diff --git a/src/util/backports.hpp b/src/util/backports.hpp
index 70f62f3..bb0c462 100644
--- a/src/util/backports.hpp
+++ b/src/util/backports.hpp
@@ -49,7 +49,9 @@
 #endif
 
 #include "backports-ostream-joiner.hpp"
+#include "nonstd/any.hpp"
 #include "nonstd/optional.hpp"
+#include "nonstd/variant.hpp"
 
 #ifndef NDN_CXX_HAVE_STD_TO_STRING
 #include <boost/lexical_cast.hpp>
@@ -86,6 +88,11 @@
 }
 #endif // __cpp_lib_clamp
 
+using ::nonstd::any;
+using ::nonstd::any_cast;
+using ::nonstd::bad_any_cast;
+using ::nonstd::make_any;
+
 using ::nonstd::optional;
 using ::nonstd::bad_optional_access;
 using ::nonstd::nullopt;
@@ -94,6 +101,14 @@
 using ::nonstd::in_place_t;
 using ::nonstd::make_optional;
 
+using ::nonstd::variant;
+using ::nonstd::bad_variant_access;
+using ::nonstd::monostate;
+using ::nonstd::visit;
+using ::nonstd::holds_alternative;
+using ::nonstd::get_if;
+using ::nonstd::variant_npos;
+
 } // namespace ndn
 
