Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for a snapshot of the develop branch, built from commit 3475a457cf.



    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

[section Header <boost/none.hpp>]

[section Synopsis]
namespace boost {

class none_t {/* 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, 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`.