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 64c293a8eb.


Header <boost/none.hpp>
Header <boost/optional/bad_optional_access.hpp>
Header <boost/optional/optional_io.hpp>
Header <boost/optional/optional_fwd.hpp>
Header <boost/optional/optional.hpp>
Header <boost/optional.hpp>

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.