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882 lines
26 KiB
Plaintext
882 lines
26 KiB
Plaintext
[/
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Boost.Optional
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Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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]
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[section Synopsis]
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namespace boost {
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template<class T>
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class optional
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{
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public :
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// (If T is of reference type, the parameters and results by reference are by value)
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optional () ; ``[link reference_optional_constructor __GO_TO__]``
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optional ( none_t ) ; ``[link reference_optional_constructor_none_t __GO_TO__]``
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optional ( T const& v ) ; ``[link reference_optional_constructor_value __GO_TO__]``
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// [new in 1.34]
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optional ( bool condition, T const& v ) ; ``[link reference_optional_constructor_bool_value __GO_TO__]``
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optional ( optional const& rhs ) ; ``[link reference_optional_constructor_optional __GO_TO__]``
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template<class U> explicit optional ( optional<U> const& rhs ) ; ``[link reference_optional_constructor_other_optional __GO_TO__]``
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template<class InPlaceFactory> explicit optional ( InPlaceFactory const& f ) ; ``[link reference_optional_constructor_factory __GO_TO__]``
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template<class TypedInPlaceFactory> explicit optional ( TypedInPlaceFactory const& f ) ; ``[link reference_optional_constructor_factory __GO_TO__]``
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optional& operator = ( none_t ) ; ``[/[link reference_optional_operator_equal_none_t __GO_TO__]]``
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optional& operator = ( T const& v ) ; ``[link reference_optional_operator_equal_value __GO_TO__]``
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optional& operator = ( optional const& rhs ) ; ``[link reference_optional_operator_equal_optional __GO_TO__]``
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template<class U> optional& operator = ( optional<U> const& rhs ) ; ``[link reference_optional_operator_equal_other_optional __GO_TO__]``
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template<class InPlaceFactory> optional& operator = ( InPlaceFactory const& f ) ; ``[/[link reference_optional_operator_equal_factory __GO_TO__]]``
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template<class TypedInPlaceFactory> optional& operator = ( TypedInPlaceFactory const& f ) ; ``[/[link reference_optional_operator_equal_factory __GO_TO__]]``
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T const& get() const ; ``[link reference_optional_get __GO_TO__]``
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T& get() ; ``[link reference_optional_get __GO_TO__]``
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// [new in 1.34]
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T const& get_value_or( T const& default ) const ; ``[link reference_optional_get_value_or_value __GO_TO__]``
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T const* operator ->() const ; ``[link reference_optional_operator_arrow __GO_TO__]``
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T* operator ->() ; ``[link reference_optional_operator_arrow __GO_TO__]``
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T const& operator *() const ; ``[link reference_optional_get __GO_TO__]``
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T& operator *() ; ``[link reference_optional_get __GO_TO__]``
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T const* get_ptr() const ; ``[link reference_optional_get_ptr __GO_TO__]``
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T* get_ptr() ; ``[link reference_optional_get_ptr __GO_TO__]``
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operator unspecified-bool-type() const ; ``[link reference_optional_operator_bool __GO_TO__]``
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bool operator!() const ; ``[link reference_optional_operator_not __GO_TO__]``
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// deprecated methods
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// (deprecated)
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void reset() ; ``[link reference_optional_reset __GO_TO__]``
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// (deprecated)
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void reset ( T const& ) ; ``[link reference_optional_reset_value __GO_TO__]``
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// (deprecated)
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bool is_initialized() const ; ``[link reference_optional_is_initialized __GO_TO__]``
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};
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template<class T> inline bool operator == ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_equal_optional_optional __GO_TO__]``
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template<class T> inline bool operator != ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_not_equal_optional_optional __GO_TO__]``
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template<class T> inline bool operator < ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_less_optional_optional __GO_TO__]``
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template<class T> inline bool operator > ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_greater_optional_optional __GO_TO__]``
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template<class T> inline bool operator <= ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_less_or_equal_optional_optional __GO_TO__]``
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template<class T> inline bool operator >= ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_greater_or_equal_optional_optional __GO_TO__]``
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// [new in 1.34]
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template<class T> inline optional<T> make_optional ( T const& v ) ; ``[link reference_make_optional_value __GO_TO__]``
