import { Iterator } from "../../lazy";
import { AnyObject, Options } from "../../types";
/**
 * Adds new fields to documents. $addFields outputs documents that contain
 * all existing fields from the input documents and newly added fields.
 *
 * See {@link https://www.mongodb.com/docs/manual/reference/operator/aggregation/addFields/ usage}.
 */
export declare function $addFields(coll: Iterator, expr: AnyObject, options: Options): Iterator;