import { mergeMap } from './mergeMap';
import { identity } from '../util/identity';
/**
 * Converts a higher-order Observable into a first-order Observable which
 * concurrently delivers all values that are emitted on the inner Observables.
 *
 * <span class="informal">Flattens an Observable-of-Observables.</span>
 *
 * <img src="./img/mergeAll.png" width="100%">
 *
 * `mergeAll` subscribes to an Observable that emits Observables, also known as
 * a higher-order Observable. Each time it observes one of these emitted inner
 * Observables, it subscribes to that and delivers all the values from the
 * inner Observable on the output Observable. The output Observable only
 * completes once all inner Observables have completed. Any error delivered by
 * a inner Observable will be immediately emitted on the output Observable.
 *
 * @example <caption>Spawn a new interval Observable for each click event, and blend their outputs as one Observable</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var higherOrder = clicks.map((ev) => Rx.Observable.interval(1000));
 * var firstOrder = higherOrder.mergeAll();
 * firstOrder.subscribe(x => console.log(x));
 *
 * @example <caption>Count from 0 to 9 every second for each click, but only allow 2 concurrent timers</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var higherOrder = clicks.map((ev) => Rx.Observable.interval(1000).take(10));
 * var firstOrder = higherOrder.mergeAll(2);
 * firstOrder.subscribe(x => console.log(x));
 *
 * @see {@link combineAll}
 * @see {@link concatAll}
 * @see {@link exhaust}
 * @see {@link merge}
 * @see {@link mergeMap}
 * @see {@link mergeMapTo}
 * @see {@link mergeScan}
 * @see {@link switch}
 * @see {@link zipAll}
 *
 * @param {number} [concurrent=Number.POSITIVE_INFINITY] Maximum number of inner
 * Observables being subscribed to concurrently.
 * @return {Observable} An Observable that emits values coming from all the
 * inner Observables emitted by the source Observable.
 * @method mergeAll
 * @owner Observable
 */
export function mergeAll(concurrent = Number.POSITIVE_INFINITY) {
    return mergeMap(identity, null, concurrent);
}
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