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// [new in 1.34]
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template<class T> inline optional<T> make_optional ( bool condition, T const& v ) ; ``[link reference_make_optional_bool_value __GO_TO__]``
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// [new in 1.34]
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template<class T> inline T const& get_optional_value_or ( optional<T> const& opt, T const& default ) ; ``[link reference_optional_get_value_or_value __GO_TO__]``
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template<class T> inline T const& get ( optional<T> const& opt ) ; ``[link reference_optional_get __GO_TO__]``
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template<class T> inline T& get ( optional<T> & opt ) ; ``[link reference_optional_get __GO_TO__]``
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template<class T> inline T const* get ( optional<T> const* opt ) ; ``[link reference_optional_get __GO_TO__]``
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template<class T> inline T* get ( optional<T>* opt ) ; ``[link reference_optional_get __GO_TO__]``
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template<class T> inline T const* get_pointer ( optional<T> const& opt ) ; ``[link reference_optional_get_ptr __GO_TO__]``
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template<class T> inline T* get_pointer ( optional<T> & opt ) ; ``[link reference_optional_get_ptr __GO_TO__]``
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template<class T> inline void swap( optional<T>& x, optional<T>& y ) ; ``[link reference_swap_optional_optional __GO_TO__]``
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} // namespace boost
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[endsect]
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[section Detailed Semantics]
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Because `T` might be of reference type, in the sequel, those entries whose
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semantic depends on `T` being of reference type or not will be distinguished
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using the following convention:
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* If the entry reads: `optional<T`['(not a ref)]`>`, the description
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corresponds only to the case where `T` is not of reference type.
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* If the entry reads: `optional<T&>`, the description corresponds only to
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the case where `T` is of reference type.
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* If the entry reads: `optional<T>`, the description is the same for both
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cases.
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[note
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The following section contains various `assert()` which are used only to show
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the postconditions as sample code. It is not implied that the type `T` must
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support each particular expression but that if the expression is supported,
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the implied condition holds.
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]
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__SPACE__
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[heading optional class member functions]
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__SPACE__
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[#reference_optional_constructor]
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[: `optional<T>::optional();`]
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* [*Effect:] Default-Constructs an `optional`.
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* [*Postconditions:] `*this` is [_uninitialized].
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* [*Throws:] Nothing.
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* Notes: T's default constructor [_is not] called.
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* [*Example:]
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``
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optional<T> def ;
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assert ( !def ) ;
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``
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__SPACE__
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[#reference_optional_constructor_none_t]
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[: `optional<T>::optional( none_t );`]
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* [*Effect:] Constructs an `optional` uninitialized.
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* [*Postconditions:] `*this` is [_uninitialized].
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* [*Throws:] Nothing.
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* [*Notes:] `T`'s default constructor [_is not] called. The expression
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`boost::none` denotes an instance of `boost::none_t` that can be used as
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the parameter.
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* [*Example:]
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``
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#include <boost/none.hpp>
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optional<T> n(none) ;
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assert ( !n ) ;
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``
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__SPACE__
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[#reference_optional_constructor_value]
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[: `optional<T `['(not a ref)]`>::optional( T const& v )`]
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* [*Effect:] Directly-Constructs an `optional`.
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* [*Postconditions:] `*this` is [_initialized] and its value is a['copy]
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of `v`.
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* [*Throws:] Whatever `T::T( T const& )` throws.
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* [*Notes: ] `T::T( T const& )` is called.
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* [*Exception Safety:] Exceptions can only be thrown during
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`T::T( T const& );` in that case, this constructor has no effect.
