tribool.hpp

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#ifndef EAGINE_TRIBOOL_HPP
#define EAGINE_TRIBOOL_HPP
 
namespace eagine {
 
enum class _tribool_value_t : unsigned char {
    _false = 0x00,
    _true = 0x01,
    _unknown = 0x02
};
 
struct indeterminate_t {};
 
constexpr static const indeterminate_t indeterminate = {};
 
class tribool;
 
class weakbool {
private:
    using _value_t = _tribool_value_t;
    _value_t _value;
 
    friend class tribool;
 
    constexpr explicit weakbool(_value_t value) noexcept
      : _value(value) {}
 
public:
    constexpr explicit operator bool() const noexcept {
        return _value != _value_t::_false;
    }
 
    constexpr auto operator!() const noexcept {
        return _value != _value_t::_true;
    }
 
    constexpr auto is(indeterminate_t) const noexcept {
        return _value == _value_t::_unknown;
    }
};
 
class tribool {
private:
    using _value_t = _tribool_value_t;
    _value_t _value{_value_t::_false};
 
public:
    constexpr tribool() noexcept = default;
 
    constexpr tribool(bool value) noexcept
      : _value(value ? _value_t::_true : _value_t::_false) {}
 
    constexpr tribool(indeterminate_t) noexcept
      : _value(_value_t::_unknown) {}
 
    constexpr tribool(bool value, bool is_unknown) noexcept
      : _value(
          is_unknown ? _value_t::_unknown
                     : value ? _value_t::_true : _value_t::_false) {}
 
    constexpr explicit operator bool() const noexcept {
        return _value == _value_t::_true;
    }
 
    constexpr auto operator!() const noexcept {
        return _value == _value_t::_false;
    }
 
    constexpr auto operator*() const noexcept -> bool {
        return _value == _value_t::_unknown;
    }
 
    constexpr auto operator~() const noexcept -> weakbool {
        return weakbool{_value};
    }
 
    constexpr auto is(bool value) const noexcept -> bool {
        return _value == (value ? _value_t::_true : _value_t::_false);
    }
 
    constexpr auto is(indeterminate_t) const noexcept -> bool {
        return *(*this);
    }
 
    friend constexpr auto operator==(tribool a, tribool b) noexcept -> tribool {
        return {a._value == b._value, (*a || *b)};
    }
 
    friend constexpr auto operator!=(tribool a, tribool b) noexcept -> tribool {
        return {a._value != b._value, (*a || *b)};
    }
};
 
constexpr auto operator&&(tribool a, tribool b) noexcept {
    return !a ? tribool{false}
              : a ? b : !b ? tribool{false} : tribool{indeterminate};
}
 
constexpr auto operator||(tribool a, tribool b) noexcept {
    return a ? tribool{true}
             : !a ? b : b ? tribool{true} : tribool{indeterminate};
}
 
} // namespace eagine
 
#endif // EAGINE_TRIBOOL_HPP