos;
}

#else // variant_USES_STD_VARIANT

#include <cstddef>
#include <limits>
#include <new>
#include <utility>

#if variant_CONFIG_NO_EXCEPTIONS
# include <cassert>
#else
# include <stdexcept>
#endif

// variant-lite type and visitor argument count configuration (script/generate_header.py):

#define variant_CONFIG_MAX_TYPE_COUNT  16
#define variant_CONFIG_MAX_VISITOR_ARG_COUNT  5

// variant-lite alignment configuration:

#ifndef  variant_CONFIG_MAX_ALIGN_HACK
# define variant_CONFIG_MAX_ALIGN_HACK  0
#endif

#ifndef  variant_CONFIG_ALIGN_AS
// no default, used in #if defined()
#endif

#ifndef  variant_CONFIG_ALIGN_AS_FALLBACK
# define variant_CONFIG_ALIGN_AS_FALLBACK  double
#endif

// half-open range [lo..hi):
#define variant_BETWEEN( v, lo, hi ) ( (lo) <= (v) && (v) < (hi) )

// Compiler versions:
//
// MSVC++ 6.0  _MSC_VER == 1200 (Visual Studio 6.0)
// MSVC++ 7.0  _MSC_VER == 1300 (Visual Studio .NET 2002)
// MSVC++ 7.1  _MSC_VER == 1310 (Visual Studio .NET 2003)
// MSVC++ 8.0  _MSC_VER == 1400 (Visual Studio 2005)
// MSVC++ 9.0  _MSC_VER == 1500 (Visual Studio 2008)
// MSVC++ 10.0 _MSC_VER == 1600 (Visual Studio 2010)
// MSVC++ 11.0 _MSC_VER == 1700 (Visual Studio 2012)
// MSVC++ 12.0 _MSC_VER == 1800 (Visual Studio 2013)
// MSVC++ 14.0 _MSC_VER == 1900 (Visual Studio 2015)
// MSVC++ 14.1 _MSC_VER >= 1910 (Visual Studio 2017)

#if defined(_MSC_VER ) && !defined(__clang__)
# define variant_COMPILER_MSVC_VER      (_MSC_VER )
# define variant_COMPILER_MSVC_VERSION  (_MSC_VER / 10 - 10 * ( 5 + (_MSC_VER < 1900 ) ) )
#else
# define variant_COMPILER_MSVC_VER      0
# define variant_COMPILER_MSVC_VERSION  0
#endif

#define variant_COMPILER_VERSION( major, minor, patch )  ( 10 * ( 10 * (major) + (minor) ) + (patch) )

#if defined(__clang__)
# define variant_COMPILER_CLANG_VERSION  variant_COMPILER_VERSION(__clang_major__, __clang_minor__, __clang_patchlevel__)
#else
# define variant_COMPILER_CLANG_VERSION  0
#endif

#if defined(__GNUC__) && !defined(__clang__)
# define variant_COMPILER_GNUC_VERSION  variant_COMPILER_VERSION(__GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__)
#else
# define variant_COMPILER_GNUC_VERSION  0
#endif

#if variant_BETWEEN( variant_COMPILER_MSVC_VER, 1300, 1900 )
# pragma warning( push )
# pragma warning( disable: 4345 )   // initialization behavior changed
#endif

// Presence of language and library features:

#define variant_HAVE( feature )  ( variant_HAVE_##feature )

#ifdef _HAS_CPP0X
# define variant_HAS_CPP0X  _HAS_CPP0X
#else
# define variant_HAS_CPP0X  0
#endif

// Unless defined otherwise below, consider VC14 as C++11 for variant-lite:

#if variant_COMPILER_MSVC_VER >= 1900
# undef  variant_CPP11_OR_GREATER
# define variant_CPP11_OR_GREATER  1
#endif

#define variant_CPP11_90   (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1500)
#define variant_CPP11_100  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1600)
#define variant_CPP11_110  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1700)
#define variant_CPP11_120  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1800)
#define variant_CPP11_140  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1900)
#define variant_CPP11_141  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1910)

#define variant_CPP14_000  (variant_CPP14_OR_GREATER)
#define variant_CPP17_000  (variant_CPP17_OR_GREATER)

// Presence of C++11 language features:

#define variant_HAVE_CONSTEXPR_11       variant_CPP11_140
#define variant_HAVE_INITIALIZER_LIST   variant_CPP11_120
#define variant_HAVE_NOEXCEPT           variant_CPP11_140
#define variant_HAVE_NULLPTR            variant_CPP11_100
#define variant_HAVE_OVERRIDE           variant_CPP11_140

// Presence of C++14 language features:

#define variant_HAVE_CONSTEXPR_14       variant_CPP14_000

// Presence of C++17 language features:

// no flag

// Presence of C++ library features:

#define variant_HAVE_CONDITIONAL        variant_CPP11_120
#define variant_HAVE_REMOVE_CV          variant_CPP11_120
#define variant_HAVE_STD_ADD_POINTER    variant_CPP11_90
#define variant_HAVE_TYPE_TRAITS        variant_CPP11_90

#define variant_HAVE_TR1_TYPE_TRAITS    (!! variant_COMPILER_GNUC_VERSION )
#define variant_HAVE_TR1_ADD_POINTER    (!! variant_COMPILER_GNUC_VERSION )

// C++ feature usage:

#if variant_HAVE_CONSTEXPR_11
# define variant_constexpr constexpr
#else
# define variant_constexpr /*constexpr*/
#endif

#if variant_HAVE_CONSTEXPR_14
# define variant_constexpr14 constexpr
#else
# define variant_constexpr14 /*constexpr*/
#endif

#if variant_HAVE_NOEXCEPT
# define variant_noexcept noexcept
#else
# define variant_noexcept /*noexcept*/
#endif

#if variant_HAVE_NULLPTR
# define variant_nullptr nullptr
#else
# define variant_nullptr NULL
#endif

#if variant_HAVE_OVERRIDE
# define variant_override override
#else
# define variant_override /*override*/
#endif

// additional includes:

#if variant_CPP11_OR_GREATER
# include <functional>      // std::hash
#endif

#if variant_HAVE_INITIALIZER_LIST
# include <initializer_list>
#endif

#if variant_HAVE_TYPE_TRAITS
# include <type_traits>
#elif variant_HAVE_TR1_TYPE_TRAITS
# include <tr1/type_traits>
#endif

// Method enabling

#if variant_CPP11_OR_GREATER

#define variant_REQUIRES_0(...) \
    template< bool B = (__VA_ARGS__), typename std::enable_if<B, int>::type = 0 >

#define variant_REQUIRES_T(...) \
    , typename = typename std::enable_if< (__VA_ARGS__), nonstd::variants::detail::enabler >::type

#define variant_REQUIRES_R(R, ...) \
    typename std::enable_if< (__VA_ARGS__), R>::type

#define variant_REQUIRES_A(...) \
    , typename std::enable_if< (__VA_ARGS__), void*>::type = nullptr

#endif

//
// variant:
//

namespace nonstd { namespace variants {

// C++11 emulation:

namespace std11 {

#if variant_HAVE_STD_ADD_POINTER

using std::add_pointer;

#elif variant_HAVE_TR1_ADD_POINTER

using std::tr1::add_pointer;

#else

template< class T > struct remove_reference     { typedef T type; };
template< class T > struct remove_reference<T&> { typedef T type; };

template< class T > struct add_pointer
{
    typedef typename remove_reference<T>::type * type;
};

#endif // variant_HAVE_STD_ADD_POINTER

#if variant_HAVE_REMOVE_CV

using std::remove_cv;

#else

template< class T > struct remove_const          { typedef T type; };
template< class T > struct remove_const<const T> { typedef T type; };

template< class T > struct remove_volatile             { typedef T type; };
template< class T > struct remove_volatile<volatile T> { typedef T type; };

template< class T >
struct remove_cv
{
    typedef typename remove_volatile<typename remove_const<T>::type>::type type;
};

#endif // variant_HAVE_REMOVE_CV

#if variant_HAVE_CONDITIONAL

using std::conditional;

#else

template< bool Cond, class Then, class Else >
struct conditional;

template< class Then, class Else >
struct conditional< true , Then, Else > { typedef Then type; };

template< class Then, class Else >
struct conditional< false, Then, Else > { typedef Else type; };

#endif // variant_HAVE_CONDITIONAL

} // namespace std11


namespace std17 {

#if variant_CPP17_OR_GREATER

using std::is_swappable;
using std::is_nothrow_swappable;

#elif variant_CPP11_OR_GREATER

namespace detail {

using std::swap;

struct is_swappable
{
    template< typename T, typename = decltype( swap( std::declval<T&>(), std::declval<T&>() ) ) >
    static std::true_type test( int );

    template< typename >
    static std::false_type test(...);
};

struct is_nothrow_swappable
{
    // wrap noexcept(epr) in separate function as work-around for VC140 (VS2015):

    template< typename T >
    static constexpr bool test()
    {
        return noexcept( swap( std::declval<T&>(), std::declval<T&>() ) );
    }

    template< typename T >
    static auto test( int ) -> std::integral_constant<bool, test<T>()>{}

    template< typename >
    static std::false_type test(...);
};

} // namespace detail

// is [nothow] swappable:

template< typename T >
struct is_swappable : decltype( detail::is_swappable::test<T>(0) ){};

template< typename T >
struct is_nothrow_swappable : decltype( detail::is_nothrow_swappable::test<T>(0) ){};

#endif // variant_CPP17_OR_GREATER

} // namespace std17

// detail:

namespace detail {

// for variant_REQUIRES_T():

/*enum*/ class enabler{};

// typelist:

