[/
    Boost.Optional

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

    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)
]

[section Header <boost/none.hpp>]

[section Synopsis]
```
namespace boost {

class none_t
{
  friend constexpr bool operator==(none_t, none_t) = default;
  /* see below */
};

inline constexpr 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 class.

It is [@https://en.cppreference.com/w/cpp/named_req/TriviallyCopyable.html trivially copyable].

It is ['not] [@https://en.cppreference.com/w/cpp/named_req/DefaultConstructible default-constructible].

It models concept [@https://en.cppreference.com/w/cpp/concepts/equality_comparable `std::equality_comparable`].

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

[endsect]

[endsect]
