// Copyright (C) 2003, Fernando Luis Cacciola Carballal.

 //

 // 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/lib/optional for documentation.

 //

 // You are welcome to contact the author at:

 //  fernando_cacciola@hotmail.com

 //

 #ifndef BOOST_OPTIONAL_OPTIONAL_FLC_19NOV2002_HPP

 #define BOOST_OPTIONAL_OPTIONAL_FLC_19NOV2002_HPP

 #include<new>

 #include<algorithm>

 #include "boost/config.hpp"

 #include "boost/assert.hpp"

 #include "boost/type.hpp"

 #include "boost/type_traits/alignment_of.hpp"

 #include "boost/type_traits/type_with_alignment.hpp"

 #include "boost/type_traits/remove_reference.hpp"

 #include "boost/type_traits/is_reference.hpp"

 #include "boost/mpl/if.hpp"

 #include "boost/mpl/bool.hpp"

 #include "boost/mpl/not.hpp"

 #include "boost/detail/reference_content.hpp"

 #include "boost/none.hpp"

 #include "boost/utility/compare_pointees.hpp"

 #include "boost/optional/optional_fwd.hpp"

 #if BOOST_WORKAROUND(BOOST_MSVC, == 1200)

 // VC6.0 has the following bug:

 //   When a templated assignment operator exist, an implicit conversion

 //   constructing an optional<T> is used when assigment of the form:

 //     optional<T> opt ; opt = T(...);

 //   is compiled.

 //   However, optional's ctor is _explicit_ and the assignemt shouldn't compile.

 //   Therefore, for VC6.0 templated assignment is disabled.

 //

 #define BOOST_OPTIONAL_NO_CONVERTING_ASSIGNMENT

 #endif

 #if BOOST_WORKAROUND(BOOST_MSVC, == 1300)

 // VC7.0 has the following bug:

 //   When both a non-template and a template copy-ctor exist

 //   and the templated version is made 'explicit', the explicit is also

 //   given to the non-templated version, making the class non-implicitely-copyable.

 //

 #define BOOST_OPTIONAL_NO_CONVERTING_COPY_CTOR

 #endif

 #if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) || BOOST_WORKAROUND(BOOST_INTEL_CXX_VERSION,<=700)

 // AFAICT only VC7.1 correctly resolves the overload set

 // that includes the in-place factory taking functions,

 // so for the other VC versions, in-place factory support

 // is disabled

 #define BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT

 #endif

 #if BOOST_WORKAROUND(__BORLANDC__, <= 0x551)

 // BCB (5.5.1) cannot parse the nested template struct in an inplace factory.

 #define BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT

 #endif

 #if !defined(BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT) \

     && BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x581) )

 // BCB (up to 5.64) has the following bug:

 //   If there is a member function/operator template of the form

 //     template<class Expr> mfunc( Expr expr ) ;

 //   some calls are resolved to this even if there are other better matches.

 //   The effect of this bug is that calls to converting ctors and assignments

 //   are incrorrectly sink to this general catch-all member function template as shown above.

 #define BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION

 #endif

 // Daniel Wallin discovered that bind/apply.hpp badly interacts with the apply<>

 // member template of a factory as used in the optional<> implementation.

 // He proposed this simple fix which is to move the call to apply<> outside

 // namespace boost.

 namespace boost_optional_detail

 {

   template <class T, class Factory>

   void construct(Factory const& factory, void* address)

   {

     factory.BOOST_NESTED_TEMPLATE apply<T>(address);

   }

 }

 namespace boost {

 class in_place_factory_base ;

 class typed_in_place_factory_base ;

 namespace optional_detail {

 // This local class is used instead of that in "aligned_storage.hpp"

 // because I've found the 'official' class to ICE BCB5.5

 // when some types are used with optional<>

 // (due to sizeof() passed down as a non-type template parameter)

 template <class T>

 class aligned_storage

 {

     // Borland ICEs if unnamed unions are used for this!

     union dummy_u

     {

         char data[ sizeof(T) ];

         BOOST_DEDUCED_TYPENAME type_with_alignment<

           ::boost::alignment_of<T>::value >::type aligner_;