#define variant_TL1( T1 ) detail::typelist< T1, detail::nulltype >
#define variant_TL2( T1, T2) detail::typelist< T1, variant_TL1( T2) >
#define variant_TL3( T1, T2, T3) detail::typelist< T1, variant_TL2( T2, T3) >
#define variant_TL4( T1, T2, T3, T4) detail::typelist< T1, variant_TL3( T2, T3, T4) >
#define variant_TL5( T1, T2, T3, T4, T5) detail::typelist< T1, variant_TL4( T2, T3, T4, T5) >
#define variant_TL6( T1, T2, T3, T4, T5, T6) detail::typelist< T1, variant_TL5( T2, T3, T4, T5, T6) >
#define variant_TL7( T1, T2, T3, T4, T5, T6, T7) detail::typelist< T1, variant_TL6( T2, T3, T4, T5, T6, T7) >
#define variant_TL8( T1, T2, T3, T4, T5, T6, T7, T8) detail::typelist< T1, variant_TL7( T2, T3, T4, T5, T6, T7, T8) >
#define variant_TL9( T1, T2, T3, T4, T5, T6, T7, T8, T9) detail::typelist< T1, variant_TL8( T2, T3, T4, T5, T6, T7, T8, T9) >
#define variant_TL10( T1, T2, T3, T4, T5, T6, T7, T8, T9, T10) detail::typelist< T1, variant_TL9( T2, T3, T4, T5, T6, T7, T8, T9, T10) >
#define variant_TL11( T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11) detail::typelist< T1, variant_TL10( T2, T3, T4, T5, T6, T7, T8, T9, T10, T11) >
#define variant_TL12( T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12) detail::typelist< T1, variant_TL11( T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12) >
#define variant_TL13( T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13) detail::typelist< T1, variant_TL12( T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13) >
#define variant_TL14( T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14) detail::typelist< T1, variant_TL13( T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14) >
#define variant_TL15( T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15) detail::typelist< T1, variant_TL14( T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15) >
#define variant_TL16( T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16) detail::typelist< T1, variant_TL15( T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16) >


// variant parameter unused type tags:

template< class T >
struct TX : T
{
                        inline TX<T> operator+ (           ) const { return TX<T>();  }
                        inline TX<T> operator- (           ) const { return TX<T>();  }

                        inline TX<T> operator! (           ) const { return TX<T>();  }
                        inline TX<T> operator~ (           ) const { return TX<T>();  }

                        inline TX<T>*operator& (           ) const { return variant_nullptr; }

    template< class U > inline TX<T> operator* ( U const & ) const { return TX<T>();  }
    template< class U > inline TX<T> operator/ ( U const & ) const { return TX<T>();  }

    template< class U > inline TX<T> operator% ( U const & ) const { return TX<T>();  }
    template< class U > inline TX<T> operator+ ( U const & ) const { return TX<T>();  }
    template< class U > inline TX<T> operator- ( U const & ) const { return TX<T>();  }

    template< class U > inline TX<T> operator<<( U const & ) const { return TX<T>();  }
    template< class U > inline TX<T> operator>>( U const & ) const { return TX<T>();  }

                        inline bool  operator==( T const & ) const { return false; }
                        inline bool  operator< ( T const & ) const { return false; }

    template< class U > inline TX<T> operator& ( U const & ) const { return TX<T>();  }
    template< class U > inline TX<T> operator| ( U const & ) const { return TX<T>();  }
    template< class U > inline TX<T> operator^ ( U const & ) const { return TX<T>();  }

    template< class U > inline TX<T> operator&&( U const & ) const { return TX<T>();  }
    template< class U > inline TX<T> operator||( U const & ) const { return TX<T>();  }
};

struct S0{}; typedef TX<S0> T0;
struct S1{}; typedef TX<S1> T1;
struct S2{}; typedef TX<S2> T2;
struct S3{}; typedef TX<S3> T3;
struct S4{}; typedef TX<S4> T4;
struct S5{}; typedef TX<S5> T5;
struct S6{}; typedef TX<S6> T6;
struct S7{}; typedef TX<S7> T7;
struct S8{}; typedef TX<S8> T8;
struct S9{}; typedef TX<S9> T9;
struct S10{}; typedef TX<S10> T10;
struct S11{}; typedef TX<S11> T11;
struct S12{}; typedef TX<S12> T12;
struct S13{}; typedef TX<S13> T13;
struct S14{}; typedef TX<S14> T14;
struct S15{}; typedef TX<S15> T15;


struct nulltype{};

template< class Head, class Tail >
struct typelist
{
    typedef Head head;
    typedef Tail tail;
};

// typelist max element size:

template< class List >
struct typelist_max;

template<>
struct typelist_max< nulltype >
{
    enum V { value = 0 } ;
    typedef void type;
};

template< class Head, class Tail >
struct typelist_max< typelist<Head, Tail> >
{
private:
    enum TV { tail_value = size_t( typelist_max<Tail>::value ) };

    typedef typename typelist_max<Tail>::type tail_type;

public:
    enum V { value = (sizeof( Head ) > tail_value) ? sizeof( Head ) : std::size_t( tail_value ) } ;

    typedef typename std11::conditional< (sizeof( Head ) > tail_value), Head, tail_type>::type type;
};

#if variant_CPP11_OR_GREATER

// typelist max alignof element type:

template< class List >
struct typelist_max_alignof;

template<>
struct typelist_max_alignof< nulltype >
{
    enum V { value = 0 } ;
};

template< class Head, class Tail >
struct typelist_max_alignof< typelist<Head, Tail> >
{
private:
    enum TV { tail_value = size_t( typelist_max_alignof<Tail>::value ) };

public:
    enum V { value = (alignof( Head ) > tail_value) ? alignof( Head ) : std::size_t( tail_value ) };
};

#endif

// typelist size (length):

template< class List >
struct typelist_size
{
   enum V { value = 1 };
};

template<> struct typelist_size< T0 > { enum V { value = 0 }; };
template<> struct typelist_size< T1 > { enum V { value = 0 }; };
template<> struct typelist_size< T2 > { enum V { value = 0 }; };
template<> struct typelist_size< T3 > { enum V { value = 0 }; };
template<> struct typelist_size< T4 > { enum V { value = 0 }; };
template<> struct typelist_size< T5 > { enum V { value = 0 }; };
template<> struct typelist_size< T6 > { enum V { value = 0 }; };
template<> struct typelist_size< T7 > { enum V { value = 0 }; };
template<> struct typelist_size< T8 > { enum V { value = 0 }; };
template<> struct typelist_size< T9 > { enum V { value = 0 }; };
template<> struct typelist_size< T10 > { enum V { value = 0 }; };
template<> struct typelist_size< T11 > { enum V { value = 0 }; };
template<> struct typelist_size< T12 > { enum V { value = 0 }; };
template<> struct typelist_size< T13 > { enum V { value = 0 }; };
template<> struct typelist_size< T14 > { enum V { value = 0 }; };
template<> struct typelist_size< T15 > { enum V { value = 0 }; };


template<> struct typelist_size< nulltype > { enum V { value = 0 } ; };

template< class Head, class Tail >
struct typelist_size< typelist<Head, Tail> >
{
    enum V { value = typelist_size<Head>::value + typelist_size<Tail>::value };
};

// typelist index of type:

template< class List, class T >
struct typelist_index_of;

template< class T >
struct typelist_index_of< nulltype, T >
{
    enum V { value = -1 };
};

template< class Tail, class T >
struct typelist_index_of< typelist<T, Tail>, T >
{
    enum V { value = 0 };
};

template< class Head, class Tail, class T >
struct typelist_index_of< typelist<Head, Tail>, T >
{
private:
    enum TV { nextVal = typelist_index_of<Tail, T>::value };

public:
    enum V { value = nextVal == -1 ? -1 : 1 + nextVal } ;
};

// typelist type at index:

template< class List, std::size_t i>
struct typelist_type_at;

template< class Head, class Tail >
struct typelist_type_at< typelist<Head, Tail>, 0 >
{
    typedef Head type;
};

template< class Head, class Tail, std::size_t i >
struct typelist_type_at< typelist<Head, Tail>, i >
{
    typedef typename typelist_type_at<Tail, i - 1>::type type;
};

#if variant_CONFIG_MAX_ALIGN_HACK

// Max align, use most restricted type for alignment:

#define variant_UNIQUE(  name )       variant_UNIQUE2( name, __LINE__ )
#define variant_UNIQUE2( name, line ) variant_UNIQUE3( name, line )
#define variant_UNIQUE3( name, line ) name ## line

#define variant_ALIGN_TYPE( type ) \
    type variant_UNIQUE( _t ); struct_t< type > variant_UNIQUE( _st )

template< class T >
struct struct_t { T _; };

union max_align_t
{
    variant_ALIGN_TYPE( char );
    variant_ALIGN_TYPE( short int );
    variant_ALIGN_TYPE( int );
    variant_ALIGN_TYPE( long int  );
    variant_ALIGN_TYPE( float  );
    variant_ALIGN_TYPE( double );
    variant_ALIGN_TYPE( long double );
    variant_ALIGN_TYPE( char * );
    variant_ALIGN_TYPE( short int * );
    variant_ALIGN_TYPE( int *  );
    variant_ALIGN_TYPE( long int * );
    variant_ALIGN_TYPE( float * );
    variant_ALIGN_TYPE( double * );
    variant_ALIGN_TYPE( long double * );
    variant_ALIGN_TYPE( void * );

#ifdef HAVE_LONG_LONG
    variant_ALIGN_TYPE( long long );
#endif

    struct Unknown;

    Unknown ( * variant_UNIQUE(_) )( Unknown );
    Unknown * Unknown::* variant_UNIQUE(_);
    Unknown ( Unknown::* variant_UNIQUE(_) )( Unknown );

    struct_t< Unknown ( * )( Unknown)         > variant_UNIQUE(_);
    struct_t< Unknown * Unknown::*            > variant_UNIQUE(_);
    struct_t< Unknown ( Unknown::* )(Unknown) > variant_UNIQUE(_);
};

