/usr/include/osgEarth/optional is in libosgearth-dev 2.4.0+dfsg-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 | /* -*-c++-*- */
/* osgEarth - Dynamic map generation toolkit for OpenSceneGraph
* Copyright 2008-2013 Pelican Mapping
* http://osgearth.org
*
* osgEarth is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>
*/
#ifndef OSGEARTH_OPTIONAL_H
#define OSGEARTH_OPTIONAL_H 1
namespace osgEarth
{
    /**
     * A template for defining "optional" class members. An optional member has a default value
     * and a flag indicating whether the member is "set".
     * This is used extensively in osgEarth's ConfigOptions subsystem.
     */
    template<typename T> struct optional {
        optional() : _set(false), _value(T()), _defaultValue(T()) { }
        optional(T defaultValue) : _set(false), _value(defaultValue), _defaultValue(defaultValue) { }
        optional(T defaultValue, T value) : _set(true), _value(value), _defaultValue(defaultValue) { }
        optional(const optional<T>& rhs) { (*this)=rhs; }
        virtual ~optional() { }
        optional<T>& operator =(const optional<T>& rhs) { _set=rhs._set; _value=rhs._value; _defaultValue=rhs._defaultValue; return *this; }
        const T& operator =(const T& value) { _set=true; _value=value; return _value; }
        bool operator ==(const optional<T>& rhs) const { return _set && rhs._set && _value==rhs._value; }
        bool operator !=(const optional<T>& rhs) const { return !( (*this)==rhs); }
        bool operator ==(const T& value) const { return _value==value; }
        bool operator !=(const T& value) const { return _value!=value; }
        bool operator > (const T& value) const { return _value>value; }
        bool operator >=(const T& value) const { return _value>=value; }
        bool operator < (const T& value) const { return _value<value; }
        bool operator <=(const T& value) const { return _value<=value; }
        bool isSetTo(const T& value) const { return _set && _value==value; } // differs from == in that the value must be explicity set
        bool isSet() const { return _set; }
        void unset() { _set = false; _value=_defaultValue; }
        const T& get() const { return _value; }
        const T& value() const { return _value; }
        const T& defaultValue() const { return _defaultValue; }
        T temp_copy() const { return _value; }
        const T& getOrUse(const T& fallback) const { return _set ? _value : fallback; }
        // gets a mutable reference, automatically setting
        T& mutable_value() { _set = true; return _value; }
        void init(T defValue) { _value=defValue; _defaultValue=defValue; unset(); }
        operator const T*() const { return &_value; }
        T* operator ->() { _set=true; return &_value; }
        const T* operator ->() const { return &_value; }
    private:
        bool _set;
        T _value;
        T _defaultValue;
        typedef T* optional::*unspecified_bool_type;
    public:
        operator unspecified_bool_type() const { return 0; }
    };
}
#endif // OSGEARTH_OPTIONAL_H
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