class Base {
  constructor(obj) {
    return obj;
  }

}

let counter = 0;

var _foo = /*#__PURE__*/new WeakMap();

class Derived extends Base {
  constructor(...args) {
    super(...args);
    babelHelpers.classPrivateFieldInitSpec(this, _foo, {
      writable: true,
      value: ++counter
    });
  }

  static get(obj) {
    return babelHelpers.classPrivateFieldGet(obj, _foo);
  }

}