text: // Copyright (C) 2003, 2008 Fernando Luis Cacciola Carballal.
  // Copyright (C) 2014-2016 Andrzej Krzemienski.
  //
  // Use, modification, and distribution is subject to the Boost Software
  // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
  // http://www.boost.org/LICENSE_1_0.txt)
  //
  // See http://www.boost.org/libs/optional for documentation.
  //
  // You are welcome to contact the maintainer at:
  //  akrzemi1@gmail.com
  
  #ifndef BOOST_OPTIONAL_DETAIL_OLD_OPTIONAL_IMPLEMENTATION_AJK_28JAN2015_HPP
  #define BOOST_OPTIONAL_DETAIL_OLD_OPTIONAL_IMPLEMENTATION_AJK_28JAN2015_HPP
  
  #include <boost/detail/reference_content.hpp>
  #include <boost/mpl/bool.hpp>
  #include <boost/mpl/if.hpp>
  #include <boost/mpl/not.hpp>
  #include <boost/type_traits/is_reference.hpp>
  
  namespace boost {
  
  namespace optional_detail {
  
  
  template<class T>
  struct types_when_isnt_ref
  {
    typedef T const& reference_const_type ;
    typedef T &      reference_type ;
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
    typedef T &&     rval_reference_type ;
    typedef T &&     reference_type_of_temporary_wrapper;
  #ifdef BOOST_MOVE_OLD_RVALUE_REF_BINDING_RULES
    // GCC 4.4 has support for an early draft of rvalue references. The conforming version below
    // causes warnings about returning references to a temporary.
    static T&& move(T&& r) { return r; }
  #else
    static rval_reference_type move(reference_type r) { return boost::move(r); }
  #endif
  #endif
    typedef T const* pointer_const_type ;
    typedef T *      pointer_type ;
    typedef T const& argument_type ;
  } ;
  
  template<class T>
  struct types_when_is_ref
  {
    typedef BOOST_DEDUCED_TYPENAME remove_reference<T>::type raw_type ;
  
    typedef raw_type&  reference_const_type ;
    typedef raw_type&  reference_type ;
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
    typedef BOOST_DEDUCED_TYPENAME remove_const<raw_type>::type&& rval_reference_type ;
    typedef raw_type&  reference_type_of_temporary_wrapper;
    static reference_type move(reference_type r) { return r; }
  #endif
    typedef raw_type*  pointer_const_type ;
    typedef raw_type*  pointer_type ;
    typedef raw_type&  argument_type ;
  } ;
  
  template <class To, class From>
  void prevent_binding_rvalue_ref_to_optional_lvalue_ref()
  {
  #ifndef BOOST_OPTIONAL_CONFIG_ALLOW_BINDING_TO_RVALUES
    BOOST_STATIC_ASSERT_MSG(
      !boost::is_lvalue_reference<To>::value || !boost::is_rvalue_reference<From>::value, 
      "binding rvalue references to optional lvalue references is disallowed");
  #endif    
  }
  
  struct optional_tag {} ;
  
  template<class T>
  class optional_base : public optional_tag
  {
    private :
  
      typedef
  #if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
      BOOST_DEDUCED_TYPENAME
  #endif
      ::boost::detail::make_reference_content<T>::type internal_type ;
  
      typedef aligned_storage<internal_type> storage_type ;
  
      typedef types_when_isnt_ref<T> types_when_not_ref ;
      typedef types_when_is_ref<T>   types_when_ref   ;
  
      typedef optional_base<T> this_type ;
  
    protected :
  
      typedef T value_type ;
  
      typedef mpl::true_  is_reference_tag ;
      typedef mpl::false_ is_not_reference_tag ;
  
      typedef BOOST_DEDUCED_TYPENAME is_reference<T>::type is_reference_predicate ;
  
    public:
      typedef BOOST_DEDUCED_TYPENAME mpl::if_<is_reference_predicate,types_when_ref,types_when_not_ref>::type types ;
  
    protected:
      typedef BOOST_DEDUCED_TYPENAME types::reference_type       reference_type ;
      typedef BOOST_DEDUCED_TYPENAME types::reference_const_type reference_const_type ;
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      typedef BOOST_DEDUCED_TYPENAME types::rval_reference_type  rval_reference_type ;
      typedef BOOST_DEDUCED_TYPENAME types::reference_type_of_temporary_wrapper reference_type_of_temporary_wrapper ;
  #endif
      typedef BOOST_DEDUCED_TYPENAME types::pointer_type         pointer_type ;
      typedef BOOST_DEDUCED_TYPENAME types::pointer_const_type   pointer_const_type ;
      typedef BOOST_DEDUCED_TYPENAME types::argument_type        argument_type ;
  