#undef variant_UNIQUE
#undef variant_UNIQUE2
#undef variant_UNIQUE3

#undef variant_ALIGN_TYPE

#elif defined( variant_CONFIG_ALIGN_AS ) // variant_CONFIG_MAX_ALIGN_HACK

// Use user-specified type for alignment:

#define variant_ALIGN_AS( unused ) \
    variant_CONFIG_ALIGN_AS

#else // variant_CONFIG_MAX_ALIGN_HACK

// Determine POD type to use for alignment:

#define variant_ALIGN_AS( to_align ) \
    typename detail::type_of_size< detail::alignment_types, detail::alignment_of< to_align >::value >::type

template< typename T >
struct alignment_of;

template< typename T >
struct alignment_of_hack
{
    char c;
    T t;
    alignment_of_hack();
};

template< size_t A, size_t S >
struct alignment_logic
{
    enum V { value = A < S ? A : S };
};

template< typename T >
struct alignment_of
{
    enum V { value = alignment_logic<
        sizeof( alignment_of_hack<T> ) - sizeof(T), sizeof(T) >::value };
};

template< typename List, size_t N >
struct type_of_size
{
    typedef typename std11::conditional<
        N == sizeof( typename List::head ),
            typename List::head,
            typename type_of_size<typename List::tail, N >::type >::type type;
};

template< size_t N >
struct type_of_size< nulltype, N >
{
    typedef variant_CONFIG_ALIGN_AS_FALLBACK type;
};

template< typename T>
struct struct_t { T _; };

#define variant_ALIGN_TYPE( type ) \
    typelist< type , typelist< struct_t< type >

struct Unknown;

typedef
    variant_ALIGN_TYPE( char ),
    variant_ALIGN_TYPE( short ),
    variant_ALIGN_TYPE( int ),
    variant_ALIGN_TYPE( long ),
    variant_ALIGN_TYPE( float ),
    variant_ALIGN_TYPE( double ),
    variant_ALIGN_TYPE( long double ),

    variant_ALIGN_TYPE( char *),
    variant_ALIGN_TYPE( short * ),
    variant_ALIGN_TYPE( int * ),
    variant_ALIGN_TYPE( long * ),
    variant_ALIGN_TYPE( float * ),
    variant_ALIGN_TYPE( double * ),
    variant_ALIGN_TYPE( long double * ),

    variant_ALIGN_TYPE( Unknown ( * )( Unknown ) ),
    variant_ALIGN_TYPE( Unknown * Unknown::*     ),
    variant_ALIGN_TYPE( Unknown ( Unknown::* )( Unknown ) ),

    nulltype
    > > > > > > >    > > > > > > >
    > > > > > > >    > > > > > > >
    > > > > > >
    alignment_types;

#undef variant_ALIGN_TYPE

#endif // variant_CONFIG_MAX_ALIGN_HACK

#if variant_CPP11_OR_GREATER

template< typename T>
inline std::size_t hash( T const & v )
{
    return std::hash<T>()( v );
}

inline std::size_t hash( T0 const & ) { return 0; }
inline std::size_t hash( T1 const & ) { return 0; }
inline std::size_t hash( T2 const & ) { return 0; }
inline std::size_t hash( T3 const & ) { return 0; }
inline std::size_t hash( T4 const & ) { return 0; }
inline std::size_t hash( T5 const & ) { return 0; }
inline std::size_t hash( T6 const & ) { return 0; }
inline std::size_t hash( T7 const & ) { return 0; }
inline std::size_t hash( T8 const & ) { return 0; }
inline std::size_t hash( T9 const & ) { return 0; }
inline std::size_t hash( T10 const & ) { return 0; }
inline std::size_t hash( T11 const & ) { return 0; }
inline std::size_t hash( T12 const & ) { return 0; }
inline std::size_t hash( T13 const & ) { return 0; }
inline std::size_t hash( T14 const & ) { return 0; }
inline std::size_t hash( T15 const & ) { return 0; }


#endif // variant_CPP11_OR_GREATER





template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
struct helper
{
    typedef signed char type_index_t;
    typedef variant_TL16( T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15 ) variant_types;

    template< class U >
    static U * as( void * data )
    {
        return reinterpret_cast<U*>( data );
    }

    template< class U >
    static U const * as( void const * data )
    {
        return reinterpret_cast<const U*>( data );
    }

    static type_index_t to_index_t( std::size_t index )
    {
        return static_cast<type_index_t>( index );
    }

    static void destroy( type_index_t index, void * data )
    {
        switch ( index )
        {
        case 0: as<T0>( data )->~T0(); break;
        case 1: as<T1>( data )->~T1(); break;
        case 2: as<T2>( data )->~T2(); break;
        case 3: as<T3>( data )->~T3(); break;
        case 4: as<T4>( data )->~T4(); break;
        case 5: as<T5>( data )->~T5(); break;
        case 6: as<T6>( data )->~T6(); break;
        case 7: as<T7>( data )->~T7(); break;
        case 8: as<T8>( data )->~T8(); break;
        case 9: as<T9>( data )->~T9(); break;
        case 10: as<T10>( data )->~T10(); break;
        case 11: as<T11>( data )->~T11(); break;
        case 12: as<T12>( data )->~T12(); break;
        case 13: as<T13>( data )->~T13(); break;
        case 14: as<T14>( data )->~T14(); break;
        case 15: as<T15>( data )->~T15(); break;
        
        }
    }

#if variant_CPP11_OR_GREATER
    template< class T, class... Args >
    static type_index_t construct_t( void * data, Args&&... args )
    {
        new( data ) T( std::forward<Args>(args)... );

        return to_index_t( detail::typelist_index_of< variant_types, T>::value );
    }

    template< std::size_t K, class... Args >
    static type_index_t construct_i( void * data, Args&&... args )
    {
        using type = typename detail::typelist_type_at< variant_types, K >::type;

        construct_t< type >( data, std::forward<Args>(args)... );

        return to_index_t( K );
    }

    static type_index_t move_construct( type_index_t const from_index, void * from_value, void * to_value )
    {
        switch ( from_index )
        {
        case 0: new( to_value ) T0( std::move( *as<T0>( from_value ) ) ); break;
        case 1: new( to_value ) T1( std::move( *as<T1>( from_value ) ) ); break;
        case 2: new( to_value ) T2( std::move( *as<T2>( from_value ) ) ); break;
        case 3: new( to_value ) T3( std::move( *as<T3>( from_value ) ) ); break;
        case 4: new( to_value ) T4( std::move( *as<T4>( from_value ) ) ); break;
        case 5: new( to_value ) T5( std::move( *as<T5>( from_value ) ) ); break;
        case 6: new( to_value ) T6( std::move( *as<T6>( from_value ) ) ); break;
        case 7: new( to_value ) T7( std::move( *as<T7>( from_value ) ) ); break;
        case 8: new( to_value ) T8( std::move( *as<T8>( from_value ) ) ); break;
        case 9: new( to_value ) T9( std::move( *as<T9>( from_value ) ) ); break;
        case 10: new( to_value ) T10( std::move( *as<T10>( from_value ) ) ); break;
        case 11: new( to_value ) T11( std::move( *as<T11>( from_value ) ) ); break;
        case 12: new( to_value ) T12( std::move( *as<T12>( from_value ) ) ); break;
        case 13: new( to_value ) T13( std::move( *as<T13>( from_value ) ) ); break;
        case 14: new( to_value ) T14( std::move( *as<T14>( from_value ) ) ); break;
        case 15: new( to_value ) T15( std::move( *as<T15>( from_value ) ) ); break;
        
        }
        return from_index;
    }

    static type_index_t move_assign( type_index_t const from_index, void * from_value, void * to_value )
    {
        switch ( from_index )
        {
        case 0: *as<T0>( to_value ) = std::move( *as<T0>( from_value ) ); break;
        case 1: *as<T1>( to_value ) = std::move( *as<T1>( from_value ) ); break;
        case 2: *as<T2>( to_value ) = std::move( *as<T2>( from_value ) ); break;
        case 3: *as<T3>( to_value ) = std::move( *as<T3>( from_value ) ); break;
        case 4: *as<T4>( to_value ) = std::move( *as<T4>( from_value ) ); break;
        case 5: *as<T5>( to_value ) = std::move( *as<T5>( from_value ) ); break;
        case 6: *as<T6>( to_value ) = std::move( *as<T6>( from_value ) ); break;
        case 7: *as<T7>( to_value ) = std::move( *as<T7>( from_value ) ); break;
        case 8: *as<T8>( to_value ) = std::move( *as<T8>( from_value ) ); break;
        case 9: *as<T9>( to_value ) = std::move( *as<T9>( from_value ) ); break;
        case 10: *as<T10>( to_value ) = std::move( *as<T10>( from_value ) ); break;
        case 11: *as<T11>( to_value ) = std::move( *as<T11>( from_value ) ); break;
        case 12: *as<T12>( to_value ) = std::move( *as<T12>( from_value ) ); break;
        case 13: *as<T13>( to_value ) = std::move( *as<T13>( from_value ) ); break;
        case 14: *as<T14>( to_value ) = std::move( *as<T14>( from_value ) ); break;
        case 15: *as<T15>( to_value ) = std::move( *as<T15>( from_value ) ); break;
        
