C++ for Scientists - Technische Universität Dresden

12.1. TRANSCENDING LEGACY APPLICATIONS 255
virtual void transition(state type& input) = 0;
};
boost::shared ptr scattering object;
template struct scattering model:scattering concept
{
T scattering instance;
scattering model(const T& x):scattering instance(x) {}
numeric type rate(const state type& input) const ;
void transition(state type& input) ;
};
numeric type rate(const state type& input) const;
void transition(state type& input) ;
template
scatter facade(const T& x):scattering object(new scattering model(x)){}
∼scatter facade() {}
};
therefore introduces a scattering facade which wraps a scattering concept part. The
virtual inheritance is used to configure the necessary interface parts, in this case rate() and
transition(), which have to be implemented by any scattering model. In the given example
the state type is still available for explicit parametrization.
In contrast to other applications of runtime concepts, e.g. in computer graphics, it is not
necessary to provide mechanisms for deep copies, as the actual physical models remain unaltered
once they have been created and would only serve unnecessarily increase the memory footprint.
Therefore a boost::shared ptr is used for memory management.
The legacy application has been writte in plain ANSI C, which makes it easily compatible with
the new C ++ implementation. Several design decisions, such as the use of global and static
variables, make it difficult to extend and update appropriately for modern multi-core CPUs.
To interface this novel approach a core structure is implemented which wraps the implementations
of the scattering models by using runtime concepts.
template
struct scattering rate A
{
...
const ParameterType& parameters;
scattering rate A(const ParameterType& parameters):parameters(parameters){}
template
numeric type
operator() (const StateType& state) const
{
return A rate(state, parameters);
}
};