declare type Fn = (state: any) => any;
/**
 * Extract destructured argument names from `fn`'s first argument and return a `Set` of `keys`.
 *
 * ```ts
 * const fn = ({ foo, bar }) => void 0
 * argtor(fn) // => Set(2) {'foo', 'bar'}
 * ```
 *
 * @param fn The function to extract argument keys from.
 * @param keys A keys `Set` to fill in with the argument names.
 * @returns The keys `Set` with the argument names.
 */
export declare function argtor<T extends string>(fn: Fn & {
    fn?: Fn;
}, keys?: Set<T>): T[] & {
    source: string;
};
export {};