import { SafeUint } from 'ts-data-forge';
import { type DropInitialValueOperator } from '../types/index.mjs';
/**
 * Emits values from the source observable while the predicate returns true.
 * Completes immediately when the predicate returns false.
 *
 * @template A - The type of values from the source
 * @param predicate - Function to test each value
 * @returns An operator that takes values while the predicate is true
 *
 * @example
 * ```ts
 * //  Timeline:
 * //
 * //  num$      1     2     3     4     5     6     1     2 (ignored)
 * //  taken$    1     2     3     4     | (completes)
 * //
 * //  Explanation:
 * //  - takeWhile emits values while the predicate returns true
 * //  - Completes immediately when the predicate returns false
 * //  - No further values are emitted after completion
 *
 * const num$ = source<number>();
 *
 * const taken$ = num$.pipe(takeWhile((x) => x < 5));
 *
 * const valueHistory: number[] = [];
 *
 * taken$.subscribe((x) => {
 *   valueHistory.push(x);
 * });
 *
 * num$.next(1); // logs: 1
 *
 * assert.deepStrictEqual(valueHistory, [1]);
 *
 * num$.next(2); // logs: 2
 *
 * num$.next(3); // logs: 3
 *
 * num$.next(4); // logs: 4
 *
 * assert.deepStrictEqual(valueHistory, [1, 2, 3, 4]);
 *
 * num$.next(5); // nothing logged (completes)
 *
 * assert.deepStrictEqual(valueHistory, [1, 2, 3, 4]);
 *
 * num$.next(6); // nothing logged (already completed)
 *
 * assert.deepStrictEqual(valueHistory, [1, 2, 3, 4]);
 *
 * num$.next(1); // logs: 1
 *
 * assert.deepStrictEqual(valueHistory, [1, 2, 3, 4]);
 * ```
 */
export declare const takeWhile: <A>(predicate: (value: A, index: SafeUint | -1) => boolean) => DropInitialValueOperator<A, A>;
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