/**
 * @fileoverview
 * @author Taketoshi Aono
 */
import { Observable, OperatorFunction } from 'rxjs';
interface FlatScanAggregateReturnType {
    aggregate: true;
    payload: any;
}
/**
 * Return type of flatscan.
 */
export declare type FlatScanReturnType<T> = T | Promise<T> | Observable<T> | FlatScanAggregateReturnType | null | undefined;
export interface FlatScanOptions<T> {
    bufferingConfig?(value: T): number;
}
export declare function flatScan<T, U>(handler: (acc: T, value: U) => FlatScanReturnType<T> | Promise<FlatScanReturnType<T>>, initial?: T | Observable<T> | Promise<T>, options?: FlatScanOptions<U>): OperatorFunction<U, T>;
export {};