forEach_(values, callback) {
    let result;
    for (let i = 0, l = values.length; i < l; i++) {
      result = callback(values[i]);
      if (result) {
        return result;
      }
    }
    return result;
  }
@param {Array<T>} values Values.
@param {function(T): R} callback Callback.
@return {R|undefined} Callback return value.
@template R
@private