 #endif // NDN_UTIL_BACKPORTS_HPP
diff --git a/src/util/nonstd/any.hpp b/src/util/nonstd/any.hpp
new file mode 100644
index 0000000..7c02c63
--- /dev/null
+++ b/src/util/nonstd/any.hpp
@@ -0,0 +1,643 @@
+//
+// Copyright (c) 2016-2018 Martin Moene
+//
+// https://github.com/martinmoene/any-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_ANY_LITE_HPP
+#define NONSTD_ANY_LITE_HPP
+
+#define any_lite_MAJOR  0
+#define any_lite_MINOR  1
+#define any_lite_PATCH  0
+
+#define any_lite_VERSION  any_STRINGIFY(any_lite_MAJOR) "." any_STRINGIFY(any_lite_MINOR) "." any_STRINGIFY(any_lite_PATCH)
+
+#define any_STRINGIFY(  x )  any_STRINGIFY_( x )
+#define any_STRINGIFY_( x )  #x
+
+// any-lite configuration:
+
+#define any_ANY_DEFAULT  0
+#define any_ANY_NONSTD   1
+#define any_ANY_STD      2
+
+#if !defined( any_CONFIG_SELECT_ANY )
+# define any_CONFIG_SELECT_ANY  ( any_HAVE_STD_ANY ? any_ANY_STD : any_ANY_NONSTD )
+#endif
+
+// C++ language version detection (C++20 is speculative):
+// Note: VC14.0/1900 (VS2015) lacks too much from C++14.
+
+#ifndef   any_CPLUSPLUS
+# if defined(_MSVC_LANG ) && !defined(__clang__)
+#  define any_CPLUSPLUS  (_MSC_VER == 1900 ? 201103L : _MSVC_LANG )
+# else
+#  define any_CPLUSPLUS  __cplusplus
+# endif
+#endif
+
+#define any_CPP98_OR_GREATER  ( any_CPLUSPLUS >= 199711L )
+#define any_CPP11_OR_GREATER  ( any_CPLUSPLUS >= 201103L )
+#define any_CPP14_OR_GREATER  ( any_CPLUSPLUS >= 201402L )
+#define any_CPP17_OR_GREATER  ( any_CPLUSPLUS >= 201703L )
+#define any_CPP20_OR_GREATER  ( any_CPLUSPLUS >= 202000L )
+
+// Use C++17 std::any if available and requested:
+
+#if any_CPP17_OR_GREATER && defined(__has_include )
+# if __has_include( <any> )
+#  define any_HAVE_STD_ANY  1
+# else
+#  define any_HAVE_STD_ANY  0
+# endif
+#else
+# define  any_HAVE_STD_ANY  0
+#endif
+
+#define  any_USES_STD_ANY  ( (any_CONFIG_SELECT_ANY == any_ANY_STD) || ((any_CONFIG_SELECT_ANY == any_ANY_DEFAULT) && any_HAVE_STD_ANY) )
+
+//
+// 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 any_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 // any_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 // any_CPP17_OR_GREATER
+#endif // nonstd_lite_HAVE_IN_PLACE_TYPES
+
+//
+// Using std::any:
+//
+
+#if any_USES_STD_ANY
+
+#include <any>
+#include <utility>
+
+namespace nonstd {
+
+    using std::any;
+    using std::any_cast;
+    using std::make_any;
+    using std::swap;
+    using std::bad_any_cast;
+}
+
+#else // any_USES_STD_ANY
+
+#include <typeinfo>
+#include <utility>
+
+// Compiler versions:
+//
+// MSVC++ 6.0  _MSC_VER == 1200 (Visual Studio 6.0)
+// MSVC++ 7.0  _MSC_VER == 1300 (Visual Studio .NET 2002)
+// MSVC++ 7.1  _MSC_VER == 1310 (Visual Studio .NET 2003)
+// MSVC++ 8.0  _MSC_VER == 1400 (Visual Studio 2005)
+// MSVC++ 9.0  _MSC_VER == 1500 (Visual Studio 2008)
+// MSVC++ 10.0 _MSC_VER == 1600 (Visual Studio 2010)
+// MSVC++ 11.0 _MSC_VER == 1700 (Visual Studio 2012)
+// MSVC++ 12.0 _MSC_VER == 1800 (Visual Studio 2013)
+// MSVC++ 14.0 _MSC_VER == 1900 (Visual Studio 2015)
+// MSVC++ 14.1 _MSC_VER >= 1910 (Visual Studio 2017)
+
+#if defined(_MSC_VER ) && !defined(__clang__)
+# define any_COMPILER_MSVC_VER      (_MSC_VER )
+# define any_COMPILER_MSVC_VERSION  (_MSC_VER / 10 - 10 * ( 5 + (_MSC_VER < 1900 ) ) )
+#else
+# define any_COMPILER_MSVC_VER      0
+# define any_COMPILER_MSVC_VERSION  0
+#endif
+
+#define any_COMPILER_VERSION( major, minor, patch )  ( 10 * ( 10 * (major) + (minor) ) + (patch) )
+
+#if defined(__clang__)
+# define any_COMPILER_CLANG_VERSION  any_COMPILER_VERSION(__clang_major__, __clang_minor__, __clang_patchlevel__)
+#else
+# define any_COMPILER_CLANG_VERSION  0
+#endif
+
+#if defined(__GNUC__) && !defined(__clang__)
+# define any_COMPILER_GNUC_VERSION  any_COMPILER_VERSION(__GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__)
+#else
+# define any_COMPILER_GNUC_VERSION  0
+#endif
+
+// half-open range [lo..hi):
+//#define any_BETWEEN( v, lo, hi ) ( (lo) <= (v) && (v) < (hi) )
+
+// Presence of language and library features:
+
+#define any_HAVE( feature )  ( any_HAVE_##feature )
+
+#ifdef _HAS_CPP0X
+# define any_HAS_CPP0X  _HAS_CPP0X
+#else
+# define any_HAS_CPP0X  0
+#endif
+
+#define any_CPP11_90   (any_CPP11_OR_GREATER || any_COMPILER_MSVC_VER >= 1500)
+#define any_CPP11_100  (any_CPP11_OR_GREATER || any_COMPILER_MSVC_VER >= 1600)
+#define any_CPP11_120  (any_CPP11_OR_GREATER || any_COMPILER_MSVC_VER >= 1800)
+#define any_CPP11_140  (any_CPP11_OR_GREATER || any_COMPILER_MSVC_VER >= 1900)
+
+#define any_CPP14_000  (any_CPP14_OR_GREATER)
+#define any_CPP17_000  (any_CPP17_OR_GREATER)
+
+// Presence of C++11 language features:
+
+#define any_HAVE_CONSTEXPR_11           any_CPP11_140
+#define any_HAVE_DEFAULT_FUNCTION_TEMPLATE_ARG \
+                                        any_CPP11_120
+#define any_HAVE_INITIALIZER_LIST       any_CPP11_120
+#define any_HAVE_NOEXCEPT               any_CPP11_140
+#define any_HAVE_NULLPTR                any_CPP11_100
+#define any_HAVE_TYPE_TRAITS            any_CPP11_90
+#define any_HAVE_STATIC_ASSERT          any_CPP11_100
+#define any_HAVE_ADD_CONST              any_CPP11_90
+#define any_HAVE_REMOVE_REFERENCE       any_CPP11_90
+
+#define any_HAVE_TR1_ADD_CONST          (!! any_COMPILER_GNUC_VERSION )
+#define any_HAVE_TR1_REMOVE_REFERENCE   (!! any_COMPILER_GNUC_VERSION )
+#define any_HAVE_TR1_TYPE_TRAITS        (!! any_COMPILER_GNUC_VERSION )
+
+// Presence of C++14 language features:
+
+#define any_HAVE_CONSTEXPR_14           any_CPP14_000
+
+// Presence of C++17 language features:
+
+#define any_HAVE_NODISCARD              any_CPP17_000
+
+// Presence of C++ library features:
+
+#if any_HAVE_CONSTEXPR_11
+# define any_constexpr constexpr
+#else
+# define any_constexpr /*constexpr*/
+#endif
+
+#if any_HAVE_CONSTEXPR_14
+# define any_constexpr14 constexpr
+#else
+# define any_constexpr14 /*constexpr*/
+#endif
+
+#if any_HAVE_NOEXCEPT
+# define any_noexcept noexcept
+#else
+# define any_noexcept /*noexcept*/
+#endif
+
+#if any_HAVE_NULLPTR
+# define any_nullptr nullptr
+#else
+# define any_nullptr NULL
+#endif
+
+#if any_HAVE_NODISCARD
+# define any_nodiscard [[nodiscard]]
+#else
+# define any_nodiscard /*[[nodiscard]]*/
+#endif
+
+// additional includes:
+
+#if ! any_HAVE_NULLPTR
+# include <cstddef>
+#endif
+
+#if any_HAVE_INITIALIZER_LIST
+# include <initializer_list>
+#endif
+
+#if any_HAVE_TYPE_TRAITS
+# include <type_traits>
+#elif any_HAVE_TR1_TYPE_TRAITS
+# include <tr1/type_traits>
+#endif
+
+//
+// any:
+//
+
+namespace nonstd {  namespace any_lite {
+
+namespace detail {
+
+// C++11 emulation:
+
+#if any_HAVE_ADD_CONST
+
+using std::add_const;
+
+#elif any_HAVE_TR1_ADD_CONST
+
+using std::tr1::add_const;
+
+#else
+
+template< class T > struct add_const { typedef const T type; };
+
+#endif // any_HAVE_ADD_CONST
+
+#if any_HAVE_REMOVE_REFERENCE
+
+using std::remove_reference;
+
+#elif any_HAVE_TR1_REMOVE_REFERENCE
+
+using std::tr1::remove_reference;
+
+#else
+
+template< class T > struct remove_reference     { typedef T type; };
+template< class T > struct remove_reference<T&> { typedef T type; };
+
+#endif // any_HAVE_REMOVE_REFERENCE
+
+} // namespace detail
+
+class bad_any_cast : public std::bad_cast
+{
+public:
+#if any_CPP11_OR_GREATER
+    virtual const char* what() const any_noexcept
+#else
+    virtual const char* what() const throw()
+#endif
+   {
+      return "any-lite: bad any_cast";
+   }
+};
+
+class any
+{
+public:
+    any_constexpr any() any_noexcept
+    : content( any_nullptr )
+    {}
+
+    any( any const & other )
+    : content( other.content ? other.content->clone() : any_nullptr )
+    {}
+
+#if any_CPP11_OR_GREATER
+
+    any( any && other ) any_noexcept
+    : content( std::move( other.content ) )
+    {
+        other.content = any_nullptr;
+    }
+
+    template<
+        class ValueType, class T = typename std::decay<ValueType>::type
+        , typename = typename std::enable_if< ! std::is_same<T, any>::value >::type
+    >
+    any( ValueType && value ) any_noexcept
+    : content( new holder<T>( std::move( value ) ) )
+    {}
+
+    template<
+        class T, class... Args
+        , typename = typename std::enable_if< std::is_constructible<T, Args...>::value >::type
+    >
+    explicit any( nonstd_lite_in_place_type_t(T), Args&&... args )
+    : content( new holder<T>( T( std::forward<Args>(args)... ) ) )
+    {}
+
+    template<
+        class T, class U, class... Args
+        , typename = typename std::enable_if< std::is_constructible<T, std::initializer_list<U>&, Args...>::value >::type
+    >
+    explicit any( nonstd_lite_in_place_type_t(T), std::initializer_list<U> il, Args&&... args )
+    : content( new holder<T>( T( il, std::forward<Args>(args)... ) ) )
+    {}
+
+#else
+
+    template< class ValueType >
+    any( ValueType const & value )
+    : content( new holder<ValueType>( value ) )
+    {}
+
+#endif // any_CPP11_OR_GREATER
+
+    ~any()
+    {
+        reset();
+    }
+
+    any & operator=( any const & other )
+    {
+        any( other ).swap( *this );
+        return *this;
+    }
+
+#if any_CPP11_OR_GREATER
+
+    any & operator=( any && other ) any_noexcept
+    {
+        any( std::move( other ) ).swap( *this );
+        return *this;
+    }
+
+    template<
+        class ValueType, class T = typename std::decay<ValueType>::type
+        , typename = typename std::enable_if< ! std::is_same<T, any>::value >::type
+    >
+    any & operator=( ValueType && value )
+    {
+        any( std::move( value ) ).swap( *this );
+        return *this;
+    }
+
+    template< class T, class... Args >
+    void emplace( Args && ... args )
+    {
+        any( T( std::forward<Args>(args)... ) ).swap( *this );
+    }
+
+    template<
+        class T, class U, class... Args
+        , typename = typename std::enable_if< std::is_constructible<T, std::initializer_list<U>&, Args...>::value >::type
+    >
+    void emplace( std::initializer_list<U> il, Args&&... args )
+    {
+        any( T( il, std::forward<Args>(args)... ) ).swap( *this );
+    }
+
+#else
+
+    template< class ValueType >
+    any & operator=( ValueType const & value )
+    {
+        any( value ).swap( *this );
+        return *this;
+    }
+
+#endif // any_CPP11_OR_GREATER
+
+    void reset() any_noexcept
+    {
+        delete content; content = any_nullptr;
+    }
+
+    void swap( any & other ) any_noexcept
+    {
+        std::swap( content, other.content );
+    }
+
+    bool has_value() const any_noexcept
+    {
+        return content != any_nullptr;
+    }
+
+    const std::type_info & type() const any_noexcept
+    {
+        return has_value() ? content->type() : typeid( void );
+    }
+
+    //
+    // non-standard:
+    //
+
+    template< class ValueType >
+    const ValueType * to_ptr() const
+    {
+        return &( static_cast<holder<ValueType> *>( content )->held );
+    }
+
+    template< class ValueType >
+    ValueType * to_ptr()
+    {
+        return &( static_cast<holder<ValueType> *>( content )->held );
+    }
+
+private:
+    class placeholder
+    {
+    public:
+        virtual ~placeholder()
+        {
+        }
+
+        virtual std::type_info const & type() const = 0;
+
+        virtual placeholder * clone() const = 0;
+    };
+
+    template< typename ValueType >
+    class holder : public placeholder
+    {
+    public:
+        holder( ValueType const & value )
+        : held( value )
+        {}
+
+#if any_CPP11_OR_GREATER
+        holder( ValueType && value )
+        : held( std::move( value ) )
+        {}
+#endif
+
+        virtual std::type_info const & type() const
+        {
+            return typeid( ValueType );
+        }
+
+        virtual placeholder * clone() const
+        {
+            return new holder( held );
+        }
+
+        ValueType held;
+    };
+
+    placeholder * content;
+};
+
+inline void swap( any & x, any & y ) any_noexcept
+{
+    x.swap( y );
+}
+
+#if any_CPP11_OR_GREATER
+
+template< class T, class ...Args >
+inline any make_any( Args&& ...args )
+{
+    return any( nonstd_lite_in_place_type(T), std::forward<Args>(args)...);
+}
+
+template< class T, class U, class ...Args >
+inline any make_any( std::initializer_list<U> il, Args&& ...args )
+{
+    return any( nonstd_lite_in_place_type(T), il, std::forward<Args>(args)...);
+}
+
+#endif // any_CPP11_OR_GREATER
+
+template<
+    class ValueType
+#if any_HAVE_DEFAULT_FUNCTION_TEMPLATE_ARG
+    , typename = typename std::enable_if< std::is_reference<ValueType>::value || std::is_copy_constructible<ValueType>::value >::type
+#endif
+>
+any_nodiscard inline ValueType any_cast( any const & operand )
+{
+   const ValueType * result = any_cast< typename detail::add_const< typename detail::remove_reference<ValueType>::type >::type >( &operand );
+
+   if ( ! result )
+   {
+      throw bad_any_cast();
+   }
+
+   return *result;
+}
+
+template<
+    class ValueType
+#if any_HAVE_DEFAULT_FUNCTION_TEMPLATE_ARG
+    , typename = typename std::enable_if< std::is_reference<ValueType>::value || std::is_copy_constructible<ValueType>::value >::type
+#endif
+>
+any_nodiscard inline ValueType any_cast( any & operand )
+{
+   const ValueType * result = any_cast< typename detail::remove_reference<ValueType>::type >( &operand );
+
+   if ( ! result )
+   {
+      throw bad_any_cast();
+   }
+
+   return *result;
+}
+
+#if any_CPP11_OR_GREATER
+
+template<
+    class ValueType
+#if any_HAVE_DEFAULT_FUNCTION_TEMPLATE_ARG
+    , typename = typename std::enable_if< std::is_reference<ValueType>::value || std::is_copy_constructible<ValueType>::value >::type
+#endif
+>
+any_nodiscard inline ValueType any_cast( any && operand )
+{
+   const ValueType * result = any_cast< typename detail::remove_reference<ValueType>::type >( &operand );
+
+   if ( ! result )
+   {
+      throw bad_any_cast();
+   }
+
+   return *result;
+}
+
+#endif // any_CPP11_OR_GREATER
+
+template< class ValueType >
+any_nodiscard inline ValueType const * any_cast( any const * operand ) any_noexcept
+{
+    return operand != any_nullptr && operand->type() == typeid(ValueType) ? operand->to_ptr<ValueType>() : any_nullptr;
+}
+
+template<class ValueType >
+any_nodiscard inline ValueType * any_cast( any * operand ) any_noexcept
+{
+    return operand != any_nullptr && operand->type() == typeid(ValueType) ? operand->to_ptr<ValueType>() : any_nullptr;
+}
+
+} // namespace any_lite
+
+using namespace any_lite;
+
+} // namespace nonstd
+
+#endif // any_USES_STD_ANY
+
+#endif // NONSTD_ANY_LITE_HPP
diff --git a/src/util/nonstd/optional.hpp b/src/util/nonstd/optional.hpp
index 764598a..c7a6554 100644
--- a/src/util/nonstd/optional.hpp
+++ b/src/util/nonstd/optional.hpp
@@ -13,7 +13,7 @@
 
 #define optional_lite_MAJOR  3
 #define optional_lite_MINOR  1
-#define optional_lite_PATCH  0
+#define optional_lite_PATCH  1
 
 #define optional_lite_VERSION  optional_STRINGIFY(optional_lite_MAJOR) "." optional_STRINGIFY(optional_lite_MINOR) "." optional_STRINGIFY(optional_lite_PATCH)
 
@@ -34,7 +34,7 @@
 // Note: VC14.0/1900 (VS2015) lacks too much from C++14.
 
