docs: function (key) {
        if (this.size === 0) {
          return false;
        }
        // don't use ES6 "delete" because it will be annoying
        // to use in browsers that are not ES6 friendly;
        var keys = this._keys;
        var values = this._values;
        var guid = _emberMetalUtils.guidFor(key);
  
        if (keys.delete(key, guid)) {
          delete values[guid];
          this.size = keys.size;
          return true;
        } else {
          return false;
        }
      }