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* [*Example:]
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``
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T v;
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optional<T> opt(v);
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assert ( *opt == v ) ;
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``
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__SPACE__
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[: `optional<T&>::optional( T& ref )`]
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* [*Effect:] Directly-Constructs an `optional`.
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* [*Postconditions:] `*this` is [_initialized] and its value is an instance
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of an internal type wrapping the reference `ref`.
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* [*Throws:] Nothing.
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* [*Example:]
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``
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T v;
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T& vref = v ;
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optional<T&> opt(vref);
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assert ( *opt == v ) ;
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++ v ; // mutate referee
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assert (*opt == v);
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``
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__SPACE__
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[#reference_optional_constructor_bool_value]
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[: `optional<T` ['(not a ref)]`>::optional( bool condition, T const& v ) ;` ]
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[: `optional<T&> ::optional( bool condition, T& v ) ;` ]
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* If condition is true, same as:
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[: `optional<T` ['(not a ref)]`>::optional( T const& v )`]
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[: `optional<T&> ::optional( T& v )`]
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* otherwise, same as:
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[: `optional<T ['(not a ref)]>::optional()`]
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[: `optional<T&> ::optional()`]
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__SPACE__
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[#reference_optional_constructor_optional]
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[: `optional<T `['(not a ref)]`>::optional( optional const& rhs );`]
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* [*Effect:] Copy-Constructs an `optional`.
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* [*Postconditions:] If rhs is initialized, `*this` is initialized and
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its value is a ['copy] of the value of `rhs`; else `*this` is uninitialized.
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* [*Throws:] Whatever `T::T( T const& )` throws.
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* [*Notes:] If rhs is initialized, `T::T(T const& )` is called.
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* [*Exception Safety:] Exceptions can only be thrown during
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`T::T( T const& );` in that case, this constructor has no effect.
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* [*Example:]
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``
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optional<T> uninit ;
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assert (!uninit);
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optional<T> uinit2 ( uninit ) ;
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assert ( uninit2 == uninit );
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optional<T> init( T(2) );
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assert ( *init == T(2) ) ;
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optional<T> init2 ( init ) ;
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assert ( init2 == init ) ;
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``
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__SPACE__
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[: `optional<T&>::optional( optional const& rhs );`]
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* [*Effect:] Copy-Constructs an `optional`.
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* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and its
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value is another reference to the same object referenced by `*rhs`; else
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`*this` is uninitialized.
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* [*Throws:] Nothing.
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* [*Notes:] If `rhs` is initialized, both `*this` and `*rhs` will reefer to the
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same object (they alias).
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* [*Example:]
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``
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optional<T&> uninit ;
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assert (!uninit);
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optional<T&> uinit2 ( uninit ) ;
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assert ( uninit2 == uninit );
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T v = 2 ; T& ref = v ;
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optional<T> init(ref);
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assert ( *init == v ) ;
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optional<T> init2 ( init ) ;
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assert ( *init2 == v ) ;
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v = 3 ;
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assert ( *init == 3 ) ;
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assert ( *init2 == 3 ) ;
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``
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__SPACE__
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[#reference_optional_constructor_other_optional]
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[: `template<U> explicit optional<T` ['(not a ref)]`>::optional( optional<U> const& rhs );`]
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* [*Effect:] Copy-Constructs an `optional`.
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* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and its
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value is a ['copy] of the value of rhs converted to type `T`; else `*this` is
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uninitialized.
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* [*Throws:] Whatever `T::T( U const& )` throws.
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* [*Notes: ] `T::T( U const& )` is called if `rhs` is initialized, which requires a
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valid conversion from `U` to `T`.
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* [*Exception Safety:] Exceptions can only be thrown during `T::T( U const& );`
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in that case, this constructor has no effect.