 #ifndef   optional_CPLUSPLUS
-# ifdef  _MSVC_LANG
+# if defined(_MSVC_LANG ) && !defined(__clang__)
 #  define optional_CPLUSPLUS  (_MSC_VER == 1900 ? 201103L : _MSVC_LANG )
 # else
 #  define optional_CPLUSPLUS  __cplusplus
@@ -43,6 +43,7 @@
 
 #define optional_CPP98_OR_GREATER  ( optional_CPLUSPLUS >= 199711L )
 #define optional_CPP11_OR_GREATER  ( optional_CPLUSPLUS >= 201103L )
+#define optional_CPP11_OR_GREATER_ ( optional_CPLUSPLUS >= 201103L )
 #define optional_CPP14_OR_GREATER  ( optional_CPLUSPLUS >= 201402L )
 #define optional_CPP17_OR_GREATER  ( optional_CPLUSPLUS >= 201703L )
 #define optional_CPP20_OR_GREATER  ( optional_CPLUSPLUS >= 202000L )
@@ -65,7 +66,97 @@
 
 #define optional_USES_STD_OPTIONAL  ( (optional_CONFIG_SELECT_OPTIONAL == optional_OPTIONAL_STD) || ((optional_CONFIG_SELECT_OPTIONAL == optional_OPTIONAL_DEFAULT) && optional_HAVE_STD_OPTIONAL) )
 
+//
+// 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 optional_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 // optional_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 // optional_CPP17_OR_GREATER
+#endif // nonstd_lite_HAVE_IN_PLACE_TYPES
+
+//
 // Using std::optional:
+//
 
 #if optional_USES_STD_OPTIONAL
 
@@ -79,12 +170,6 @@
 
     using std::nullopt;
     using std::nullopt_t;
-    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;
 
     using std::operator==;
     using std::operator!=;
@@ -118,32 +203,47 @@
 
 // Compiler warning suppression:
 
-#if defined (__clang__)
+#if defined(__clang__)
 # pragma clang diagnostic push
 # pragma clang diagnostic ignored "-Wundef"
-#elif defined (__GNUC__)
+#elif defined(__GNUC__)
 # pragma GCC   diagnostic push
 # pragma GCC   diagnostic ignored "-Wundef"
 #endif
 
 // half-open range [lo..hi):
-#define optional_BETWEEN( v, lo, hi ) ( lo <= v && v < hi )
+#define optional_BETWEEN( v, lo, hi ) ( (lo) <= (v) && (v) < (hi) )
 
-#if defined(_MSC_VER) && !defined(__clang__)
-# define optional_COMPILER_MSVC_VERSION   (_MSC_VER / 10 - 10 * ( 5 + (_MSC_VER < 1900)) )
+// Compiler versions:
+//
+// MSVC++ 6.0  _MSC_VER == 1200 (Visual Studio 6.0)
+// MSVC++ 7.0  _MSC_VER == 1300 (Visual Studio .NET 2002)
+// MSVC++ 7.1  _MSC_VER == 1310 (Visual Studio .NET 2003)
+// MSVC++ 8.0  _MSC_VER == 1400 (Visual Studio 2005)
+// MSVC++ 9.0  _MSC_VER == 1500 (Visual Studio 2008)
+// MSVC++ 10.0 _MSC_VER == 1600 (Visual Studio 2010)
+// MSVC++ 11.0 _MSC_VER == 1700 (Visual Studio 2012)
+// MSVC++ 12.0 _MSC_VER == 1800 (Visual Studio 2013)
+// MSVC++ 14.0 _MSC_VER == 1900 (Visual Studio 2015)
+// MSVC++ 14.1 _MSC_VER >= 1910 (Visual Studio 2017)
+
+#if defined(_MSC_VER ) && !defined(__clang__)
+# define optional_COMPILER_MSVC_VER      (_MSC_VER )
+# define optional_COMPILER_MSVC_VERSION  (_MSC_VER / 10 - 10 * ( 5 + (_MSC_VER < 1900 ) ) )
 #else
-# define optional_COMPILER_MSVC_VERSION   0
+# define optional_COMPILER_MSVC_VER      0
+# define optional_COMPILER_MSVC_VERSION  0
 #endif
 
 #define optional_COMPILER_VERSION( major, minor, patch )  ( 10 * (10 * major + minor ) + patch )
 
-#if defined (__GNUC__) && !defined(__clang__)
+#if defined(__GNUC__) && !defined(__clang__)
 # define optional_COMPILER_GNUC_VERSION   optional_COMPILER_VERSION(__GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__)
 #else
 # define optional_COMPILER_GNUC_VERSION   0
 #endif
 
-#if defined (__clang__)
+#if defined(__clang__)
 # define optional_COMPILER_CLANG_VERSION  optional_COMPILER_VERSION(__clang_major__, __clang_minor__, __clang_patchlevel__)
 #else
 # define optional_COMPILER_CLANG_VERSION  0
@@ -163,81 +263,53 @@
 
 #define optional_HAVE(FEATURE) ( optional_HAVE_##FEATURE )
 
-// Presence of C++11 language features:
-
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 100
-# define optional_HAVE_AUTO  1
-# define optional_HAVE_NULLPTR  1
-# define optional_HAVE_STATIC_ASSERT  1
+#ifdef _HAS_CPP0X
+# define optional_HAS_CPP0X  _HAS_CPP0X
+#else
+# define optional_HAS_CPP0X  0
 #endif
 
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 120
-# define optional_HAVE_DEFAULT_FUNCTION_TEMPLATE_ARG  1
-# define optional_HAVE_INITIALIZER_LIST  1
-#endif
+// Unless defined otherwise below, consider VC14 as C++11 for optional-lite:
 
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 140
-# define optional_HAVE_ALIAS_TEMPLATE  1
-# define optional_HAVE_CONSTEXPR_11  1
-# define optional_HAVE_ENUM_CLASS  1
-# define optional_HAVE_EXPLICIT_CONVERSION  1
-# define optional_HAVE_IS_DEFAULT  1
-# define optional_HAVE_IS_DELETE  1
-# define optional_HAVE_NOEXCEPT  1
-# define optional_HAVE_REF_QUALIFIER  1
-#endif
-
-// Presence of C++14 language features:
-
-#if optional_CPP14_OR_GREATER
-# define optional_HAVE_CONSTEXPR_14  1
-#endif
-
-// Presence of C++17 language features:
-
-#if optional_CPP17_OR_GREATER
-# define optional_HAVE_ENUM_CLASS_CONSTRUCTION_FROM_UNDERLYING_TYPE  1
-#endif
-
-// Presence of C++ library features:
-
-#if optional_COMPILER_GNUC_VERSION
-# define optional_HAVE_TR1_TYPE_TRAITS  1
-# define optional_HAVE_TR1_ADD_POINTER  1
-#endif
-
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 90
-# define optional_HAVE_TYPE_TRAITS  1
-# define optional_HAVE_STD_ADD_POINTER  1
-#endif
-
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 110
-# define optional_HAVE_ARRAY  1
-#endif
-
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 120
-# define optional_HAVE_CONDITIONAL  1
-#endif
-
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 140 || (optional_COMPILER_MSVC_VERSION >= 90 && _HAS_CPP0X)
-# define optional_HAVE_CONTAINER_DATA_METHOD  1
-#endif
-
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 120
-# define optional_HAVE_REMOVE_CV  1
-#endif
-
-#if optional_CPP11_OR_GREATER || optional_COMPILER_MSVC_VERSION >= 140
-# define optional_HAVE_SIZED_TYPES  1
-#endif
-
-// For the rest, consider VC14 as C++11 for optional-lite:
-
-#if optional_COMPILER_MSVC_VERSION >= 140
+#if optional_COMPILER_MSVC_VER >= 1900
 # undef  optional_CPP11_OR_GREATER
 # define optional_CPP11_OR_GREATER  1
 #endif
 
+#define optional_CPP11_90   (optional_CPP11_OR_GREATER_ || optional_COMPILER_MSVC_VER >= 1500)
+#define optional_CPP11_100  (optional_CPP11_OR_GREATER_ || optional_COMPILER_MSVC_VER >= 1600)
+#define optional_CPP11_110  (optional_CPP11_OR_GREATER_ || optional_COMPILER_MSVC_VER >= 1700)
+#define optional_CPP11_120  (optional_CPP11_OR_GREATER_ || optional_COMPILER_MSVC_VER >= 1800)
+#define optional_CPP11_140  (optional_CPP11_OR_GREATER_ || optional_COMPILER_MSVC_VER >= 1900)
+#define optional_CPP11_141  (optional_CPP11_OR_GREATER_ || optional_COMPILER_MSVC_VER >= 1910)
+
+#define optional_CPP14_000  (optional_CPP14_OR_GREATER)
+#define optional_CPP17_000  (optional_CPP17_OR_GREATER)
+
+// Presence of C++11 language features:
+
+#define optional_HAVE_CONSTEXPR_11      optional_CPP11_140
+#define optional_HAVE_NOEXCEPT          optional_CPP11_140
+#define optional_HAVE_NULLPTR           optional_CPP11_100
+#define optional_HAVE_REF_QUALIFIER     optional_CPP11_140
+
+// Presence of C++14 language features:
+
+#define optional_HAVE_CONSTEXPR_14      optional_CPP14_000
+
+// Presence of C++17 language features:
+
+// no flag
+
+// Presence of C++ library features:
+
+#define optional_HAVE_CONDITIONAL       optional_CPP11_120
+#define optional_HAVE_REMOVE_CV         optional_CPP11_120
+#define optional_HAVE_TYPE_TRAITS       optional_CPP11_90
+
+#define optional_HAVE_TR1_TYPE_TRAITS   (!! optional_COMPILER_GNUC_VERSION )
+#define optional_HAVE_TR1_ADD_POINTER   (!! optional_COMPILER_GNUC_VERSION )
+
 // C++ feature usage:
 
