/**
 * Variable Expression Operators: https://docs.mongodb.com/manual/reference/operator/aggregation/#variable-expression-operators
 */
import { Options } from '../../../core';
/**
 * Defines variables for use within the scope of a sub-expression and returns the result of the sub-expression.
 *
 * @param obj The target object for this expression
 * @param expr The right-hand side of the operator
 * @param options Options to use for this operattion
 * @returns {*}
 */
export declare function $let(obj: object, expr: any, options: Options): any;