      // Creates an optional<T> uninitialized.
      // No-throw
      optional_base()
        :
        m_initialized(false) {}
  
      // Creates an optional<T> uninitialized.
      // No-throw
      optional_base ( none_t )
        :
        m_initialized(false) {}
  
      // Creates an optional<T> initialized with 'val'.
      // Can throw if T::T(T const&) does
      optional_base ( argument_type val )
        :
        m_initialized(false)
      {
          construct(val);
      }
  
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // move-construct an optional<T> initialized from an rvalue-ref to 'val'.
      // Can throw if T::T(T&&) does
      optional_base ( rval_reference_type val )
        :
        m_initialized(false)
      {
        construct( boost::move(val) );
      }
  #endif
  
      // Creates an optional<T> initialized with 'val' IFF cond is true, otherwise creates an uninitialized optional<T>.
      // Can throw if T::T(T const&) does
      optional_base ( bool cond, argument_type val )
        :
        m_initialized(false)
      {
        if ( cond )
          construct(val);
      }
  
      // Creates a deep copy of another optional<T>
      // Can throw if T::T(T const&) does
      optional_base ( optional_base const& rhs )
        :
        m_initialized(false)
      {
        if ( rhs.is_initialized() )
          construct(rhs.get_impl());
      }
  
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Creates a deep move of another optional<T>
      // Can throw if T::T(T&&) does
      optional_base ( optional_base&& rhs )
        :
        m_initialized(false)
      {
        if ( rhs.is_initialized() )
          construct( boost::move(rhs.get_impl()) );
      }
  #endif
  
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
  
      template<class Expr, class PtrExpr>
      explicit optional_base ( Expr&& expr, PtrExpr const* tag )
        :
        m_initialized(false)
      {
        construct(boost::forward<Expr>(expr),tag);
      }
  
  #else
      // This is used for both converting and in-place constructions.
      // Derived classes use the 'tag' to select the appropriate
      // implementation (the correct 'construct()' overload)
      template<class Expr>
      explicit optional_base ( Expr const& expr, Expr const* tag )
        :
        m_initialized(false)
      {
        construct(expr,tag);
      }
  
  #endif
  
  
      // No-throw (assuming T::~T() doesn't)
      ~optional_base() { destroy() ; }
  
      // Assigns from another optional<T> (deep-copies the rhs value)
      void assign ( optional_base const& rhs )
      {
        if (is_initialized())
        {
          if ( rhs.is_initialized() )
               assign_value(rhs.get_impl(), is_reference_predicate() );
          else destroy();
        }
        else
        {
          if ( rhs.is_initialized() )
            construct(rhs.get_impl());
        }
      }
      
  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Assigns from another optional<T> (deep-moves the rhs value)
      void assign ( optional_base&& rhs )
      {
        if (is_initialized())
        {
          if ( rhs.is_initialized() )
               assign_value(boost::move(rhs.get_impl()), is_reference_predicate() );
          else destroy();
        }
        else
        {
          if ( rhs.is_initialized() )
            construct(boost::move(rhs.get_impl()));
        }
      }
  #endif 
  
      // Assigns from another _convertible_ optional<U> (deep-copies the rhs value)
      template<class U>
      void assign ( optional<U> const& rhs )
      {
        if (is_initialized())
        {
          if ( rhs.is_initialized() )
  #ifndef BOOST_OPTIONAL_CONFIG_RESTORE_ASSIGNMENT_OF_NONCONVERTIBLE_TYPES
            assign_value(rhs.get(), is_reference_predicate() );
  #else
            assign_value(static_cast<value_type>(rhs.get()), is_reference_predicate() );
  #endif
            
          else destroy();
        }
        else
        {
          if ( rhs.is_initialized() )
  #ifndef BOOST_OPTIONAL_CONFIG_RESTORE_ASSIGNMENT_OF_NONCONVERTIBLE_TYPES
            construct(rhs.get());
  #else
            construct(static_cast<value_type>(rhs.get()));
  #endif
        }
      }
  