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* [*Example:]
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``
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optional<double> x(123.4);
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assert ( *x == 123.4 ) ;
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optional<int> y(x) ;
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assert( *y == 123 ) ;
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``
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__SPACE__
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[#reference_optional_constructor_factory]
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[: `template<InPlaceFactory> explicit optional<T` ['(not a ref)]`>::optional( InPlaceFactory const& f );`]
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[: `template<TypedInPlaceFactory> explicit optional<T` ['(not a ref)]`>::optional( TypedInPlaceFactory const& f );`]
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* [*Effect:] Constructs an `optional` with a value of `T` obtained from the
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factory.
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* [*Postconditions: ] `*this` is [_initialized] and its value is ['directly given]
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from the factory `f` (i.e., the value [_is not copied]).
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* [*Throws:] Whatever the `T` constructor called by the factory throws.
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* [*Notes:] See [link boost_optional.in_place_factories In-Place Factories]
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* [*Exception Safety:] Exceptions can only be thrown during the call to
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the `T` constructor used by the factory; in that case, this constructor has
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no effect.
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* [*Example:]
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``
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class C { C ( char, double, std::string ) ; } ;
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C v('A',123.4,"hello");
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optional<C> x( in_place ('A', 123.4, "hello") ); // InPlaceFactory used
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optional<C> y( in_place<C>('A', 123.4, "hello") ); // TypedInPlaceFactory used
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assert ( *x == v ) ;
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assert ( *y == v ) ;
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``
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__SPACE__
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[#reference_optional_operator_equal_value]
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[: `optional& optional<T` ['(not a ref)]`>::operator= ( T const& rhs ) ;`]
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* [*Effect:] Assigns the value `rhs` to an `optional`.
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* [*Postconditions: ] `*this` is initialized and its value is a ['copy] of `rhs`.
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* [*Throws:] Whatever `T::operator=( T const& )` or `T::T(T const&)` throws.
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* [*Notes:] If `*this` was initialized, `T`'s assignment operator is used,
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otherwise, its copy-constructor is used.
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* [*Exception Safety:] In the event of an exception, the initialization
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state of `*this` is unchanged and its value unspecified as far as `optional`
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is concerned (it is up to `T`'s `operator=()`). If `*this` is initially
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uninitialized and `T`'s ['copy constructor] fails, `*this` is left properly
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uninitialized.
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* [*Example:]
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``
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T x;
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optional<T> def ;
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optional<T> opt(x) ;
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T y;
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def = y ;
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assert ( *def == y ) ;
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opt = y ;
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assert ( *opt == y ) ;
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``
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__SPACE__
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[: `optional<T&>& optional<T&>::operator= ( T& const& rhs ) ;`]
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* [*Effect:] (Re)binds thee wrapped reference.
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* [*Postconditions: ] `*this` is initialized and it references the same
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object referenced by `rhs`.
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* [*Notes:] If `*this` was initialized, is is ['rebound] to the new object.
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See [link boost_optional.rebinding_semantics_for_assignment_of_optional_references here] for details on this behavior.
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* [*Example:]
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``
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int a = 1 ;
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int b = 2 ;
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T& ra = a ;
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T& rb = b ;
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optional<int&> def ;
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optional<int&> opt(ra) ;
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def = rb ; // binds 'def' to 'b' through 'rb'
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assert ( *def == b ) ;
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*def = a ; // changes the value of 'b' to a copy of the value of 'a'
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assert ( b == a ) ;
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int c = 3;
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int& rc = c ;
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opt = rc ; // REBINDS to 'c' through 'rc'
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c = 4 ;
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assert ( *opt == 4 ) ;
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``
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__SPACE__
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[#reference_optional_operator_equal_optional]
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[: `optional& optional<T` ['(not a ref)]`>::operator= ( optional const& rhs ) ;`]
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* [*Effect:] Assigns another `optional` to an `optional`.
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* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and
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its value is a ['copy] of the value of `rhs`; else `*this` is uninitialized.
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* [*Throws:] Whatever `T::operator( T const&)` or `T::T( T const& )` throws.
