import type { PipeStep } from './pipe$.js';
import type { AnySubscribable } from './types/inputs/Subscribable.js';
import type { Observable } from './types/outputs/Observable.js';
/**
 * For each value emitted by the origin, this step will call `fn`, then will subscribe to its result and re-emit each
 * emitted value, until this "inner" subscription completes. All value emitted by the origin will be queued, and
 * processed in order
 * @param fn
 *
 * @since 1.0.0
 */
export declare function concatMap$<T, R>(fn: (item: T) => AnySubscribable<R>): PipeStep<AnySubscribable<T>, Observable<R>>;