class SurfaceShiftFunctionFactory {

  public static SurfaceShiftFunction<?> getFunction(final Class<?> clazz) {
    final SurfaceShiftFunction<?> f = s_instances.get(clazz);
    if (f == null) {
      throw new IllegalArgumentException("Could not get function for " + clazz.getName());
    }
    return f;
  }

}