private void swigDirectorConnect() {
    …
    director_basic.director_basic_im.SwigDirector_A_Callback3 callback3;
    if (swigIsMethodOverridden!(int delegate(), int function(), rg)()) {
      …
    }
    …
  }

  private bool swigIsMethodOverridden(DelegateType, FunctionType, alias fn)() {
    DelegateType dg = &fn;
    return dg.funcptr != SwigNonVirtualAddressOf!(FunctionType, fn);
  }

  private static Function SwigNonVirtualAddressOf(Function, alias fn)() {
    return cast(Function) &fn;
  }