[build] add vendored dependency optional

1 files changed, 1549 insertions, 0 deletions

diff --git a/vendor/optional/include/nonstd/optional.hpp b/vendor/optional/include/nonstd/optional.hpp
new file mode 100644
index 0000000000..d29709b5b5
--- /dev/null
+++ b/vendor/optional/include/nonstd/optional.hpp
@@ -0,0 +1,1549 @@
+//
+// Copyright (c) 2014-2018 Martin Moene
+//
+// https://github.com/martinmoene/optional-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_OPTIONAL_LITE_HPP
+#define NONSTD_OPTIONAL_LITE_HPP
+
+#define optional_lite_MAJOR  3
+#define optional_lite_MINOR  1
+#define optional_lite_PATCH  1
+
+#define optional_lite_VERSION  optional_STRINGIFY(optional_lite_MAJOR) "." optional_STRINGIFY(optional_lite_MINOR) "." optional_STRINGIFY(optional_lite_PATCH)
+
+#define optional_STRINGIFY(  x )  optional_STRINGIFY_( x )
+#define optional_STRINGIFY_( x )  #x
+
+// optional-lite configuration:
+
+#define optional_OPTIONAL_DEFAULT  0
+#define optional_OPTIONAL_NONSTD   1
+#define optional_OPTIONAL_STD      2
+
+#if !defined( optional_CONFIG_SELECT_OPTIONAL )
+# define optional_CONFIG_SELECT_OPTIONAL  ( optional_HAVE_STD_OPTIONAL ? optional_OPTIONAL_STD : optional_OPTIONAL_NONSTD )
+#endif
+
+// C++ language version detection (C++20 is speculative):
+// Note: VC14.0/1900 (VS2015) lacks too much from C++14.
+
+#ifndef   optional_CPLUSPLUS
+# ifdef  _MSVC_LANG
+#  define optional_CPLUSPLUS  (_MSC_VER == 1900 ? 201103L : _MSVC_LANG )
+# else
+#  define optional_CPLUSPLUS  __cplusplus
+# endif
+#endif
+
+#define optional_CPP98_OR_GREATER  ( optional_CPLUSPLUS >= 199711L )
+#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 )
+
+// C++ language version (represent 98 as 3):
+
+#define optional_CPLUSPLUS_V  ( optional_CPLUSPLUS / 100 - (optional_CPLUSPLUS > 200000 ? 2000 : 1994) )
+
+// Use C++17 std::optional if available and requested:
+
+#if optional_CPP17_OR_GREATER && defined(__has_include )
+# if __has_include( <optional> )
+#  define optional_HAVE_STD_OPTIONAL  1
+# else
+#  define optional_HAVE_STD_OPTIONAL  0
+# endif
+#else
+# define  optional_HAVE_STD_OPTIONAL  0
+#endif
+
+#define optional_USES_STD_OPTIONAL  ( (optional_CONFIG_SELECT_OPTIONAL == optional_OPTIONAL_STD) || ((optional_CONFIG_SELECT_OPTIONAL == optional_OPTIONAL_DEFAULT) && optional_HAVE_STD_OPTIONAL) )
+
+// Using std::optional:
+
+#if optional_USES_STD_OPTIONAL
+
+#include <optional>
+
+namespace nonstd {
+
+    using std::optional;
+    using std::bad_optional_access;
+    using std::hash;
+
+    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!=;
+    using std::operator<;
+    using std::operator<=;
+    using std::operator>;
+    using std::operator>=;
+    using std::make_optional;
+    using std::swap;
+}
+
+#else // optional_USES_STD_OPTIONAL
+
+#include <cassert>
+#include <stdexcept>
+#include <utility>
+
+// optional-lite alignment configuration:
+
+#ifndef  optional_CONFIG_MAX_ALIGN_HACK
+# define optional_CONFIG_MAX_ALIGN_HACK  0
+#endif
+
+#ifndef  optional_CONFIG_ALIGN_AS
+// no default, used in #if defined()
+#endif
+
+#ifndef  optional_CONFIG_ALIGN_AS_FALLBACK
+# define optional_CONFIG_ALIGN_AS_FALLBACK  double
+#endif
+
+// Compiler warning suppression:
+
+#if defined (__clang__)
+# pragma clang diagnostic push
+# pragma clang diagnostic ignored "-Wundef"
+#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 )
+
+#if defined(_MSC_VER) && !defined(__clang__)
+# define optional_COMPILER_MSVC_VERSION   (_MSC_VER / 10 - 10 * ( 5 + (_MSC_VER < 1900)) )
+#else
+# define optional_COMPILER_MSVC_VERSION   0
+#endif
+
+#define optional_COMPILER_VERSION( major, minor, patch )  ( 10 * (10 * major + minor ) + patch )
+
+#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__)
+# define optional_COMPILER_CLANG_VERSION  optional_COMPILER_VERSION(__clang_major__, __clang_minor__, __clang_patchlevel__)
+#else
+# define optional_COMPILER_CLANG_VERSION  0
+#endif
+
+#if optional_BETWEEN(optional_COMPILER_MSVC_VERSION, 70, 140 )
+# pragma warning( push )
+# pragma warning( disable: 4345 )   // initialization behavior changed
+#endif
+
+#if optional_BETWEEN(optional_COMPILER_MSVC_VERSION, 70, 150 )
+# pragma warning( push )
+# pragma warning( disable: 4814 )   // in C++14 'constexpr' will not imply 'const'
+#endif
+
+// Presence of language and library features:
+
+#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
+#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
+
+#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
+# undef  optional_CPP11_OR_GREATER
+# define optional_CPP11_OR_GREATER  1
+#endif
+
+// C++ feature usage:
+
+#if optional_HAVE( CONSTEXPR_11 )
+# define optional_constexpr  constexpr
+#else
+# define optional_constexpr  /*constexpr*/
+#endif
+
+#if optional_HAVE( CONSTEXPR_14 )
+# define optional_constexpr14  constexpr