  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // move-assigns from another _convertible_ optional<U> (deep-moves from the rhs value)
      template<class U>
      void assign ( optional<U>&& rhs )
      {
        typedef BOOST_DEDUCED_TYPENAME optional<U>::rval_reference_type ref_type;
        if (is_initialized())
        {
          if ( rhs.is_initialized() )
               assign_value(static_cast<ref_type>(rhs.get()), is_reference_predicate() );
          else destroy();
        }
        else
        {
          if ( rhs.is_initialized() )
            construct(static_cast<ref_type>(rhs.get()));
        }
      }
  #endif
      
      // Assigns from a T (deep-copies the rhs value)
      void assign ( argument_type val )
      {
        if (is_initialized())
             assign_value(val, is_reference_predicate() );
        else construct(val);
      }
      
  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Assigns from a T (deep-moves the rhs value)
      void assign ( rval_reference_type val )
      {
        if (is_initialized())
             assign_value( boost::move(val), is_reference_predicate() );
        else construct( boost::move(val) );
      }
  #endif
  
      // Assigns from "none", destroying the current value, if any, leaving this UNINITIALIZED
      // No-throw (assuming T::~T() doesn't)
      void assign ( none_t ) BOOST_NOEXCEPT { destroy(); }
  
  #ifndef BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
  
  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      template<class Expr, class ExprPtr>
      void assign_expr ( Expr&& expr, ExprPtr const* tag )
      {
        if (is_initialized())
          assign_expr_to_initialized(boost::forward<Expr>(expr),tag);
        else construct(boost::forward<Expr>(expr),tag);
      }
  #else
      template<class Expr>
      void assign_expr ( Expr const& expr, Expr const* tag )
      {
        if (is_initialized())
          assign_expr_to_initialized(expr,tag);
        else construct(expr,tag);
      }
  #endif
  
  #endif
  
    public :
  
      // **DEPPRECATED** Destroys the current value, if any, leaving this UNINITIALIZED
      // No-throw (assuming T::~T() doesn't)
      void reset() BOOST_NOEXCEPT { destroy(); }
  
      // **DEPPRECATED** Replaces the current value -if any- with 'val'
      void reset ( argument_type val ) { assign(val); }
  
      // Returns a pointer to the value if this is initialized, otherwise,
      // returns NULL.
      // No-throw
      pointer_const_type get_ptr() const { return m_initialized ? get_ptr_impl() : 0 ; }
      pointer_type       get_ptr()       { return m_initialized ? get_ptr_impl() : 0 ; }
  
      bool is_initialized() const { return m_initialized ; }
  
    protected :
  
      void construct ( argument_type val )
       {
         ::new (m_storage.address()) internal_type(val) ;
         m_initialized = true ;
       }
       
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      void construct ( rval_reference_type val )
       {
         ::new (m_storage.address()) internal_type( types::move(val) ) ;
         m_initialized = true ;
       }
  #endif
  
  
  #if (!defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES) && (!defined BOOST_NO_CXX11_VARIADIC_TEMPLATES)
      // Constructs in-place
      // upon exception *this is always uninitialized
      template<class... Args>
      void emplace_assign ( Args&&... args )
       {
         destroy();
         ::new (m_storage.address()) internal_type( boost::forward<Args>(args)... );
         m_initialized = true ;
       }
  #elif (!defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES)
      template<class Arg>
      void emplace_assign ( Arg&& arg )
       {
         destroy();
         ::new (m_storage.address()) internal_type( boost::forward<Arg>(arg) );
         m_initialized = true ;
       }
       
      void emplace_assign ()
       {
         destroy();
         ::new (m_storage.address()) internal_type();
         m_initialized = true ;
       }
  #else
      template<class Arg>
      void emplace_assign ( const Arg& arg )
       {
         destroy();
         ::new (m_storage.address()) internal_type( arg );
         m_initialized = true ;
       }
       
      template<class Arg>
      void emplace_assign ( Arg& arg )
       {
         destroy();
         ::new (m_storage.address()) internal_type( arg );
         m_initialized = true ;
       }
       
      void emplace_assign ()
       {
         destroy();
         ::new (m_storage.address()) internal_type();
         m_initialized = true ;
       }
  #endif
  
  #ifndef BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
  
  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Constructs in-place using the given factory
      template<class Expr>
      void construct ( Expr&& factory, in_place_factory_base const* )
       {
         BOOST_STATIC_ASSERT ( ::boost::mpl::not_<is_reference_predicate>::value ) ;
         boost_optional_detail::construct<value_type>(factory, m_storage.address());
         m_initialized = true ;
       }
  