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* [*Notes:] If both `*this` and `rhs` are initially initialized, `T`'s
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['assignment operator] is used. If `*this` is initially initialized but `rhs` is
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uninitialized, `T`'s [destructor] is called. If `*this` is initially uninitialized
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but `rhs` is initialized, `T`'s ['copy constructor] is called.
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* [*Exception Safety:] In the event of an exception, the initialization state of
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`*this` is unchanged and its value unspecified as far as optional is concerned
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(it is up to `T`'s `operator=()`). If `*this` is initially uninitialized and
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`T`'s ['copy constructor] fails, `*this` is left properly uninitialized.
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* [*Example:]
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``
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T v;
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optional<T> opt(v);
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optional<T> def ;
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opt = def ;
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assert ( !def ) ;
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// previous value (copy of 'v') destroyed from within 'opt'.
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``
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__SPACE__
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[: `optional<T&> & optional<T&>::operator= ( optional<T&> const& rhs ) ;`]
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* [*Effect:] (Re)binds thee wrapped reference.
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* [*Postconditions:] If `*rhs` is initialized, `*this` is initialized and it
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references the same object referenced by `*rhs`; otherwise, `*this` is
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uninitialized (and references no object).
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* [*Notes:] If `*this` was initialized and so is *rhs, this is is ['rebound] to
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the new object. See [link boost_optional.rebinding_semantics_for_assignment_of_optional_references here] for details on this behavior.
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* [*Example:]
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``
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int a = 1 ;
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int b = 2 ;
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T& ra = a ;
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T& rb = b ;
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optional<int&> def ;
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optional<int&> ora(ra) ;
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optional<int&> orb(rb) ;
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def = orb ; // binds 'def' to 'b' through 'rb' wrapped within 'orb'
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assert ( *def == b ) ;
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*def = ora ; // changes the value of 'b' to a copy of the value of 'a'
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assert ( b == a ) ;
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|
int c = 3;
|
|
int& rc = c ;
|
|
optional<int&> orc(rc) ;
|
|
ora = orc ; // REBINDS ora to 'c' through 'rc'
|
|
c = 4 ;
|
|
assert ( *ora == 4 ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_equal_other_optional]
|
|
|
|
[: `template<U> optional& optional<T` ['(not a ref)]`>::operator= ( optional<U> const& rhs ) ;`]
|
|
|
|
* [*Effect:] Assigns another convertible optional to an optional.
|
|
* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and
|
|
its value is a ['copy] of the value of `rhs` ['converted] to type `T`; else
|
|
`*this` is uninitialized.
|
|
* [*Throws:] Whatever `T::operator=( U const& )` or `T::T( U const& )` throws.
|
|
* [*Notes:] If both `*this` and rhs are initially initialized, `T`'s
|
|
['assignment operator] (from `U`) is used. If `*this` is initially initialized
|
|
but `rhs` is uninitialized, `T`'s ['destructor] is called. If `*this` is
|
|
initially uninitialized but rhs is initialized, `T`'s ['converting constructor]
|
|
(from `U`) is called.
|
|
* [*Exception Safety:] In the event of an exception, the initialization state
|
|
of `*this` is unchanged and its value unspecified as far as optional is
|
|
concerned (it is up to `T`'s `operator=()`). If `*this` is initially
|
|
uninitialized and `T`'s converting constructor fails, `*this` is left properly
|
|
uninitialized.
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
optional<T> opt0(v);
|
|
optional<U> opt1;
|
|
|
|
opt1 = opt0 ;
|
|
assert ( *opt1 == static_cast<U>(v) ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_reset_value]
|
|
|
|
[: `void optional<T` ['(not a ref)]`>::reset( T const& v ) ;`]
|
|
* [*Deprecated:] same as `operator= ( T const& v) ;`
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_reset]
|
|
|
|
[: `void optional<T>::reset() ;`]
|
|
* [*Deprecated:] Same as `operator=( detail::none_t );`
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_get]
|
|
|
|
[: `T const& optional<T` ['(not a ref)]`>::operator*() const ;`]
|
|
[: `T& optional<T` ['(not a ref)]`>::operator*();`]
|
|
[: `T const& optional<T` ['(not a ref)]`>::get() const ;`]
|
|
[: `T& optional<T` ['(not a ref)]`>::get() ;`]
|
|
|
|
[: `inline T const& get ( optional<T` ['(not a ref)]`> const& ) ;`]
|
|
[: `inline T& get ( optional<T` ['(not a ref)]`> &) ;`]
|
|
|
|
* [*Requirements:] `*this` is initialized
|
|
* [*Returns:] A reference to the contained value
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`.
