sclass AutoInitVar<A> extends Var<A> {
  O make;
  bool has;
  Lock lock = lock();
  
  *() {}
  *(O *make) {}
  
  A get() {
    if (has) ret super.get();
    lock lock;
    if (has) ret super.get();
    set(pcallF(make));
    make = null;
    has = true;
    ret super.get();
  }
}