/**
 * Returns an element if and only if that element is the only one matching the given condition. Returns `undefined` otherwise.
 *
 * Example:
 *
 * ```ts
 * import { findSingle } from "https://deno.land/std@$STD_VERSION/collections/mod.ts";
 * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
 *
 * const bookings = [
 *     { month: 'January', active: false },
 *     { month: 'March', active: false },
 *     { month: 'June', active: true },
 * ];
 * const activeBooking = findSingle(bookings, (it) => it.active);
 * const inactiveBooking = findSingle(bookings, (it) => !it.active);
 *
 * assertEquals(activeBooking, { month: "June", active: true });
 * assertEquals(inactiveBooking, undefined); // there are two applicable items
 * ```
 */
export declare function findSingle<T>(array: readonly T[], predicate: (el: T) => boolean): T | undefined;