+#else
+# define optional_constexpr14  /*constexpr*/
+#endif
+
+#if optional_HAVE( NOEXCEPT )
+# define optional_noexcept  noexcept
+#else
+# define optional_noexcept  /*noexcept*/
+#endif
+
+#if optional_HAVE( NULLPTR )
+# define optional_nullptr  nullptr
+#else
+# define optional_nullptr  NULL
+#endif
+
+#if optional_HAVE( REF_QUALIFIER )
+# define optional_ref_qual  &
+# define optional_refref_qual  &&
+#else
+# define optional_ref_qual  /*&*/
+# define optional_refref_qual  /*&&*/
+#endif
+
+// additional includes:
+
+#if optional_CPP11_OR_GREATER
+# include <functional>
+#endif
+
+#if optional_HAVE( INITIALIZER_LIST )
+# include <initializer_list>
+#endif
+
+#if optional_HAVE( TYPE_TRAITS )
+# include <type_traits>
+#elif optional_HAVE( TR1_TYPE_TRAITS )
+# include <tr1/type_traits>
+#endif
+
+// Method enabling
+
+#if optional_CPP11_OR_GREATER
+
+# define optional_REQUIRES_T(...) \
+    , typename = typename std::enable_if<__VA_ARGS__>::type
+
+# define optional_REQUIRES_R(R, ...) \
+    typename std::enable_if<__VA_ARGS__, R>::type
+
+# define optional_REQUIRES_A(...) \
+    , typename std::enable_if<__VA_ARGS__, void*>::type = optional_nullptr
+
+#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(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
+
+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
+
+//
+// optional:
+//
+
+namespace nonstd { namespace optional_lite {
+
+namespace detail {
+
+#if optional_HAVE( CONDITIONAL )
+    using std::conditional;
+#else
+    template< bool B, typename T, typename F > struct conditional              { typedef T type; };
+    template<         typename T, typename F > struct conditional<false, T, F> { typedef F type; };
+#endif // optional_HAVE_CONDITIONAL
+
+} // namespace detail
+
+#if optional_CPP11_OR_GREATER
+
+namespace std20 {
+
+// type traits C++20:
+
+template< typename T >
+struct remove_cvref
+{
+    typedef typename std::remove_cv< typename std::remove_reference<T>::type >::type type;
+};
+
+} // namespace std20
+
+#endif // optional_CPP11_OR_GREATER
+
+/// class optional
+
+template< typename T >
+class optional;
+
+namespace detail {
+
+// C++11 emulation:
+
+struct nulltype{};
+
+template< typename Head, typename Tail >
+struct typelist
+{
+    typedef Head head;
+    typedef Tail tail;
+};
+
+#if optional_CONFIG_MAX_ALIGN_HACK
+
+// Max align, use most restricted type for alignment:
+
+#define optional_UNIQUE(  name )       optional_UNIQUE2( name, __LINE__ )
+#define optional_UNIQUE2( name, line ) optional_UNIQUE3( name, line )
+#define optional_UNIQUE3( name, line ) name ## line
+
+#define optional_ALIGN_TYPE( type ) \
+    type optional_UNIQUE( _t ); struct_t< type > optional_UNIQUE( _st )
+
+template< typename T >
+struct struct_t { T _; };
+
+union max_align_t
+{
+    optional_ALIGN_TYPE( char );
+    optional_ALIGN_TYPE( short int );
+    optional_ALIGN_TYPE( int );
+    optional_ALIGN_TYPE( long int  );
+    optional_ALIGN_TYPE( float  );
+    optional_ALIGN_TYPE( double );
+    optional_ALIGN_TYPE( long double );
+    optional_ALIGN_TYPE( char * );
+    optional_ALIGN_TYPE( short int * );
+    optional_ALIGN_TYPE( int *  );
+    optional_ALIGN_TYPE( long int * );
+    optional_ALIGN_TYPE( float * );
+    optional_ALIGN_TYPE( double * );
+    optional_ALIGN_TYPE( long double * );
+    optional_ALIGN_TYPE( void * );
+
+#ifdef HAVE_LONG_LONG
+    optional_ALIGN_TYPE( long long );
+#endif
+
+    struct Unknown;
+
+    Unknown ( * optional_UNIQUE(_) )( Unknown );
+    Unknown * Unknown::* optional_UNIQUE(_);
+    Unknown ( Unknown::* optional_UNIQUE(_) )( Unknown );
+
+    struct_t< Unknown ( * )( Unknown)         > optional_UNIQUE(_);
+    struct_t< Unknown * Unknown::*            > optional_UNIQUE(_);
+    struct_t< Unknown ( Unknown::* )(Unknown) > optional_UNIQUE(_);
+};
+
+#undef optional_UNIQUE
+#undef optional_UNIQUE2
+#undef optional_UNIQUE3
+
+#undef optional_ALIGN_TYPE
+
+#elif defined( optional_CONFIG_ALIGN_AS ) // optional_CONFIG_MAX_ALIGN_HACK
+
+// Use user-specified type for alignment:
+
+#define optional_ALIGN_AS( unused ) \
+    optional_CONFIG_ALIGN_AS
+
+#else // optional_CONFIG_MAX_ALIGN_HACK
+
+// Determine POD type to use for alignment:
+
+#define optional_ALIGN_AS( to_align ) \
+    typename type_of_size< alignment_types, 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 { value = A < S ? A : S };
+};
+
+template< typename T >
+struct alignment_of
+{
+    enum { 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 optional_CONFIG_ALIGN_AS_FALLBACK type;
+};
+
+template< typename T>
+struct struct_t { T _; };
+
+#define optional_ALIGN_TYPE( type ) \
+    typelist< type , typelist< struct_t< type >
+
+struct Unknown;
+
+typedef
+    optional_ALIGN_TYPE( char ),
+    optional_ALIGN_TYPE( short ),