     } dummy_ ;

   public:

     void const* address() const { return &dummy_.data[0]; }

     void      * address()       { return &dummy_.data[0]; }

 } ;

 template<class T>

 struct types_when_isnt_ref

 {

   typedef T const& reference_const_type ;

   typedef T &      reference_type ;

   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 ;

   typedef raw_type* pointer_const_type ;

   typedef raw_type* pointer_type ;

   typedef raw_type& argument_type ;

 } ;

 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 ;

     typedef BOOST_DEDUCED_TYPENAME mpl::if_<is_reference_predicate,types_when_ref,types_when_not_ref>::type types ;

     typedef bool (this_type::*unspecified_bool_type)() const;

     typedef BOOST_DEDUCED_TYPENAME types::reference_type       reference_type ;

     typedef BOOST_DEDUCED_TYPENAME types::reference_const_type reference_const_type ;

     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);

     }

     // Creates an optional<T> initialized with 'val' IFF cond is true, otherwise creates an uninitialzed 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());

     }

     // 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);

     }

     // 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());

       }

     }

     // 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() )

              assign_value(static_cast<value_type>(rhs.get()), is_reference_predicate() );

         else destroy();

       }

       else

       {

         if ( rhs.is_initialized() )

           construct(static_cast<value_type>(rhs.get()));

       }

     }

     // 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);

     }

     // Assigns from "none", destroying the current value, if any, leaving this UNINITIALIZED

     // No-throw (assuming T::~T() doesn't)

     void assign ( none_t ) { destroy(); }

 #ifndef BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT

     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

   public :

     // Destroys the current value, if any, leaving this UNINITIALIZED

     // No-throw (assuming T::~T() doesn't)

     void reset() { destroy(); }

     // 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_NO_INPLACE_FACTORY_SUPPORT

     // 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

     // Constructs using any expression implicitely 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 implicitely 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());

      }

 #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

     //

     // 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

     void assign_value ( argument_type val, is_not_reference_tag ) { get_impl() = val; }

     void assign_value ( argument_type val, is_reference_tag     ) { construct(val); }

     void destroy()

     {

       if ( m_initialized )

         destroy_impl(is_reference_predicate()) ;

     }

     unspecified_bool_type safe_bool() const { return m_initialized ? &this_type::is_initialized : 0 ; }

     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>

     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()); }

     // 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::~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 ;

     typedef BOOST_DEDUCED_TYPENAME base::unspecified_bool_type  unspecified_bool_type ;

   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 ;

     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() : base() {}

     // Creates an optional<T> uninitialized.

     // No-throw

     optional( none_t none_ ) : base(none_) {}

     // Creates an optional<T> initialized with 'val'.

     // Can throw if T::T(T const&) does

     optional ( argument_type val ) : base(val) {}

     // 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) {}

 #ifndef BOOST_OPTIONAL_NO_CONVERTING_COPY_CTOR

     // 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());

     }

 #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 implicitely 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 is the resolved T ctor throws.

     template<class Expr>

     explicit optional ( Expr const& expr ) : base(expr,&expr) {}

 #endif

     // Creates a deep copy of another optional<T>

     // Can throw if T::T(T const&) does

     optional ( optional const& rhs ) : base(rhs) {}

    // 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

     template<class Expr>

     optional& operator= ( Expr expr )

       {

         this->assign_expr(expr,&expr);

         return *this ;

       }

 #endif

 #ifndef BOOST_OPTIONAL_NO_CONVERTING_ASSIGNMENT

     // 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 ;

       }

 #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( rhs ) ;

         return *this ;

       }

     // 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 ;

       }

     // 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_ )

       {

         this->assign( none_ ) ;

         return *this ;

       }

     // 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

     reference_const_type operator *() const { return this->get() ; }

     reference_type       operator *()       { return this->get() ; }

     // implicit conversion to "bool"

     // No-throw

     operator unspecified_bool_type() const { return this->safe_bool() ; }

        // This is provided for those compilers which don't like the conversion to bool

        // on some contexts.

        bool operator!() const { return !this->is_initialized() ; }

 } ;

 // Returns optional<T>(v)

 template<class T> 

 inline 

 optional<T> make_optional ( T const& v  )

 {

   return optional<T>(v);

 }

 // Returns optional<T>(cond,v)

 template<class T> 

 inline 

 optional<T> make_optional ( bool cond, T const& v )

 {

   return optional<T>(cond,v);

 }

 // Returns a reference to the value if this is initialized, otherwise, the behaviour is UNDEFINED.

