diff --git a/COPYING.md b/COPYING.md
index bdcb0e3..9c4cb03 100644
--- a/COPYING.md
+++ b/COPYING.md
@@ -18,9 +18,6 @@
 - span-lite by Martin Moene is licensed under the
   [Boost Software License 1.0](https://github.com/martinmoene/span-lite/blob/master/LICENSE.txt)
 
-- variant-lite by Martin Moene is licensed under the
-  [Boost Software License 1.0](https://github.com/martinmoene/variant-lite/blob/master/LICENSE.txt)
-
 - SQLite is in the [public domain](https://www.sqlite.org/copyright.html)
 
 - The waf build system is licensed under the terms of the
diff --git a/ndn-cxx/detail/nonstd/variant-lite.hpp b/ndn-cxx/detail/nonstd/variant-lite.hpp
deleted file mode 100644
index 05a8cd9..0000000
--- a/ndn-cxx/detail/nonstd/variant-lite.hpp
+++ /dev/null
@@ -1,2742 +0,0 @@
-// 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  2
-#define variant_lite_MINOR  0
-#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
-
-// tweak header support:
-
-#ifdef __has_include
-# if __has_include(<nonstd/variant.tweak.hpp>)
-#  include <nonstd/variant.tweak.hpp>
-# endif
-#define variant_HAVE_TWEAK_HEADER  1
-#else
-#define variant_HAVE_TWEAK_HEADER  0
-//# pragma message("variant.hpp: Note: Tweak header not supported.")
-#endif
-
-// variant selection and configuration:
-
-#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 _MSC_VER
-#  include <cstddef>    // for _HAS_EXCEPTIONS
-# endif
-# if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || (_HAS_EXCEPTIONS)
-#  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
-
-#if !defined( variant_CONFIG_SELECT_VARIANT )
-# define variant_CONFIG_SELECT_VARIANT  ( variant_HAVE_STD_VARIANT ? variant_VARIANT_STD : variant_VARIANT_NONSTD )
-#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
-
-// in_place_index-like disambiguation tag identical for all C++ versions:
-
-namespace nonstd {
-namespace variants {
-namespace detail {
-
-template< std::size_t K >
-struct index_tag_t {};
-
-template< std::size_t K >
-inline void index_tag ( index_tag_t<K> = index_tag_t<K>() ) { }
-
-#define variant_index_tag_t(K)  void(&)( nonstd::variants::detail::index_tag_t<K> )
-#define variant_index_tag(K)    nonstd::variants::detail::index_tag<K>
-
-} // namespace detail
-} // namespace variants
-} // namespace nonstd
-
-//
-// 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  variant_COMPILER_MSVC_VERSION ==  60  (Visual Studio 6.0)
-// MSVC++  7.0  _MSC_VER == 1300  variant_COMPILER_MSVC_VERSION ==  70  (Visual Studio .NET 2002)
-// MSVC++  7.1  _MSC_VER == 1310  variant_COMPILER_MSVC_VERSION ==  71  (Visual Studio .NET 2003)
-// MSVC++  8.0  _MSC_VER == 1400  variant_COMPILER_MSVC_VERSION ==  80  (Visual Studio 2005)
-// MSVC++  9.0  _MSC_VER == 1500  variant_COMPILER_MSVC_VERSION ==  90  (Visual Studio 2008)
-// MSVC++ 10.0  _MSC_VER == 1600  variant_COMPILER_MSVC_VERSION == 100  (Visual Studio 2010)
-// MSVC++ 11.0  _MSC_VER == 1700  variant_COMPILER_MSVC_VERSION == 110  (Visual Studio 2012)
-// MSVC++ 12.0  _MSC_VER == 1800  variant_COMPILER_MSVC_VERSION == 120  (Visual Studio 2013)
-// MSVC++ 14.0  _MSC_VER == 1900  variant_COMPILER_MSVC_VERSION == 140  (Visual Studio 2015)
-// MSVC++ 14.1  _MSC_VER >= 1910  variant_COMPILER_MSVC_VERSION == 141  (Visual Studio 2017)
-// MSVC++ 14.2  _MSC_VER >= 1920  variant_COMPILER_MSVC_VERSION == 142  (Visual Studio 2019)
-
-#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_ENABLE_IF          variant_CPP11_90
-#define variant_HAVE_IS_SAME            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
-
-//
-// 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
-
-#if variant_HAVE_ENABLE_IF
-
-using std::enable_if;
-
-#else
-
-template< bool B, class T = void >
