/**
 * A basic comparator for incrementally watched queries. This performs a single comparison which
 * determines if the result set has changed. The {@link WatchedQuery} will only emit the new result
 * if a change has been detected.
 */
export interface WatchedQueryComparator<Data> {
    checkEquality: (current: Data, previous: Data) => boolean;
}
/**
 * Options for {@link ArrayComparator}
 */
export type ArrayComparatorOptions<ItemType> = {
    /**
     * Returns a string to uniquely identify an item in the array.
     */
    compareBy: (item: ItemType) => string;
};
/**
 * An efficient comparator for {@link WatchedQuery} created with {@link Query#watch}. This has the ability to determine if a query
 * result has changes without necessarily processing all items in the result.
 */
export declare class ArrayComparator<ItemType> implements WatchedQueryComparator<ItemType[]> {
    protected options: ArrayComparatorOptions<ItemType>;
    constructor(options: ArrayComparatorOptions<ItemType>);
    checkEquality(current: ItemType[], previous: ItemType[]): boolean;
}
/**
 * Watched query comparator that always reports changed result sets.
 */
export declare const FalsyComparator: WatchedQueryComparator<unknown>;