generic-golden-ratio.cpp

template<class TestF class Map>
auto golden(TestF test, Map f) {
  int a = 0;
  int b = 1;
  double ratio = 1;
 
  while (1) {
    tie(a, b) = tuple{b, a+b};
    auto delta = b/(double)a - ratio;
    ratio = b/(double)a;
    if (test(delta, ratio, a, b)) 
      return f(abs(delta), ratio, a, b);
    }
  }
}

int main() {
  auto test = [i=0](auto delta, …) mutable {
    if (++i>100 || delta<0.0001)
      return true;
 
    cout << ratio <<endl;
    return false;
  };
 
  auto map = [](auto, auto, auto a, auto b) {
    return tuple{b, a};
  };
 
  auto [b, a] = golden(test, map);
  cout << b << a << endl;
}