C++ for Scientists - Technische Universität Dresden

114 CHAPTER 4. GENERIC PROGRAMMING
}
private:
double parameter ;
} ;
int main() {
para sin plus cos sin 1( 1.0 ) ;
std::cout ≪ finite difference( sin 1, 1., 0.001 ) ≪ std::endl ;
std::cout ≪ finite difference( para sin plus cos(2.0), 1., 0.001 ) ≪ std::endl ;
std::cout ≪ finite difference( para sin plus cos(2.0), 0., 0.001 ) ≪ std::endl ;
}
4.8.2 Functors via generic programming
If we make the functor argument in finite difference generic, we do not need a functor base
any longer. There is also no need to alter our previously defined functors sin plus cos and
para sin plus cos. This is a perfect example of the fact that using generic programming makes
extending software easier. The program now looks like:
#include
#include
template
T inline finite difference(F const& f, const T& x, const T& h)
{
return ( f(x+h) − f(x) ) / h ;
}
class para sin plus cos
{
public:
para sin plus cos(double p) : parameter(p) {}
double operator() ( double x ) const
{
return sin( parameter ∗ x ) + cos(x);
}
private:
double parameter;
};
int main()
{
para sin plus cos sin 1( 1.0 ) ;
std::cout ≪ finite difference( sin 1, 1., 0.001 ) ≪ std::endl ;
std::cout ≪ finite difference( para sin plus cos(2.0), 1., 0.001 ) ≪ std::endl ;
std::cout ≪ finite difference( para sin plus cos(2.0), 0., 0.001 ) ≪ std::endl ;
}
return 0;