      // Constructs in-place using the given typed factory
      template<class Expr>
      void construct ( Expr&& factory, typed_in_place_factory_base const* )
       {
         BOOST_STATIC_ASSERT ( ::boost::mpl::not_<is_reference_predicate>::value ) ;
         factory.apply(m_storage.address()) ;
         m_initialized = true ;
       }
  
      template<class Expr>
      void assign_expr_to_initialized ( Expr&& factory, in_place_factory_base const* tag )
       {
         destroy();
         construct(factory,tag);
       }
  
      // Constructs in-place using the given typed factory
      template<class Expr>
      void assign_expr_to_initialized ( Expr&& factory, typed_in_place_factory_base const* tag )
       {
         destroy();
         construct(factory,tag);
       }
  
  #else
      // Constructs in-place using the given factory
      template<class Expr>
      void construct ( Expr const& factory, in_place_factory_base const* )
       {
         BOOST_STATIC_ASSERT ( ::boost::mpl::not_<is_reference_predicate>::value ) ;
         boost_optional_detail::construct<value_type>(factory, m_storage.address());
         m_initialized = true ;
       }
  
      // Constructs in-place using the given typed factory
      template<class Expr>
      void construct ( Expr const& factory, typed_in_place_factory_base const* )
       {
         BOOST_STATIC_ASSERT ( ::boost::mpl::not_<is_reference_predicate>::value ) ;
         factory.apply(m_storage.address()) ;
         m_initialized = true ;
       }
  
      template<class Expr>
      void assign_expr_to_initialized ( Expr const& factory, in_place_factory_base const* tag )
       {
         destroy();
         construct(factory,tag);
       }
  
      // Constructs in-place using the given typed factory
      template<class Expr>
      void assign_expr_to_initialized ( Expr const& factory, typed_in_place_factory_base const* tag )
       {
         destroy();
         construct(factory,tag);
       }
  #endif
  
  #endif
  
  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Constructs using any expression implicitly convertible to the single argument
      // of a one-argument T constructor.
      // Converting constructions of optional<T> from optional<U> uses this function with
      // 'Expr' being of type 'U' and relying on a converting constructor of T from U.
      template<class Expr>
      void construct ( Expr&& expr, void const* )
      {
        new (m_storage.address()) internal_type(boost::forward<Expr>(expr)) ;
        m_initialized = true ;
      }
  
      // Assigns using a form any expression implicitly convertible to the single argument
      // of a T's assignment operator.
      // Converting assignments of optional<T> from optional<U> uses this function with
      // 'Expr' being of type 'U' and relying on a converting assignment of T from U.
      template<class Expr>
      void assign_expr_to_initialized ( Expr&& expr, void const* )
      {
        assign_value(boost::forward<Expr>(expr), is_reference_predicate());
      }
  #else
      // Constructs using any expression implicitly convertible to the single argument
      // of a one-argument T constructor.
      // Converting constructions of optional<T> from optional<U> uses this function with
      // 'Expr' being of type 'U' and relying on a converting constructor of T from U.
      template<class Expr>
      void construct ( Expr const& expr, void const* )
       {
         new (m_storage.address()) internal_type(expr) ;
         m_initialized = true ;
       }
  
      // Assigns using a form any expression implicitly convertible to the single argument
      // of a T's assignment operator.
      // Converting assignments of optional<T> from optional<U> uses this function with
      // 'Expr' being of type 'U' and relying on a converting assignment of T from U.
      template<class Expr>
      void assign_expr_to_initialized ( Expr const& expr, void const* )
       {
         assign_value(expr, is_reference_predicate());
       }
  
  #endif
  
  #ifdef BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION
      // BCB5.64 (and probably lower versions) workaround.
      //   The in-place factories are supported by means of catch-all constructors
      //   and assignment operators (the functions are parameterized in terms of
      //   an arbitrary 'Expr' type)
      //   This compiler incorrectly resolves the overload set and sinks optional<T> and optional<U>
      //   to the 'Expr'-taking functions even though explicit overloads are present for them.
      //   Thus, the following overload is needed to properly handle the case when the 'lhs'
      //   is another optional.
      //
      // For VC<=70 compilers this workaround dosen't work becasue the comnpiler issues and error
      // instead of choosing the wrong overload
      //
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Notice that 'Expr' will be optional<T> or optional<U> (but not optional_base<..>)
      template<class Expr>
      void construct ( Expr&& expr, optional_tag const* )
       {
         if ( expr.is_initialized() )
         {
           // An exception can be thrown here.
           // It it happens, THIS will be left uninitialized.
           new (m_storage.address()) internal_type(types::move(expr.get())) ;
           m_initialized = true ;
         }
       }
  #else
      // Notice that 'Expr' will be optional<T> or optional<U> (but not optional_base<..>)
      template<class Expr>
      void construct ( Expr const& expr, optional_tag const* )
       {
         if ( expr.is_initialized() )
         {
           // An exception can be thrown here.
           // It it happens, THIS will be left uninitialized.
           new (m_storage.address()) internal_type(expr.get()) ;
           m_initialized = true ;
         }
       }
  #endif
  #endif // defined BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION
  