        }
        return from_index;
    }
#endif

    static type_index_t copy_construct( type_index_t const from_index, const void * from_value, void * to_value )
    {
        switch ( from_index )
        {
        case 0: new( to_value ) T0( *as<T0>( from_value ) ); break;
        case 1: new( to_value ) T1( *as<T1>( from_value ) ); break;
        case 2: new( to_value ) T2( *as<T2>( from_value ) ); break;
        case 3: new( to_value ) T3( *as<T3>( from_value ) ); break;
        case 4: new( to_value ) T4( *as<T4>( from_value ) ); break;
        case 5: new( to_value ) T5( *as<T5>( from_value ) ); break;
        case 6: new( to_value ) T6( *as<T6>( from_value ) ); break;
        case 7: new( to_value ) T7( *as<T7>( from_value ) ); break;
        case 8: new( to_value ) T8( *as<T8>( from_value ) ); break;
        case 9: new( to_value ) T9( *as<T9>( from_value ) ); break;
        case 10: new( to_value ) T10( *as<T10>( from_value ) ); break;
        case 11: new( to_value ) T11( *as<T11>( from_value ) ); break;
        case 12: new( to_value ) T12( *as<T12>( from_value ) ); break;
        case 13: new( to_value ) T13( *as<T13>( from_value ) ); break;
        case 14: new( to_value ) T14( *as<T14>( from_value ) ); break;
        case 15: new( to_value ) T15( *as<T15>( from_value ) ); break;
        
        }
        return from_index;
    }

    static type_index_t copy_assign( type_index_t const from_index, const void * from_value, void * to_value )
    {
        switch ( from_index )
        {
        case 0: *as<T0>( to_value ) = *as<T0>( from_value ); break;
        case 1: *as<T1>( to_value ) = *as<T1>( from_value ); break;
        case 2: *as<T2>( to_value ) = *as<T2>( from_value ); break;
        case 3: *as<T3>( to_value ) = *as<T3>( from_value ); break;
        case 4: *as<T4>( to_value ) = *as<T4>( from_value ); break;
        case 5: *as<T5>( to_value ) = *as<T5>( from_value ); break;
        case 6: *as<T6>( to_value ) = *as<T6>( from_value ); break;
        case 7: *as<T7>( to_value ) = *as<T7>( from_value ); break;
        case 8: *as<T8>( to_value ) = *as<T8>( from_value ); break;
        case 9: *as<T9>( to_value ) = *as<T9>( from_value ); break;
        case 10: *as<T10>( to_value ) = *as<T10>( from_value ); break;
        case 11: *as<T11>( to_value ) = *as<T11>( from_value ); break;
        case 12: *as<T12>( to_value ) = *as<T12>( from_value ); break;
        case 13: *as<T13>( to_value ) = *as<T13>( from_value ); break;
        case 14: *as<T14>( to_value ) = *as<T14>( from_value ); break;
        case 15: *as<T15>( to_value ) = *as<T15>( from_value ); break;
        
        }
        return from_index;
    }
};

} // namespace detail

//
// Variant:
//

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
class variant;

// 19.7.8 Class monostate

class monostate{};

// 19.7.9 monostate relational operators

inline variant_constexpr bool operator< ( monostate, monostate ) variant_noexcept { return false; }
inline variant_constexpr bool operator> ( monostate, monostate ) variant_noexcept { return false; }
inline variant_constexpr bool operator<=( monostate, monostate ) variant_noexcept { return true;  }
inline variant_constexpr bool operator>=( monostate, monostate ) variant_noexcept { return true;  }
inline variant_constexpr bool operator==( monostate, monostate ) variant_noexcept { return true;  }
inline variant_constexpr bool operator!=( monostate, monostate ) variant_noexcept { return false; }

// 19.7.4 variant helper classes

// obtain the size of the variant's list of alternatives at compile time

template< class T >
struct variant_size; /* undefined */

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
struct variant_size< variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >
{
    enum _ { value = detail::typelist_size< variant_TL16(T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15) >::value };
};

#if variant_CPP14_OR_GREATER
template< class T >
constexpr std::size_t variant_size_v = variant_size<T>::value;
#endif

#if ! variant_CONFIG_OMIT_VARIANT_SIZE_V_MACRO
# define variant_size_V(T)  nonstd::variant_size<T>::value
#endif

// obtain the type of the alternative specified by its index, at compile time:

template< std::size_t K, class T >
struct variant_alternative; /* undefined */

template< std::size_t K, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
struct variant_alternative< K, variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >
{
    typedef typename detail::typelist_type_at<variant_TL16(T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15), K>::type type;
};

#if variant_CPP11_OR_GREATER
template< std::size_t K, class T >
using variant_alternative_t = typename variant_alternative<K, T>::type;
#endif

#if ! variant_CONFIG_OMIT_VARIANT_ALTERNATIVE_T_MACRO
# define variant_alternative_T(K,T)  typename nonstd::variant_alternative<K,T >::type
#endif

// NTS:implement specializes the std::uses_allocator type trait
// std::uses_allocator<nonstd::variant>

// index of the variant in the invalid state (constant)

#if variant_CPP11_OR_GREATER
variant_constexpr std::size_t variant_npos = static_cast<std::size_t>( -1 );
#else
static const std::size_t variant_npos = static_cast<std::size_t>( -1 );
#endif

#if ! variant_CONFIG_NO_EXCEPTIONS

// 19.7.11 Class bad_variant_access

class bad_variant_access : public std::exception
{
public:
#if variant_CPP11_OR_GREATER
    virtual const char* what() const variant_noexcept variant_override
#else
    virtual const char* what() const throw()
#endif
    {
        return "bad variant access";
    }
};

#endif // variant_CONFIG_NO_EXCEPTIONS

// 19.7.3 Class template variant

template<
    class T0,
    class T1 = detail::T1,
    class T2 = detail::T2,
    class T3 = detail::T3,
    class T4 = detail::T4,
    class T5 = detail::T5,
    class T6 = detail::T6,
    class T7 = detail::T7,
    class T8 = detail::T8,
    class T9 = detail::T9,
    class T10 = detail::T10,
    class T11 = detail::T11,
    class T12 = detail::T12,
    class T13 = detail::T13,
    class T14 = detail::T14,
    class T15 = detail::T15
    >
class variant
{
    typedef detail::helper< T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15 > helper_type;
    typedef variant_TL16( T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15 ) variant_types;

public:
    // 19.7.3.1 Constructors
    
    variant() : type_index( 0 ) { new( ptr() ) T0(); }

    variant( T0 const & t0 ) : type_index( 0 ) { new( ptr() ) T0( t0 ); }
    variant( T1 const & t1 ) : type_index( 1 ) { new( ptr() ) T1( t1 ); }
    variant( T2 const & t2 ) : type_index( 2 ) { new( ptr() ) T2( t2 ); }
    variant( T3 const & t3 ) : type_index( 3 ) { new( ptr() ) T3( t3 ); }
    variant( T4 const & t4 ) : type_index( 4 ) { new( ptr() ) T4( t4 ); }
    variant( T5 const & t5 ) : type_index( 5 ) { new( ptr() ) T5( t5 ); }
    variant( T6 const & t6 ) : type_index( 6 ) { new( ptr() ) T6( t6 ); }
    variant( T7 const & t7 ) : type_index( 7 ) { new( ptr() ) T7( t7 ); }
    variant( T8 const & t8 ) : type_index( 8 ) { new( ptr() ) T8( t8 ); }
    variant( T9 const & t9 ) : type_index( 9 ) { new( ptr() ) T9( t9 ); }
    variant( T10 const & t10 ) : type_index( 10 ) { new( ptr() ) T10( t10 ); }
    variant( T11 const & t11 ) : type_index( 11 ) { new( ptr() ) T11( t11 ); }
    variant( T12 const & t12 ) : type_index( 12 ) { new( ptr() ) T12( t12 ); }
    variant( T13 const & t13 ) : type_index( 13 ) { new( ptr() ) T13( t13 ); }
    variant( T14 const & t14 ) : type_index( 14 ) { new( ptr() ) T14( t14 ); }
    variant( T15 const & t15 ) : type_index( 15 ) { new( ptr() ) T15( t15 ); }
    

#if variant_CPP11_OR_GREATER
    variant( T0 && t0 ) : type_index( 0 ) { new( ptr() ) T0( std::move(t0) ); }
    variant( T1 && t1 ) : type_index( 1 ) { new( ptr() ) T1( std::move(t1) ); }
    variant( T2 && t2 ) : type_index( 2 ) { new( ptr() ) T2( std::move(t2) ); }
    variant( T3 && t3 ) : type_index( 3 ) { new( ptr() ) T3( std::move(t3) ); }
    variant( T4 && t4 ) : type_index( 4 ) { new( ptr() ) T4( std::move(t4) ); }
    variant( T5 && t5 ) : type_index( 5 ) { new( ptr() ) T5( std::move(t5) ); }
    variant( T6 && t6 ) : type_index( 6 ) { new( ptr() ) T6( std::move(t6) ); }
    variant( T7 && t7 ) : type_index( 7 ) { new( ptr() ) T7( std::move(t7) ); }
    variant( T8 && t8 ) : type_index( 8 ) { new( ptr() ) T8( std::move(t8) ); }
    variant( T9 && t9 ) : type_index( 9 ) { new( ptr() ) T9( std::move(t9) ); }
    variant( T10 && t10 ) : type_index( 10 ) { new( ptr() ) T10( std::move(t10) ); }
    variant( T11 && t11 ) : type_index( 11 ) { new( ptr() ) T11( std::move(t11) ); }
    variant( T12 && t12 ) : type_index( 12 ) { new( ptr() ) T12( std::move(t12) ); }
    variant( T13 && t13 ) : type_index( 13 ) { new( ptr() ) T13( std::move(t13) ); }
    variant( T14 && t14 ) : type_index( 14 ) { new( ptr() ) T14( std::move(t14) ); }
    variant( T15 && t15 ) : type_index( 15 ) { new( ptr() ) T15( std::move(t15) ); }
    
#endif

    variant(variant const & other)
    : type_index( other.type_index )
    {
        (void) helper_type::copy_construct( other.type_index, other.ptr(), ptr() );
    }

