import { type KeepInitialValueOperator, type Observable } from '../types/index.mjs';
/**
 * Emits values from the source until the notifier observable emits.
 * When the notifier emits, this observable completes.
 *
 * @template A - The type of values from the source
 * @param notifier - An observable that signals when to complete
 * @returns An operator that takes values until notifier emits
 *
 * @example
 * ```ts
 * //  Timeline:
 * //
 * //  num$          1         2         stop      3 (ignored)
 * //  stopNotifier                      X
 * //  limited$      1         2         |------- (completed)
 * //
 * //  Explanation:
 * //  - takeUntil completes the observable when the notifier emits
 * //  - After stop() is called, no further values are emitted
 * //  - Useful for cleanup and cancellation patterns
 *
 * const num$ = source<number>();
 *
 * const [stopNotifier, stop_] = createEventEmitter();
 *
 * const limited$ = num$.pipe(takeUntil(stopNotifier));
 *
 * const valueHistory: number[] = [];
 *
 * limited$.subscribe((x) => {
 *   valueHistory.push(x);
 * });
 *
 * num$.next(1); // logs: 1
 *
 * assert.deepStrictEqual(valueHistory, [1]);
 *
 * num$.next(2); // logs: 2
 *
 * assert.deepStrictEqual(valueHistory, [1, 2]);
 *
 * stop_();
 *
 * num$.next(3); // nothing logged (completed)
 *
 * assert.deepStrictEqual(valueHistory, [1, 2]);
 * ```
 */
export declare const takeUntil: <A>(notifier: Observable<unknown>) => KeepInitialValueOperator<A, A>;
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