radians

#include <iostream>
#include <cmath>

struct RadiansImpl {
    static RadiansImpl INSTANCE;
};
double operator-(double deg, RadiansImpl radImpl) {
    return deg / 180.0 * M_PI;
}
#define degrees -RadiansImpl::INSTANCE

struct DegreesImpl {
    static DegreesImpl INSTANCE;
};
double operator-(double rad, DegreesImpl degImpl) {
    return rad / M_PI * 180.0;
}
#define radians -DegreesImpl::INSTANCE

int main() {
  std::cout << "Hello World!\n";
  std::cout << 90 degrees << "\n";
  std::cout << M_PI radians << "\n";
}