ceph/src/boost/libs/optional/doc/21_ref_none.qbk

   1 [/
   2     Boost.Optional
   3
   4     Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
   5     Copyright (c) 2015 Andrzej Krzemienski
   6
   7     Distributed under the Boost Software License, Version 1.0.
   8     (See accompanying file LICENSE_1_0.txt or copy at
   9     http://www.boost.org/LICENSE_1_0.txt)
  10 ]
  11
  12 [section Header <boost/none.hpp>]
  13
  14 [section Synopsis]
  15 ```
  16 namespace boost {
  17
  18 class none_t {/* see below */};
  19
  20 const none_t none (/* see below */);
  21
  22 } // namespace boost
  23 ```
  24
  25 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.
  26
  27 Constant `none` is used to indicate an optional object that does not contain a value in initialization, assignment and relational operations of `optional`.
  28
  29 [endsect]
  30
  31 [endsect]