 #if optional_HAVE( CONSTEXPR_11 )
@@ -304,90 +376,6 @@
 #endif
 
 //
-// in_place: code duplicated in any-lite, expected-lite, optional-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 optional_CPP17_OR_GREATER
-
-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(T)  std::in_place_index_t<I>
-
-#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(T)    std::in_place_index_t<I>{}
-
-} // namespace nonstd
-
-#else // optional_CPP17_OR_GREATER
-
-namespace nonstd {
-namespace detail {
-
-template< class T >
-struct in_place_type_tag {};
-
-template< std::size_t I >
-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 I >
-inline in_place_t in_place( detail::in_place_index_tag<I> = detail::in_place_index_tag<I>() )
-{
-    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 I >
-inline in_place_t in_place_index( detail::in_place_index_tag<I> = detail::in_place_index_tag<I>() )
-{
-    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(T)  nonstd::in_place_t(&)( nonstd::detail::in_place_index_tag<I> )
-
-#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(T)    nonstd::in_place_index<I>
-
-} // namespace nonstd
-
-#endif // optional_CPP17_OR_GREATER
-#endif // nonstd_lite_HAVE_IN_PLACE_TYPES
-
-//
 // optional:
 //
 
@@ -1211,7 +1199,7 @@
 
 #if optional_HAVE( REF_QUALIFIER )
 
-    optional_constexpr14 value_type const && value() const optional_refref_qual
+    optional_constexpr value_type const && value() const optional_refref_qual
     {
         return std::move( value() );
     }
@@ -1232,7 +1220,7 @@
     }
 
     template< typename U >
-    optional_constexpr value_type value_or( U && v ) const optional_refref_qual
+    optional_constexpr14 value_type value_or( U && v ) optional_refref_qual
     {
         return has_value() ? std::move( contained.value() ) : static_cast<T>(std::forward<U>( v ) );
     }
@@ -1538,9 +1526,9 @@
 
 #endif // optional_CPP11_OR_GREATER
 
-#if defined (__clang__)
+#if defined(__clang__)
 # pragma clang diagnostic pop
-#elif defined (__GNUC__)
+#elif defined(__GNUC__)
 # pragma GCC   diagnostic pop
 #endif
 