|
|
* [*Example:]
|
|
``
|
|
T v ;
|
|
optional<T> opt ( v );
|
|
T const& u = *opt;
|
|
assert ( u == v ) ;
|
|
T w ;
|
|
*opt = w ;
|
|
assert ( *opt == w ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_get_value_or_value]
|
|
|
|
[: `T const& optional<T` ['(not a ref)]`>::get_value_or( T const& default) const ;`]
|
|
[: `T& optional<T` ['(not a ref)]`>::get_value_or( T& default ) ;`]
|
|
|
|
[: `inline T const& get_optional_value_or ( optional<T` ['(not a ref)]`> const& o, T const& default ) ;`]
|
|
[: `inline T& get_optional_value_or ( optional<T` ['(not a ref)]`>& o, T& default ) ;`]
|
|
|
|
* [*Returns:] A reference to the contained value, if any, or `default`.
|
|
* [*Throws:] Nothing.
|
|
* [*Example:]
|
|
``
|
|
T v, z ;
|
|
optional<T> def;
|
|
T const& y = def.get_value_or(z);
|
|
assert ( y == z ) ;
|
|
|
|
optional<T> opt ( v );
|
|
T const& u = get_optional_value_or(opt,z);
|
|
assert ( u == v ) ;
|
|
assert ( u != z ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[: `T const& optional<T&>::operator*() const ;`]
|
|
[: `T & optional<T&>::operator*();`]
|
|
[: `T const& optional<T&>::get() const ;`]
|
|
[: `T& optional<T&>::get() ;`]
|
|
|
|
[: `inline T const& get ( optional<T&> const& ) ;`]
|
|
[: `inline T& get ( optional<T&> &) ;`]
|
|
|
|
* [*Requirements: ] `*this` is initialized
|
|
* [*Returns:] [_The] reference contained.
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`.
|
|
* [*Example:]
|
|
``
|
|
T v ;
|
|
T& vref = v ;
|
|
optional<T&> opt ( vref );
|
|
T const& vref2 = *opt;
|
|
assert ( vref2 == v ) ;
|
|
++ v ;
|
|
assert ( *opt == v ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_get_ptr]
|
|
|
|
[: `T const* optional<T` ['(not a ref)]`>::get_ptr() const ;`]
|
|
[: `T* optional<T` ['(not a ref)]`>::get_ptr() ;`]
|
|
|
|
[: `inline T const* get_pointer ( optional<T` ['(not a ref)]`> const& ) ;`]
|
|
[: `inline T* get_pointer ( optional<T` ['(not a ref)]`> &) ;`]
|
|
|
|
* [*Returns:] If `*this` is initialized, a pointer to the contained value;
|
|
else `0` (['null]).
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] The contained value is permanently stored within `*this`, so you
|
|
should not hold nor delete this pointer
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
optional<T> opt(v);
|
|
optional<T> const copt(v);
|
|
T* p = opt.get_ptr() ;
|
|
T const* cp = copt.get_ptr();
|
|
assert ( p == get_pointer(opt) );
|
|
assert ( cp == get_pointer(copt) ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_arrow]
|
|
|
|
[: `T const* optional<T` ['(not a ref)]`>::operator ->() const ;`]
|
|
[: `T* optional<T` ['(not a ref)]`>::operator ->() ;`]
|
|
|
|
* [*Requirements: ] `*this` is initialized.
|
|
* [*Returns:] A pointer to the contained value.
