static File userDesktopDir() {
  File f = toFileOpt(loadTextFile(userDesktopDirPointerFile()));
  if (f != null) ret f;
  final new Var<File> v;
  selectDir("Please select your desktop directory", userDir("Desktop"), voidfunc(File f) { v.set(f); });
  waitForVarToBeNotNull(v);
  saveTextFile(userDesktopDirPointerFile(), f2s(v!));
  ret v!;
}

static File userDesktopDir(S sub) {
  ret newFile(userDesktopDir(), sub);
}