static DoublePt toDoublePt(Pt p) {
  ret p == null ?: DoublePt(p.x, p.y);
}

static DoublePt toDoublePt(IDoublePt p) {
  if (p == null) null;
  if (p cast DoublePt) ret p;
  ret DoublePt(p.x_double(), p.y_double());
}