 // No-throw

 template<class T>

 inline

 BOOST_DEDUCED_TYPENAME optional<T>::reference_const_type

 get ( optional<T> const& opt )

 {

   return opt.get() ;

 }

 template<class T>

 inline

 BOOST_DEDUCED_TYPENAME optional<T>::reference_type

 get ( optional<T>& opt )

 {

   return opt.get() ;

 }

 // Returns a pointer to the value if this is initialized, otherwise, returns NULL.

 // No-throw

 template<class T>

 inline

 BOOST_DEDUCED_TYPENAME optional<T>::pointer_const_type

 get ( optional<T> const* opt )

 {

   return opt->get_ptr() ;

 }

 template<class T>

 inline

 BOOST_DEDUCED_TYPENAME optional<T>::pointer_type

 get ( optional<T>* opt )

 {

   return opt->get_ptr() ;

 }

 // Returns a reference to the value if this is initialized, otherwise, the behaviour is UNDEFINED.

 // No-throw

 template<class T>

 inline

 BOOST_DEDUCED_TYPENAME optional<T>::reference_const_type

 get_optional_value_or ( optional<T> const& opt, BOOST_DEDUCED_TYPENAME optional<T>::reference_const_type v )

 {

   return opt.get_value_or(v) ;

 }

 template<class T>

 inline

 BOOST_DEDUCED_TYPENAME optional<T>::reference_type

 get_optional_value_or ( optional<T>& opt, BOOST_DEDUCED_TYPENAME optional<T>::reference_type v )

 {

   return opt.get_value_or(v) ;

 }

 // Returns a pointer to the value if this is initialized, otherwise, returns NULL.

 // No-throw

 template<class T>

 inline

 BOOST_DEDUCED_TYPENAME optional<T>::pointer_const_type

 get_pointer ( optional<T> const& opt )

 {

   return opt.get_ptr() ;

 }

 template<class T>

 inline

 BOOST_DEDUCED_TYPENAME optional<T>::pointer_type

 get_pointer ( optional<T>& opt )

 {

   return opt.get_ptr() ;

 }

 // optional's relational operators ( ==, !=, <, >, <=, >= ) have deep-semantics (compare values).

 // WARNING: This is UNLIKE pointers. Use equal_pointees()/less_pointess() in generic code instead.

 //

 // optional<T> vs optional<T> cases

 //

 template<class T>

 inline

 bool operator == ( optional<T> const& x, optional<T> const& y )

 { return equal_pointees(x,y); }

 template<class T>

 inline

 bool operator < ( optional<T> const& x, optional<T> const& y )

 { return less_pointees(x,y); }

 template<class T>

 inline

 bool operator != ( optional<T> const& x, optional<T> const& y )

 { return !( x == y ) ; }

 template<class T>

 inline

 bool operator > ( optional<T> const& x, optional<T> const& y )

 { return y < x ; }

 template<class T>

 inline

 bool operator <= ( optional<T> const& x, optional<T> const& y )

 { return !( y < x ) ; }

 template<class T>

 inline

 bool operator >= ( optional<T> const& x, optional<T> const& y )

 { return !( x < y ) ; }

 //

 // optional<T> vs T cases

 //

 template<class T>

 inline

 bool operator == ( optional<T> const& x, T const& y )

 { return equal_pointees(x, optional<T>(y)); }

 template<class T>

 inline

 bool operator < ( optional<T> const& x, T const& y )

 { return less_pointees(x, optional<T>(y)); }

 template<class T>

 inline

 bool operator != ( optional<T> const& x, T const& y )

 { return !( x == y ) ; }

 template<class T>

 inline

 bool operator > ( optional<T> const& x, T const& y )

 { return y < x ; }

 template<class T>

 inline

 bool operator <= ( optional<T> const& x, T const& y )

 { return !( y < x ) ; }

 template<class T>

 inline

 bool operator >= ( optional<T> const& x, T const& y )