diff --git a/src/util/nonstd/variant.hpp b/src/util/nonstd/variant.hpp
new file mode 100644
index 0000000..08c78ab
--- /dev/null
+++ b/src/util/nonstd/variant.hpp
@@ -0,0 +1,2137 @@
+// Copyright 2016-2018 by Martin Moene
+//
+// https://github.com/martinmoene/variant-lite
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#pragma once
+
+#ifndef NONSTD_VARIANT_LITE_HPP
+#define NONSTD_VARIANT_LITE_HPP
+
+#define variant_lite_MAJOR  1
+#define variant_lite_MINOR  1
+#define variant_lite_PATCH  0
+
+#define variant_lite_VERSION  variant_STRINGIFY(variant_lite_MAJOR) "." variant_STRINGIFY(variant_lite_MINOR) "." variant_STRINGIFY(variant_lite_PATCH)
+
+#define variant_STRINGIFY(  x )  variant_STRINGIFY_( x )
+#define variant_STRINGIFY_( x )  #x
+
+// variant-lite configuration:
+
+#define variant_VARIANT_DEFAULT  0
+#define variant_VARIANT_NONSTD   1
+#define variant_VARIANT_STD      2
+
+#if !defined( variant_CONFIG_SELECT_VARIANT )
+# define variant_CONFIG_SELECT_VARIANT  ( variant_HAVE_STD_VARIANT ? variant_VARIANT_STD : variant_VARIANT_NONSTD )
+#endif
+
+#ifndef  variant_CONFIG_OMIT_VARIANT_SIZE_V_MACRO
+# define variant_CONFIG_OMIT_VARIANT_SIZE_V_MACRO  0
+#endif
+
+#ifndef  variant_CONFIG_OMIT_VARIANT_ALTERNATIVE_T_MACRO
+# define variant_CONFIG_OMIT_VARIANT_ALTERNATIVE_T_MACRO  0
+#endif
+
+// C++ language version detection (C++20 is speculative):
+// Note: VC14.0/1900 (VS2015) lacks too much from C++14.
+
+#ifndef   variant_CPLUSPLUS
+# if defined(_MSVC_LANG ) && !defined(__clang__)
+#  define variant_CPLUSPLUS  (_MSC_VER == 1900 ? 201103L : _MSVC_LANG )
+# else
+#  define variant_CPLUSPLUS  __cplusplus
+# endif
+#endif
+
+#define variant_CPP98_OR_GREATER  ( variant_CPLUSPLUS >= 199711L )
+#define variant_CPP11_OR_GREATER  ( variant_CPLUSPLUS >= 201103L )
+#define variant_CPP11_OR_GREATER_ ( variant_CPLUSPLUS >= 201103L )
+#define variant_CPP14_OR_GREATER  ( variant_CPLUSPLUS >= 201402L )
+#define variant_CPP17_OR_GREATER  ( variant_CPLUSPLUS >= 201703L )
+#define variant_CPP20_OR_GREATER  ( variant_CPLUSPLUS >= 202000L )
+
+// Use C++17 std::variant if available and requested:
+
+#if variant_CPP17_OR_GREATER && defined(__has_include )
+# if __has_include( <variant> )
+#  define variant_HAVE_STD_VARIANT  1
+# else
+#  define variant_HAVE_STD_VARIANT  0
+# endif
+#else
+# define  variant_HAVE_STD_VARIANT  0
+#endif
+
+#define  variant_USES_STD_VARIANT  ( (variant_CONFIG_SELECT_VARIANT == variant_VARIANT_STD) || ((variant_CONFIG_SELECT_VARIANT == variant_VARIANT_DEFAULT) && variant_HAVE_STD_VARIANT) )
+
+//
+// in_place: code duplicated in any-lite, expected-lite, optional-lite, value-ptr-lite, variant-lite:
+//
+
+#ifndef nonstd_lite_HAVE_IN_PLACE_TYPES
+#define nonstd_lite_HAVE_IN_PLACE_TYPES  1
+
+// C++17 std::in_place in <utility>:
+
+#if variant_CPP17_OR_GREATER
+
+#include <utility>
+
+namespace nonstd {
+
+using std::in_place;
+using std::in_place_type;
+using std::in_place_index;
+using std::in_place_t;
+using std::in_place_type_t;
+using std::in_place_index_t;
+
+#define nonstd_lite_in_place_t(      T)  std::in_place_t
+#define nonstd_lite_in_place_type_t( T)  std::in_place_type_t<T>
+#define nonstd_lite_in_place_index_t(K)  std::in_place_index_t<K>
+
+#define nonstd_lite_in_place(      T)    std::in_place_t{}
+#define nonstd_lite_in_place_type( T)    std::in_place_type_t<T>{}
+#define nonstd_lite_in_place_index(K)    std::in_place_index_t<K>{}
+
+} // namespace nonstd
+
+#else // variant_CPP17_OR_GREATER
+
+#include <cstddef>
+
+namespace nonstd {
+namespace detail {
+
+template< class T >
+struct in_place_type_tag {};
+
+template< std::size_t K >
+struct in_place_index_tag {};
+
+} // namespace detail
+
+struct in_place_t {};
+
+template< class T >
+inline in_place_t in_place( detail::in_place_type_tag<T> = detail::in_place_type_tag<T>() )
+{
+    return in_place_t();
+}
+
+template< std::size_t K >
+inline in_place_t in_place( detail::in_place_index_tag<K> = detail::in_place_index_tag<K>() )
+{
+    return in_place_t();
+}
+
+template< class T >
+inline in_place_t in_place_type( detail::in_place_type_tag<T> = detail::in_place_type_tag<T>() )
+{
+    return in_place_t();
+}
+
+template< std::size_t K >
+inline in_place_t in_place_index( detail::in_place_index_tag<K> = detail::in_place_index_tag<K>() )
+{
+    return in_place_t();
+}
+
+// mimic templated typedef:
+
+#define nonstd_lite_in_place_t(      T)  nonstd::in_place_t(&)( nonstd::detail::in_place_type_tag<T>  )
+#define nonstd_lite_in_place_type_t( T)  nonstd::in_place_t(&)( nonstd::detail::in_place_type_tag<T>  )
+#define nonstd_lite_in_place_index_t(K)  nonstd::in_place_t(&)( nonstd::detail::in_place_index_tag<K> )
+
+#define nonstd_lite_in_place(      T)    nonstd::in_place_type<T>
+#define nonstd_lite_in_place_type( T)    nonstd::in_place_type<T>
+#define nonstd_lite_in_place_index(K)    nonstd::in_place_index<K>
+
+} // namespace nonstd
+
+#endif // variant_CPP17_OR_GREATER
+#endif // nonstd_lite_HAVE_IN_PLACE_TYPES
+
+//
+// Use C++17 std::variant:
+//
+
+#if variant_USES_STD_VARIANT
+
+#include <functional>   // std::hash<>
+#include <variant>
+
+#if ! variant_CONFIG_OMIT_VARIANT_SIZE_V_MACRO
+# define variant_size_V(T)  nonstd::variant_size<T>::value
+#endif
+
+#if ! variant_CONFIG_OMIT_VARIANT_ALTERNATIVE_T_MACRO
+# define variant_alternative_T(K,T)  typename nonstd::variant_alternative<K,T >::type
+#endif
+
+namespace nonstd {
+
+    using std::variant;
+    using std::monostate;
+    using std::bad_variant_access;
+    using std::variant_size;
+    using std::variant_size_v;
+    using std::variant_alternative;
+    using std::variant_alternative_t;
+    using std::hash;
+
+    using std::visit;
+    using std::holds_alternative;
+    using std::get;
+    using std::get_if;
+    using std::operator==;
+    using std::operator!=;
+    using std::operator<;
+    using std::operator<=;
+    using std::operator>;
+    using std::operator>=;
+    using std::swap;
+
+    constexpr auto variant_npos = std::variant_npos;
+}
+
+#else // variant_USES_STD_VARIANT
+
+#include <cstddef>
+#include <limits>
+#include <new>
+#include <stdexcept>
+#include <utility>
+
+// variant-lite alignment configuration:
+
+#ifndef  variant_CONFIG_MAX_ALIGN_HACK
+# define variant_CONFIG_MAX_ALIGN_HACK  0
+#endif
+
+#ifndef  variant_CONFIG_ALIGN_AS
+// no default, used in #if defined()
+#endif
+
+#ifndef  variant_CONFIG_ALIGN_AS_FALLBACK
+# define variant_CONFIG_ALIGN_AS_FALLBACK  double
+#endif
+
+// half-open range [lo..hi):
+#define variant_BETWEEN( v, lo, hi ) ( lo <= v && v < hi )
+
+// Compiler versions:
+//
+// MSVC++ 6.0  _MSC_VER == 1200 (Visual Studio 6.0)
+// MSVC++ 7.0  _MSC_VER == 1300 (Visual Studio .NET 2002)
+// MSVC++ 7.1  _MSC_VER == 1310 (Visual Studio .NET 2003)
+// MSVC++ 8.0  _MSC_VER == 1400 (Visual Studio 2005)
+// MSVC++ 9.0  _MSC_VER == 1500 (Visual Studio 2008)
+// MSVC++ 10.0 _MSC_VER == 1600 (Visual Studio 2010)
+// MSVC++ 11.0 _MSC_VER == 1700 (Visual Studio 2012)
+// MSVC++ 12.0 _MSC_VER == 1800 (Visual Studio 2013)
+// MSVC++ 14.0 _MSC_VER == 1900 (Visual Studio 2015)
+// MSVC++ 14.1 _MSC_VER >= 1910 (Visual Studio 2017)
+
+#if defined(_MSC_VER ) && !defined(__clang__)
+# define variant_COMPILER_MSVC_VER      (_MSC_VER )
+# define variant_COMPILER_MSVC_VERSION  (_MSC_VER / 10 - 10 * ( 5 + (_MSC_VER < 1900 ) ) )
+#else
+# define variant_COMPILER_MSVC_VER      0
+# define variant_COMPILER_MSVC_VERSION  0
+#endif
+
+#define variant_COMPILER_VERSION( major, minor, patch )  ( 10 * ( 10 * (major) + (minor) ) + (patch) )
+
+#if defined(__clang__)
+# define variant_COMPILER_CLANG_VERSION  variant_COMPILER_VERSION(__clang_major__, __clang_minor__, __clang_patchlevel__)
+#else
+# define variant_COMPILER_CLANG_VERSION  0
+#endif
+
+#if defined(__GNUC__) && !defined(__clang__)
+# define variant_COMPILER_GNUC_VERSION  variant_COMPILER_VERSION(__GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__)
+#else
+# define variant_COMPILER_GNUC_VERSION  0
+#endif
+
+#if variant_BETWEEN( variant_COMPILER_MSVC_VER, 1300, 1900 )
+# pragma warning( push )
+# pragma warning( disable: 4345 )   // initialization behavior changed
+#endif
+
+// Presence of language and library features:
+
+#define variant_HAVE( feature )  ( variant_HAVE_##feature )
+
+#ifdef _HAS_CPP0X
+# define variant_HAS_CPP0X  _HAS_CPP0X
+#else
+# define variant_HAS_CPP0X  0
+#endif
+
+// Unless defined otherwise below, consider VC14 as C++11 for variant-lite:
+
+#if variant_COMPILER_MSVC_VER >= 1900
+# undef  variant_CPP11_OR_GREATER
+# define variant_CPP11_OR_GREATER  1
+#endif
+
+#define variant_CPP11_90   (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1500)
+#define variant_CPP11_100  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1600)
+#define variant_CPP11_110  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1700)
+#define variant_CPP11_120  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1800)
+#define variant_CPP11_140  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1900)
+#define variant_CPP11_141  (variant_CPP11_OR_GREATER_ || variant_COMPILER_MSVC_VER >= 1910)
+
+#define variant_CPP14_000  (variant_CPP14_OR_GREATER)
+#define variant_CPP17_000  (variant_CPP17_OR_GREATER)
+
+// Presence of C++11 language features:
+
+#define variant_HAVE_CONSTEXPR_11       variant_CPP11_140
+#define variant_HAVE_INITIALIZER_LIST   variant_CPP11_120
+#define variant_HAVE_NOEXCEPT           variant_CPP11_140
+#define variant_HAVE_NULLPTR            variant_CPP11_100
+#define variant_HAVE_OVERRIDE           variant_CPP11_140
+
+// Presence of C++14 language features:
+
+#define variant_HAVE_CONSTEXPR_14       variant_CPP14_000
+
+// Presence of C++17 language features:
+
+// no flag
+
+// Presence of C++ library features:
+
+#define variant_HAVE_TR1_TYPE_TRAITS    (!! variant_COMPILER_GNUC_VERSION )
+#define variant_HAVE_TR1_ADD_POINTER    (!! variant_COMPILER_GNUC_VERSION )
+
+#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
+
+// C++ feature usage:
+
+#if variant_HAVE_CONSTEXPR_11
+# define variant_constexpr constexpr
+#else
+# define variant_constexpr /*constexpr*/
+#endif
+
+#if variant_HAVE_CONSTEXPR_14
+# define variant_constexpr14 constexpr
+#else
+# define variant_constexpr14 /*constexpr*/
+#endif
+
+#if variant_HAVE_NOEXCEPT
+# define variant_noexcept noexcept
+#else
+# define variant_noexcept /*noexcept*/
+#endif
+
+#if variant_HAVE_NULLPTR
+# define variant_nullptr nullptr
+#else
+# define variant_nullptr NULL
+#endif
+
+#if variant_HAVE_OVERRIDE
