// Vendored from git tag v3.2.0

// 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  2
#define optional_lite_PATCH  0

#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

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

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

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

#ifndef   optional_CPLUSPLUS
# if defined(_MSVC_LANG ) && !defined(__clang__)
#  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_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) )

//
// 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> /*unused*/ = 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> /*unused*/ = 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> /*unused*/ = 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> /*unused*/ = 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

#include <optional>

namespace nonstd {

    using std::optional;
    using std::bad_optional_access;
    using std::hash;

    using std::nullopt;
    using std::nullopt_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 <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"
#elif defined(_MSC_VER )
# pragma warning( push )
#endif

// half-open range [lo..hi):
#define optional_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 optional_COMPILER_MSVC_VER      (_MSC_VER )
# define optional_COMPILER_MSVC_VERSION  (_MSC_VER / 10 - 10 * ( 5 + (_MSC_VER < 1900 ) ) )
#else
# 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__)
# 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( disable: 4345 )   // initialization behavior changed
#endif

#if optional_BETWEEN(optional_COMPILER_MSVC_VERSION, 70, 150 )
# 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 )

#ifdef _HAS_CPP0X
# define optional_HAS_CPP0X  _HAS_CPP0X
#else
# define optional_HAS_CPP0X  0
#endif

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

#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_IS_DEFAULT        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:

#define optional_HAVE_NODISCARD         optional_CPP17_000

// 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 )
# define optional_constexpr  constexpr
#else
# define optional_constexpr  /*constexpr*/
#endif

#if optional_HAVE( IS_DEFAULT )
# define optional_is_default  = default;
#else
# define optional_is_default  {}
#endif

#if optional_HAVE( CONSTEXPR_14 )
# define optional_constexpr14  constexpr
#else
# define optional_constexpr14  /*constexpr*/
#endif

#if optional_HAVE( NODISCARD )
# define optional_nodiscard  [[nodiscard]]
#else
# define optional_nodiscard  /*[[nodiscard]]*/
#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 )
// NOLINTNEXTLINE( bugprone-macro-parentheses )
# define optional_ref_qual  &
# define optional_refref_qual  &&
#else
# define optional_ref_qual  /*&*/
# define optional_refref_qual  /*&&*/
#endif

// additional includes:

#if optional_CONFIG_NO_EXCEPTIONS
// already included: <cassert>
#else
# include <stdexcept>
#endif

#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_0(...) \
    template< bool B = (__VA_ARGS__), typename std::enable_if<B, int>::type = 0 >

#define optional_REQUIRES_T(...) \
    , typename = typename std::enable_if< (__VA_ARGS__), nonstd::optional_lite::detail::enabler >::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 = nullptr

#endif

//
// optional:
//

namespace nonstd { namespace optional_lite {

namespace std11 {

#if optional_CPP11_OR_GREATER
    using std::move;
#else
    template< typename T > T & move( T & t ) { return t; }
#endif

#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 std11

#if optional_CPP11_OR_GREATER

/// type traits C++17:

namespace std17 {

#if optional_CPP17_OR_GREATER

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

#elif optional_CPP11_OR_GREATER

namespace detail {

using std::swap;

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

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

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

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

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

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

} // namespace detail

// is [nothow] swappable:

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

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

#endif // optional_CPP17_OR_GREATER

} // namespace std17

/// type traits C++20:

namespace std20 {

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 {

// for optional_REQUIRES_T

#if optional_CPP11_OR_GREATER
enum class enabler{};
#endif

// 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 std11::conditional<
        N == sizeof( typename List::head ),
            typename List::head,
            typename type_of_size<typename List::tail, N >::type >::type type;
};

template< size_t N >
struct type_of_size< nulltype, N >
{
    typedef 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() optional_is_default

      explicit 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

  explicit 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(); }

  optional_nodiscard value_type const* value_ptr() const { return as<value_type>(); }

  value_type* value_ptr() { return as<value_type>(); }

  optional_nodiscard 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

  optional_nodiscard 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

  optional_nodiscard void* ptr() optional_noexcept { return &data; }

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

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

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

}  // namespace detail

/// disengaged state tag

struct nullopt_t {
  struct init {};
  explicit optional_constexpr nullopt_t(init /*unused*/) optional_noexcept {}
};

#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

#if !optional_CONFIG_NO_EXCEPTIONS

class bad_optional_access : public std::logic_error {
 public:
  explicit bad_optional_access() : logic_error("bad optional access") {}
};

#endif  // optional_CONFIG_NO_EXCEPTIONS

/// 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
  // NOLINTNEXTLINE( google-explicit-constructor, hicpp-explicit-conversions )
  optional_constexpr optional(nullopt_t /*unused*/) 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)
      // NOLINTNEXTLINE( performance-noexcept-move-constructor )
      ) 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()));
    }
  }

  // 4a (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(T{other.contained.value()});
    }
  }
#endif  // optional_CPP11_OR_GREATER

  // 4b (C++98 and later) - non-explicit converting copy-construct from optional
  template <typename U>
  // NOLINTNEXTLINE( google-explicit-constructor, hicpp-explicit-conversions )
  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>
  explicit optional(optional<U>&& other optional_REQUIRES_A(
      std::is_constructible<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_convertible<U&&, T>::value /*=> explicit */
      ))
      : has_value_(other.has_value()) {
    if (other.has_value()) {
      contained.construct_value(T{std::move(other.contained.value())});
    }
  }

