OpenSceneGraph/include/osgIntrospection/variant_cast

/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield 
 *
 * This library is open source and may be redistributed and/or modified under  
 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or 
 * (at your option) any later version.  The full license is in LICENSE file
 * included with this distribution, and on the openscenegraph.org website.
 * 
 * This library 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 
 * OpenSceneGraph Public License for more details.
*/
//osgIntrospection - Copyright (C) 2005 Marco Jez

#ifndef OSGINTROSPECTION_VARIANT_CAST_
#define OSGINTROSPECTION_VARIANT_CAST_

#include <osgIntrospection/Value>
#include <osgIntrospection/ReaderWriter>

#include <sstream>

namespace osgIntrospection
{

    /// Tries to convert an instance of Value to an object of type T.
    /// If T is a plain type or a pointer type (either const or non-const),
    /// and it matches the type of the value contained in v, then the actual
    /// value of type T is returned. If T is a [const] reference type, and 
    /// its base (non reference) type matches the internal value's type, 
    /// then a [const] reference to the internal value is returned.
    /// If none of the above conditions are met, a conversion is attempted
    /// as described in Value::convert() and then variant_cast is called again 
    /// with the converted value as parameter.
    /// If the conversion can't be completed, an exception is thrown.
    /// Conversions that attempt to make a const pointer non-const will fail.
    template<typename T> T variant_cast(const Value& v)
    {
        // return value
        Value::Instance<T> *i = dynamic_cast<Value::Instance<T> *>(v._inbox->inst_);
        if (i) return i->_data;

        // return reference to value
        i = dynamic_cast<Value::Instance<T> *>(v._inbox->_ref_inst);
        if (i) return i->_data;

        // return const reference to value
        i = dynamic_cast<Value::Instance<T> *>(v._inbox->_const_ref_inst);
        if (i) return i->_data;

        // try to convert v to type T and restart
        return variant_cast<T>(v.convertTo(typeof(T)));
    }
    
    
    /// Returns true if the Value passed as parameter can't be casted to
    /// the specified type without a (potentially slow) conversion.
    /// Returns false otherwise.
    template<typename T> bool requires_conversion(const Value& v)
    {
        // direct value
        Value::Instance<T> *i = dynamic_cast<Value::Instance<T> *>(v._inbox->inst_);
        if (i) return false;

        // reference to value
        i = dynamic_cast<Value::Instance<T> *>(v._inbox->_ref_inst);
        if (i) return false;

        // const reference to value
        i = dynamic_cast<Value::Instance<T> *>(v._inbox->_const_ref_inst);
        if (i) return false;
        
        return true;
    }

    /// Returns a typed pointer to the data contained in a Value 
    /// instance. If the value's type is not identical to type T,
    /// a null pointer is returned.
    template<typename T> T* extract_raw_data(Value& v)
    {
        Value::Instance<T>* i = dynamic_cast<Value::Instance<T> *>(v._inbox->inst_);
        if (i) return &i->_data;
        return 0;
    }

    /// Returns a typed pointer to the data contained in a const Value 
    /// instance. If the value's type is not identical to type T, a
    /// null pointer is returned.
    template<typename T> const T* extract_raw_data(const Value& v)
    {
        Value::Instance<T>* i = dynamic_cast<Value::Instance<T> *>(v._inbox->inst_);
        if (i) return &i->_data;
        return 0;
    }

}

#endif