import { z } from 'zod';
/**
 * Creates a superRefine function that validates array elements are unique by a given key.
 *
 * @param keyFn - Function to extract the key from each element
 * @param errorMessage - Function to generate error message for duplicates
 * @returns A superRefine callback for use with z.array().superRefine()
 */
export declare function uniqueBy<T>(keyFn: (item: T) => string, errorMessage: (key: string) => string): (items: T[], ctx: z.RefinementCtx) => void;
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