sclass MechListDependentCaches<A> {
  Map<S, MechListDependentCache<A>> byList = ciMap();
  O maker; // func(S) -> A
  transient Lock lock = lock();
  
  *(O *maker) {}

  A get(S name) {
    MechListDependentCache<A> listCache;
    {
      lock lock;
      listCache = byList.get(name);
      if (listCache == null)
        byList.put(name, listCache
          = MechListDependentCache(name, maker));
    }
    ret listCache!;
  }
}

Began life as a copy of #1022393