+# define variant_override override
+#else
+# define variant_override /*override*/
+#endif
+
+// additional includes:
+
+#if variant_CPP11_OR_GREATER
+# include <functional>      // std::hash
+#endif
+
+#if variant_HAVE_INITIALIZER_LIST
+# include <initializer_list>
+#endif
+
+#if variant_HAVE_TYPE_TRAITS
+# include <type_traits>
+#elif variant_HAVE_TR1_TYPE_TRAITS
+# include <tr1/type_traits>
+#endif
+
+// Method enabling
+
+#if variant_CPP11_OR_GREATER
+
+# define variant_REQUIRES_T(...) \
+    , typename = typename std::enable_if<__VA_ARGS__>::type
+
+# define variant_REQUIRES_R(R, ...) \
+    typename std::enable_if<__VA_ARGS__, R>::type
+
+# define variant_REQUIRES_A(...) \
+    , typename std::enable_if<__VA_ARGS__, void*>::type = variant_nullptr
+
+#endif
+
+//
+// variant:
+//
+
+namespace nonstd { namespace variants {
+
+namespace detail {
+
+// C++11 emulation:
+
+#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
+
+// 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 conditional< (sizeof( Head ) > tail_value), Head, tail_type>::type type;
+};
+
+#if variant_CPP11_OR_GREATER
+
+// typelist max alignof element type:
+
+template< class List >
+struct typelist_max_alignof;
+
+template<>
+struct typelist_max_alignof< nulltype >
+{
+    enum V { value = 0 } ;
+};
+
+template< class Head, class Tail >
+struct typelist_max_alignof< typelist<Head, Tail> >
+{
+private:
+    enum TV { tail_value = size_t( typelist_max_alignof<Tail>::value ) };
+
+public:
+    enum V { value = (alignof( Head ) > tail_value) ? alignof( Head ) : std::size_t( tail_value ) };
+};
+
+#endif
+
+// typelist size (length):
+
+template< class List >
+struct typelist_size
+{
+   enum V { value = 1 };
+};
+
+template<> struct typelist_size< T0 > { enum V { value = 0 }; };
+template<> struct typelist_size< T1 > { enum V { value = 0 }; };
+template<> struct typelist_size< T2 > { enum V { value = 0 }; };
+template<> struct typelist_size< T3 > { enum V { value = 0 }; };
+template<> struct typelist_size< T4 > { enum V { value = 0 }; };
+template<> struct typelist_size< T5 > { enum V { value = 0 }; };
+template<> struct typelist_size< T6 > { enum V { value = 0 }; };
+template<> struct typelist_size< T7 > { enum V { value = 0 }; };
+template<> struct typelist_size< T8 > { enum V { value = 0 }; };
+template<> struct typelist_size< T9 > { enum V { value = 0 }; };
+template<> struct typelist_size< T10 > { enum V { value = 0 }; };
+template<> struct typelist_size< T11 > { enum V { value = 0 }; };
+template<> struct typelist_size< T12 > { enum V { value = 0 }; };
+template<> struct typelist_size< T13 > { enum V { value = 0 }; };
+template<> struct typelist_size< T14 > { enum V { value = 0 }; };
+template<> struct typelist_size< T15 > { enum V { value = 0 }; };
+
+
+template<> struct typelist_size< nulltype > { enum V { value = 0 } ; };
+
+template< class Head, class Tail >
+struct typelist_size< typelist<Head, Tail> >
+{
+    enum V { value = typelist_size<Head>::value + typelist_size<Tail>::value };
+};
+
+// typelist index of type:
+
+template< class List, class T >
+struct typelist_index_of;
+
+template< class T >
+struct typelist_index_of< nulltype, T >
+{
+    enum V { value = -1 };
+};
+
+template< class Tail, class T >
+struct typelist_index_of< typelist<T, Tail>, T >
+{
+    enum V { value = 0 };
+};
+
+template< class Head, class Tail, class T >
+struct typelist_index_of< typelist<Head, Tail>, T >
+{
+private:
+    enum TV { nextVal = typelist_index_of<Tail, T>::value };
+
+public:
+    enum V { value = nextVal == -1 ? -1 : 1 + nextVal } ;
+};
+
+// typelist type at index:
+
+template< class List, std::size_t i>
+struct typelist_type_at;
+
+template< class Head, class Tail >
+struct typelist_type_at< typelist<Head, Tail>, 0 >
+{
+    typedef Head type;
+};
+
+template< class Head, class Tail, std::size_t i >
+struct typelist_type_at< typelist<Head, Tail>, i >
+{
+    typedef typename typelist_type_at<Tail, i - 1>::type type;
+};
+
+#if variant_CONFIG_MAX_ALIGN_HACK
+
+// Max align, use most restricted type for alignment:
+
+#define variant_UNIQUE(  name )       variant_UNIQUE2( name, __LINE__ )
+#define variant_UNIQUE2( name, line ) variant_UNIQUE3( name, line )
+#define variant_UNIQUE3( name, line ) name ## line
+
+#define variant_ALIGN_TYPE( type ) \
+    type variant_UNIQUE( _t ); struct_t< type > variant_UNIQUE( _st )
+
+template< class T >
+struct struct_t { T _; };
+
+union max_align_t
+{
+    variant_ALIGN_TYPE( char );
+    variant_ALIGN_TYPE( short int );
+    variant_ALIGN_TYPE( int );
+    variant_ALIGN_TYPE( long int  );
+    variant_ALIGN_TYPE( float  );
+    variant_ALIGN_TYPE( double );
+    variant_ALIGN_TYPE( long double );
+    variant_ALIGN_TYPE( char * );
+    variant_ALIGN_TYPE( short int * );
+    variant_ALIGN_TYPE( int *  );
+    variant_ALIGN_TYPE( long int * );
+    variant_ALIGN_TYPE( float * );
+    variant_ALIGN_TYPE( double * );
+    variant_ALIGN_TYPE( long double * );
+    variant_ALIGN_TYPE( void * );
+
+#ifdef HAVE_LONG_LONG
+    variant_ALIGN_TYPE( long long );
+#endif
+
+    struct Unknown;
+
+    Unknown ( * variant_UNIQUE(_) )( Unknown );
+    Unknown * Unknown::* variant_UNIQUE(_);
+    Unknown ( Unknown::* variant_UNIQUE(_) )( Unknown );
+
+    struct_t< Unknown ( * )( Unknown)         > variant_UNIQUE(_);
+    struct_t< Unknown * Unknown::*            > variant_UNIQUE(_);
+    struct_t< Unknown ( Unknown::* )(Unknown) > variant_UNIQUE(_);
+};
+
+#undef variant_UNIQUE
+#undef variant_UNIQUE2
+#undef variant_UNIQUE3
+
+#undef variant_ALIGN_TYPE
+
+#elif defined( variant_CONFIG_ALIGN_AS ) // variant_CONFIG_MAX_ALIGN_HACK
+
+// Use user-specified type for alignment:
+
+#define variant_ALIGN_AS( unused ) \
+    variant_CONFIG_ALIGN_AS
+
+#else // variant_CONFIG_MAX_ALIGN_HACK
+
+// Determine POD type to use for alignment:
+
+#define variant_ALIGN_AS( to_align ) \
+    typename detail::type_of_size< detail::alignment_types, detail::alignment_of< to_align >::value >::type
+
+template< typename T >
+struct alignment_of;
+
+template< typename T >
+struct alignment_of_hack
+{
+    char c;
+    T t;
+    alignment_of_hack();
+};
+
+template< size_t A, size_t S >
+struct alignment_logic
+{
+    enum V { value = A < S ? A : S };
+};
+
+template< typename T >
+struct alignment_of
+{
+    enum V { value = alignment_logic<
+        sizeof( alignment_of_hack<T> ) - sizeof(T), sizeof(T) >::value, };
+};
+
+template< typename List, size_t N >
+struct type_of_size
+{
+    typedef typename 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
+
+template< typename T>
+inline std::size_t hash( T const & v )
+{
+    // primes:
+    unsigned const int a  = 54059;
+    unsigned const int b  = 76963;
+    unsigned const int h0 = 37;
+
+    unsigned int h = h0;
+    unsigned char const * s = reinterpret_cast<unsigned char const *>( &v );
+
+    for ( std::size_t i = 0; i < sizeof(v); ++i, ++s )
+    {
+        h = (h * a) ^ (*s * b);
+    }
+    return h;
+}
+
+
+
+
+
+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( type_index_t const from_index, void * from_value, void * to_value )
+    {
+        switch ( from_index )
+        {
+        case 0: new( to_value ) T0( std::forward<T0>( *as<T0>( from_value ) ) ); break;
+        case 1: new( to_value ) T1( std::forward<T1>( *as<T1>( from_value ) ) ); break;
+        case 2: new( to_value ) T2( std::forward<T2>( *as<T2>( from_value ) ) ); break;
+        case 3: new( to_value ) T3( std::forward<T3>( *as<T3>( from_value ) ) ); break;
+        case 4: new( to_value ) T4( std::forward<T4>( *as<T4>( from_value ) ) ); break;
+        case 5: new( to_value ) T5( std::forward<T5>( *as<T5>( from_value ) ) ); break;
+        case 6: new( to_value ) T6( std::forward<T6>( *as<T6>( from_value ) ) ); break;
+        case 7: new( to_value ) T7( std::forward<T7>( *as<T7>( from_value ) ) ); break;
+        case 8: new( to_value ) T8( std::forward<T8>( *as<T8>( from_value ) ) ); break;
+        case 9: new( to_value ) T9( std::forward<T9>( *as<T9>( from_value ) ) ); break;
+        case 10: new( to_value ) T10( std::forward<T10>( *as<T10>( from_value ) ) ); break;
+        case 11: new( to_value ) T11( std::forward<T11>( *as<T11>( from_value ) ) ); break;
+        case 12: new( to_value ) T12( std::forward<T12>( *as<T12>( from_value ) ) ); break;
+        case 13: new( to_value ) T13( std::forward<T13>( *as<T13>( from_value ) ) ); break;
+        case 14: new( to_value ) T14( std::forward<T14>( *as<T14>( from_value ) ) ); break;
+        case 15: new( to_value ) T15( std::forward<T15>( *as<T15>( from_value ) ) ); break;
+        
+        }
+        return from_index;
+    }
+#endif
+
+    static type_index_t copy( 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;
+    }
+};
+
+} // 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;
+
+class monostate{};
+
+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; }
+
+// 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
+
+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";
+    }
+};
+
+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:
+    variant() : type_index( 0 ) { new( ptr() ) T0(); }
+
+    variant( T0 const & t0 ) : type_index( 0 ) { new( ptr() ) T0( t0 ); }
+    variant( T1 const & t1 ) : type_index( 1 ) { new( ptr() ) T1( t1 ); }
+    variant( T2 const & t2 ) : type_index( 2 ) { new( ptr() ) T2( t2 ); }
+    variant( T3 const & t3 ) : type_index( 3 ) { new( ptr() ) T3( t3 ); }
+    variant( T4 const & t4 ) : type_index( 4 ) { new( ptr() ) T4( t4 ); }
+    variant( T5 const & t5 ) : type_index( 5 ) { new( ptr() ) T5( t5 ); }
+    variant( T6 const & t6 ) : type_index( 6 ) { new( ptr() ) T6( t6 ); }
+    variant( T7 const & t7 ) : type_index( 7 ) { new( ptr() ) T7( t7 ); }
+    variant( T8 const & t8 ) : type_index( 8 ) { new( ptr() ) T8( t8 ); }
+    variant( T9 const & t9 ) : type_index( 9 ) { new( ptr() ) T9( t9 ); }
+    variant( T10 const & t10 ) : type_index( 10 ) { new( ptr() ) T10( t10 ); }
+    variant( T11 const & t11 ) : type_index( 11 ) { new( ptr() ) T11( t11 ); }
+    variant( T12 const & t12 ) : type_index( 12 ) { new( ptr() ) T12( t12 ); }
+    variant( T13 const & t13 ) : type_index( 13 ) { new( ptr() ) T13( t13 ); }
+    variant( T14 const & t14 ) : type_index( 14 ) { new( ptr() ) T14( t14 ); }
+    variant( T15 const & t15 ) : type_index( 15 ) { new( ptr() ) T15( t15 ); }
+    
+
+#if variant_CPP11_OR_GREATER
+    variant( T0 && t0 ) : type_index( 0 ) { new( ptr() ) T0( std::move(t0) ); }
