TriState.h

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/*
 * This file is part of sphgeom.
 *
 * Developed for the LSST Data Management System.
 * This product includes software developed by the LSST Project
 * (http://www.lsst.org).
 * See the COPYRIGHT file at the top-level directory of this distribution
 * for details of code ownership.
 *
 * This software is dual licensed under the GNU General Public License and also
 * under a 3-clause BSD license. Recipients may choose which of these licenses
 * to use; please see the files gpl-3.0.txt and/or bsd_license.txt,
 * respectively.  If you choose the GPL option then the following text applies
 * (but note that there is still no warranty even if you opt for BSD instead):
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef LSST_SPHGEOM_TRISTATE_H_
#define LSST_SPHGEOM_TRISTATE_H_

 
#include <iostream>
#include <stdexcept>
 
 
namespace lsst {
namespace sphgeom {

class TriState {
public:
    TriState() {}

    explicit TriState(bool value) : _known(true), _value(value) {}
 
    TriState& operator=(TriState const & other) = default;

    bool operator==(TriState const & other) const {
        if (not _known) {
            return not other._known;
        } else {
            return other._known && _value == other._value;
        }
    }
 
    bool operator!=(TriState const & other) const {
        return not this->operator==(other);
    }

    bool operator==(bool value) const {
        return _known && _value == value;
    }
 
    bool operator!=(bool value) const {
        return not this->operator==(value);
    }

    TriState operator|(TriState const & other) const {
        if (*this == true || other == true) {
            return TriState(true);
        } else if (*this == false && other == false) {
            return TriState(false);
        } else {
            return TriState();
        }
    }

    TriState operator&(TriState const & other) const {
        if (*this == false || other == false) {
            return TriState(false);
        } else if (*this == true && other == true) {
            return TriState(true);
        } else {
            return TriState();
        }
    }

    TriState operator~() const {
        if (known()) {
            return TriState(!_value);
        }
        return TriState();
    }

    bool known() const { return _known; }
 
private:
    bool _known = false;
    bool _value = false;
};
 
inline
std::ostream & operator<<(std::ostream & stream, TriState const & value) {
    const char* str = "unknown";
    if (value == true) {
        str = "true";
    } else if (value == false) {
        str = "false";
    }
    return stream << str;
}
 
}} // namespace lsst::sphgeom
 
#endif // LSST_SPHGEOM_TRISTATE_H_