/**
 * A special kind of map that makes it easy to store items by a number, automatically ensuring that
 * these identifiers increment and don't collide.
 */
export declare class NumberMap<Generic> extends Map<number, Generic> {
    #private;
    constructor(start?: number);
    getNextAvailableKey(): number;
    /**
     * Add new data to the map, and return the new unique key.
     */
    add(data: Generic): number;
    /**
     * Get all values in an array.
     */
    array(): Array<Generic>;
}