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node_modules/rxjs/src/internal/operators/concatMapTo.ts

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+import { concatMap } from './concatMap';
+import { ObservableInput, OperatorFunction, ObservedValueOf } from '../types';
+import { isFunction } from '../util/isFunction';
+
+/** @deprecated Will be removed in v9. Use {@link concatMap} instead: `concatMap(() => result)` */
+export function concatMapTo<O extends ObservableInput<unknown>>(observable: O): OperatorFunction<unknown, ObservedValueOf<O>>;
+/** @deprecated The `resultSelector` parameter will be removed in v8. Use an inner `map` instead. Details: https://rxjs.dev/deprecations/resultSelector */
+export function concatMapTo<O extends ObservableInput<unknown>>(
+  observable: O,
+  resultSelector: undefined
+): OperatorFunction<unknown, ObservedValueOf<O>>;
+/** @deprecated The `resultSelector` parameter will be removed in v8. Use an inner `map` instead. Details: https://rxjs.dev/deprecations/resultSelector */
+export function concatMapTo<T, R, O extends ObservableInput<unknown>>(
+  observable: O,
+  resultSelector: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R
+): OperatorFunction<T, R>;
+
+/**
+ * Projects each source value to the same Observable which is merged multiple
+ * times in a serialized fashion on the output Observable.
+ *
+ * <span class="informal">It's like {@link concatMap}, but maps each value
+ * always to the same inner Observable.</span>
+ *
+ * ![](concatMapTo.png)
+ *
+ * Maps each source value to the given Observable `innerObservable` regardless
+ * of the source value, and then flattens those resulting Observables into one
+ * single Observable, which is the output Observable. Each new `innerObservable`
+ * instance emitted on the output Observable is concatenated with the previous
+ * `innerObservable` instance.
+ *
+ * __Warning:__ if source values arrive endlessly and faster than their
+ * corresponding inner Observables can complete, it will result in memory issues
+ * as inner Observables amass in an unbounded buffer waiting for their turn to
+ * be subscribed to.
+ *
+ * Note: `concatMapTo` is equivalent to `mergeMapTo` with concurrency parameter
+ * set to `1`.
+ *
+ * ## Example
+ *
+ * For each click event, tick every second from 0 to 3, with no concurrency
+ *
+ * ```ts
+ * import { fromEvent, concatMapTo, interval, take } from 'rxjs';
+ *
+ * const clicks = fromEvent(document, 'click');
+ * const result = clicks.pipe(
+ *   concatMapTo(interval(1000).pipe(take(4)))
+ * );
+ * result.subscribe(x => console.log(x));
+ *
+ * // Results in the following:
+ * // (results are not concurrent)
+ * // For every click on the "document" it will emit values 0 to 3 spaced
+ * // on a 1000ms interval
+ * // one click = 1000ms-> 0 -1000ms-> 1 -1000ms-> 2 -1000ms-> 3
+ * ```
+ *
+ * @see {@link concat}
+ * @see {@link concatAll}
+ * @see {@link concatMap}
+ * @see {@link mergeMapTo}
+ * @see {@link switchMapTo}
+ *
+ * @param innerObservable An `ObservableInput` to replace each value from the
+ * source Observable.
+ * @return A function that returns an Observable of values merged together by
+ * joining the passed Observable with itself, one after the other, for each
+ * value emitted from the source.
+ * @deprecated Will be removed in v9. Use {@link concatMap} instead: `concatMap(() => result)`
+ */
+export function concatMapTo<T, R, O extends ObservableInput<unknown>>(
+  innerObservable: O,
+  resultSelector?: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R
+): OperatorFunction<T, ObservedValueOf<O> | R> {
+  return isFunction(resultSelector) ? concatMap(() => innerObservable, resultSelector) : concatMap(() => innerObservable);
+}