-struct enable_if { };
-
-template< class T >
-struct enable_if< true, T > { typedef T type; };
-
-#endif // variant_HAVE_ENABLE_IF
-
-#if variant_HAVE_IS_SAME
-
-using std::is_same;
-
-#else
-
-template< class T, class U >
-struct is_same {
-    enum V { value = 0 } ;
-};
-
-template< class T >
-struct is_same< T, T > {
-    enum V { value = 1 } ;
-};
-
-#endif // variant_HAVE_IS_SAME
-
-} // namespace std11
-
-// Method enabling
-
-#if variant_CPP11_OR_GREATER
-
-#define variant_REQUIRES_T(...) \
-    , typename std::enable_if< (__VA_ARGS__), int >::type = 0
-
-#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_CPP11_OR_GREATER
-
-#define variant_REQUIRES_0(...) \
-    template< bool B = (__VA_ARGS__), typename std11::enable_if<B, int>::type = 0 >
-
-#define variant_REQUIRES_B(...) \
-    , bool B = (__VA_ARGS__), typename std11::enable_if<B, int>::type = 0
-
-/// type traits C++17:
-
-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 {
-
-// 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 = size_t(typelist_size<Head>::value) + size_t(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;
-};
-
-// typelist type is unique:
-
-template< class List, std::size_t CmpIndex, std::size_t LastChecked = typelist_size<List>::value >
-struct typelist_type_is_unique
-{
-private:
-    typedef typename typelist_type_at<List, CmpIndex>::type cmp_type;
-    typedef typename typelist_type_at<List, LastChecked - 1>::type cur_type;
-
-public:
-    enum V { value = ((CmpIndex == (LastChecked - 1)) | !std11::is_same<cmp_type, cur_type>::value)
-        && typelist_type_is_unique<List, CmpIndex, LastChecked - 1>::value } ;
-};
-
-template< class List, std::size_t CmpIndex >
-struct typelist_type_is_unique< List, CmpIndex, 0 >
-{
-    enum V { value = 1 } ;
-};
-
-template< class List, class T >
-struct typelist_contains_unique_type : typelist_type_is_unique< List, typelist_index_of< List, T >::value >
-{
-};
-
-#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(); }
-
-#if variant_CPP11_OR_GREATER
-    template < variant_index_tag_t( 0 ) = variant_index_tag( 0 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 0 >::value) >
-    variant( T0 const & t0 ) : type_index( 0 ) { new( ptr() ) T0( t0 ); }
-
-    template < variant_index_tag_t( 1 ) = variant_index_tag( 1 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 1 >::value) >
-    variant( T1 const & t1 ) : type_index( 1 ) { new( ptr() ) T1( t1 ); }
-
-    template < variant_index_tag_t( 2 ) = variant_index_tag( 2 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 2 >::value) >
-    variant( T2 const & t2 ) : type_index( 2 ) { new( ptr() ) T2( t2 ); }
-
-    template < variant_index_tag_t( 3 ) = variant_index_tag( 3 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 3 >::value) >
-    variant( T3 const & t3 ) : type_index( 3 ) { new( ptr() ) T3( t3 ); }
-
-    template < variant_index_tag_t( 4 ) = variant_index_tag( 4 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 4 >::value) >
-    variant( T4 const & t4 ) : type_index( 4 ) { new( ptr() ) T4( t4 ); }
-
-    template < variant_index_tag_t( 5 ) = variant_index_tag( 5 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 5 >::value) >
-    variant( T5 const & t5 ) : type_index( 5 ) { new( ptr() ) T5( t5 ); }
-
-    template < variant_index_tag_t( 6 ) = variant_index_tag( 6 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 6 >::value) >
-    variant( T6 const & t6 ) : type_index( 6 ) { new( ptr() ) T6( t6 ); }
-
-    template < variant_index_tag_t( 7 ) = variant_index_tag( 7 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 7 >::value) >
-    variant( T7 const & t7 ) : type_index( 7 ) { new( ptr() ) T7( t7 ); }
-
