import { AccumulatorOperator } from "../../types";
/**
 * Returns the sum of all the values in a group.
 *
 * See {@link https://www.mongodb.com/docs/manual/reference/operator/aggregation/sum/ usage.}
 *
 * @param collection The input array
 * @param expr The right-hand side expression value of the operator
 * @returns
 */
export declare const $sum: AccumulatorOperator<number>;