/**
 * Filter an iterable for values which pass a test.
 *
 * @param object - The iterable object of interest.
 *
 * @param fn - The predicate function to invoke for each value.
 *
 * @returns An iterator which yields the values which pass the test.
 *
 * #### Example
 * ```typescript
 * import { filter } from '@lumino/algorithm';
 *
 * let data = [1, 2, 3, 4, 5, 6];
 *
 * let stream = filter(data, value => value % 2 === 0);
 *
 * Array.from(stream);  // [2, 4, 6]
 * ```
 */
export declare function filter<T>(object: Iterable<T>, fn: (value: T, index: number) => boolean): IterableIterator<T>;