      void assign_value ( argument_type val, is_not_reference_tag ) { get_impl() = val; }
      void assign_value ( argument_type val, is_reference_tag     ) { construct(val); }
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      void assign_value ( rval_reference_type val, is_not_reference_tag ) { get_impl() = static_cast<rval_reference_type>(val); }
      void assign_value ( rval_reference_type val, is_reference_tag     ) { construct( static_cast<rval_reference_type>(val) ); }
  #endif
  
      void destroy()
      {
        if ( m_initialized )
          destroy_impl(is_reference_predicate()) ;
      }
  
      reference_const_type get_impl() const { return dereference(get_object(), is_reference_predicate() ) ; }
      reference_type       get_impl()       { return dereference(get_object(), is_reference_predicate() ) ; }
  
      pointer_const_type get_ptr_impl() const { return cast_ptr(get_object(), is_reference_predicate() ) ; }
      pointer_type       get_ptr_impl()       { return cast_ptr(get_object(), is_reference_predicate() ) ; }
  
    private :
  
      // internal_type can be either T or reference_content<T>
  #if defined(BOOST_OPTIONAL_DETAIL_USE_ATTRIBUTE_MAY_ALIAS)
      // This workaround is supposed to silence GCC warnings about broken strict aliasing rules
      internal_type const* get_object() const
      {
          union { void const* ap_pvoid; internal_type const* as_ptype; } caster = { m_storage.address() };
          return caster.as_ptype;
      }
      internal_type *      get_object()
      {
          union { void* ap_pvoid; internal_type* as_ptype; } caster = { m_storage.address() };
          return caster.as_ptype;
      }
  #else
      internal_type const* get_object() const { return static_cast<internal_type const*>(m_storage.address()); }
      internal_type *      get_object()       { return static_cast<internal_type *>     (m_storage.address()); }
  #endif
  
      // reference_content<T> lacks an implicit conversion to T&, so the following is needed to obtain a proper reference.
      reference_const_type dereference( internal_type const* p, is_not_reference_tag ) const { return *p ; }
      reference_type       dereference( internal_type*       p, is_not_reference_tag )       { return *p ; }
      reference_const_type dereference( internal_type const* p, is_reference_tag     ) const { return p->get() ; }
      reference_type       dereference( internal_type*       p, is_reference_tag     )       { return p->get() ; }
  
  #if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x581))
      void destroy_impl ( is_not_reference_tag ) { get_ptr_impl()->internal_type::~internal_type() ; m_initialized = false ; }
  #else
      void destroy_impl ( is_not_reference_tag ) { get_ptr_impl()->~T() ; m_initialized = false ; }
  #endif
  
      void destroy_impl ( is_reference_tag     ) { m_initialized = false ; }
  
      // If T is of reference type, trying to get a pointer to the held value must result in a compile-time error.
      // Decent compilers should disallow conversions from reference_content<T>* to T*, but just in case,
      // the following olverloads are used to filter out the case and guarantee an error in case of T being a reference.
      pointer_const_type cast_ptr( internal_type const* p, is_not_reference_tag ) const { return p ; }
      pointer_type       cast_ptr( internal_type *      p, is_not_reference_tag )       { return p ; }
      pointer_const_type cast_ptr( internal_type const* p, is_reference_tag     ) const { return &p->get() ; }
      pointer_type       cast_ptr( internal_type *      p, is_reference_tag     )       { return &p->get() ; }
  
      bool m_initialized ;
      storage_type m_storage ;
  } ;
  