+    optional_ALIGN_TYPE( int ),
+    optional_ALIGN_TYPE( long ),
+    optional_ALIGN_TYPE( float ),
+    optional_ALIGN_TYPE( double ),
+    optional_ALIGN_TYPE( long double ),
+
+    optional_ALIGN_TYPE( char *),
+    optional_ALIGN_TYPE( short * ),
+    optional_ALIGN_TYPE( int * ),
+    optional_ALIGN_TYPE( long * ),
+    optional_ALIGN_TYPE( float * ),
+    optional_ALIGN_TYPE( double * ),
+    optional_ALIGN_TYPE( long double * ),
+
+    optional_ALIGN_TYPE( Unknown ( * )( Unknown ) ),
+    optional_ALIGN_TYPE( Unknown * Unknown::*     ),
+    optional_ALIGN_TYPE( Unknown ( Unknown::* )( Unknown ) ),
+
+    nulltype
+    > > > > > > >    > > > > > > >
+    > > > > > > >    > > > > > > >
+    > > > > > >
+    alignment_types;
+
+#undef optional_ALIGN_TYPE
+
+#endif // optional_CONFIG_MAX_ALIGN_HACK
+
+/// C++03 constructed union to hold value.
+
+template< typename T >
+union storage_t
+{
+//private:
+//    template< typename > friend class optional;
+
+    typedef T value_type;
+
+    storage_t() {}
+
+    storage_t( value_type const & v )
+    {
+        construct_value( v );
+    }
+
+    void construct_value( value_type const & v )
+    {
+        ::new( value_ptr() ) value_type( v );
+    }
+
+#if optional_CPP11_OR_GREATER
+
+    storage_t( value_type && v )
+    {
+        construct_value( std::move( v ) );
+    }
+
+    void construct_value( value_type && v )
+    {
+        ::new( value_ptr() ) value_type( std::move( v ) );
+    }
+
+    template< class... Args >
+    void emplace( Args&&... args )
+    {
+        ::new( value_ptr() ) value_type( std::forward<Args>(args)... );
+    }
+
+    template< class U, class... Args >
+    void emplace( std::initializer_list<U> il, Args&&... args )
+    {
+        ::new( value_ptr() ) value_type( il, std::forward<Args>(args)... );
+    }
+
+#endif
+
+    void destruct_value()
+    {
+        value_ptr()->~T();
+    }
+
+    value_type const * value_ptr() const
+    {
+        return as<value_type>();
+    }
+
+    value_type * value_ptr()
+    {
+        return as<value_type>();
+    }
+
+    value_type const & value() const optional_ref_qual
+    {
+        return * value_ptr();
+    }
+
+    value_type & value() optional_ref_qual
+    {
+        return * value_ptr();
+    }
+
+#if optional_CPP11_OR_GREATER
+
+    value_type const && value() const optional_refref_qual
+    {
+        return std::move( value() );
+    }
+
+    value_type && value() optional_refref_qual
+    {
+        return std::move( value() );
+    }
+
+#endif
+
+#if optional_CPP11_OR_GREATER
+
+    using aligned_storage_t = typename std::aligned_storage< sizeof(value_type), alignof(value_type) >::type;
+    aligned_storage_t data;
+
+#elif optional_CONFIG_MAX_ALIGN_HACK
+
+    typedef struct { unsigned char data[ sizeof(value_type) ]; } aligned_storage_t;
+
+    max_align_t hack;
+    aligned_storage_t data;
+
+#else
+    typedef optional_ALIGN_AS(value_type) align_as_type;
+
+    typedef struct { align_as_type data[ 1 + ( sizeof(value_type) - 1 ) / sizeof(align_as_type) ]; } aligned_storage_t;
+    aligned_storage_t data;
+
+#   undef optional_ALIGN_AS
+
+#endif // optional_CONFIG_MAX_ALIGN_HACK
+
+    void * ptr() optional_noexcept
+    {
+        return &data;
+    }
+
+    void const * ptr() const optional_noexcept
+    {
+        return &data;
+    }
+
+    template <typename U>
+    U * as()
+    {
+        return reinterpret_cast<U*>( ptr() );
+    }
+
+    template <typename U>
+    U const * as() const
+    {
+        return reinterpret_cast<U const *>( ptr() );
+    }
+};
+
+} // namespace detail
+
+/// disengaged state tag
+
+struct nullopt_t
+{
+    struct init{};
+    optional_constexpr nullopt_t( init ) {}
+};
+
+#if optional_HAVE( CONSTEXPR_11 )
+constexpr nullopt_t nullopt{ nullopt_t::init{} };
+#else
+// extra parenthesis to prevent the most vexing parse:
+const nullopt_t nullopt(( nullopt_t::init() ));
+#endif
+
+/// optional access error
+
+class bad_optional_access : public std::logic_error
+{
+public:
+  explicit bad_optional_access()
+  : logic_error( "bad optional access" ) {}
+};
+
+/// optional
+
+template< typename T>
+class optional
+{
+private:
+    template< typename > friend class optional;
+
+    typedef void (optional::*safe_bool)() const;
+
+public:
+    typedef T value_type;
+
+    // x.x.3.1, constructors
+
+    // 1a - default construct
+    optional_constexpr optional() optional_noexcept
+    : has_value_( false )
+    , contained()
+    {}
+
+    // 1b - construct explicitly empty
+    optional_constexpr optional( nullopt_t ) optional_noexcept
+    : has_value_( false )
+    , contained()
+    {}
+
+    // 2 - copy-construct
+    optional_constexpr14 optional( optional const & other
+#if optional_CPP11_OR_GREATER
+        optional_REQUIRES_A(
+            true || std::is_copy_constructible<T>::value