#if variant_CPP11_OR_GREATER

    variant( variant && other ) noexcept(
        std::is_nothrow_move_constructible<T0>::value &&
        std::is_nothrow_move_constructible<T1>::value &&
        std::is_nothrow_move_constructible<T2>::value &&
        std::is_nothrow_move_constructible<T3>::value &&
        std::is_nothrow_move_constructible<T4>::value &&
        std::is_nothrow_move_constructible<T5>::value &&
        std::is_nothrow_move_constructible<T6>::value &&
        std::is_nothrow_move_constructible<T7>::value &&
        std::is_nothrow_move_constructible<T8>::value &&
        std::is_nothrow_move_constructible<T9>::value &&
        std::is_nothrow_move_constructible<T10>::value &&
        std::is_nothrow_move_constructible<T11>::value &&
        std::is_nothrow_move_constructible<T12>::value &&
        std::is_nothrow_move_constructible<T13>::value &&
        std::is_nothrow_move_constructible<T14>::value &&
        std::is_nothrow_move_constructible<T15>::value)
        : type_index( other.type_index )
    {
        (void) helper_type::move_construct( other.type_index, other.ptr(), ptr() );
    }

    template< std::size_t K >
    using type_at_t = typename detail::typelist_type_at< variant_types, K >::type;

    template< class T, class... Args
        variant_REQUIRES_T( std::is_constructible< T, Args...>::value )
    >
    explicit variant( nonstd_lite_in_place_type_t(T), Args&&... args)
    {
        type_index = variant_npos_internal();
        type_index = helper_type::template construct_t<T>( ptr(), std::forward<Args>(args)... );
    }

    template< class T, class U, class... Args
        variant_REQUIRES_T( std::is_constructible< T, std::initializer_list<U>&, Args...>::value )
    >
    explicit variant( nonstd_lite_in_place_type_t(T), std::initializer_list<U> il, Args&&... args )
    {
        type_index = variant_npos_internal();
        type_index = helper_type::template construct_t<T>( ptr(), il, std::forward<Args>(args)... );
    }

    template< std::size_t K, class... Args
        variant_REQUIRES_T( std::is_constructible< type_at_t<K>, Args...>::value )
    >
    explicit variant( nonstd_lite_in_place_index_t(K), Args&&... args )
    {
        type_index = variant_npos_internal();
        type_index = helper_type::template construct_i<K>( ptr(), std::forward<Args>(args)... );
    }

    template< size_t K, class U, class... Args
        variant_REQUIRES_T( std::is_constructible< type_at_t<K>, std::initializer_list<U>&, Args...>::value )
    >
    explicit variant( nonstd_lite_in_place_index_t(K), std::initializer_list<U> il, Args&&... args )
    {
        type_index = variant_npos_internal();
        type_index = helper_type::template construct_i<K>( ptr(), il, std::forward<Args>(args)... );
    }

#endif // variant_CPP11_OR_GREATER

    // 19.7.3.2 Destructor
    
    ~variant()
    {
        if ( ! valueless_by_exception() )
        {
            helper_type::destroy( type_index, ptr() );
        }
    }

    // 19.7.3.3 Assignment
    
    variant & operator=( variant const & other )
    {
        return copy_assign( other );
    }

#if variant_CPP11_OR_GREATER

    variant & operator=( variant && other ) noexcept(
        std::is_nothrow_move_assignable<T0>::value &&
        std::is_nothrow_move_assignable<T1>::value &&
        std::is_nothrow_move_assignable<T2>::value &&
        std::is_nothrow_move_assignable<T3>::value &&
        std::is_nothrow_move_assignable<T4>::value &&
        std::is_nothrow_move_assignable<T5>::value &&
        std::is_nothrow_move_assignable<T6>::value &&
        std::is_nothrow_move_assignable<T7>::value &&
        std::is_nothrow_move_assignable<T8>::value &&
        std::is_nothrow_move_assignable<T9>::value &&
        std::is_nothrow_move_assignable<T10>::value &&
        std::is_nothrow_move_assignable<T11>::value &&
        std::is_nothrow_move_assignable<T12>::value &&
        std::is_nothrow_move_assignable<T13>::value &&
        std::is_nothrow_move_assignable<T14>::value &&
        std::is_nothrow_move_assignable<T15>::value)
        {
        return move_assign( std::move( other ) );
    }

    variant & operator=( T0 &&      t0 ) { return assign_value<0>( std::move( t0 ) ); }
    variant & operator=( T1 &&      t1 ) { return assign_value<1>( std::move( t1 ) ); }
    variant & operator=( T2 &&      t2 ) { return assign_value<2>( std::move( t2 ) ); }
    variant & operator=( T3 &&      t3 ) { return assign_value<3>( std::move( t3 ) ); }
    variant & operator=( T4 &&      t4 ) { return assign_value<4>( std::move( t4 ) ); }
    variant & operator=( T5 &&      t5 ) { return assign_value<5>( std::move( t5 ) ); }
    variant & operator=( T6 &&      t6 ) { return assign_value<6>( std::move( t6 ) ); }
    variant & operator=( T7 &&      t7 ) { return assign_value<7>( std::move( t7 ) ); }
    variant & operator=( T8 &&      t8 ) { return assign_value<8>( std::move( t8 ) ); }
    variant & operator=( T9 &&      t9 ) { return assign_value<9>( std::move( t9 ) ); }
    variant & operator=( T10 &&      t10 ) { return assign_value<10>( std::move( t10 ) ); }
    variant & operator=( T11 &&      t11 ) { return assign_value<11>( std::move( t11 ) ); }
    variant & operator=( T12 &&      t12 ) { return assign_value<12>( std::move( t12 ) ); }
    variant & operator=( T13 &&      t13 ) { return assign_value<13>( std::move( t13 ) ); }
    variant & operator=( T14 &&      t14 ) { return assign_value<14>( std::move( t14 ) ); }
    variant & operator=( T15 &&      t15 ) { return assign_value<15>( std::move( t15 ) ); }
    

#endif

    variant & operator=( T0 const & t0 ) { return assign_value<0>( t0 ); }
    variant & operator=( T1 const & t1 ) { return assign_value<1>( t1 ); }
    variant & operator=( T2 const & t2 ) { return assign_value<2>( t2 ); }
    variant & operator=( T3 const & t3 ) { return assign_value<3>( t3 ); }
    variant & operator=( T4 const & t4 ) { return assign_value<4>( t4 ); }
    variant & operator=( T5 const & t5 ) { return assign_value<5>( t5 ); }
    variant & operator=( T6 const & t6 ) { return assign_value<6>( t6 ); }
    variant & operator=( T7 const & t7 ) { return assign_value<7>( t7 ); }
    variant & operator=( T8 const & t8 ) { return assign_value<8>( t8 ); }
    variant & operator=( T9 const & t9 ) { return assign_value<9>( t9 ); }
    variant & operator=( T10 const & t10 ) { return assign_value<10>( t10 ); }
    variant & operator=( T11 const & t11 ) { return assign_value<11>( t11 ); }
    variant & operator=( T12 const & t12 ) { return assign_value<12>( t12 ); }
    variant & operator=( T13 const & t13 ) { return assign_value<13>( t13 ); }
    variant & operator=( T14 const & t14 ) { return assign_value<14>( t14 ); }
    variant & operator=( T15 const & t15 ) { return assign_value<15>( t15 ); }
    

    std::size_t index() const
    {
        return variant_npos_internal() == type_index ? variant_npos : static_cast<std::size_t>( type_index );
    }

    // 19.7.3.4 Modifiers
    
#if variant_CPP11_OR_GREATER
    template< class T, class... Args
        variant_REQUIRES_T( std::is_constructible< T, Args...>::value )
    >
    T& emplace( Args&&... args )
    {
        helper_type::destroy( type_index, ptr() );
        type_index = variant_npos_internal();
        type_index = helper_type::template construct_t<T>( ptr(), std::forward<Args>(args)... );

        return *as<T>();
    }

    template< class T, class U, class... Args
        variant_REQUIRES_T( std::is_constructible< T, std::initializer_list<U>&, Args...>::value )
    >
    T& emplace( std::initializer_list<U> il, Args&&... args )
    {
        helper_type::destroy( type_index, ptr() );
        type_index = variant_npos_internal();
        type_index = helper_type::template construct_t<T>( ptr(), il, std::forward<Args>(args)... );

        return *as<T>();
    }

    template< size_t K, class... Args
        variant_REQUIRES_T( std::is_constructible< type_at_t<K>, Args...>::value )
    >
    variant_alternative_t<K, variant> & emplace( Args&&... args )
    {
        return this->template emplace< type_at_t<K> >( std::forward<Args>(args)... );
    }

    template< size_t K, class U, class... Args
        variant_REQUIRES_T( std::is_constructible< type_at_t<K>, std::initializer_list<U>&, Args...>::value )
    >
    variant_alternative_t<K, variant> & emplace( std::initializer_list<U> il, Args&&... args )
    {
        return this->template emplace< type_at_t<K> >( il, std::forward<Args>(args)... );
    }

#endif // variant_CPP11_OR_GREATER

    // 19.7.3.5 Value status
    
    bool valueless_by_exception() const
    {
        return type_index == variant_npos_internal();
    }

