optional_value.h

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// Copyright (C) 2014-2015 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
#ifndef OPTIONAL_VALUE_H
#define OPTIONAL_VALUE_H
 
#include <ostream>
 
namespace isc {
namespace util {
 
struct OptionalValueState {
 
    OptionalValueState(const bool specified)
        : specified_(specified) {
    }
    bool specified_;
};
 
template<typename T>
class OptionalValue {
public:
 
    OptionalValue()
        : value_(T()), specified_(false) {
    }
 
    explicit OptionalValue(const T& value, const OptionalValueState& state =
                           OptionalValueState(false))
        : value_(value), specified_(state.specified_) {
    }
 
    T get() const {
        return (value_);
    }
 
    void set(const T& value) {
        value_ = value;
    }
 
    void specify(const T& value) {
        set(value);
        specify(OptionalValueState(true));
    }
 
    void specify(const OptionalValueState& state) {
        specified_ = state.specified_;
    }
 
    bool isSpecified() const {
        return (specified_);
    }
 
    void operator=(const T& value) {
        specify(value);
    }
 
    bool operator==(const T& value) const {
        return (specified_ && (value_ == value));
    }
 
    bool operator!=(const T& value) const {
        return (!operator==(value));
    }
 
    operator T() const {
        return (value_);
    }
 
private:
    T value_;         
    bool specified_;  
};
 
template<typename T>
std::ostream&
operator<<(std::ostream& os, const OptionalValue<T>& optional_value) {
    os << optional_value.get();
    return (os);
}
 
 
} // end of namespace isc::util
} // end of namespace isc
 
#endif // OPTIONAL_VALUE_H