-    template < variant_index_tag_t( 8 ) = variant_index_tag( 8 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 8 >::value) >
-    variant( T8 const & t8 ) : type_index( 8 ) { new( ptr() ) T8( t8 ); }
-
-    template < variant_index_tag_t( 9 ) = variant_index_tag( 9 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 9 >::value) >
-    variant( T9 const & t9 ) : type_index( 9 ) { new( ptr() ) T9( t9 ); }
-
-    template < variant_index_tag_t( 10 ) = variant_index_tag( 10 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 10 >::value) >
-    variant( T10 const & t10 ) : type_index( 10 ) { new( ptr() ) T10( t10 ); }
-
-    template < variant_index_tag_t( 11 ) = variant_index_tag( 11 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 11 >::value) >
-    variant( T11 const & t11 ) : type_index( 11 ) { new( ptr() ) T11( t11 ); }
-
-    template < variant_index_tag_t( 12 ) = variant_index_tag( 12 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 12 >::value) >
-    variant( T12 const & t12 ) : type_index( 12 ) { new( ptr() ) T12( t12 ); }
-
-    template < variant_index_tag_t( 13 ) = variant_index_tag( 13 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 13 >::value) >
-    variant( T13 const & t13 ) : type_index( 13 ) { new( ptr() ) T13( t13 ); }
-
-    template < variant_index_tag_t( 14 ) = variant_index_tag( 14 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 14 >::value) >
-    variant( T14 const & t14 ) : type_index( 14 ) { new( ptr() ) T14( t14 ); }
-
-    template < variant_index_tag_t( 15 ) = variant_index_tag( 15 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 15 >::value) >
-    variant( T15 const & t15 ) : type_index( 15 ) { new( ptr() ) T15( t15 ); }
-
-#else
-
-    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 ); }
-
-#endif
-
-#if variant_CPP11_OR_GREATER
-    template < variant_index_tag_t( 0 ) = variant_index_tag( 0 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 0 >::value) >
-    variant( T0 && t0 )
-        : type_index( 0 ) { new( ptr() ) T0( std::move(t0) ); }
-
-    template < variant_index_tag_t( 1 ) = variant_index_tag( 1 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 1 >::value) >
-    variant( T1 && t1 )
-        : type_index( 1 ) { new( ptr() ) T1( std::move(t1) ); }
-
-    template < variant_index_tag_t( 2 ) = variant_index_tag( 2 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 2 >::value) >
-    variant( T2 && t2 )
-        : type_index( 2 ) { new( ptr() ) T2( std::move(t2) ); }
-
-    template < variant_index_tag_t( 3 ) = variant_index_tag( 3 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 3 >::value) >
-    variant( T3 && t3 )
-        : type_index( 3 ) { new( ptr() ) T3( std::move(t3) ); }
-
-    template < variant_index_tag_t( 4 ) = variant_index_tag( 4 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 4 >::value) >
-    variant( T4 && t4 )
-        : type_index( 4 ) { new( ptr() ) T4( std::move(t4) ); }
-
-    template < variant_index_tag_t( 5 ) = variant_index_tag( 5 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 5 >::value) >
-    variant( T5 && t5 )
-        : type_index( 5 ) { new( ptr() ) T5( std::move(t5) ); }
-
-    template < variant_index_tag_t( 6 ) = variant_index_tag( 6 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 6 >::value) >
-    variant( T6 && t6 )
-        : type_index( 6 ) { new( ptr() ) T6( std::move(t6) ); }
-
-    template < variant_index_tag_t( 7 ) = variant_index_tag( 7 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 7 >::value) >
-    variant( T7 && t7 )
-        : type_index( 7 ) { new( ptr() ) T7( std::move(t7) ); }
-
-    template < variant_index_tag_t( 8 ) = variant_index_tag( 8 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 8 >::value) >