  } // namespace optional_detail
  
  template<class T>
  class optional : public optional_detail::optional_base<T>
  {
      typedef optional_detail::optional_base<T> base ;
  
    public :
  
      typedef optional<T> this_type ;
  
      typedef BOOST_DEDUCED_TYPENAME base::value_type           value_type ;
      typedef BOOST_DEDUCED_TYPENAME base::reference_type       reference_type ;
      typedef BOOST_DEDUCED_TYPENAME base::reference_const_type reference_const_type ;
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      typedef BOOST_DEDUCED_TYPENAME base::rval_reference_type  rval_reference_type ;
      typedef BOOST_DEDUCED_TYPENAME base::reference_type_of_temporary_wrapper reference_type_of_temporary_wrapper ;
  #endif
      typedef BOOST_DEDUCED_TYPENAME base::pointer_type         pointer_type ;
      typedef BOOST_DEDUCED_TYPENAME base::pointer_const_type   pointer_const_type ;
      typedef BOOST_DEDUCED_TYPENAME base::argument_type        argument_type ;
  
      // Creates an optional<T> uninitialized.
      // No-throw
      optional() BOOST_NOEXCEPT : base() {}
  
      // Creates an optional<T> uninitialized.
      // No-throw
      optional( none_t none_ ) BOOST_NOEXCEPT : base(none_) {}
  
      // Creates an optional<T> initialized with 'val'.
      // Can throw if T::T(T const&) does
      optional ( argument_type val ) : base(val) {}
  
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Creates an optional<T> initialized with 'move(val)'.
      // Can throw if T::T(T &&) does
      optional ( rval_reference_type val ) : base( boost::forward<T>(val) ) 
        {optional_detail::prevent_binding_rvalue_ref_to_optional_lvalue_ref<T, rval_reference_type>();}
  #endif
  
      // Creates an optional<T> initialized with 'val' IFF cond is true, otherwise creates an uninitialized optional.
      // Can throw if T::T(T const&) does
      optional ( bool cond, argument_type val ) : base(cond,val) {}
  
      // NOTE: MSVC needs templated versions first
  
      // Creates a deep copy of another convertible optional<U>
      // Requires a valid conversion from U to T.
      // Can throw if T::T(U const&) does
      template<class U>
      explicit optional ( optional<U> const& rhs )
        :
        base()
      {
        if ( rhs.is_initialized() )
          this->construct(rhs.get());
      }
      
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Creates a deep move of another convertible optional<U>
      // Requires a valid conversion from U to T.
      // Can throw if T::T(U&&) does
      template<class U>
      explicit optional ( optional<U> && rhs )
        :
        base()
      {
        if ( rhs.is_initialized() )
          this->construct( boost::move(rhs.get()) );
      }
  #endif
  
  #ifndef BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
      // Creates an optional<T> with an expression which can be either
      //  (a) An instance of InPlaceFactory (i.e. in_place(a,b,...,n);
      //  (b) An instance of TypedInPlaceFactory ( i.e. in_place<T>(a,b,...,n);
      //  (c) Any expression implicitly convertible to the single type
      //      of a one-argument T's constructor.
      //  (d*) Weak compilers (BCB) might also resolved Expr as optional<T> and optional<U>
      //       even though explicit overloads are present for these.
      // Depending on the above some T ctor is called.
      // Can throw if the resolved T ctor throws.
  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
  
  
    template<class Expr>
    explicit optional ( Expr&& expr, 
                        BOOST_DEDUCED_TYPENAME boost::disable_if_c<
                          (boost::is_base_of<optional_detail::optional_tag, BOOST_DEDUCED_TYPENAME boost::decay<Expr>::type>::value) || 
                          boost::is_same<BOOST_DEDUCED_TYPENAME boost::decay<Expr>::type, none_t>::value, bool >::type = true 
    ) 
      : base(boost::forward<Expr>(expr),boost::addressof(expr)) 
      {optional_detail::prevent_binding_rvalue_ref_to_optional_lvalue_ref<T, Expr&&>();}
  
  #else
      template<class Expr>
      explicit optional ( Expr const& expr ) : base(expr,boost::addressof(expr)) {}
  #endif // !defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
  #endif // !defined BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
  
      // Creates a deep copy of another optional<T>
      // Can throw if T::T(T const&) does
      optional ( optional const& rhs ) : base( static_cast<base const&>(rhs) ) {}
  
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Creates a deep move of another optional<T>
      // Can throw if T::T(T&&) does
      optional ( optional && rhs )
        BOOST_NOEXCEPT_IF(::boost::is_nothrow_move_constructible<T>::value)
        : base( boost::move(rhs) )
      {}
  