    // 19.7.3.6 Swap
    
    void swap( variant & other )
#if variant_CPP11_OR_GREATER
        noexcept(
            std::is_nothrow_move_constructible<T0>::value && std17::is_nothrow_swappable<T0>::value &&
            std::is_nothrow_move_constructible<T1>::value && std17::is_nothrow_swappable<T1>::value &&
            std::is_nothrow_move_constructible<T2>::value && std17::is_nothrow_swappable<T2>::value &&
            std::is_nothrow_move_constructible<T3>::value && std17::is_nothrow_swappable<T3>::value &&
            std::is_nothrow_move_constructible<T4>::value && std17::is_nothrow_swappable<T4>::value &&
            std::is_nothrow_move_constructible<T5>::value && std17::is_nothrow_swappable<T5>::value &&
            std::is_nothrow_move_constructible<T6>::value && std17::is_nothrow_swappable<T6>::value &&
            std::is_nothrow_move_constructible<T7>::value && std17::is_nothrow_swappable<T7>::value &&
            std::is_nothrow_move_constructible<T8>::value && std17::is_nothrow_swappable<T8>::value &&
            std::is_nothrow_move_constructible<T9>::value && std17::is_nothrow_swappable<T9>::value &&
            std::is_nothrow_move_constructible<T10>::value && std17::is_nothrow_swappable<T10>::value &&
            std::is_nothrow_move_constructible<T11>::value && std17::is_nothrow_swappable<T11>::value &&
            std::is_nothrow_move_constructible<T12>::value && std17::is_nothrow_swappable<T12>::value &&
            std::is_nothrow_move_constructible<T13>::value && std17::is_nothrow_swappable<T13>::value &&
            std::is_nothrow_move_constructible<T14>::value && std17::is_nothrow_swappable<T14>::value &&
            std::is_nothrow_move_constructible<T15>::value && std17::is_nothrow_swappable<T15>::value 
            
        )
#endif
    {
        if ( valueless_by_exception() && other.valueless_by_exception() )
        {
            // no effect
        }
        else if ( type_index == other.type_index )
        {
            this->swap_value( type_index, other );
        }
        else
        {
#if variant_CPP11_OR_GREATER
            variant tmp( std::move( *this ) );
            *this = std::move( other );
            other = std::move( tmp );
#else
            variant tmp( *this );
            *this = other;
            other = tmp;
#endif
        }
    }

    //
    // non-standard:
    //

    template< class T >
    static variant_constexpr std::size_t index_of() variant_noexcept
    {
        return to_size_t( detail::typelist_index_of<variant_types, typename std11::remove_cv<T>::type >::value );
    }

    template< class T >
    T & get()
    {
        const std::size_t i = index_of<T>();

#if variant_CONFIG_NO_EXCEPTIONS
        assert( i == index() );
#else
        if ( i != index() )
        {
            throw bad_variant_access();
        }
#endif
        return *as<T>();
    }

    template< class T >
    T const & get() const
    {
        const std::size_t i = index_of<T>();

#if variant_CONFIG_NO_EXCEPTIONS
        assert( i == index() );
#else
        if ( i != index() )
        {
            throw bad_variant_access();
        }
#endif
        return *as<const T>();
    }

    template< std::size_t K >
    typename variant_alternative< K, variant >::type &
    get()
    {
        return this->template get< typename detail::typelist_type_at< variant_types, K >::type >();
    }

    template< std::size_t K >
    typename variant_alternative< K, variant >::type const &
    get() const
    {
        return this->template get< typename detail::typelist_type_at< variant_types, K >::type >();
    }

private:
    typedef typename helper_type::type_index_t type_index_t;

    void * ptr() variant_noexcept
    {
        return &data;
    }

    void const * ptr() const variant_noexcept
    {
        return &data;
    }

    template< class U >
    U * as()
    {
        return reinterpret_cast<U*>( ptr() );
    }

    template< class U >
    U const * as() const
    {
        return reinterpret_cast<U const *>( ptr() );
    }

    template< class U >
    static variant_constexpr std::size_t to_size_t( U index )
    {
        return static_cast<std::size_t>( index );
    }

    variant_constexpr type_index_t variant_npos_internal() const variant_noexcept
    {
        return static_cast<type_index_t>( -1 );
    }

    variant & copy_assign( variant const & other )
    {
        if ( valueless_by_exception() && other.valueless_by_exception() )
        {
            // no effect
        }
        else if ( ! valueless_by_exception() && other.valueless_by_exception() )
        {
            helper_type::destroy( type_index, ptr() );
            type_index = variant_npos_internal();
        }
        else if ( index() == other.index() )
        {
            type_index = helper_type::copy_assign( other.type_index, other.ptr(), ptr() );
        }
        else
        {
            helper_type::destroy( type_index, ptr() );
            type_index = variant_npos_internal();
            type_index = helper_type::copy_construct( other.type_index, other.ptr(), ptr() );
        }
        return *this;
    }

#if variant_CPP11_OR_GREATER

    variant & move_assign( variant && other )
    {
        if ( valueless_by_exception() && other.valueless_by_exception() )
        {
            // no effect
        }
        else if ( ! valueless_by_exception() && other.valueless_by_exception() )
        {
            helper_type::destroy( type_index, ptr() );
            type_index = variant_npos_internal();
        }
        else if ( index() == other.index() )
        {
            type_index = helper_type::move_assign( other.type_index, other.ptr(), ptr() );
        }
        else
        {
            helper_type::destroy( type_index, ptr() );
            type_index = variant_npos_internal();
            type_index = helper_type::move_construct( other.type_index, other.ptr(), ptr() );
        }
        return *this;
    }

    template< std::size_t K, class T >
    variant & assign_value( T && value )
    {
        if( index() == K )
        {
            *as<T>() = std::forward<T>( value );
        }
        else
        {
            helper_type::destroy( type_index, ptr() );
            type_index = variant_npos_internal();
            new( ptr() ) T( std::forward<T>( value ) );
            type_index = K;
        }
        return *this;
    }

#endif // variant_CPP11_OR_GREATER

    template< std::size_t K, class T >
    variant & assign_value( T const & value )
    {
        if( index() == K )
        {
            *as<T>() = value;
        }
        else
        {
            helper_type::destroy( type_index, ptr() );
            type_index = variant_npos_internal();
            new( ptr() ) T( value );
            type_index = K;
        }
        return *this;
    }

    void swap_value( type_index_t index, variant & other )
    {
        using std::swap;
        switch( index )
        {
            case 0: swap( this->get<0>(), other.get<0>() ); break;
            case 1: swap( this->get<1>(), other.get<1>() ); break;
            case 2: swap( this->get<2>(), other.get<2>() ); break;
            case 3: swap( this->get<3>(), other.get<3>() ); break;
            case 4: swap( this->get<4>(), other.get<4>() ); break;
            case 5: swap( this->get<5>(), other.get<5>() ); break;
            case 6: swap( this->get<6>(), other.get<6>() ); break;
            case 7: swap( this->get<7>(), other.get<7>() ); break;
            case 8: swap( this->get<8>(), other.get<8>() ); break;
            case 9: swap( this->get<9>(), other.get<9>() ); break;
            case 10: swap( this->get<10>(), other.get<10>() ); break;
            case 11: swap( this->get<11>(), other.get<11>() ); break;
            case 12: swap( this->get<12>(), other.get<12>() ); break;
            case 13: swap( this->get<13>(), other.get<13>() ); break;
            case 14: swap( this->get<14>(), other.get<14>() ); break;
            case 15: swap( this->get<15>(), other.get<15>() ); break;
            
        }
    }

private:
    enum { data_size  = detail::typelist_max< variant_types >::value };

#if variant_CPP11_OR_GREATER

    enum { data_align = detail::typelist_max_alignof< variant_types >::value };

    using aligned_storage_t = typename std::aligned_storage< data_size, data_align >::type;
    aligned_storage_t data;

#elif variant_CONFIG_MAX_ALIGN_HACK

    typedef union { unsigned char data[ data_size ]; } aligned_storage_t;

    detail::max_align_t hack;
    aligned_storage_t data;

#else
    typedef typename detail::typelist_max< variant_types >::type max_type;

    typedef variant_ALIGN_AS( max_type ) align_as_type;

    typedef union { align_as_type data[ 1 + ( data_size - 1 ) / sizeof(align_as_type) ]; } aligned_storage_t;
    aligned_storage_t data;

// #   undef variant_ALIGN_AS

#endif // variant_CONFIG_MAX_ALIGN_HACK

    type_index_t type_index;
};

// 19.7.5 Value access

template< class T, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline bool holds_alternative( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v ) variant_noexcept
{
    return v.index() == variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15>::template index_of<T>();
}

template< class R, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline R & get( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> & v, nonstd_lite_in_place_type_t(R) = nonstd_lite_in_place_type(R) )
{
    return v.template get<R>();
}

template< class R, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline R const & get( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v, nonstd_lite_in_place_type_t(R) = nonstd_lite_in_place_type(R) )
{
    return v.template get<R>();
}

template< std::size_t K, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline typename variant_alternative< K, variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >::type &
get( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> & v, nonstd_lite_in_place_index_t(K) = nonstd_lite_in_place_index(K) )
{
#if variant_CONFIG_NO_EXCEPTIONS
    assert( K == v.index() );
#else
    if ( K != v.index() )
    {
        throw bad_variant_access();
    }
#endif
    return v.template get<K>();
}

template< std::size_t K, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline typename variant_alternative< K, variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >::type const &
get( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v, nonstd_lite_in_place_index_t(K) = nonstd_lite_in_place_index(K) )
{
#if variant_CONFIG_NO_EXCEPTIONS
    assert( K == v.index() );
#else
    if ( K != v.index() )
    {
        throw bad_variant_access();
    }
#endif
    return v.template get<K>();
}

