optional/doc/optional.qbk

[library Boost.Optional
    [quickbook 1.4]
    [authors [Cacciola Carballal, Fernando Luis]]
    [copyright 2003-2007 Fernando Luis Cacciola Carballal]
    [copyright 2014 Andrzej Krzemieński]
    [category miscellaneous]
    [id optional]
    [dirname optional]
    [purpose
        Discriminated-union wrapper for optional values
    ]
    [source-mode c++]
    [license
Distributed under 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])
    ]
]

[/ Macros will be used for links so we have a central place to change them ]


[/ Cited Boost resources ]

[def __BOOST_VARIANT__ [@../../../variant/index.html Boost.Variant]]
[def __BOOST_TRIBOOL__ [@../../../../doc/html/tribool.html boost::tribool]]

[def __OPTIONAL_POINTEE__ [@../../../utility/OptionalPointee.html OptionalPointee]]
[def __COPY_CONSTRUCTIBLE__ [@../../../utility/CopyConstructible.html Copy Constructible]]
[def __FUNCTION_EQUAL_POINTEES__ [@../../../utility/OptionalPointee.html#equal `equal_pointees()`]]
[def __FUNCTION_LESS_POINTEES__ [@../../../utility/OptionalPointee.html#less `less_pointees()`]]

[def __IN_PLACE_FACTORY_HPP__ [@../../../../boost/utility/in_place_factory.hpp in_place_factory.hpp]]
[def __TYPED_IN_PLACE_FACTORY_HPP__ [@../../../../boost/utility/typed_in_place_factory.hpp typed_in_place_factory.hpp]]

[/ Other web resources ]

[def __HASKELL__ [@http://www.haskell.org/ Haskell]]
[def __SGI_DEFAULT_CONSTRUCTIBLE__ [@http://www.sgi.com/tech/stl/DefaultConstructible.html Default Constructible]]


[/ Icons ]

[def __SPACE__ [$images/space.png]]
[def __GO_TO__ [$images/callouts/R.png]]


[section Introduction]
This library can be used to represent 'optional' (or 'nullable') objects that can be safely passed by value:

    optional<int> readInt(); // this function may return either an int or a not-an-int

    if (optional<int> oi = readInt()) // did I get a real int
      cout << "my int is: " << *oi;   // use my int
    else
      cout << "I have no int";
  
[endsect]

[include motivation.qbk]
[include development.qbk]
[include reference.qbk]
[include examples.qbk]
[include special_cases.qbk]
[include dependencies.qbk]
[include acknowledgments.qbk]