code: func (ps *PrintSettings) GetDoubleWithDefault(key string, def float64) float64 {
  	cstr := C.CString(key)
  	defer C.free(unsafe.Pointer(cstr))
  	c := C.gtk_print_settings_get_double_with_default(ps.native(),
  		(*C.gchar)(cstr), C.gdouble(def))
  	return float64(c)
  }
docs: // GetDoubleWithDefault() is a wrapper around gtk_print_settings_get_double_with_default().