// A FlexibleVarContext is thread-safe AFTER the first variable has been defined
// or after you call makeThreadSafe(), whichever comes first
sclass FlexibleVarContext > VarContext {
  MapSO vars;
  
  *() {}
  *(VarContext parent) { super(parent); }
  
  O get(S name) {
    if (containsKey(vars, name))
      ret mapGet(vars, name);
    if (parent != null)
      ret parent.get(name);
    null;
  }
  
  void set(S name, O value) {
    vars = putOrCreateSyncMap(vars, name, value);
  }
  
  AutoCloseable tempSet(S name, O value) {
    initMap();
    ret main tempPut(vars, name, value);
  }
  
  void unset(S name) {
    remove(vars, name);
  }
  
  MapSO varMap() { ret vars; }

  void makeThreadSafe aka initMap() {
    vars if null = syncHashMap();
  }
}