/**
 * Like Set, but serializes to JSON as an array.
 *
 * Fixes the "issue" of stock Set being json-serialized as `{}`.
 *
 * @experimental
 */
export declare class Set2<T = any> extends Set<T> {
    static of<T>(items?: Iterable<T> | null): Set2<T>;
    /**
     * Like .add(), but allows to add multiple items at once.
     * Mutates the Set, but also returns it conveniently.
     */
    addMany(items: Iterable<T>): this;
    first(): T;
    firstOrUndefined(): T | undefined;
    toArray(): T[];
    toJSON(): T[];
    toString(): string;
}