  Definition &operator~() {
    ignoreSemanticValue = true;
    return *this;
  }

  void accept(Ope::Visitor &v) { holder_->accept(v); }
  Definition &operator~() {
    ignoreSemanticValue = true;
    return *this;
  }

  void accept(Ope::Visitor &v) { holder_->accept(v); }