static HashMap<Set<S>, Class> loadFunctions_cache = new HashMap;
static Lock loadFunctions_cached_lock = lock();

static Class loadFunctions_cached(S... functions) {
  ret loadFunctions_cached(asList(functions));
}

static Class loadFunctions_cached(Collection<S> functions) {
  Set<S> functionSet = new TreeSet<S>(functions);
  lock loadFunctions_cached_lock;
  Class c = loadFunctions_cache.get(functionSet);
  if (c == null) {
    loadFunctions_cache.put(functionSet, c = loadFunctions(functionSet));
    assertNotNull(loadFunctions_cache.get(functionSet));
  }
  ret c;
}