/**
 * Measured item heights, cached by item identity.
 *
 * Heights used to be cached in a plain array indexed by position, which is only
 * correct while positions are stable. Prepend a single item to a virtualized
 * list and every cached height shifts onto the wrong item: the layout is then
 * computed from heights belonging to somebody else, and the items that would
 * reveal the error are exactly the ones virtualization has removed from the
 * DOM, so nothing re-measures them.
 *
 * Keying by the caller's `getItemKey` fixes that at the source — a height
 * follows its item through reorders, filters, and prepends. Without
 * `getItemKey` the key *is* the index, which reproduces the old behaviour
 * exactly; that is the documented reason for recommending the option whenever
 * items can move.
 */
/** Item identity. `bigint` is included because React's `Key` allows it. */
export type ItemKey = string | number | bigint;
export interface HeightCache {
    /** Measured height for a key, or `undefined` if it has never been measured. */
    get(key: ItemKey): number | undefined;
    /** Record a measured height. Non-positive values are ignored. */
    set(key: ItemKey, height: number): void;
    /** Heights for `keys`, in order, with `undefined` where unmeasured. */
    read(keys: readonly ItemKey[]): (number | undefined)[];
    /**
     * Drop every entry whose key is absent from `keys`, so a long-lived grid
     * does not accumulate heights for items that are gone.
     *
     * @returns how many entries were dropped.
     */
    retain(keys: readonly ItemKey[]): number;
    /** Forget everything — used when the column width changes and every measurement is stale. */
    clear(): void;
    /** Number of cached heights. */
    readonly size: number;
}
export declare function createHeightCache(): HeightCache;