optional/doc/21_ref_none.qbk

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    Boost.Optional

    Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
    Copyright (c) 2015 Andrzej Krzemienski

    Distributed under the Boost Software License, Version 1.0.
    (See accompanying file LICENSE_1_0.txt or copy at
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[section Header <boost/none.hpp>]

[section Synopsis]
```
namespace boost {

class none_t {/* see below */};

const none_t none (/* see below */); 
    
} // namespace boost
```

Class `none_t` is meant to serve as a tag for selecting appropriate overloads of from `optional`'s interface. It is an empty, trivially copyable class with disabled default constructor.

Constant `none` is used to indicate an optional object that does not contain a value in initialization, assignment and relational operations of `optional`.

[endsect]

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