+        )
+#endif
+    )
+    : has_value_( other.has_value() )
+    {
+        if ( other.has_value() )
+            contained.construct_value( other.contained.value() );
+    }
+
+#if optional_CPP11_OR_GREATER
+
+    // 3 (C++11) - move-construct from optional
+    optional_constexpr14 optional( optional && other
+        optional_REQUIRES_A(
+            true || std::is_move_constructible<T>::value
+        )
+    ) noexcept( std::is_nothrow_move_constructible<T>::value )
+    : has_value_( other.has_value() )
+    {
+        if ( other.has_value() )
+            contained.construct_value( std::move( other.contained.value() ) );
+    }
+
+    // 4 (C++11) - explicit converting copy-construct from optional
+    template< typename U >
+    explicit optional( optional<U> const & other
+        optional_REQUIRES_A(
+            std::is_constructible<T, U const &>::value
+            && !std::is_constructible<T, optional<U> &          >::value
+            && !std::is_constructible<T, optional<U> &&         >::value
+            && !std::is_constructible<T, optional<U> const &    >::value
+            && !std::is_constructible<T, optional<U> const &&   >::value
+            && !std::is_convertible<     optional<U> &       , T>::value
+            && !std::is_convertible<     optional<U> &&      , T>::value
+            && !std::is_convertible<     optional<U> const & , T>::value
+            && !std::is_convertible<     optional<U> const &&, T>::value
+            && !std::is_convertible<               U const & , T>::value /*=> explicit */
+        )
+    )
+    : has_value_( other.has_value() )
+    {
+        if ( other.has_value() )
+            contained.construct_value( other.contained.value() );
+    }
+#endif // optional_CPP11_OR_GREATER
+
+    // 4 (C++98 and later) - non-explicit converting copy-construct from optional
+    template< typename U >
+    optional( optional<U> const & other
+#if optional_CPP11_OR_GREATER
+        optional_REQUIRES_A(
+            std::is_constructible<T, U const &>::value
+            && !std::is_constructible<T, optional<U> &          >::value
+            && !std::is_constructible<T, optional<U> &&         >::value
+            && !std::is_constructible<T, optional<U> const &    >::value
+            && !std::is_constructible<T, optional<U> const &&   >::value
+            && !std::is_convertible<     optional<U> &       , T>::value
+            && !std::is_convertible<     optional<U> &&      , T>::value
+            && !std::is_convertible<     optional<U> const & , T>::value
+            && !std::is_convertible<     optional<U> const &&, T>::value
+            &&  std::is_convertible<               U const & , T>::value /*=> non-explicit */
+        )
+#endif // optional_CPP11_OR_GREATER
+    )
+    : has_value_( other.has_value() )
+    {
+        if ( other.has_value() )
+            contained.construct_value( other.contained.value() );
+    }
+
+#if optional_CPP11_OR_GREATER
+
+    // 5a (C++11) - explicit converting move-construct from optional
+    template< typename U >
+    optional( optional<U> && other
+        optional_REQUIRES_A(
+            std::is_constructible<T, U const &>::value
+            && !std::is_constructible<T, optional<U> &          >::value
+            && !std::is_constructible<T, optional<U> &&         >::value
+            && !std::is_constructible<T, optional<U> const &    >::value
+            && !std::is_constructible<T, optional<U> const &&   >::value
+            && !std::is_convertible<     optional<U> &       , T>::value
+            && !std::is_convertible<     optional<U> &&      , T>::value
+            && !std::is_convertible<     optional<U> const & , T>::value
+            && !std::is_convertible<     optional<U> const &&, T>::value
+            && !std::is_convertible<                     U &&, T>::value /*=> explicit */
+        )
+    )
+    : has_value_( other.has_value() )
+    {
+        if ( other.has_value() )
+            contained.construct_value( std::move( other.contained.value() ) );
+    }
+
+    // 5a (C++11) - non-explicit converting move-construct from optional
+    template< typename U >
+    optional( optional<U> && other
+        optional_REQUIRES_A(
+            std::is_constructible<T, U const &>::value
+            && !std::is_constructible<T, optional<U> &          >::value
+            && !std::is_constructible<T, optional<U> &&         >::value
+            && !std::is_constructible<T, optional<U> const &    >::value
+            && !std::is_constructible<T, optional<U> const &&   >::value
+            && !std::is_convertible<     optional<U> &       , T>::value
+            && !std::is_convertible<     optional<U> &&      , T>::value
+            && !std::is_convertible<     optional<U> const & , T>::value