-    variant( T8 && t8 )
-        : type_index( 8 ) { new( ptr() ) T8( std::move(t8) ); }
-
-    template < variant_index_tag_t( 9 ) = variant_index_tag( 9 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 9 >::value) >
-    variant( T9 && t9 )
-        : type_index( 9 ) { new( ptr() ) T9( std::move(t9) ); }
-
-    template < variant_index_tag_t( 10 ) = variant_index_tag( 10 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 10 >::value) >
-    variant( T10 && t10 )
-        : type_index( 10 ) { new( ptr() ) T10( std::move(t10) ); }
-
-    template < variant_index_tag_t( 11 ) = variant_index_tag( 11 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 11 >::value) >
-    variant( T11 && t11 )
-        : type_index( 11 ) { new( ptr() ) T11( std::move(t11) ); }
-
-    template < variant_index_tag_t( 12 ) = variant_index_tag( 12 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 12 >::value) >
-    variant( T12 && t12 )
-        : type_index( 12 ) { new( ptr() ) T12( std::move(t12) ); }
-
-    template < variant_index_tag_t( 13 ) = variant_index_tag( 13 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 13 >::value) >
-    variant( T13 && t13 )
-        : type_index( 13 ) { new( ptr() ) T13( std::move(t13) ); }
-
-    template < variant_index_tag_t( 14 ) = variant_index_tag( 14 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 14 >::value) >
-    variant( T14 && t14 )
-        : type_index( 14 ) { new( ptr() ) T14( std::move(t14) ); }
-
-    template < variant_index_tag_t( 15 ) = variant_index_tag( 15 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 15 >::value) >
-    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 ) );
-    }
-
-    template < variant_index_tag_t( 0 ) = variant_index_tag( 0 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 0 >::value) >
-    variant & operator=( T0 &&      t0 ) { return assign_value<0>( std::move( t0 ) ); }
-
-    template < variant_index_tag_t( 1 ) = variant_index_tag( 1 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 1 >::value) >
-    variant & operator=( T1 &&      t1 ) { return assign_value<1>( std::move( t1 ) ); }
-
-    template < variant_index_tag_t( 2 ) = variant_index_tag( 2 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 2 >::value) >
-    variant & operator=( T2 &&      t2 ) { return assign_value<2>( std::move( t2 ) ); }
-
-    template < variant_index_tag_t( 3 ) = variant_index_tag( 3 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 3 >::value) >
-    variant & operator=( T3 &&      t3 ) { return assign_value<3>( std::move( t3 ) ); }
-
-    template < variant_index_tag_t( 4 ) = variant_index_tag( 4 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 4 >::value) >
-    variant & operator=( T4 &&      t4 ) { return assign_value<4>( std::move( t4 ) ); }
-
-    template < variant_index_tag_t( 5 ) = variant_index_tag( 5 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 5 >::value) >
-    variant & operator=( T5 &&      t5 ) { return assign_value<5>( std::move( t5 ) ); }
-
-    template < variant_index_tag_t( 6 ) = variant_index_tag( 6 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 6 >::value) >
-    variant & operator=( T6 &&      t6 ) { return assign_value<6>( std::move( t6 ) ); }
-
-    template < variant_index_tag_t( 7 ) = variant_index_tag( 7 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 7 >::value) >
-    variant & operator=( T7 &&      t7 ) { return assign_value<7>( std::move( t7 ) ); }
-
-    template < variant_index_tag_t( 8 ) = variant_index_tag( 8 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 8 >::value) >
-    variant & operator=( T8 &&      t8 ) { return assign_value<8>( std::move( t8 ) ); }
-
