It's a common situation, when we have a class template that implements some functionality:

// Generic implementation.
template <class T> 
class data_processor { 
    double process(const T& v1, const T& v2, const T& v3); 
};

Now, imagine that we have two additional versions of that class, one for integral, and another for real types:

// Integral types optimized version. 
template <class T>
class data_processor_integral {
    typedef int fast_int_t;
    double process(fast_int_t v1, fast_int_t v2, fast_int_t v3);
}; 

// SSE optimized version for float types.
template <class T>
class data_processor_sse {
    double process(double v1, double v2, double v3);
};

Now the question: How to make the compiler to automatically choose the correct class for a specified type?