+            && !std::is_convertible<     optional<U> const &&, T>::value
+            &&  std::is_convertible<                     U &&, T>::value /*=> non-explicit */
+        )
+    )
+    : has_value_( other.has_value() )
+    {
+        if ( other.has_value() )
+            contained.construct_value( std::move( other.contained.value() ) );
+    }
+
+    // 6 (C++11) - in-place construct
+    template< typename... Args
+        optional_REQUIRES_T(
+            std::is_constructible<T, Args&&...>::value
+        )
+    >
+    optional_constexpr explicit optional( nonstd_lite_in_place_t(T), Args&&... args )
+    : has_value_( true )
+    , contained( T( std::forward<Args>(args)...) )
+    {}
+
+    // 7 (C++11) - in-place construct,  initializer-list
+    template< typename U, typename... Args
+        optional_REQUIRES_T(
+            std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value
+        )
+    >
+    optional_constexpr explicit optional( nonstd_lite_in_place_t(T), std::initializer_list<U> il, Args&&... args )
+    : has_value_( true )
+    , contained( T( il, std::forward<Args>(args)...) )
+    {}
+
+    // 8a (C++11) - explicit move construct from value
+    template< typename U = value_type >
+    optional_constexpr explicit optional( U && value
+        optional_REQUIRES_A(
+            std::is_constructible<T, U&&>::value
+            && !std::is_same<typename std20::remove_cvref<U>::type, nonstd_lite_in_place_t(U)>::value
+            && !std::is_same<typename std20::remove_cvref<U>::type, optional<T>>::value
+            && !std::is_convertible<U&&, T>::value /*=> explicit */
+        )
+    )
+    : has_value_( true )
+    , contained( std::forward<U>( value ) )
+    {}
+
+    // 8a (C++11) - non-explicit move construct from value
+    template< typename U = value_type >
+    optional_constexpr optional( U && value
+        optional_REQUIRES_A(
+            std::is_constructible<T, U&&>::value
+            && !std::is_same<typename std20::remove_cvref<U>::type, nonstd_lite_in_place_t(U)>::value
+            && !std::is_same<typename std20::remove_cvref<U>::type, optional<T>>::value
+            && std::is_convertible<U&&, T>::value /*=> non-explicit */
+        )
+    )
+    : has_value_( true )
+    , contained( std::forward<U>( value ) )
+    {}
+
+#else // optional_CPP11_OR_GREATER
+
+    // 8 (C++98)
+    optional( value_type const & value )
+    : has_value_( true )
+    , contained( value )
+    {}
+
+#endif // optional_CPP11_OR_GREATER
+
+    // x.x.3.2, destructor
+
+    ~optional()
+    {
+        if ( has_value() )
+            contained.destruct_value();
+    }
+
+    // x.x.3.3, assignment
+
+    // 1 (C++98and later) -  assign explicitly empty
+    optional & operator=( nullopt_t ) optional_noexcept
+    {
+        reset();
+        return *this;
+    }
+
+    // 2 (C++98and later) - copy-assign from optional
+#if optional_CPP11_OR_GREATER
+    optional_REQUIRES_R(
+        optional &,
+        true
+//      std::is_copy_constructible<T>::value
+//      && std::is_copy_assignable<T>::value
+    )
+    operator=( optional const & other )
+        noexcept(
+            std::is_nothrow_move_assignable<T>::value
+            && std::is_nothrow_move_constructible<T>::value
+        )
+#else
+    optional & operator=( optional const & other )
+#endif
+    {
+        if      ( has_value() == true  && other.has_value() == false ) reset();
+        else if ( has_value() == false && other.has_value() == true  ) initialize( *other );
+        else if ( has_value() == true  && other.has_value() == true  ) contained.value() = *other;
+        return *this;
+    }
+
+#if optional_CPP11_OR_GREATER
+
+    // 3 (C++11) - move-assign from optional
+    optional_REQUIRES_R(
+        optional &,
+        true
+//      std::is_move_constructible<T>::value
+//      && std::is_move_assignable<T>::value
+    )
+    operator=( optional && other ) noexcept
+    {
+        if      ( has_value() == true  && other.has_value() == false ) reset();
+        else if ( has_value() == false && other.has_value() == true  ) initialize( std::move( *other ) );
+        else if ( has_value() == true  && other.has_value() == true  ) contained.value() = std::move( *other );
+        return *this;
+    }
+
+    // 4 (C++11) - move-assign from value
+    template< typename U = T >
+        optional_REQUIRES_R(
+            optional &,
+            std::is_constructible<T , U>::value
+            && std::is_assignable<T&, U>::value
+            && !std::is_same<typename std20::remove_cvref<U>::type, nonstd_lite_in_place_t(U)>::value
+            && !std::is_same<typename std20::remove_cvref<U>::type, optional<T>>::value
+//          && !(std::is_scalar<T>::value && std::is_same<T, typename std::decay<U>::type>::value)
