anchor.diff:    void set(T state, P subState) => _setter(state, subState);
   }
   
  -class ConnOp<S, P> extends BaseConn<S, P> {
  +class ConnOp<S, P> extends ImmutableConn<S, P> {
     final P Function(S) _getter;
     final void Function(S, P) _setter;
   
  
positive.code:   }
  }
  
  abstract class BaseConn<T, P> implements AbstractConnector<T, P> {
    const BaseConn();
  
    void set(T state, P subState);
  
  
negative.code:   }
  }
  
  class Connector<T, P> extends ImmutableConn<T, P> {
    final P Function(T) _getter;
    final void Function(T, P) _setter;
  
  