 { return !( x < y ) ; }

 //

 // T vs optional<T> cases

 //

 template<class T>

 inline

 bool operator == ( T const& x, optional<T> const& y )

 { return equal_pointees( optional<T>(x), y ); }

 template<class T>

 inline

 bool operator < ( T const& x, optional<T> const& y )

 { return less_pointees( optional<T>(x), y ); }

 template<class T>

 inline

 bool operator != ( T const& x, optional<T> const& y )

 { return !( x == y ) ; }

 template<class T>

 inline

 bool operator > ( T const& x, optional<T> const& y )

 { return y < x ; }

 template<class T>

 inline

 bool operator <= ( T const& x, optional<T> const& y )

 { return !( y < x ) ; }

 template<class T>

 inline

 bool operator >= ( T const& x, optional<T> const& y )

 { return !( x < y ) ; }

 //

 // optional<T> vs none cases

 //

 template<class T>

 inline

 bool operator == ( optional<T> const& x, none_t )

 { return equal_pointees(x, optional<T>() ); }

 template<class T>

 inline

 bool operator < ( optional<T> const& x, none_t )

 { return less_pointees(x,optional<T>() ); }

 template<class T>

 inline

 bool operator != ( optional<T> const& x, none_t y )

 { return !( x == y ) ; }

 template<class T>

 inline

 bool operator > ( optional<T> const& x, none_t y )

 { return y < x ; }

 template<class T>

 inline

 bool operator <= ( optional<T> const& x, none_t y )

 { return !( y < x ) ; }

 template<class T>

 inline

 bool operator >= ( optional<T> const& x, none_t y )

 { return !( x < y ) ; }

 //

 // none vs optional<T> cases

 //

 template<class T>

 inline

 bool operator == ( none_t x, optional<T> const& y )

 { return equal_pointees(optional<T>() ,y); }

 template<class T>

 inline

 bool operator < ( none_t x, optional<T> const& y )

 { return less_pointees(optional<T>() ,y); }

 template<class T>

 inline

 bool operator != ( none_t x, optional<T> const& y )

 { return !( x == y ) ; }

 template<class T>

 inline

 bool operator > ( none_t x, optional<T> const& y )

 { return y < x ; }

 template<class T>

 inline

 bool operator <= ( none_t x, optional<T> const& y )

 { return !( y < x ) ; }

 template<class T>

 inline

 bool operator >= ( none_t x, optional<T> const& y )

 { return !( x < y ) ; }

 //

 // The following swap implementation follows the GCC workaround as found in

 //  "boost/detail/compressed_pair.hpp"

 //

 namespace optional_detail {

 // GCC < 3.2 gets the using declaration at namespace scope (FLC, DWA)

 #if BOOST_WORKAROUND(__GNUC__, < 3)                             \

     || BOOST_WORKAROUND(__GNUC__, == 3) && __GNUC_MINOR__ <= 2

    using std::swap;

 #define BOOST_OPTIONAL_STD_SWAP_INTRODUCED_AT_NS_SCOPE

 #endif

 // optional's swap:

 // If both are initialized, calls swap(T&, T&). If this swap throws, both will remain initialized but their values are now unspecified.

 // If only one is initialized, calls U.reset(*I), THEN I.reset().

 // If U.reset(*I) throws, both are left UNCHANGED (U is kept uinitialized and I is never reset)

 // If both are uninitialized, do nothing (no-throw)

 template<class T>

 inline

 void optional_swap ( optional<T>& x, optional<T>& y )

 {

   if ( !x && !!y )

   {

     x.reset(*y);

     y.reset();

   }

   else if ( !!x && !y )

   {

     y.reset(*x);

     x.reset();

   }

   else if ( !!x && !!y )

   {

 // GCC > 3.2 and all other compilers have the using declaration at function scope (FLC)

 #ifndef BOOST_OPTIONAL_STD_SWAP_INTRODUCED_AT_NS_SCOPE

     // allow for Koenig lookup

     using std::swap ;

 #endif

     swap(*x,*y);

   }

 }

 } // namespace optional_detail

 template<class T> inline void swap ( optional<T>& x, optional<T>& y )

 {

   optional_detail::optional_swap(x,y);

 }

 } // namespace boost

 #endif