+        )
+    operator=( U && value )
+    {
+        if ( has_value() ) contained.value() = std::forward<U>( value );
+        else               initialize( T( std::forward<U>( value ) ) );
+        return *this;
+    }
+
+#else // optional_CPP11_OR_GREATER
+
+    // 4 (C++98) - copy-assign from value
+    template< typename U /*= T*/ >
+    optional & operator=( U const & value )
+    {
+        if ( has_value() ) contained.value() = value;
+        else               initialize( T( value ) );
+        return *this;
+    }
+
+#endif // optional_CPP11_OR_GREATER
+
+    // 5 (C++98 and later) - converting copy-assign from optional
+    template< typename U >
+#if optional_CPP11_OR_GREATER
+        optional_REQUIRES_R(
+            optional&,
+            std::is_constructible<  T , U const &>::value
+            &&  std::is_assignable< T&, U const &>::value
+            && !std::is_constructible<T, optional<U> &          >::value
+            && !std::is_constructible<T, optional<U> &&         >::value
+            && !std::is_constructible<T, optional<U> const &    >::value
+            && !std::is_constructible<T, optional<U> const &&   >::value
+            && !std::is_convertible<     optional<U> &       , T>::value
+            && !std::is_convertible<     optional<U> &&      , T>::value
+            && !std::is_convertible<     optional<U> const & , T>::value
+            && !std::is_convertible<     optional<U> const &&, T>::value
+            && !std::is_assignable<  T&, optional<U> &          >::value
+            && !std::is_assignable<  T&, optional<U> &&         >::value
+            && !std::is_assignable<  T&, optional<U> const &    >::value
+            && !std::is_assignable<  T&, optional<U> const &&   >::value
+        )
+#else
+    optional&
+#endif // optional_CPP11_OR_GREATER
+    operator=( optional<U> const & other )
+    {
+        return *this = optional( other );
+    }
+
+#if optional_CPP11_OR_GREATER
+
+    // 6 (C++11) -  converting move-assign from optional
+    template< typename U >
+        optional_REQUIRES_R(
+            optional&,
+            std::is_constructible<  T , U>::value
+            &&  std::is_assignable< T&, U>::value
+            && !std::is_constructible<T, optional<U> &          >::value
+            && !std::is_constructible<T, optional<U> &&         >::value
+            && !std::is_constructible<T, optional<U> const &    >::value
+            && !std::is_constructible<T, optional<U> const &&   >::value
+            && !std::is_convertible<     optional<U> &       , T>::value
+            && !std::is_convertible<     optional<U> &&      , T>::value
+            && !std::is_convertible<     optional<U> const & , T>::value
+            && !std::is_convertible<     optional<U> const &&, T>::value
+            && !std::is_assignable<  T&, optional<U> &          >::value
+            && !std::is_assignable<  T&, optional<U> &&         >::value
+            && !std::is_assignable<  T&, optional<U> const &    >::value
+            && !std::is_assignable<  T&, optional<U> const &&   >::value
+        )
+    operator=( optional<U> && other )
+    {
+        return *this = optional( std::move( other ) );
+    }
+
+    // 7 (C++11) - emplace
+    template< typename... Args
+        optional_REQUIRES_T(
+            std::is_constructible<T, Args&&...>::value
+        )
+    >
+    T& emplace( Args&&... args )
+    {
+        *this = nullopt;
+        contained.emplace( std::forward<Args>(args)...  );
+        has_value_ = true;
+        return contained.value();
+    }
+
+    // 8 (C++11) - emplace, initializer-list
+    template< typename U, typename... Args
+        optional_REQUIRES_T(
+            std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value
+        )
+    >
+    T& emplace( std::initializer_list<U> il, Args&&... args )
+    {
+        *this = nullopt;
+        contained.emplace( il, std::forward<Args>(args)...  );
+        has_value_ = true;
+        return contained.value();
+    }
+
+#endif // optional_CPP11_OR_GREATER
+
+    // x.x.3.4, swap
+
+    void swap( optional & other )
+#if optional_CPP11_OR_GREATER
+        noexcept(
+            std::is_nothrow_move_constructible<T>::value
+            && noexcept( std::swap( std::declval<T&>(), std::declval<T&>() ) )
+        )
+#endif
+    {
+        using std::swap;
+        if      ( has_value() == true  && other.has_value() == true  ) { swap( **this, *other ); }
+        else if ( has_value() == false && other.has_value() == true  ) { initialize( *other ); other.reset(); }
+        else if ( has_value() == true  && other.has_value() == false ) { other.initialize( **this ); reset(); }
+    }
+
+    // x.x.3.5, observers
+
+    optional_constexpr value_type const * operator ->() const
+    {
