cached_value.h

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/**
 * @file cached_value.h
 * Hold a cached value.
 *
 * @remark Copyright 2005 OProfile authors
 * @remark Read the file COPYING
 *
 * @author John Levon
 */

#ifndef CACHED_VALUE_H
#define CACHED_VALUE_H

#include "op_exception.h"

/**
 * Hold a single value, returning a cached value if there is one.
 */
template <class T>
class cached_value
{
public:
        cached_value() : set(false) {}

        typedef T value_type;

        /// return the cached value
        value_type const get() const {
                if (!set)
                        throw op_fatal_error("cached value not set");
                return value;
        }

        /// return true if a value is cached
        bool cached() const { return set; }

        /// set the contained value
        value_type const reset(value_type const & val) {
                value = val;
                set = true;
                return value;
        }

private:
        /// the cached value
        value_type value;
        /// is the value valid?
        bool set;
};


#endif /* !CACHED_VALUE_H */

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