+    variant( T1 && t1 ) : type_index( 1 ) { new( ptr() ) T1( std::move(t1) ); }
+    variant( T2 && t2 ) : type_index( 2 ) { new( ptr() ) T2( std::move(t2) ); }
+    variant( T3 && t3 ) : type_index( 3 ) { new( ptr() ) T3( std::move(t3) ); }
+    variant( T4 && t4 ) : type_index( 4 ) { new( ptr() ) T4( std::move(t4) ); }
+    variant( T5 && t5 ) : type_index( 5 ) { new( ptr() ) T5( std::move(t5) ); }
+    variant( T6 && t6 ) : type_index( 6 ) { new( ptr() ) T6( std::move(t6) ); }
+    variant( T7 && t7 ) : type_index( 7 ) { new( ptr() ) T7( std::move(t7) ); }
+    variant( T8 && t8 ) : type_index( 8 ) { new( ptr() ) T8( std::move(t8) ); }
+    variant( T9 && t9 ) : type_index( 9 ) { new( ptr() ) T9( std::move(t9) ); }
+    variant( T10 && t10 ) : type_index( 10 ) { new( ptr() ) T10( std::move(t10) ); }
+    variant( T11 && t11 ) : type_index( 11 ) { new( ptr() ) T11( std::move(t11) ); }
+    variant( T12 && t12 ) : type_index( 12 ) { new( ptr() ) T12( std::move(t12) ); }
+    variant( T13 && t13 ) : type_index( 13 ) { new( ptr() ) T13( std::move(t13) ); }
+    variant( T14 && t14 ) : type_index( 14 ) { new( ptr() ) T14( std::move(t14) ); }
+    variant( T15 && t15 ) : type_index( 15 ) { new( ptr() ) T15( std::move(t15) ); }
+    
+#endif
+
+    variant(variant const & other)
+    : type_index( other.type_index )
+    {
+        (void) helper_type::copy( 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( 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
+
+    ~variant()
+    {
+        helper_type::destroy( type_index, ptr() );
+    }
+
+    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::forward<variant>( other ) );
+    }
+
+    variant & operator=( T0 &&      t0 ) { return move_assign_value<T0,0>( std::forward<T0>( t0 ) ); }
+    variant & operator=( T1 &&      t1 ) { return move_assign_value<T1,1>( std::forward<T1>( t1 ) ); }
+    variant & operator=( T2 &&      t2 ) { return move_assign_value<T2,2>( std::forward<T2>( t2 ) ); }
+    variant & operator=( T3 &&      t3 ) { return move_assign_value<T3,3>( std::forward<T3>( t3 ) ); }
+    variant & operator=( T4 &&      t4 ) { return move_assign_value<T4,4>( std::forward<T4>( t4 ) ); }
+    variant & operator=( T5 &&      t5 ) { return move_assign_value<T5,5>( std::forward<T5>( t5 ) ); }
+    variant & operator=( T6 &&      t6 ) { return move_assign_value<T6,6>( std::forward<T6>( t6 ) ); }
+    variant & operator=( T7 &&      t7 ) { return move_assign_value<T7,7>( std::forward<T7>( t7 ) ); }
+    variant & operator=( T8 &&      t8 ) { return move_assign_value<T8,8>( std::forward<T8>( t8 ) ); }
+    variant & operator=( T9 &&      t9 ) { return move_assign_value<T9,9>( std::forward<T9>( t9 ) ); }
+    variant & operator=( T10 &&      t10 ) { return move_assign_value<T10,10>( std::forward<T10>( t10 ) ); }
+    variant & operator=( T11 &&      t11 ) { return move_assign_value<T11,11>( std::forward<T11>( t11 ) ); }
+    variant & operator=( T12 &&      t12 ) { return move_assign_value<T12,12>( std::forward<T12>( t12 ) ); }
+    variant & operator=( T13 &&      t13 ) { return move_assign_value<T13,13>( std::forward<T13>( t13 ) ); }
+    variant & operator=( T14 &&      t14 ) { return move_assign_value<T14,14>( std::forward<T14>( t14 ) ); }
+    variant & operator=( T15 &&      t15 ) { return move_assign_value<T15,15>( std::forward<T15>( t15 ) ); }
+    
+#else
+    variant & operator=( T0 const & t0 ) { return copy_assign_value<T0,0>( t0 ); }
+    variant & operator=( T1 const & t1 ) { return copy_assign_value<T1,1>( t1 ); }
+    variant & operator=( T2 const & t2 ) { return copy_assign_value<T2,2>( t2 ); }
+    variant & operator=( T3 const & t3 ) { return copy_assign_value<T3,3>( t3 ); }
+    variant & operator=( T4 const & t4 ) { return copy_assign_value<T4,4>( t4 ); }
+    variant & operator=( T5 const & t5 ) { return copy_assign_value<T5,5>( t5 ); }
+    variant & operator=( T6 const & t6 ) { return copy_assign_value<T6,6>( t6 ); }
+    variant & operator=( T7 const & t7 ) { return copy_assign_value<T7,7>( t7 ); }
+    variant & operator=( T8 const & t8 ) { return copy_assign_value<T8,8>( t8 ); }
+    variant & operator=( T9 const & t9 ) { return copy_assign_value<T9,9>( t9 ); }
+    variant & operator=( T10 const & t10 ) { return copy_assign_value<T10,10>( t10 ); }
+    variant & operator=( T11 const & t11 ) { return copy_assign_value<T11,11>( t11 ); }
+    variant & operator=( T12 const & t12 ) { return copy_assign_value<T12,12>( t12 ); }
+    variant & operator=( T13 const & t13 ) { return copy_assign_value<T13,13>( t13 ); }
+    variant & operator=( T14 const & t14 ) { return copy_assign_value<T14,14>( t14 ); }
+    variant & operator=( T15 const & t15 ) { return copy_assign_value<T15,15>( t15 ); }
+    
+#endif
+
+    std::size_t index() const
+    {
+        return variant_npos_internal() == type_index ? variant_npos : static_cast<std::size_t>( type_index );
+    }
+
+    bool valueless_by_exception() const
+    {
+        return type_index == variant_npos_internal();
+    }
+
+#if variant_CPP11_OR_GREATER
+    template< class T, class... Args
+        variant_REQUIRES_T( std::is_constructible< T, Args...>::value )
+    >
+    T& emplace( Args&&... args )
+    {
+        helper_type::destroy( type_index, ptr() );
+        type_index = variant_npos_internal();
+        type_index = helper_type::template construct_t<T>( ptr(), std::forward<Args>(args)... );
+
+        return *as<T>();
+    }
+
+    template< class T, class U, class... Args
+        variant_REQUIRES_T( std::is_constructible< T, std::initializer_list<U>&, Args...>::value )
+    >
+    T& emplace( std::initializer_list<U> il, Args&&... args )
+    {
+        helper_type::destroy( type_index, ptr() );
+        type_index = variant_npos_internal();
+        type_index = helper_type::template construct_t<T>( ptr(), il, std::forward<Args>(args)... );
+
+        return *as<T>();
+    }
+
+    template< size_t K, class... Args
+        variant_REQUIRES_T( std::is_constructible< type_at_t<K>, Args...>::value )
+    >
+    variant_alternative_t<K, variant> & emplace( Args&&... args )
+    {
+        return this->template emplace< type_at_t<K> >( std::forward<Args>(args)... );
+    }
+
+    template< size_t K, class U, class... Args
+        variant_REQUIRES_T( std::is_constructible< type_at_t<K>, std::initializer_list<U>&, Args...>::value )
+    >
+    variant_alternative_t<K, variant> & emplace( std::initializer_list<U> il, Args&&... args )
+    {
+        return this->template emplace< type_at_t<K> >( il, std::forward<Args>(args)... );
+    }
+
+#endif // variant_CPP11_OR_GREATER
+
+    void swap( variant & other ) variant_noexcept
+    {
+        if ( valueless_by_exception() && other.valueless_by_exception() )
+        {
+            // no effect
+        }
+        else if ( type_index == other.type_index )
+        {
+            this->swap_value( type_index, other );
+        }
+        else
+        {
+            variant tmp( *this );
+            *this = other;
+            other = tmp;
+        }
+    }
+
+    //
+    // non-standard:
+    //
+
+    template< class T >
+    variant_constexpr std::size_t index_of() const variant_noexcept
+    {
+        return to_size_t( detail::typelist_index_of<variant_types, typename detail::remove_cv<T>::type >::value );
+    }
+
+    template< class T >
+    T & get()
+    {
+        const std::size_t i = index_of<T>();
+
+        if ( i != index() || i == max_index() )
+        {
+            throw bad_variant_access();
+        }
+
+        return *as<T>();
+    }
+
+    template< class T >
+    T const & get() const
+    {
+        const std::size_t i = index_of<T>();
+
+        if ( i != index() || i == max_index() )
+        {
+            throw bad_variant_access();
+        }
+
+        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 std::size_t to_size_t( U index )
+    {
+        return static_cast<std::size_t >( index );
+    }
+
+    variant_constexpr std::size_t max_index() const variant_noexcept
+    {
+        return data_size;
+    }
+
+    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( other.type_index, other.ptr(), ptr() );
+        }
+        else
+        {
+            // alas exception safety with pre-C++11 needs an extra copy:
+
+            variant tmp( other );
+            helper_type::destroy( type_index, ptr() );
+            type_index = variant_npos_internal();
+#if variant_CPP11_OR_GREATER
+            type_index = helper_type::move( other.type_index, tmp.ptr(), ptr() );
+#else
+            type_index = helper_type::copy( other.type_index, tmp.ptr(), ptr() );
+#endif
+        }
+        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( other.type_index, other.ptr(), ptr() );
+        }
+        else
+        {
+            helper_type::destroy( type_index, ptr() );
+            type_index = variant_npos_internal();
+            type_index = helper_type::move( other.type_index, other.ptr(), ptr() );
+        }
+        return *this;
+    }
+
+    template< class T, std::size_t K >
+    variant & move_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;
+    }
+#else
+    template< class T, std::size_t K >
+    variant & copy_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;
+    }
+
+#endif // variant_CPP11_OR_GREATER
+
+    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;
+};
+
+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() == v.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 ( K != v.index() )
+    {
+        throw bad_variant_access();
+    }
+
+    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 ( K != v.index() )
+    {
+        throw bad_variant_access();
+    }
+
+    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 ( K != v.index() )
+    {
+        throw bad_variant_access();
+    }
+
+    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 ( K != v.index() )
+    {
+        throw bad_variant_access();
+    }
+
+    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 detail::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() == pv->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 detail::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() == pv->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 detail::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 detail::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;
+}
+
+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 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 ) variant_noexcept
+{
+    a.swap( b );
