import type { ValidationOptions } from 'class-validator';
/** @hidden */
export declare const MAP_UNIQUE = "mapUnique";
/**
 * Checks if the given value is a [Map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
 * without duplicates with regard to the given projection.
 *
 * #### Example
 * ```typescript
 * // Ensure the map does not include duplicate users.
 * @MapUnique<User>(user => user.id)
 * usersByEmail: Map<string, User>
 * ```
 *
 * @category Map
 * @param projection The function mapping each map entry to the value that is used for the uniqueness check.
 * @param options Generic class-validator options.
 * @typeParam Value The type of the map's values.
 * @typeParam Projection The type returned by `projection`.
 */
export declare function MapUnique<Value = unknown, Projection = Value>(projection: (item: Value) => Projection, options?: ValidationOptions): PropertyDecorator;