import { Observable } from '../Observable'; /** * Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from previous items. * * If a keySelector function is provided, then it will project each value from the source observable into a new value that it will * check for equality with previously projected values. If a keySelector function is not provided, it will use each value from the * source observable directly with an equality check against previous values. * * In JavaScript runtimes that support `Set`, this operator will use a `Set` to improve performance of the distinct value checking. * * In other runtimes, this operator will use a minimal implementation of `Set` that relies on an `Array` and `indexOf` under the * hood, so performance will degrade as more values are checked for distinction. Even in newer browsers, a long-running `distinct` * use might result in memory leaks. To help alleviate this in some scenarios, an optional `flushes` parameter is also provided so * that the internal `Set` can be "flushed", basically clearing it of values. * * @example A simple example with numbers * Observable.of(1, 1, 2, 2, 2, 1, 2, 3, 4, 3, 2, 1) * .distinct() * .subscribe(x => console.log(x)); // 1, 2, 3, 4 * * @example An example using a keySelector function * interface Person { * age: number, * name: string * } * * Observable.of( * { age: 4, name: 'Foo'}, * { age: 7, name: 'Bar'}, * { age: 5, name: 'Foo'}) * .distinct((p: Person) => p.name) * .subscribe(x => console.log(x)); * * // displays: * // { age: 4, name: 'Foo' } * // { age: 7, name: 'Bar' } * * @see {@link distinctUntilChanged} * @see {@link distinctUntilKeyChanged} * * @param {function} [keySelector] Optional function to select which value you want to check as distinct. * @param {Observable} [flushes] Optional Observable for flushing the internal HashSet of the operator. * @return {Observable} An Observable that emits items from the source Observable with distinct values. * @method distinct * @owner Observable */ export declare function distinct(this: Observable, keySelector?: (value: T) => K, flushes?: Observable): Observable;