+}
+
+// Variant 'visitor' implementation
+
+namespace detail
+{
+
+template< typename R, typename VT >
+struct VisitorApplicatorImpl
+{
+    template< typename Visitor, typename T >
+    static R apply(Visitor const& v, T const& arg)
+    {
+        return v(arg);
+    }
+};
+
+template< typename R, typename VT >
+struct VisitorApplicatorImpl<R, TX<VT> >
+{
+    template< typename Visitor, typename T >
+    static R apply(Visitor const&, T)
+    {
+        return R();
+    }
+};
+
+template<typename R>
+struct VisitorApplicator;
+
+template< typename R, typename Visitor, typename V1 >
+struct VisitorUnwrapper;
+
+#if variant_CPP11_OR_GREATER
+template< size_t NumVars, typename R, typename Visitor, typename ... T >
+#else
+template< size_t NumVars, typename R, typename Visitor, typename T1, typename T2 = S0, typename T3 = S0, typename T4 = S0, typename T5 = S0 >
+#endif
+struct TypedVisitorUnwrapper;
+
+template< typename R, typename Visitor, typename T2 >
+struct TypedVisitorUnwrapper<2, R, Visitor, T2>
+{
+    const Visitor& visitor;
+    T2 const& val2;
+    
+    TypedVisitorUnwrapper(const Visitor& visitor_, T2 const& val2_)
+        : visitor(visitor_)
+        , val2(val2_)
+        
+    {
+    }
+
+    template<typename T>
+    R operator()(const T& val1) const
+    {
+        return visitor(val1, val2);
+    }
+};
+
+template< typename R, typename Visitor, typename T2, typename T3 >
+struct TypedVisitorUnwrapper<3, R, Visitor, T2, T3>
+{
+    const Visitor& visitor;
+    T2 const& val2;
+    T3 const& val3;
+    
+    TypedVisitorUnwrapper(const Visitor& visitor_, T2 const& val2_, T3 const& val3_)
+        : visitor(visitor_)
+        , val2(val2_)
+        , val3(val3_)
+        
+    {
+    }
+
+    template<typename T>
+    R operator()(const T& val1) const
+    {
+        return visitor(val1, val2, val3);
+    }
+};
+
+template< typename R, typename Visitor, typename T2, typename T3, typename T4 >
+struct TypedVisitorUnwrapper<4, R, Visitor, T2, T3, T4>
+{
+    const Visitor& visitor;
+    T2 const& val2;
+    T3 const& val3;
+    T4 const& val4;
+    
+    TypedVisitorUnwrapper(const Visitor& visitor_, T2 const& val2_, T3 const& val3_, T4 const& val4_)
+        : visitor(visitor_)
+        , val2(val2_)
+        , val3(val3_)
+        , val4(val4_)
+        
+    {
+    }
+
+    template<typename T>
+    R operator()(const T& val1) const
+    {
+        return visitor(val1, val2, val3, val4);
+    }
+};
+
+template< typename R, typename Visitor, typename T2, typename T3, typename T4, typename T5 >
+struct TypedVisitorUnwrapper<5, R, Visitor, T2, T3, T4, T5>
+{
+    const Visitor& visitor;
+    T2 const& val2;
+    T3 const& val3;
+    T4 const& val4;
+    T5 const& val5;
+    
+    TypedVisitorUnwrapper(const Visitor& visitor_, T2 const& val2_, T3 const& val3_, T4 const& val4_, T5 const& val5_)
+        : visitor(visitor_)
+        , val2(val2_)
+        , val3(val3_)
+        , val4(val4_)
+        , val5(val5_)
+        
+    {
+    }
+
+    template<typename T>
+    R operator()(const T& val1) const
+    {
+        return visitor(val1, val2, val3, val4, val5);
+    }
+};
+
+
+
+template<typename R, typename Visitor, typename V2>
+struct VisitorUnwrapper
+{
+    const Visitor& visitor;
+    const V2& r;
+
+    VisitorUnwrapper(const Visitor& visitor_, const V2& r_)
+        : visitor(visitor_)
+        , r(r_)
+    {
+    }
+
+    
+    template< typename T1 >
+    R operator()(T1 const& val1) const
+    {
+        typedef TypedVisitorUnwrapper<2, R, Visitor, T1> visitor_type;
+        return VisitorApplicator<R>::apply(visitor_type(visitor, val1), r);
+    }
+    
+    template< typename T1, typename T2 >
+    R operator()(T1 const& val1, T2 const& val2) const
+    {
+        typedef TypedVisitorUnwrapper<3, R, Visitor, T1, T2> visitor_type;
+        return VisitorApplicator<R>::apply(visitor_type(visitor, val1, val2), r);
+    }
+    
+    template< typename T1, typename T2, typename T3 >
+    R operator()(T1 const& val1, T2 const& val2, T3 const& val3) const
+    {
+        typedef TypedVisitorUnwrapper<4, R, Visitor, T1, T2, T3> visitor_type;
+        return VisitorApplicator<R>::apply(visitor_type(visitor, val1, val2, val3), r);
+    }
+    
+    template< typename T1, typename T2, typename T3, typename T4 >
+    R operator()(T1 const& val1, T2 const& val2, T3 const& val3, T4 const& val4) const
+    {
+        typedef TypedVisitorUnwrapper<5, R, Visitor, T1, T2, T3, T4> visitor_type;
+        return VisitorApplicator<R>::apply(visitor_type(visitor, val1, val2, val3, val4), r);
+    }
+    
+    template< typename T1, typename T2, typename T3, typename T4, typename T5 >
+    R operator()(T1 const& val1, T2 const& val2, T3 const& val3, T4 const& val4, T5 const& val5) const
+    {
+        typedef TypedVisitorUnwrapper<6, R, Visitor, T1, T2, T3, T4, T5> visitor_type;
+        return VisitorApplicator<R>::apply(visitor_type(visitor, val1, val2, val3, val4, val5), r);
+    }
+    
+};
+
+
+template<typename R>
+struct VisitorApplicator
+{
+    template<typename Visitor, typename V1>
+    static R apply(const Visitor& v, const V1& arg)
+    {
+        switch( arg.index() )
+        {
+            case 0: return apply_visitor<0>(v, arg);
+            case 1: return apply_visitor<1>(v, arg);
+            case 2: return apply_visitor<2>(v, arg);
+            case 3: return apply_visitor<3>(v, arg);
+            case 4: return apply_visitor<4>(v, arg);
+            case 5: return apply_visitor<5>(v, arg);
+            case 6: return apply_visitor<6>(v, arg);
+            case 7: return apply_visitor<7>(v, arg);
+            case 8: return apply_visitor<8>(v, arg);
+            case 9: return apply_visitor<9>(v, arg);
+            case 10: return apply_visitor<10>(v, arg);
+            case 11: return apply_visitor<11>(v, arg);
+            case 12: return apply_visitor<12>(v, arg);
+            case 13: return apply_visitor<13>(v, arg);
+            case 14: return apply_visitor<14>(v, arg);
+            case 15: return apply_visitor<15>(v, arg);
+            
+            default: return R();
+        }
+    }
+
+    template<size_t Idx, typename Visitor, typename V1>
+    static R apply_visitor(const Visitor& v, const V1& arg)
+    {
+
+#if variant_CPP11_OR_GREATER
+        typedef typename variant_alternative<Idx, typename std::decay<V1>::type>::type value_type;
+#else
+        typedef typename variant_alternative<Idx, V1>::type value_type;
+#endif
+        return VisitorApplicatorImpl<R, value_type>::apply(v, get<Idx>(arg));
+    }
+
+#if variant_CPP11_OR_GREATER
+    template<typename Visitor, typename V1, typename V2, typename ... V>
+    static R apply(const Visitor& v, const V1& arg1, const V2& arg2, const V ... args)
+    {
+        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
+        Unwrapper unwrapper(v, arg1);
+        return apply(unwrapper, arg2, args ...);
+    }
+#else
+    
+    template< typename Visitor, typename V1, typename V2 >
+    static R apply(const Visitor& v, V1 const& arg1, V2 const& arg2)
+    {
+        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
+        Unwrapper unwrapper(v, arg1);
+        return apply(unwrapper, arg2);
+    }
+    
+    template< typename Visitor, typename V1, typename V2, typename V3 >
+    static R apply(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3)
+    {
+        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
+        Unwrapper unwrapper(v, arg1);
+        return apply(unwrapper, arg2, arg3);
+    }
+    
+    template< typename Visitor, typename V1, typename V2, typename V3, typename V4 >
+    static R apply(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3, V4 const& arg4)
+    {
+        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
+        Unwrapper unwrapper(v, arg1);
+        return apply(unwrapper, arg2, arg3, arg4);
+    }
+    
+    template< typename Visitor, typename V1, typename V2, typename V3, typename V4, typename V5 >
+    static R apply(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3, V4 const& arg4, V5 const& arg5)
+    {
+        typedef VisitorUnwrapper<R, Visitor, V1> Unwrapper;
+        Unwrapper unwrapper(v, arg1);
+        return apply(unwrapper, arg2, arg3, arg4, arg5);
+    }
+    
+#endif
+};
+
+#if variant_CPP11_OR_GREATER
+template< size_t NumVars, typename Visitor, typename ... V >
+struct VisitorImpl
+{
+    typedef decltype(std::declval<Visitor>()(get<0>(static_cast<const V&>(std::declval<V>()))...)) result_type;
+    typedef VisitorApplicator<result_type> applicator_type;
+};
+#endif
+} // detail
+
+#if variant_CPP11_OR_GREATER
+// No perfect forwarding here in order to simplify code
+template< typename Visitor, typename ... V >
+inline auto visit(Visitor const& v, V const& ... vars) -> typename detail::VisitorImpl<sizeof ... (V), Visitor, V... > ::result_type
+{
+    typedef detail::VisitorImpl<sizeof ... (V), Visitor, V... > impl_type;
+    return impl_type::applicator_type::apply(v, vars...);
+}
+#else
+
+template< typename R, typename Visitor, typename V1 >
+inline R visit(const Visitor& v, V1 const& arg1)
+{
+    return detail::VisitorApplicator<R>::apply(v, arg1);
+}
+
+template< typename R, typename Visitor, typename V1, typename V2 >
+inline R visit(const Visitor& v, V1 const& arg1, V2 const& arg2)
+{
+    return detail::VisitorApplicator<R>::apply(v, arg1, arg2);
+}
+
+template< typename R, typename Visitor, typename V1, typename V2, typename V3 >
+inline R visit(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3)
+{
+    return detail::VisitorApplicator<R>::apply(v, arg1, arg2, arg3);
+}
+
+template< typename R, typename Visitor, typename V1, typename V2, typename V3, typename V4 >
+inline R visit(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3, V4 const& arg4)
+{
+    return detail::VisitorApplicator<R>::apply(v, arg1, arg2, arg3, arg4);
+}
+
+template< typename R, typename Visitor, typename V1, typename V2, typename V3, typename V4, typename V5 >
+inline R visit(const Visitor& v, V1 const& arg1, V2 const& arg2, V3 const& arg3, V4 const& arg4, V5 const& arg5)
+{
+    return detail::VisitorApplicator<R>::apply(v, arg1, arg2, arg3, arg4, arg5);
+}
+
+#endif
+
+
+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
+
+// specialize the std::hash algorithm:
+
+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
+    {
+        return nonstd::variants::detail::hash( v );
+    }
+};
+
+} //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