import { PipelineOperator } from "../../core";
/**
 * 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}.
 *
 * @param collection
 * @param expr
 * @param options
 * @returns
 */
export declare const $addFields: PipelineOperator;