#if variant_CPP11_OR_GREATER

template< class R, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline R && get( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> && v, nonstd_lite_in_place_type_t(R) = nonstd_lite_in_place_type(R) )
{
    return std::move(v.template get<R>());
}

template< class R, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline R const && get( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const && v, nonstd_lite_in_place_type_t(R) = nonstd_lite_in_place_type(R) )
{
    return std::move(v.template get<R>());
}

template< std::size_t K, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline typename variant_alternative< K, variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >::type &&
get( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> && v, nonstd_lite_in_place_index_t(K) = nonstd_lite_in_place_index(K) )
{
#if variant_CONFIG_NO_EXCEPTIONS
    assert( K == v.index() );
#else
    if ( K != v.index() )
    {
        throw bad_variant_access();
    }
#endif
    return std::move(v.template get<K>());
}

template< std::size_t K, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline typename variant_alternative< K, variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >::type const &&
get( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const && v, nonstd_lite_in_place_index_t(K) = nonstd_lite_in_place_index(K) )
{
#if variant_CONFIG_NO_EXCEPTIONS
    assert( K == v.index() );
#else
    if ( K != v.index() )
    {
        throw bad_variant_access();
    }
#endif
    return std::move(v.template get<K>());
}

#endif // variant_CPP11_OR_GREATER

template< class T, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline typename std11::add_pointer<T>::type
get_if( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> * pv, nonstd_lite_in_place_type_t(T) = nonstd_lite_in_place_type(T) )
{
    return ( pv->index() == variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15>::template index_of<T>() ) ? &get<T>( *pv ) : variant_nullptr;
}

template< class T, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline typename std11::add_pointer<const T>::type
get_if( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const * pv, nonstd_lite_in_place_type_t(T) = nonstd_lite_in_place_type(T))
{
    return ( pv->index() == variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15>::template index_of<T>() ) ? &get<T>( *pv ) : variant_nullptr;
}

template< std::size_t K, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline typename std11::add_pointer< typename variant_alternative<K, variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >::type >::type
get_if( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> * pv, nonstd_lite_in_place_index_t(K) = nonstd_lite_in_place_index(K) )
{
    return ( pv->index() == K ) ? &get<K>( *pv ) : variant_nullptr;
}

template< std::size_t K, class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline typename std11::add_pointer< const typename variant_alternative<K, variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >::type >::type
get_if( variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const * pv, nonstd_lite_in_place_index_t(K) = nonstd_lite_in_place_index(K) )
{
    return ( pv->index() == K ) ? &get<K>( *pv )  : variant_nullptr;
}

// 19.7.10 Specialized algorithms

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15
#if variant_CPP11_OR_GREATER
    variant_REQUIRES_T(
        std::is_move_constructible<T0>::value && std17::is_swappable<T0>::value &&
        std::is_move_constructible<T1>::value && std17::is_swappable<T1>::value &&
        std::is_move_constructible<T2>::value && std17::is_swappable<T2>::value &&
        std::is_move_constructible<T3>::value && std17::is_swappable<T3>::value &&
        std::is_move_constructible<T4>::value && std17::is_swappable<T4>::value &&
        std::is_move_constructible<T5>::value && std17::is_swappable<T5>::value &&
        std::is_move_constructible<T6>::value && std17::is_swappable<T6>::value &&
        std::is_move_constructible<T7>::value && std17::is_swappable<T7>::value &&
        std::is_move_constructible<T8>::value && std17::is_swappable<T8>::value &&
        std::is_move_constructible<T9>::value && std17::is_swappable<T9>::value &&
        std::is_move_constructible<T10>::value && std17::is_swappable<T10>::value &&
        std::is_move_constructible<T11>::value && std17::is_swappable<T11>::value &&
        std::is_move_constructible<T12>::value && std17::is_swappable<T12>::value &&
        std::is_move_constructible<T13>::value && std17::is_swappable<T13>::value &&
        std::is_move_constructible<T14>::value && std17::is_swappable<T14>::value &&
        std::is_move_constructible<T15>::value && std17::is_swappable<T15>::value 
         )
#endif
>
inline void swap(
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> & a,
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> & b ) 
#if variant_CPP11_OR_GREATER
    noexcept( noexcept( a.swap( b ) ) )
#endif
{
    a.swap( b );
}

// 19.7.7 Visitation

// Variant 'visitor' implementation

namespace detail
{

template< typename R, typename VT >
struct VisitorApplicatorImpl
{
    template< typename Visitor, typename T >
    static R apply(Visitor const& v, T const& arg)
    {
        return v(arg);
    }
};

template< typename R, typename VT >
struct VisitorApplicatorImpl<R, TX<VT> >
{
    template< typename Visitor, typename T >
    static R apply(Visitor const&, T)
    {
        return R();
    }
};

template<typename R>
struct VisitorApplicator;

template< typename R, typename Visitor, typename V1 >
struct VisitorUnwrapper;

#if variant_CPP11_OR_GREATER
template< size_t NumVars, typename R, typename Visitor, typename ... T >
#else
template< size_t NumVars, typename R, typename Visitor, typename T1, typename T2 = S0, typename T3 = S0, typename T4 = S0, typename T5 = S0 >
#endif
struct TypedVisitorUnwrapper;

template< typename R, typename Visitor, typename T2 >
struct TypedVisitorUnwrapper<2, R, Visitor, T2>
{
    const Visitor& visitor;
    T2 const& val2;
    
    TypedVisitorUnwrapper(const Visitor& visitor_, T2 const& val2_)
        : visitor(visitor_)
        , val2(val2_)
        
    {
    }

    template<typename T>
    R operator()(const T& val1) const
    {
        return visitor(val1, val2);
    }
};

template< typename R, typename Visitor, typename T2, typename T3 >
struct TypedVisitorUnwrapper<3, R, Visitor, T2, T3>
{
    const Visitor& visitor;
    T2 const& val2;
    T3 const& val3;
    
    TypedVisitorUnwrapper(const Visitor& visitor_, T2 const& val2_, T3 const& val3_)
        : visitor(visitor_)
        , val2(val2_)
        , val3(val3_)
        
    {
    }

    template<typename T>
    R operator()(const T& val1) const
    {
        return visitor(val1, val2, val3);
    }
};

template< typename R, typename Visitor, typename T2, typename T3, typename T4 >
struct TypedVisitorUnwrapper<4, R, Visitor, T2, T3, T4>
{
    const Visitor& visitor;
    T2 const& val2;
    T3 const& val3;
    T4 const& val4;
    
    TypedVisitorUnwrapper(const Visitor& visitor_, T2 const& val2_, T3 const& val3_, T4 const& val4_)
        : visitor(visitor_)
        , val2(val2_)
        , val3(val3_)
        , val4(val4_)
        
    {
    }

    template<typename T>
    R operator()(const T& val1) const
    {
        return visitor(val1, val2, val3, val4);
    }
};

template< typename R, typename Visitor, typename T2, typename T3, typename T4, typename T5 >
struct TypedVisitorUnwrapper<5, R, Visitor, T2, T3, T4, T5>
{
    const Visitor& visitor;
    T2 const& val2;
    T3 const& val3;
    T4 const& val4;
    T5 const& val5;
    
    TypedVisitorUnwrapper(const Visitor& visitor_, T2 const& val2_, T3 const& val3_, T4 const& val4_, T5 const& val5_)
        : visitor(visitor_)
        , val2(val2_)
        , val3(val3_)
        , val4(val4_)
        , val5(val5_)
        
    {
    }

    template<typename T>
    R operator()(const T& val1) const
    {
        return visitor(val1, val2, val3, val4, val5);
    }
};



template<typename R, typename Visitor, typename V2>
struct VisitorUnwrapper
{
    const Visitor& visitor;
    const V2& r;

    VisitorUnwrapper(const Visitor& visitor_, const V2& r_)
        : visitor(visitor_)
        , r(r_)
    {
    }

    
    template< typename T1 >
    R operator()(T1 const& val1) const
    {
        typedef TypedVisitorUnwrapper<2, R, Visitor, T1> visitor_type;
        return VisitorApplicator<R>::apply(visitor_type(visitor, val1), r);
    }
    
    template< typename T1, typename T2 >
    R operator()(T1 const& val1, T2 const& val2) const
    {
        typedef TypedVisitorUnwrapper<3, R, Visitor, T1, T2> visitor_type;
        return VisitorApplicator<R>::apply(visitor_type(visitor, val1, val2), r);
    }
    
    template< typename T1, typename T2, typename T3 >
    R operator()(T1 const& val1, T2 const& val2, T3 const& val3) const
    {
        typedef TypedVisitorUnwrapper<4, R, Visitor, T1, T2, T3> visitor_type;
        return VisitorApplicator<R>::apply(visitor_type(visitor, val1, val2, val3), r);
    }
    
    template< typename T1, typename T2, typename T3, typename T4 >
    R operator()(T1 const& val1, T2 const& val2, T3 const& val3, T4 const& val4) const
    {
        typedef TypedVisitorUnwrapper<5, R, Visitor, T1, T2, T3, T4> visitor_type;
        return VisitorApplicator<R>::apply(visitor_type(visitor, val1, val2, val3, val4), r);
    }
    
    template< typename T1, typename T2, typename T3, typename T4, typename T5 >
    R operator()(T1 const& val1, T2 const& val2, T3 const& val3, T4 const& val4, T5 const& val5) const
    {
        typedef TypedVisitorUnwrapper<6, R, Visitor, T1, T2, T3, T4, T5> visitor_type;
        return VisitorApplicator<R>::apply(visitor_type(visitor, val1, val2, val3, val4, val5), r);
    }
    
};


template<typename R>
struct VisitorApplicator
{
    template<typename Visitor, typename V1>
    static R apply(const Visitor& v, const V1& arg)
    {
        switch( arg.index() )
        {
            case 0: return apply_visitor<0>(v, arg);
            case 1: return apply_visitor<1>(v, arg);
            case 2: return apply_visitor<2>(v, arg);
            case 3: return apply_visitor<3>(v, arg);
            case 4: return apply_visitor<4>(v, arg);
            case 5: return apply_visitor<5>(v, arg);
            case 6: return apply_visitor<6>(v, arg);
            case 7: return apply_visitor<7>(v, arg);
            case 8: return apply_visitor<8>(v, arg);
            case 9: return apply_visitor<9>(v, arg);
            case 10: return apply_visitor<10>(v, arg);
            case 11: return apply_visitor<11>(v, arg);
            case 12: return apply_visitor<12>(v, arg);
            case 13: return apply_visitor<13>(v, arg);
            case 14: return apply_visitor<14>(v, arg);
            case 15: return apply_visitor<15>(v, arg);
            
            default: return R();
        }
    }

    template<size_t Idx, typename Visitor, typename V1>
    static R apply_visitor(const Visitor& v, const V1& arg)
    {

