xref: /minix3/external/bsd/kyua-cli/dist/utils/optional.hpp (revision 11be35a165022172ed3cea20f2b5df0307540b0e)

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/// \file utils/optional.hpp
/// Provides the utils::optional class.
///
/// The class is provided as a separate module on its own to minimize
/// header-inclusion side-effects.

#if !defined(UTILS_OPTIONAL_HPP)
#define UTILS_OPTIONAL_HPP

#include <ostream>


namespace utils {


namespace detail {


/// Internal type-safe representation for the none type.
struct none_t {};


}  // namespace detail


/// The none value.
///
/// This has internal linkage so it is OK to define it in the header file.
/// However, pointers to none from different translation units will be
/// different.  Just don't do that.
const detail::none_t none = {};


/// Holds a data value or none.
///
/// This class allows users to represent values that may be uninitialized.
/// Instead of having to keep separate variables to track whether a variable is
/// supposed to have a value or not, this class allows multiplexing the
/// behaviors.
///
/// This class is a simplified version of Boost.Optional.
template< class T >
class optional {
    /// Internal representation of the optional data value.
    T* _data;

public:
    optional(void);
    optional(utils::detail::none_t);
    optional(const optional< T >&);
    explicit optional(const T&);
    ~optional(void);

    optional& operator=(utils::detail::none_t);
    optional& operator=(const T&);
    optional& operator=(const optional< T >&);

    bool operator==(const optional< T >&) const;
    bool operator!=(const optional< T >&) const;

    operator bool(void) const;

    const T& get(void) const;
    const T& get_default(const T&) const;
    T& get(void);
};


template< class T >
std::ostream& operator<<(std::ostream&, const optional< T >&);


template< class T >
optional< T > make_optional(const T&);


}  // namespace utils


#endif  // !defined(UTILS_OPTIONAL_HPP)