import { MonoTypeOperatorFunction } from 'rxjs';
/**
 * Returns an Observable that emits maximum value on each iteration.
 *
 * If a comparator function is provided, then it will be called for each item to test for whether or not that value should be emitted.
 *
 * If a comparator function is not provided, an equality check is used by default.
 *
 * ## Example
 * A simple example with numbers
 * ```javascript
 * of(1, 1, 2, 2, 2, 0, 1, 2, 3, -1, 4).pipe(
 *     maxStream(),
 *   )
 *   .subscribe(x => console.log(x)); // 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 4
 * ```
 *
 * An example using a compare function
 * ```typescript
 * interface Person {
 *    age: number,
 *    name: string
 * }
 *
 * of<Person>(
 *     { age: 4, name: 'Foo'},
 *     { age: 7, name: 'Bar'},
 *     { age: 3, name: 'Foo'},
 *     { age: 6, name: 'Foo'},
 *   ).pipe(
 *     maxStream((p: Person, q: Person) => p.age < q.age),
 *   )
 *   .subscribe(x => console.log(x));
 *
 * // displays:
 * // { age: 4, name: 'Foo' }
 * // { age: 7, name: 'Bar' }
 * // { age: 7, name: 'Bar'},
 * // { age: 7, name: 'Bar'},
 * ```
 *
 *
 * @param {function} [comparer] Optional comparison function called to test if an item on iteration
 * @return {Observable} An Observable that emits maximum value on each iteration.
 * @method maxStream
 * @owner Observable
 */
export declare function maxStream<T>(comparer?: (x: T, y: T) => boolean): MonoTypeOperatorFunction<T>;