#if variant_CPP11_OR_GREATER
        typedef typename variant_alternative<Idx, typename std::decay<V1>::type>::type value_type;
#else
        typedef typename variant_alternative<Idx, V1>::type value_type;
#endif
        return VisitorApplicatorImpl<R, value_type>::apply(v, get<Idx>(arg));
    }

#if variant_CPP11_OR_GREATER
    template<typename Visitor, typename V1, typename V2, typename ... V>
    static R apply(const Visitor& v, const V1& arg1, const V2& arg2, const V ... args)
    {
        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
        Unwrapper unwrapper(v, arg1);
        return apply(unwrapper, arg2, args ...);
    }
#else
    
    template< typename Visitor, typename V1, typename V2 >
    static R apply(const Visitor& v, V1 const& arg1, V2 const& arg2)
    {
        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
        Unwrapper unwrapper(v, arg1);
        return apply(unwrapper, arg2);
    }
    
    template< typename Visitor, typename V1, typename V2, typename V3 >
    static R apply(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3)
    {
        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
        Unwrapper unwrapper(v, arg1);
        return apply(unwrapper, arg2, arg3);
    }
    
    template< typename Visitor, typename V1, typename V2, typename V3, typename V4 >
    static R apply(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3, V4 const& arg4)
    {
        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
        Unwrapper unwrapper(v, arg1);
        return apply(unwrapper, arg2, arg3, arg4);
    }
    
    template< typename Visitor, typename V1, typename V2, typename V3, typename V4, typename V5 >
    static R apply(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3, V4 const& arg4, V5 const& arg5)
    {
        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
        Unwrapper unwrapper(v, arg1);
        return apply(unwrapper, arg2, arg3, arg4, arg5);
    }
    
#endif
};

#if variant_CPP11_OR_GREATER
template< size_t NumVars, typename Visitor, typename ... V >
struct VisitorImpl
{
    typedef decltype(std::declval<Visitor>()(get<0>(static_cast<const V&>(std::declval<V>()))...)) result_type;
    typedef VisitorApplicator<result_type> applicator_type;
};
#endif
} // detail

#if variant_CPP11_OR_GREATER
// No perfect forwarding here in order to simplify code
template< typename Visitor, typename ... V >
inline auto visit(Visitor const& v, V const& ... vars) -> typename detail::VisitorImpl<sizeof ... (V), Visitor, V... > ::result_type
{
    typedef detail::VisitorImpl<sizeof ... (V), Visitor, V... > impl_type;
    return impl_type::applicator_type::apply(v, vars...);
}
#else

template< typename R, typename Visitor, typename V1 >
inline R visit(const Visitor& v, V1 const& arg1)
{
    return detail::VisitorApplicator<R>::apply(v, arg1);
}

template< typename R, typename Visitor, typename V1, typename V2 >
inline R visit(const Visitor& v, V1 const& arg1, V2 const& arg2)
{
    return detail::VisitorApplicator<R>::apply(v, arg1, arg2);
}

template< typename R, typename Visitor, typename V1, typename V2, typename V3 >
inline R visit(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3)
{
    return detail::VisitorApplicator<R>::apply(v, arg1, arg2, arg3);
}

template< typename R, typename Visitor, typename V1, typename V2, typename V3, typename V4 >
inline R visit(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3, V4 const& arg4)
{
    return detail::VisitorApplicator<R>::apply(v, arg1, arg2, arg3, arg4);
}

template< typename R, typename Visitor, typename V1, typename V2, typename V3, typename V4, typename V5 >
inline R visit(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3, V4 const& arg4, V5 const& arg5)
{
    return detail::VisitorApplicator<R>::apply(v, arg1, arg2, arg3, arg4, arg5);
}

#endif

// 19.7.6 Relational operators

namespace detail {

template< class Variant >
struct Comparator
{
    static inline bool equal( Variant const & v, Variant const & w )
    {
        switch( v.index() )
        {
            case 0: return get<0>( v ) == get<0>( w );
            case 1: return get<1>( v ) == get<1>( w );
            case 2: return get<2>( v ) == get<2>( w );
            case 3: return get<3>( v ) == get<3>( w );
            case 4: return get<4>( v ) == get<4>( w );
            case 5: return get<5>( v ) == get<5>( w );
            case 6: return get<6>( v ) == get<6>( w );
            case 7: return get<7>( v ) == get<7>( w );
            case 8: return get<8>( v ) == get<8>( w );
            case 9: return get<9>( v ) == get<9>( w );
            case 10: return get<10>( v ) == get<10>( w );
            case 11: return get<11>( v ) == get<11>( w );
            case 12: return get<12>( v ) == get<12>( w );
            case 13: return get<13>( v ) == get<13>( w );
            case 14: return get<14>( v ) == get<14>( w );
            case 15: return get<15>( v ) == get<15>( w );
            
            default: return false;
        }
    }

    static inline bool less_than( Variant const & v, Variant const & w )
    {
        switch( v.index() )
        {
            case 0: return get<0>( v ) < get<0>( w );
            case 1: return get<1>( v ) < get<1>( w );
            case 2: return get<2>( v ) < get<2>( w );
            case 3: return get<3>( v ) < get<3>( w );
            case 4: return get<4>( v ) < get<4>( w );
            case 5: return get<5>( v ) < get<5>( w );
            case 6: return get<6>( v ) < get<6>( w );
            case 7: return get<7>( v ) < get<7>( w );
            case 8: return get<8>( v ) < get<8>( w );
            case 9: return get<9>( v ) < get<9>( w );
            case 10: return get<10>( v ) < get<10>( w );
            case 11: return get<11>( v ) < get<11>( w );
            case 12: return get<12>( v ) < get<12>( w );
            case 13: return get<13>( v ) < get<13>( w );
            case 14: return get<14>( v ) < get<14>( w );
            case 15: return get<15>( v ) < get<15>( w );
            
            default: return false;
        }
    }
};

} //namespace detail

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline bool operator==(
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v,
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & w )
{
    if      ( v.index() != w.index()     ) return false;
    else if ( v.valueless_by_exception() ) return true;
    else                                   return detail::Comparator< variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >::equal( v, w );
}

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline bool operator!=(
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v,
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & w )
{
    return ! ( v == w );
}

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline bool operator<(
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v,
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & w )
{
    if      ( w.valueless_by_exception() ) return false;
    else if ( v.valueless_by_exception() ) return true;
    else if ( v.index() < w.index()      ) return true;
    else if ( v.index() > w.index()      ) return false;
    else                                   return detail::Comparator< variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >::less_than( v, w );
}

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline bool operator>(
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v,
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & w )
{
    return w < v;
}

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline bool operator<=(
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v,
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & w )
{
    return ! ( v > w );
}

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
inline bool operator>=(
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v,
    variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & w )
{
    return ! ( v < w );
}

} // namespace variants

using namespace variants;

} // namespace nonstd

#if variant_CPP11_OR_GREATER

// 19.7.12 Hash support

namespace std {

template<>
struct hash< nonstd::monostate >
{
    std::size_t operator()( nonstd::monostate ) const variant_noexcept
    {
        return 42;
    }
};

template< class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8, class T9, class T10, class T11, class T12, class T13, class T14, class T15 >
struct hash< nonstd::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> >
{
    std::size_t operator()( nonstd::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> const & v ) const variant_noexcept
    {
        namespace nvd = nonstd::variants::detail;

        switch( v.index() )
        {
            case 0: return nvd::hash( 0 ) ^ nvd::hash( get<0>( v ) );
            case 1: return nvd::hash( 1 ) ^ nvd::hash( get<1>( v ) );
            case 2: return nvd::hash( 2 ) ^ nvd::hash( get<2>( v ) );
            case 3: return nvd::hash( 3 ) ^ nvd::hash( get<3>( v ) );
            case 4: return nvd::hash( 4 ) ^ nvd::hash( get<4>( v ) );
            case 5: return nvd::hash( 5 ) ^ nvd::hash( get<5>( v ) );
            case 6: return nvd::hash( 6 ) ^ nvd::hash( get<6>( v ) );
            case 7: return nvd::hash( 7 ) ^ nvd::hash( get<7>( v ) );
            case 8: return nvd::hash( 8 ) ^ nvd::hash( get<8>( v ) );
            case 9: return nvd::hash( 9 ) ^ nvd::hash( get<9>( v ) );
            case 10: return nvd::hash( 10 ) ^ nvd::hash( get<10>( v ) );
            case 11: return nvd::hash( 11 ) ^ nvd::hash( get<11>( v ) );
            case 12: return nvd::hash( 12 ) ^ nvd::hash( get<12>( v ) );
            case 13: return nvd::hash( 13 ) ^ nvd::hash( get<13>( v ) );
            case 14: return nvd::hash( 14 ) ^ nvd::hash( get<14>( v ) );
            case 15: return nvd::hash( 15 ) ^ nvd::hash( get<15>( v ) );
            
            default: return false;
        }
    }
};

} //namespace std

#endif // variant_CPP11_OR_GREATER

#if variant_BETWEEN( variant_COMPILER_MSVC_VER, 1300, 1900 )
# pragma warning( pop )
#endif

#endif // variant_USES_STD_VARIANT

#endif // NONSTD_VARIANT_LITE_HPP