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`.
|
|
* [*Example:]
|
|
``
|
|
struct X { int mdata ; } ;
|
|
X x ;
|
|
optional<X> opt (x);
|
|
opt->mdata = 2 ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_bool]
|
|
|
|
[: `optional<T>::operator `['unspecified-bool-type]`() const ;`]
|
|
|
|
* [*Returns:] An unspecified value which if used on a boolean context
|
|
is equivalent to (`get() != 0`)
|
|
* [*Throws:] Nothing.
|
|
* [*Example:]
|
|
``
|
|
optional<T> def ;
|
|
assert ( def == 0 );
|
|
optional<T> opt ( v ) ;
|
|
assert ( opt );
|
|
assert ( opt != 0 );
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_not]
|
|
|
|
[: `bool optional<T>::operator!() ;`]
|
|
|
|
* [*Returns:] If `*this` is uninitialized, `true`; else `false`.
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] This operator is provided for those compilers which can't
|
|
use the ['unspecified-bool-type operator] in certain boolean contexts.
|
|
* [*Example:]
|
|
``
|
|
optional<T> opt ;
|
|
assert ( !opt );
|
|
*opt = some_T ;
|
|
|
|
// Notice the "double-bang" idiom here.
|
|
assert ( !!opt ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_is_initialized]
|
|
|
|
[: `bool optional<T>::is_initialized() const ;`]
|
|
|
|
* [*Returns: ] `true` if the `optional` is initialized, `false` otherwise.
|
|
* [*Throws:] Nothing.
|
|
* [*Example:]
|
|
``
|
|
optional<T> def ;
|
|
assert ( !def.is_initialized() );
|
|
optional<T> opt ( v ) ;
|
|
assert ( opt.is_initialized() );
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[heading Free functions]
|
|
|
|
__SPACE__
|
|
|
|
[#reference_make_optional_value]
|
|
|
|
[: `optional<T` ['(not a ref)]`> make_optional( T const& v )`]
|
|
|
|
* [*Returns: ] `optional<T>(v)` for the ['deduced] type `T` of `v`.
|
|
* [*Example:]
|
|
``
|
|
template<class T> void foo ( optional<T> const& opt ) ;
|
|
|
|
foo ( make_optional(1+1) ) ; // Creates an optional<int>
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_make_optional_bool_value]
|
|
|
|
[: `optional<T` ['(not a ref)]`> make_optional( bool condition, T const& v )`]
|
|
|
|
* [*Returns: ] `optional<T>(condition,v)` for the ['deduced] type `T` of `v`.
|
|
* [*Example:]
|
|
``
|
|
optional<double> calculate_foo()
|
|
{
|
|
double val = compute_foo();
|
|
return make_optional(is_not_nan_and_finite(val),val);
|
|
}
|
|
|
|
optional<double> v = calculate_foo();
|
|
if ( !v )
|
|
error("foo wasn't computed");
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_equal_optional_optional]
|
|
|
|
[: `bool operator == ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns:] If both `x` and `y` are initialized, `(*x == *y)`. If only
|
|
`x` or `y` is initialized, `false`. If both are uninitialized, `true`.
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] Pointers have shallow relational operators while `optional` has
|
|
deep relational operators. Do not use `operator ==` directly in generic
|
|
code which expect to be given either an `optional<T>` or a pointer; use
|
|
__FUNCTION_EQUAL_POINTEES__ instead
|
|
* [*Example:]
|
|
``
|
|
T x(12);
|
|
T y(12);
|
|
T z(21);
|
|
optional<T> def0 ;
|
|
optional<T> def1 ;
|
|
optional<T> optX(x);
|
|
optional<T> optY(y);
|
|
optional<T> optZ(z);
|
|
|
|
// Identity always hold
|
|
assert ( def0 == def0 );
|
|
assert ( optX == optX );
|
|
|
|
// Both uninitialized compare equal
|
|
assert ( def0 == def1 );
|
|
|
|
// Only one initialized compare unequal.
|
|
assert ( def0 != optX );
|
|
|
|
// Both initialized compare as (*lhs == *rhs)
|
|
assert ( optX == optY ) ;
|
|
assert ( optX != optZ ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_less_optional_optional]
|
|
|
|
[: `bool operator < ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns:] If `y` is not initialized, `false`. If `y` is initialized
|
|
and `x` is not initialized, `true`. If both `x` and `y` are initialized,
|
|
`(*x < *y)`.
