import type { Callable } from '../types';
/**
 * ensure function to be called once, and only once
 *
 * note: `this` is dropped
 * @param fn - the function to call for the first time
 * @param subsequent - the function to call after the first one
 * @returns function that will call `fn` for the first time, and then `subsequent`
 */
export declare function once<T extends Callable>(fn: T & ThisType<null>, subsequent?: (lastResult: ReturnType<T>, ...args: Parameters<T>) => any): T;
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