+        return assert( has_value() ),
+            contained.value_ptr();
+    }
+
+    optional_constexpr14 value_type * operator ->()
+    {
+        return assert( has_value() ),
+            contained.value_ptr();
+    }
+
+    optional_constexpr value_type const & operator *() const optional_ref_qual
+    {
+        return assert( has_value() ),
+            contained.value();
+    }
+
+    optional_constexpr14 value_type & operator *() optional_ref_qual
+    {
+        return assert( has_value() ),
+            contained.value();
+    }
+
+#if optional_CPP11_OR_GREATER
+
+    optional_constexpr value_type const && operator *() const optional_refref_qual
+    {
+        return std::move( **this );
+    }
+
+    optional_constexpr14 value_type && operator *() optional_refref_qual
+    {
+        return std::move( **this );
+    }
+
+#endif
+
+#if optional_CPP11_OR_GREATER
+    optional_constexpr explicit operator bool() const optional_noexcept
+    {
+        return has_value();
+    }
+#else
+    optional_constexpr operator safe_bool() const optional_noexcept
+    {
+        return has_value() ? &optional::this_type_does_not_support_comparisons : 0;
+    }
+#endif
+
+    optional_constexpr bool has_value() const optional_noexcept
+    {
+        return has_value_;
+    }
+
+    optional_constexpr14 value_type const & value() const optional_ref_qual
+    {
+        if ( ! has_value() )
+            throw bad_optional_access();
+
+        return contained.value();
+    }
+
+    optional_constexpr14 value_type & value() optional_ref_qual
+    {
+        if ( ! has_value() )
+            throw bad_optional_access();
+
+        return contained.value();
+    }
+
+#if optional_HAVE( REF_QUALIFIER )
+
+    optional_constexpr14 value_type const && value() const optional_refref_qual
+    {
+        return std::move( value() );
+    }
+
+    optional_constexpr14 value_type && value() optional_refref_qual
+    {
+        return std::move( value() );
+    }
+
+#endif
+
+#if optional_CPP11_OR_GREATER
+
+    template< typename U >
+    optional_constexpr value_type value_or( U && v ) const optional_ref_qual
+    {
+        return has_value() ? contained.value() : static_cast<T>(std::forward<U>( v ) );
+    }
+
+    template< typename U >
+    optional_constexpr value_type value_or( U && v ) const optional_refref_qual
+    {
+        return has_value() ? std::move( contained.value() ) : static_cast<T>(std::forward<U>( v ) );
+    }
+
+#else
+
+    template< typename U >
+    optional_constexpr value_type value_or( U const & v ) const
+    {
+        return has_value() ? contained.value() : static_cast<value_type>( v );
+    }
+
+#endif // optional_CPP11_OR_GREATER
+
+    // x.x.3.6, modifiers
+
+    void reset() optional_noexcept
+    {
+        if ( has_value() )
+            contained.destruct_value();
+
+        has_value_ = false;
+    }
+
+private:
+    void this_type_does_not_support_comparisons() const {}
+
+    template< typename V >
+    void initialize( V const & value )
+    {
+        assert( ! has_value()  );
+        contained.construct_value( value );
+        has_value_ = true;
+    }
+
+#if optional_CPP11_OR_GREATER
+    template< typename V >
+    void initialize( V && value )
+    {
+        assert( ! has_value()  );
+        contained.construct_value( std::move( value ) );
+        has_value_ = true;
+    }
+
+#endif
+
+private:
+    bool has_value_;
+    detail::storage_t< value_type > contained;
+
+};
+
+// Relational operators
+
+template< typename T, typename U >
+inline optional_constexpr bool operator==( optional<T> const & x, optional<U> const & y )
+{
+    return bool(x) != bool(y) ? false : !bool( x ) ? true : *x == *y;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator!=( optional<T> const & x, optional<U> const & y )
+{
+    return !(x == y);
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator<( optional<T> const & x, optional<U> const & y )
+{
+    return (!y) ? false : (!x) ? true : *x < *y;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator>( optional<T> const & x, optional<U> const & y )
+{
+    return (y < x);
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator<=( optional<T> const & x, optional<U> const & y )
+{
+    return !(y < x);
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator>=( optional<T> const & x, optional<U> const & y )
+{
+    return !(x < y);
+}
+
+// Comparison with nullopt
+
+template< typename T >
+inline optional_constexpr bool operator==( optional<T> const & x, nullopt_t ) optional_noexcept
+{
+    return (!x);
+}
+
+template< typename T >
+inline optional_constexpr bool operator==( nullopt_t, optional<T> const & x ) optional_noexcept
+{
+    return (!x);
+}
+
+template< typename T >
+inline optional_constexpr bool operator!=( optional<T> const & x, nullopt_t ) optional_noexcept