-    template < variant_index_tag_t( 9 ) = variant_index_tag( 9 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 9 >::value) >
-    variant & operator=( T9 &&      t9 ) { return assign_value<9>( std::move( t9 ) ); }
-
-    template < variant_index_tag_t( 10 ) = variant_index_tag( 10 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 10 >::value) >
-    variant & operator=( T10 &&      t10 ) { return assign_value<10>( std::move( t10 ) ); }
-
-    template < variant_index_tag_t( 11 ) = variant_index_tag( 11 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 11 >::value) >
-    variant & operator=( T11 &&      t11 ) { return assign_value<11>( std::move( t11 ) ); }
-
-    template < variant_index_tag_t( 12 ) = variant_index_tag( 12 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 12 >::value) >
-    variant & operator=( T12 &&      t12 ) { return assign_value<12>( std::move( t12 ) ); }
-
-    template < variant_index_tag_t( 13 ) = variant_index_tag( 13 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 13 >::value) >
-    variant & operator=( T13 &&      t13 ) { return assign_value<13>( std::move( t13 ) ); }
-
-    template < variant_index_tag_t( 14 ) = variant_index_tag( 14 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 14 >::value) >
-    variant & operator=( T14 &&      t14 ) { return assign_value<14>( std::move( t14 ) ); }
-
-    template < variant_index_tag_t( 15 ) = variant_index_tag( 15 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 15 >::value) >
-    variant & operator=( T15 &&      t15 ) { return assign_value<15>( std::move( t15 ) ); }
-
-#endif
-
-#if variant_CPP11_OR_GREATER
-
-    template < variant_index_tag_t( 0 ) = variant_index_tag( 0 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 0 >::value) >
-    variant & operator=( T0 const & t0 ) { return assign_value<0>( t0 ); }
-
-    template < variant_index_tag_t( 1 ) = variant_index_tag( 1 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 1 >::value) >
-    variant & operator=( T1 const & t1 ) { return assign_value<1>( t1 ); }
-
-    template < variant_index_tag_t( 2 ) = variant_index_tag( 2 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 2 >::value) >
-    variant & operator=( T2 const & t2 ) { return assign_value<2>( t2 ); }
-
-    template < variant_index_tag_t( 3 ) = variant_index_tag( 3 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 3 >::value) >
-    variant & operator=( T3 const & t3 ) { return assign_value<3>( t3 ); }
-
-    template < variant_index_tag_t( 4 ) = variant_index_tag( 4 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 4 >::value) >
-    variant & operator=( T4 const & t4 ) { return assign_value<4>( t4 ); }
-
-    template < variant_index_tag_t( 5 ) = variant_index_tag( 5 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 5 >::value) >
-    variant & operator=( T5 const & t5 ) { return assign_value<5>( t5 ); }
-
-    template < variant_index_tag_t( 6 ) = variant_index_tag( 6 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 6 >::value) >
-    variant & operator=( T6 const & t6 ) { return assign_value<6>( t6 ); }
-
-    template < variant_index_tag_t( 7 ) = variant_index_tag( 7 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 7 >::value) >
-    variant & operator=( T7 const & t7 ) { return assign_value<7>( t7 ); }
-
-    template < variant_index_tag_t( 8 ) = variant_index_tag( 8 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 8 >::value) >
-    variant & operator=( T8 const & t8 ) { return assign_value<8>( t8 ); }
-
-    template < variant_index_tag_t( 9 ) = variant_index_tag( 9 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 9 >::value) >
-    variant & operator=( T9 const & t9 ) { return assign_value<9>( t9 ); }
