optional.hpp

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    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