import HackleClient from "./HackleClient";
/**
 * Legacy singleton holder for HackleClient.
 *
 * For backward compatibility, once initialized it always returns the first client
 * instance even when a different sdkKey is requested later.
 */
export declare class HackleClientHolder<T extends HackleClient> {
    private client;
    getOrNull(): T | null;
    get(): T;
    set(client: T): void;
}