import { IndexedPredicate } from "../types/IndexedPredicate";
/**
 * Returns the unique element that satisfies the optional predicate, or `undefined` when no match is found.
 *
 * @typeParam T - Element type produced by the source iterable.
 * @param src - Source iterable to evaluate.
 * @param pred - Predicate receiving each element and its index; the matching element must be unique when provided.
 * @returns The sole element accepted by `pred`, or `undefined` when no element matches.
 * @throws Error Thrown when more than one element satisfies `pred`.
 * @throws Error Rethrows any error thrown by `pred`.
 *
 * @example
 * ```ts
 * const value = _singleOrDefault([1, 2, 3], (item) => item > 3);
 * console.log(value); // undefined
 * ```
 *
 * or using the curried version:
 * ```ts
 * const value = pipeInto(
 *   [1, 2, 3],
 *   singleOrDefault((item) => item > 3)
 * );
 * console.log(value); // undefined
 * ```
 */
export declare function _singleOrDefault<T>(src: Iterable<T>, pred?: IndexedPredicate<T>): T | undefined;
/**
 * Curried version of {@link _singleOrDefault}.
 */
export declare const singleOrDefault: <T>(pred?: IndexedPredicate<T> | undefined) => (src: Iterable<T>) => T | undefined;