  #endif
     // No-throw (assuming T::~T() doesn't)
      ~optional() {}
  
  #if !defined(BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT) && !defined(BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION)
      // Assigns from an expression. See corresponding constructor.
      // Basic Guarantee: If the resolved T ctor throws, this is left UNINITIALIZED
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
  
      template<class Expr>
      BOOST_DEDUCED_TYPENAME boost::disable_if_c<
        boost::is_base_of<optional_detail::optional_tag, BOOST_DEDUCED_TYPENAME boost::decay<Expr>::type>::value || 
          boost::is_same<BOOST_DEDUCED_TYPENAME boost::decay<Expr>::type, none_t>::value,
        optional&
      >::type 
      operator= ( Expr&& expr )
        {
          optional_detail::prevent_binding_rvalue_ref_to_optional_lvalue_ref<T, Expr&&>();
          this->assign_expr(boost::forward<Expr>(expr),boost::addressof(expr));
          return *this ;
        }
  
  #else
      template<class Expr>
      optional& operator= ( Expr const& expr )
        {
          this->assign_expr(expr,boost::addressof(expr));
          return *this ;
        }
  #endif // !defined  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
  #endif // !defined(BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT) && !defined(BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION)
  
      // Copy-assigns from another convertible optional<U> (converts && deep-copies the rhs value)
      // Requires a valid conversion from U to T.
      // Basic Guarantee: If T::T( U const& ) throws, this is left UNINITIALIZED
      template<class U>
      optional& operator= ( optional<U> const& rhs )
        {
          this->assign(rhs);
          return *this ;
        }
        
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Move-assigns from another convertible optional<U> (converts && deep-moves the rhs value)
      // Requires a valid conversion from U to T.
      // Basic Guarantee: If T::T( U && ) throws, this is left UNINITIALIZED
      template<class U>
      optional& operator= ( optional<U> && rhs )
        {
          this->assign(boost::move(rhs));
          return *this ;
        }
  #endif
  
      // Assigns from another optional<T> (deep-copies the rhs value)
      // Basic Guarantee: If T::T( T const& ) throws, this is left UNINITIALIZED
      //  (NOTE: On BCB, this operator is not actually called and left is left UNMODIFIED in case of a throw)
      optional& operator= ( optional const& rhs )
        {
          this->assign( static_cast<base const&>(rhs) ) ;
          return *this ;
        }
  
  #ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Assigns from another optional<T> (deep-moves the rhs value)
      optional& operator= ( optional && rhs ) 
        BOOST_NOEXCEPT_IF(::boost::is_nothrow_move_constructible<T>::value && ::boost::is_nothrow_move_assignable<T>::value)
        {
          this->assign( static_cast<base &&>(rhs) ) ;
          return *this ;
        }
  #endif
  
      // Assigns from a T (deep-copies the rhs value)
      // Basic Guarantee: If T::( T const& ) throws, this is left UNINITIALIZED
      optional& operator= ( argument_type val )
        {
          this->assign( val ) ;
          return *this ;
        }
  
  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      // Assigns from a T (deep-moves the rhs value)
      optional& operator= ( rval_reference_type val )
        {
          optional_detail::prevent_binding_rvalue_ref_to_optional_lvalue_ref<T, rval_reference_type>();
          this->assign( boost::move(val) ) ;
          return *this ;
        }
  #endif
  
      // Assigns from a "none"
      // Which destroys the current value, if any, leaving this UNINITIALIZED
      // No-throw (assuming T::~T() doesn't)
      optional& operator= ( none_t none_ ) BOOST_NOEXCEPT
        {
          this->assign( none_ ) ;
          return *this ;
        }
        
  #if (!defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES) && (!defined BOOST_NO_CXX11_VARIADIC_TEMPLATES)
      // Constructs in-place
      // upon exception *this is always uninitialized
      template<class... Args>
      void emplace ( Args&&... args )
       {
         this->emplace_assign( boost::forward<Args>(args)... );
       }
  #elif (!defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES)
      template<class Arg>
      void emplace ( Arg&& arg )
       {
         this->emplace_assign( boost::forward<Arg>(arg) );
       }
       
      void emplace ()
       {
         this->emplace_assign();
       }
  #else
      template<class Arg>
      void emplace ( const Arg& arg )
       {
         this->emplace_assign( arg );
       }
       
      template<class Arg>
      void emplace ( Arg& arg )
       {
         this->emplace_assign( arg );
       }
       
      void emplace ()
       {
         this->emplace_assign();
       }
  #endif
  
      void swap( optional & arg )
        BOOST_NOEXCEPT_IF(::boost::is_nothrow_move_constructible<T>::value && ::boost::is_nothrow_move_assignable<T>::value)
        {
          // allow for Koenig lookup
          boost::swap(*this, arg);
        }
  
