/**
 * @hidden
 */
export declare type _OptionalKeys<O extends object> = {
    [K in keyof O]-?: {} extends Pick<O, K> ? K : never;
}[keyof O];
/**
 * Get the keys of `O` that are optional
 * @param O
 * @returns [[Key]]
 * @example
 * ```ts
 * ```
 */
export declare type OptionalKeys<O extends object> = O extends unknown ? _OptionalKeys<O> : never;