+{
+    return bool(x);
+}
+
+template< typename T >
+inline optional_constexpr bool operator!=( nullopt_t, optional<T> const & x ) optional_noexcept
+{
+    return bool(x);
+}
+
+template< typename T >
+inline optional_constexpr bool operator<( optional<T> const &, nullopt_t ) optional_noexcept
+{
+    return false;
+}
+
+template< typename T >
+inline optional_constexpr bool operator<( nullopt_t, optional<T> const & x ) optional_noexcept
+{
+    return bool(x);
+}
+
+template< typename T >
+inline optional_constexpr bool operator<=( optional<T> const & x, nullopt_t ) optional_noexcept
+{
+    return (!x);
+}
+
+template< typename T >
+inline optional_constexpr bool operator<=( nullopt_t, optional<T> const & ) optional_noexcept
+{
+    return true;
+}
+
+template< typename T >
+inline optional_constexpr bool operator>( optional<T> const & x, nullopt_t ) optional_noexcept
+{
+    return bool(x);
+}
+
+template< typename T >
+inline optional_constexpr bool operator>( nullopt_t, optional<T> const & ) optional_noexcept
+{
+    return false;
+}
+
+template< typename T >
+inline optional_constexpr bool operator>=( optional<T> const &, nullopt_t ) optional_noexcept
+{
+    return true;
+}
+
+template< typename T >
+inline optional_constexpr bool operator>=( nullopt_t, optional<T> const & x ) optional_noexcept
+{
+    return (!x);
+}
+
+// Comparison with T
+
+template< typename T, typename U >
+inline optional_constexpr bool operator==( optional<T> const & x, U const & v )
+{
+    return bool(x) ? *x == v : false;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator==( U const & v, optional<T> const & x )
+{
+    return bool(x) ? v == *x : false;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator!=( optional<T> const & x, U const & v )
+{
+    return bool(x) ? *x != v : true;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator!=( U const & v, optional<T> const & x )
+{
+    return bool(x) ? v != *x : true;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator<( optional<T> const & x, U const & v )
+{
+    return bool(x) ? *x < v : true;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator<( U const & v, optional<T> const & x )
+{
+    return bool(x) ? v < *x : false;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator<=( optional<T> const & x, U const & v )
+{
+    return bool(x) ? *x <= v : true;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator<=( U const & v, optional<T> const & x )
+{
+    return bool(x) ? v <= *x : false;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator>( optional<T> const & x, U const & v )
+{
+    return bool(x) ? *x > v : false;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator>( U const & v, optional<T> const & x )
+{
+    return bool(x) ? v > *x : true;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator>=( optional<T> const & x, U const & v )
+{
+    return bool(x) ? *x >= v : false;
+}
+
+template< typename T, typename U >
+inline optional_constexpr bool operator>=( U const & v, optional<T> const & x )
+{
+    return bool(x) ? v >= *x : true;
+}
+
+// Specialized algorithms
+
+template< typename T >
+void swap( optional<T> & x, optional<T> & y )
+#if optional_CPP11_OR_GREATER
+    noexcept( noexcept( x.swap(y) ) )
+#endif
+{
+    x.swap( y );
+}
+
+#if optional_CPP11_OR_GREATER
+
+template< typename T >
+optional_constexpr optional< typename std::decay<T>::type > make_optional( T && value )
+{
+    return optional< typename std::decay<T>::type >( std::forward<T>( value ) );
+}
+
+template< typename T, typename...Args >
+optional_constexpr optional<T> make_optional( Args&&... args )
+{
+    return optional<T>( nonstd_lite_in_place(T), std::forward<Args>(args)...);
+}
+
+template< typename T, typename U, typename... Args >
+optional_constexpr optional<T> make_optional( std::initializer_list<U> il, Args&&... args )
+{
+    return optional<T>( nonstd_lite_in_place(T), il, std::forward<Args>(args)...);
+}
+
+#else
+
+template< typename T >
+optional<T> make_optional( T const & value )
+{
+    return optional<T>( value );
+}
+
+#endif // optional_CPP11_OR_GREATER
+
+} // namespace optional_lite
+
+using namespace optional_lite;
+
+} // namespace nonstd
+
+#if optional_CPP11_OR_GREATER
+
+// specialize the std::hash algorithm:
+
+namespace std {
+
+template< class T >
+struct hash< nonstd::optional<T> >
+{
+public:
+    std::size_t operator()( nonstd::optional<T> const & v ) const optional_noexcept
+    {
+        return bool( v ) ? hash<T>()( *v ) : 0;
+    }
+};
+
+} //namespace std
+
+#endif // optional_CPP11_OR_GREATER
+
+#if defined (__clang__)
+# pragma clang diagnostic pop
+#elif defined (__GNUC__)
+# pragma GCC   diagnostic pop
+#endif
+
+#endif // optional_USES_STD_OPTIONAL
+
+#endif // NONSTD_OPTIONAL_LITE_HPP