// Function object - functor 
#include <iostream>
#include <cmath>
#include <functional>
class TrigFuns{
public:
  void operator()(double x) {
    std::cout<<"x="<<x<<std::endl;
    std::cout<<"sin(x)      cos(x)     tan(x)\n";
    std::cout<<sin(x)<<" "<<cos(x)<<" "<<tan(x)<<std::endl;
  }
};
int main()
{
  TrigFuns trig;
  trig(20.0);
  std::invoke(TrigFuns(),10.0);
}