  // 5a (C++11) - non-explicit converting move-construct from optional
  template <typename U>
  // NOLINTNEXTLINE( google-explicit-constructor, hicpp-explicit-conversions )
  optional(optional<U>&& other optional_REQUIRES_A(
      std::is_constructible<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_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(T{std::forward<U>(value)}) {}

  // 8b (C++11) - non-explicit move construct from value
  template <typename U = value_type>
  // NOLINTNEXTLINE( google-explicit-constructor, hicpp-explicit-conversions )
  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 /*unused*/) optional_noexcept {
    reset();
    return *this;
  }

  // 2 (C++98and later) - copy-assign from optional
#if optional_CPP11_OR_GREATER
  // NOLINTNEXTLINE( cppcoreguidelines-c-copy-assignment-signature,
  // misc-unconventional-assign-operator )
  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
  // NOLINTNEXTLINE( cppcoreguidelines-c-copy-assignment-signature,
  // misc-unconventional-assign-operator )
  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>
  // NOLINTNEXTLINE( cppcoreguidelines-c-copy-assignment-signature,
  // misc-unconventional-assign-operator )
  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
  // NOLINTNEXTLINE( cppcoreguidelines-c-copy-assignment-signature,
  // misc-unconventional-assign-operator )
  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>
  // NOLINTNEXTLINE( cppcoreguidelines-c-copy-assignment-signature,
  // misc-unconventional-assign-operator )
  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&&
                   std17::is_nothrow_swappable<T>::value)
#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(std11::move(*other));
      other.reset();
    } else if ((has_value() == true) && (other.has_value() == false)) {
      other.initialize(std11::move(**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_HAVE(REF_QUALIFIER) && \
    (!optional_COMPILER_GNUC_VERSION || optional_COMPILER_GNUC_VERSION >= 490)

  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

  // NOLINTNEXTLINE( modernize-use-nodiscard )
  /*optional_nodiscard*/ optional_constexpr bool has_value() const optional_noexcept {
    return has_value_;
  }

  // NOLINTNEXTLINE( modernize-use-nodiscard )
  /*optional_nodiscard*/ optional_constexpr14 value_type const& value() const
      optional_ref_qual {
#if optional_CONFIG_NO_EXCEPTIONS
    assert(has_value());
#else
    if (!has_value()) {
      throw bad_optional_access();
    }
#endif
    return contained.value();
  }

  optional_constexpr14 value_type& value() optional_ref_qual {
#if optional_CONFIG_NO_EXCEPTIONS
    assert(has_value());
#else
    if (!has_value()) {
      throw bad_optional_access();
    }
#endif
    return contained.value();
  }

#if optional_HAVE(REF_QUALIFIER) && \
    (!optional_COMPILER_GNUC_VERSION || optional_COMPILER_GNUC_VERSION >= 490)

  // NOLINTNEXTLINE( modernize-use-nodiscard )
  /*optional_nodiscard*/ optional_constexpr 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_constexpr14 value_type value_or(U&& v) 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 /*unused*/) optional_noexcept {
  return (!x);
}

template <typename T>
inline optional_constexpr bool operator==(nullopt_t /*unused*/,
                                          optional<T> const& x) optional_noexcept {
  return (!x);
}

template <typename T>
inline optional_constexpr bool operator!=(optional<T> const& x,
                                          nullopt_t /*unused*/) optional_noexcept {
  return bool(x);
}

template <typename T>
inline optional_constexpr bool operator!=(nullopt_t /*unused*/,
                                          optional<T> const& x) optional_noexcept {
  return bool(x);
}

template <typename T>
inline optional_constexpr bool operator<(optional<T> const& /*unused*/,
                                         nullopt_t /*unused*/) optional_noexcept {
  return false;
}

template <typename T>
inline optional_constexpr bool operator<(nullopt_t /*unused*/,
                                         optional<T> const& x) optional_noexcept {
  return bool(x);
}

template <typename T>
inline optional_constexpr bool operator<=(optional<T> const& x,
                                          nullopt_t /*unused*/) optional_noexcept {
  return (!x);
}

template <typename T>
inline optional_constexpr bool operator<=(
    nullopt_t /*unused*/, optional<T> const& /*unused*/) optional_noexcept {
  return true;
}

template <typename T>
inline optional_constexpr bool operator>(optional<T> const& x,
                                         nullopt_t /*unused*/) optional_noexcept {
  return bool(x);
}

template <typename T>
inline optional_constexpr bool operator>(
    nullopt_t /*unused*/, optional<T> const& /*unused*/) optional_noexcept {
  return false;
}

template <typename T>
inline optional_constexpr bool operator>=(optional<T> const& /*unused*/,
                                          nullopt_t /*unused*/) optional_noexcept {
  return true;
}

template <typename T>
inline optional_constexpr bool operator>=(nullopt_t /*unused*/,
                                          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
#if optional_CPP11_OR_GREATER
              optional_REQUIRES_T(
                  std::is_move_constructible<T>::value&& std17::is_swappable<T>::value)
#endif
          >
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 optional_lite::bad_optional_access;
using optional_lite::nullopt;
using optional_lite::nullopt_t;
using optional_lite::optional;

using optional_lite::make_optional;

}  // 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) ? std::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
#elif defined(_MSC_VER)
#pragma warning(pop)
#endif

#endif  // optional_USES_STD_OPTIONAL

#endif  // NONSTD_OPTIONAL_LITE_HPP