import type { ValidationOptions } from 'class-validator';
/** @hidden */
export declare const MAP_UNIQUE_KEYS = "mapUniqueKeys";
/**
 * Checks if the given value is a [Map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
 * whose keys are all unique with regard to the given projection.
 *
 * #### Example
 * ```typescript
 * // Ensure there are no duplicate user ids in the map.
 * @MapUniqueKeys<User>(user => user.id)
 * postsByUser: Map<User, Post[]>
 * ```
 *
 * @category Map
 * @param projection The function mapping each key to the value that is used for the uniqueness check.
 * @param options Generic class-validator options.
 * @typeParam Key The type of the map's keys.
 * @typeParam Projection The type returned by `projection`.
 */
export declare function MapUniqueKeys<Key = unknown, Projection = unknown>(projection: (item: Key) => Projection, options?: ValidationOptions): PropertyDecorator;