-
-    template < variant_index_tag_t( 10 ) = variant_index_tag( 10 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 10 >::value) >
-    variant & operator=( T10 const & t10 ) { return assign_value<10>( t10 ); }
-
-    template < variant_index_tag_t( 11 ) = variant_index_tag( 11 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 11 >::value) >
-    variant & operator=( T11 const & t11 ) { return assign_value<11>( t11 ); }
-
-    template < variant_index_tag_t( 12 ) = variant_index_tag( 12 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 12 >::value) >
-    variant & operator=( T12 const & t12 ) { return assign_value<12>( t12 ); }
-
-    template < variant_index_tag_t( 13 ) = variant_index_tag( 13 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 13 >::value) >
-    variant & operator=( T13 const & t13 ) { return assign_value<13>( t13 ); }
-
-    template < variant_index_tag_t( 14 ) = variant_index_tag( 14 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 14 >::value) >
-    variant & operator=( T14 const & t14 ) { return assign_value<14>( t14 ); }
-
-    template < variant_index_tag_t( 15 ) = variant_index_tag( 15 )
-        variant_REQUIRES_B(detail::typelist_type_is_unique< variant_types, 15 >::value) >
-    variant & operator=( T15 const & t15 ) { return assign_value<15>( t15 ); }
-
-#else
-
-    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 ); }
-
-#endif
-
-    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 )
-        variant_REQUIRES_T( detail::typelist_contains_unique_type< variant_types, T >::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 )
-        variant_REQUIRES_T( detail::typelist_contains_unique_type< variant_types, T >::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()
-    {
-#if variant_CONFIG_NO_EXCEPTIONS
-        assert( index_of<T>() == index() );
-#else
-        if ( index_of<T>() != index() )
-        {
-            throw bad_variant_access();
-        }
-#endif
-        return *as<T>();
-    }
-
-    template< class T >
-    T const & get() const
-    {
-#if variant_CONFIG_NO_EXCEPTIONS
-        assert( index_of<T>() == index() );
-#else
-        if ( index_of<T>() != 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)
-    {
-        // prevent default construction of a const reference, see issue #39:
-        std::terminate();
-    }
-};
-
-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);
-
-            // prevent default construction of a const reference, see issue #39:
-            default: std::terminate();
-        }
-    }
-
-    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 0;
-        }
-    }
-};
-
-} //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
diff --git a/ndn-cxx/key-locator.cpp b/ndn-cxx/key-locator.cpp
index 78eed07..989a2e4 100644
--- a/ndn-cxx/key-locator.cpp
+++ b/ndn-cxx/key-locator.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2022 Regents of the University of California.
+ * Copyright (c) 2013-2023 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -58,7 +58,7 @@
   size_t totalLength = 0;
 
   auto visitor = boost::hana::overload(
-    []  (monostate)           {}, // nothing to encode, TLV-VALUE is empty
+    []  (std::monostate)      {}, // nothing to encode, TLV-VALUE is empty
     [&] (const Name& name)    { totalLength += name.wireEncode(encoder); },
     [&] (const Block& digest) { totalLength += prependBlock(encoder, digest); },
     []  (uint32_t type)       { NDN_THROW(Error("Unsupported KeyLocator type " + to_string(type))); });
@@ -126,7 +126,7 @@
   case 2:
     return tlv::KeyDigest;
   case 3:
-    return get<uint32_t>(m_locator);
+    return std::get<uint32_t>(m_locator);
   default:
     NDN_CXX_UNREACHABLE;
   }
@@ -135,7 +135,7 @@
 KeyLocator&
 KeyLocator::clear()
 {
-  m_locator = monostate{};
+  m_locator = std::monostate{};
   m_wire.reset();
   return *this;
 }
@@ -144,9 +144,9 @@
 KeyLocator::getName() const
 {
   try {
-    return get<Name>(m_locator);
+    return std::get<Name>(m_locator);
   }
-  catch (const bad_variant_access&) {
+  catch (const std::bad_variant_access&) {
     NDN_THROW(Error("KeyLocator does not contain a Name"));
   }
 }
@@ -163,9 +163,9 @@
 KeyLocator::getKeyDigest() const
 {
   try {
-    return get<Block>(m_locator);
+    return std::get<Block>(m_locator);
   }
-  catch (const bad_variant_access&) {
+  catch (const std::bad_variant_access&) {
     NDN_THROW(Error("KeyLocator does not contain a KeyDigest"));
   }
 }
@@ -194,7 +194,7 @@
 operator<<(std::ostream& os, const KeyLocator& keyLocator)
 {
   auto visitor = boost::hana::overload(
-    [&] (monostate) {
+    [&] (std::monostate) {
       os << "None";
     },
     [&] (const Name& name) {
diff --git a/ndn-cxx/key-locator.hpp b/ndn-cxx/key-locator.hpp
index ec5688f..4c32261 100644
--- a/ndn-cxx/key-locator.hpp
+++ b/ndn-cxx/key-locator.hpp
@@ -23,7 +23,8 @@
 #define NDN_CXX_KEY_LOCATOR_HPP
 
 #include "ndn-cxx/name.hpp"
-#include "ndn-cxx/util/variant.hpp"
+
+#include <variant>
 
 namespace ndn {
 
@@ -74,7 +75,7 @@
   [[nodiscard]] bool
   empty() const
   {
-    return holds_alternative<monostate>(m_locator);
+    return std::holds_alternative<std::monostate>(m_locator);
   }
 
   uint32_t
@@ -144,7 +145,7 @@
   // - Name is used when the nested TLV contains a name
   // - Block is used when the nested TLV is a KeyDigest
   // - in all other (unsupported) cases the nested TLV type is stored as uint32_t
-  variant<monostate, Name, Block, uint32_t> m_locator;
+  std::variant<std::monostate, Name, Block, uint32_t> m_locator;
 
   mutable Block m_wire;
 
diff --git a/ndn-cxx/util/variant.hpp b/ndn-cxx/util/variant.hpp
deleted file mode 100644
index 51acacb..0000000
--- a/ndn-cxx/util/variant.hpp
+++ /dev/null
@@ -1,51 +0,0 @@
-/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/*
- * Copyright (c) 2013-2021 Regents of the University of California.
- *
- * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
- *
- * ndn-cxx library is free software: you can redistribute it and/or modify it under the
- * terms of the GNU Lesser General Public License as published by the Free Software
- * Foundation, either version 3 of the License, or (at your option) any later version.
- *
- * ndn-cxx library is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
- * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
- *
- * You should have received copies of the GNU General Public License and GNU Lesser
- * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
- * <http://www.gnu.org/licenses/>.
- *
- * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
- */
-
-#ifndef NDN_CXX_UTIL_VARIANT_HPP
-#define NDN_CXX_UTIL_VARIANT_HPP
-
-#define variant_CONFIG_SELECT_VARIANT variant_VARIANT_NONSTD
-#define variant_CONFIG_OMIT_VARIANT_SIZE_V_MACRO 1
-#define variant_CONFIG_OMIT_VARIANT_ALTERNATIVE_T_MACRO 1
-#include "ndn-cxx/detail/nonstd/variant-lite.hpp"
-
-namespace ndn {
-
-using ::nonstd::variant;
-using ::nonstd::monostate;
-using ::nonstd::bad_variant_access;
-using ::nonstd::variant_npos;
-using ::nonstd::variant_size;
-using ::nonstd::variant_size_v;
-using ::nonstd::variant_alternative;
-using ::nonstd::variant_alternative_t;
-
-using ::nonstd::visit;
-using ::nonstd::holds_alternative;
-using ::nonstd::get;
-using ::nonstd::get_if;
-
-using ::nonstd::in_place;
-using ::nonstd::in_place_t;
-
-} // namespace ndn
-
-#endif // NDN_CXX_UTIL_VARIANT_HPP