  
      // Returns a reference to the value if this is initialized, otherwise,
      // the behaviour is UNDEFINED
      // No-throw
      reference_const_type get() const { BOOST_ASSERT(this->is_initialized()) ; return this->get_impl(); }
      reference_type       get()       { BOOST_ASSERT(this->is_initialized()) ; return this->get_impl(); }
  
      // Returns a copy of the value if this is initialized, 'v' otherwise
      reference_const_type get_value_or ( reference_const_type v ) const { return this->is_initialized() ? get() : v ; }
      reference_type       get_value_or ( reference_type       v )       { return this->is_initialized() ? get() : v ; }
  
      // Returns a pointer to the value if this is initialized, otherwise,
      // the behaviour is UNDEFINED
      // No-throw
      pointer_const_type operator->() const { BOOST_ASSERT(this->is_initialized()) ; return this->get_ptr_impl() ; }
      pointer_type       operator->()       { BOOST_ASSERT(this->is_initialized()) ; return this->get_ptr_impl() ; }
  
      // Returns a reference to the value if this is initialized, otherwise,
      // the behaviour is UNDEFINED
      // No-throw
  #if (!defined BOOST_NO_CXX11_REF_QUALIFIERS) && (!defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES) 
      reference_const_type operator *() const& { return this->get() ; }
      reference_type       operator *() &      { return this->get() ; }
      reference_type_of_temporary_wrapper operator *() && { return base::types::move(this->get()) ; }
  #else
      reference_const_type operator *() const { return this->get() ; }
      reference_type       operator *()       { return this->get() ; }
  #endif // !defined BOOST_NO_CXX11_REF_QUALIFIERS
  
  #if (!defined BOOST_NO_CXX11_REF_QUALIFIERS) && (!defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES) 
      reference_const_type value() const&
        { 
          if (this->is_initialized())
            return this->get() ;
          else
            throw_exception(bad_optional_access());
        }
        
      reference_type value() &
        { 
          if (this->is_initialized())
            return this->get() ;
          else
            throw_exception(bad_optional_access());
        }
        
      reference_type_of_temporary_wrapper value() &&
        { 
          if (this->is_initialized())
            return base::types::move(this->get()) ;
          else
            throw_exception(bad_optional_access());
        }
  
  #else 
      reference_const_type value() const
        { 
          if (this->is_initialized())
            return this->get() ;
          else
            throw_exception(bad_optional_access());
        }
        
      reference_type value()
        { 
          if (this->is_initialized())
            return this->get() ;
          else
            throw_exception(bad_optional_access());
        }
  #endif
  
  
  #ifndef BOOST_NO_CXX11_REF_QUALIFIERS
      template <class U>
      value_type value_or ( U&& v ) const&
        { 
          if (this->is_initialized())
            return get();
          else
            return boost::forward<U>(v);
        }
      
      template <class U>
      value_type value_or ( U&& v ) && 
        { 
          if (this->is_initialized())
            return base::types::move(get());
          else
            return boost::forward<U>(v);
        }
  #elif !defined BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
      template <class U>
      value_type value_or ( U&& v ) const 
        {
          if (this->is_initialized())
            return get();
          else
            return boost::forward<U>(v);
        }
  #else
      template <class U>
      value_type value_or ( U const& v ) const 
        { 
          if (this->is_initialized())
            return get();
          else
            return v;
        }
        
      template <class U>
      value_type value_or ( U& v ) const 
        { 
          if (this->is_initialized())
            return get();
          else
            return v;
        }
  #endif
  
  
  #ifndef BOOST_NO_CXX11_REF_QUALIFIERS
      template <typename F>
      value_type value_or_eval ( F f ) const&
        {
          if (this->is_initialized())
            return get();
          else
            return f();
        }
        
      template <typename F>
      value_type value_or_eval ( F f ) &&
        {
          if (this->is_initialized())
            return base::types::move(get());
          else
            return f();
        }
  #else
      template <typename F>
      value_type value_or_eval ( F f ) const
        {
          if (this->is_initialized())
            return get();
          else
            return f();
        }
  #endif
        
      bool operator!() const BOOST_NOEXCEPT { return !this->is_initialized() ; }
      
      BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()
  } ;
  
  } // namespace boost
  
  
  #endif // header guard
  