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/**
* @file lllazyvalue.h
* @brief generic functor/value abstraction for lazy evaluation of a value
* parsing construction parameters from xml and LLSD
*
* $LicenseInfo:firstyear=2008&license=viewergpl$
*
* Copyright (c) 2008-2009, Linden Research, Inc.
*
* Second Life Viewer Source Code
* The source code in this file ("Source Code") is provided by Linden Lab
* to you under the terms of the GNU General Public License, version 2.0
* ("GPL"), unless you have obtained a separate licensing agreement
* ("Other License"), formally executed by you and Linden Lab. Terms of
* the GPL can be found in doc/GPL-license.txt in this distribution, or
* online at http://secondlifegrid.net/programs/open_source/licensing/gplv2
*
* There are special exceptions to the terms and conditions of the GPL as
* it is applied to this Source Code. View the full text of the exception
* in the file doc/FLOSS-exception.txt in this software distribution, or
* online at
* http://secondlifegrid.net/programs/open_source/licensing/flossexception
*
* By copying, modifying or distributing this software, you acknowledge
* that you have read and understood your obligations described above,
* and agree to abide by those obligations.
*
* ALL LINDEN LAB SOURCE CODE IS PROVIDED "AS IS." LINDEN LAB MAKES NO
* WARRANTIES, EXPRESS, IMPLIED OR OTHERWISE, REGARDING ITS ACCURACY,
* COMPLETENESS OR PERFORMANCE.
* $/LicenseInfo$
*/
#ifndef LL_LAZY_VALUE_H
#define LL_LAZY_VALUE_H
#include <boost/function.hpp>
// Holds on to a value of type T *or* calls a functor to generate a value of type T
template<typename T>
class LLLazyValue
{
public:
typedef typename boost::add_reference<typename boost::add_const<T>::type>::type T_const_ref;
typedef typename boost::function<T_const_ref (void)> function_type;
public:
LLLazyValue(const function_type& value)
: mValueGetter(value)
{}
LLLazyValue(T_const_ref value)
: mValue(value)
{}
LLLazyValue()
: mValue()
{}
void set(const LLLazyValue& val)
{
mValueGetter = val.mValueGetter;
}
void set(T_const_ref val)
{
mValue = val;
mValueGetter = NULL;
}
T_const_ref get() const
{
if (!mValueGetter.empty())
{
return mValueGetter();
}
return mValue;
}
bool isUsingFunction() const
{
return mValueGetter != NULL;
}
private:
function_type mValueGetter;
T mValue;
};
#endif // LL_LAZY_VALUE_H
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