staged_value.h

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// Copyright (C) 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 STAGED_VALUE_H
#define STAGED_VALUE_H

#include <boost/noncopyable.hpp>
#include <boost/shared_ptr.hpp>

namespace isc {
namespace util {

template<typename ValueType>
class StagedValue : public boost::noncopyable {
public:

    StagedValue()
        : staging_(new ValueType()), current_(new ValueType()),
          modified_(false) {
    }

    const ValueType& getValue() const {
        return (modified_ ? *staging_ : *current_);
    }

    void setValue(const ValueType& new_value) {
        *staging_ = new_value;
        modified_ = true;
    }

    void commit() {
        // Only apply changes if any modifications made.
        if (modified_) {
            current_ = staging_;
        }
        revert();
    }

    void reset() {
        revert();
        current_.reset(new ValueType());
    }

    void revert() {
        staging_.reset(new ValueType());
        modified_ = false;
    }

    StagedValue& operator=(const ValueType& value) {
        setValue(value);
        return (*this);
    }

    operator const ValueType&() const {
        return (getValue());
    }

private:

    boost::shared_ptr<ValueType> staging_;

    boost::shared_ptr<ValueType> current_;

    bool modified_;

};

} // namespace isc::util
} // namespace isc

#endif // STAGED_VALUE_H