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] Pointers have shallow relational operators while `optional` has
|
|
deep relational operators. Do not use `operator <` directly in generic code
|
|
which expect to be given either an `optional<T>` or a pointer; use __FUNCTION_LESS_POINTEES__ instead.
|
|
* [*Example:]
|
|
``
|
|
T x(12);
|
|
T y(34);
|
|
optional<T> def ;
|
|
optional<T> optX(x);
|
|
optional<T> optY(y);
|
|
|
|
// Identity always hold
|
|
assert ( !(def < def) );
|
|
assert ( optX == optX );
|
|
|
|
// Both uninitialized compare equal
|
|
assert ( def0 == def1 );
|
|
|
|
// Only one initialized compare unequal.
|
|
assert ( def0 != optX );
|
|
|
|
// Both initialized compare as (*lhs == *rhs)
|
|
assert ( optX == optY ) ;
|
|
assert ( optX != optZ ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_not_equal_optional_optional]
|
|
|
|
[: `bool operator != ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns: ] `!( x == y );`
|
|
* [*Throws:] Nothing.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_greater_optional_optional]
|
|
|
|
[: `bool operator > ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns: ] `( y < x );`
|
|
* [*Throws:] Nothing.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_less_or_equal_optional_optional]
|
|
|
|
[: `bool operator <= ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns: ] `!( y<x );`
|
|
* [*Throws:] Nothing.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_greater_or_equal_optional_optional]
|
|
|
|
[: `bool operator >= ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns: ] `!( x<y );`
|
|
* [*Throws:] Nothing.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_swap_optional_optional]
|
|
|
|
[: `void swap ( optional<T>& x, optional<T>& y );`]
|
|
|
|
* [*Effect:] If both `x` and `y` are initialized, calls `swap(*x,*y)`
|
|
using `std::swap`. If only one is initialized, say `x`, calls:
|
|
`y.reset(*x); x.reset();` If none is initialized, does nothing.
|
|
* [*Postconditions:] The states of `x` and `y` interchanged.
|
|
* [*Throws:] If both are initialized, whatever `swap(T&,T&)` throws. If only
|
|
one is initialized, whatever `T::T ( T const& )` throws.
|
|
* [*Notes:] If both are initialized, `swap(T&,T&)` is used unqualified but
|
|
with `std::swap` introduced in scope.
|
|
If only one is initialized, `T::~T()` and `T::T( T const& )` is called.
|
|
* [*Exception Safety:] If both are initialized, this operation has the
|
|
exception safety guarantees of `swap(T&,T&)`.
|
|
If only one is initialized, it has the same basic guarantee as
|
|
`optional<T>::reset( T const& )`.
|
|
* [*Example:]
|
|
``
|
|
T x(12);
|
|
T y(21);
|
|
optional<T> def0 ;
|
|
optional<T> def1 ;
|
|
optional<T> optX(x);
|
|
optional<T> optY(y);
|
|
|
|
boost::swap(def0,def1); // no-op
|
|
|
|
boost::swap(def0,optX);
|
|
assert ( *def0 == x );
|
|
assert ( !optX );
|
|
|
|
boost::swap(def0,optX); // Get back to original values
|
|
|
|
boost::swap(optX,optY);
|
|
assert ( *optX == y );
|
|
assert ( *optY == x );
|
|
``
|
|
|
|
[endsect]
|