feat(concat): can infer N types

- Removes superfluous return typing
- Updates deprecation messages

BREAKING CHANGE: `concat` generic signature changed. Recommend not explicitly passing generics, just let inference do its job. If you must, cast with `as`.

Author: benlesh

spec-dtslint/observables/concat-spec.ts

@@ -29,7 +29,7 @@ it('should accept more than 6 params', () => {
 });
 
 it('should return Observable<unknown> for more than 6 different types of params', () => {
-  const o = concat(of(1), of('a'), of(2), of(true), of(3), of([1, 2, 3]), of(4)); // $ExpectType Observable<unknown>
+  const o = concat(of(1), of('a'), of(2), of(true), of(3), of([1, 2, 3]), of(4)); // $ExpectType Observable<string | number | boolean | number[]>
 });
 
 it('should accept scheduler after params', () => {

src/internal/observable/concat.ts

@@ -1,34 +1,24 @@
 import { Observable } from '../Observable';
-import { ObservableInput, SchedulerLike, ObservedValueOf } from '../types';
+import { ObservableInput, SchedulerLike, ObservedValueOf, ObservedValuesFromArray } from '../types';
 import { of } from './of';
 import { concatAll } from '../operators/concatAll';
 
 /* tslint:disable:max-line-length */
-/** @deprecated Use {@link scheduled} and {@link concatAll} (e.g. `scheduled([o1, o2, o3], scheduler).pipe(concatAll())`) */
+/** @deprecated remove in v8. Passing a scheduler to concat is deprecated, please use {@link scheduled} and {@link concatAll} `scheduled([o1, o2], scheduler).pipe(concatAll())` */
 export function concat<O1 extends ObservableInput<any>>(v1: O1, scheduler: SchedulerLike): Observable<ObservedValueOf<O1>>;
-/** @deprecated Use {@link scheduled} and {@link concatAll} (e.g. `scheduled([o1, o2, o3], scheduler).pipe(concatAll())`) */
+/** @deprecated remove in v8. Passing a scheduler to concat is deprecated, please use {@link scheduled} and {@link concatAll} `scheduled([o1, o2], scheduler).pipe(concatAll())` */
 export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>>(v1: O1, v2: O2, scheduler: SchedulerLike): Observable<ObservedValueOf<O1> | ObservedValueOf<O2>>;
-/** @deprecated Use {@link scheduled} and {@link concatAll} (e.g. `scheduled([o1, o2, o3], scheduler).pipe(concatAll())`) */
+/** @deprecated remove in v8. Passing a scheduler to concat is deprecated, please use {@link scheduled} and {@link concatAll} `scheduled([o1, o2], scheduler).pipe(concatAll())` */
 export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>>(v1: O1, v2: O2, v3: O3, scheduler: SchedulerLike): Observable<ObservedValueOf<O1> | ObservedValueOf<O2> | ObservedValueOf<O3>>;
-/** @deprecated Use {@link scheduled} and {@link concatAll} (e.g. `scheduled([o1, o2, o3], scheduler).pipe(concatAll())`) */
+/** @deprecated remove in v8. Passing a scheduler to concat is deprecated, please use {@link scheduled} and {@link concatAll} `scheduled([o1, o2], scheduler).pipe(concatAll())` */
 export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>, O4 extends ObservableInput<any>>(v1: O1, v2: O2, v3: O3, v4: O4, scheduler: SchedulerLike): Observable<ObservedValueOf<O1> | ObservedValueOf<O2> | ObservedValueOf<O3> | ObservedValueOf<O4>>;
-/** @deprecated Use {@link scheduled} and {@link concatAll} (e.g. `scheduled([o1, o2, o3], scheduler).pipe(concatAll())`) */
+/** @deprecated remove in v8. Passing a scheduler to concat is deprecated, please use {@link scheduled} and {@link concatAll} `scheduled([o1, o2], scheduler).pipe(concatAll())` */
 export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>, O4 extends ObservableInput<any>, O5 extends ObservableInput<any>>(v1: O1, v2: O2, v3: O3, v4: O4, v5: O5, scheduler: SchedulerLike): Observable<ObservedValueOf<O1> | ObservedValueOf<O2> | ObservedValueOf<O3> | ObservedValueOf<O4> | ObservedValueOf<O5>>;
-/** @deprecated Use {@link scheduled} and {@link concatAll} (e.g. `scheduled([o1, o2, o3], scheduler).pipe(concatAll())`) */
+/** @deprecated remove in v8. Passing a scheduler to concat is deprecated, please use {@link scheduled} and {@link concatAll} `scheduled([o1, o2], scheduler).pipe(concatAll())` */
 export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>, O4 extends ObservableInput<any>, O5 extends ObservableInput<any>, O6 extends ObservableInput<any>>(v1: O1, v2: O2, v3: O3, v4: O4, v5: O5, v6: O6, scheduler: SchedulerLike): Observable<ObservedValueOf<O1> | ObservedValueOf<O2> | ObservedValueOf<O3> | ObservedValueOf<O4> | ObservedValueOf<O5> | ObservedValueOf<O6>>;
 
-export function concat<O1 extends ObservableInput<any>>(v1: O1): Observable<ObservedValueOf<O1>>;
-export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>>(v1: O1, v2: O2): Observable<ObservedValueOf<O1> | ObservedValueOf<O2>>;
-export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>>(v1: O1, v2: O2, v3: O3): Observable<ObservedValueOf<O1> | ObservedValueOf<O2> | ObservedValueOf<O3>>;
-export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>, O4 extends ObservableInput<any>>(v1: O1, v2: O2, v3: O3, v4: O4): Observable<ObservedValueOf<O1> | ObservedValueOf<O2> | ObservedValueOf<O3> | ObservedValueOf<O4>>;
-export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>, O4 extends ObservableInput<any>, O5 extends ObservableInput<any>>(v1: O1, v2: O2, v3: O3, v4: O4, v5: O5): Observable<ObservedValueOf<O1> | ObservedValueOf<O2> | ObservedValueOf<O3> | ObservedValueOf<O4> | ObservedValueOf<O5>>;
-export function concat<O1 extends ObservableInput<any>, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>, O4 extends ObservableInput<any>, O5 extends ObservableInput<any>, O6 extends ObservableInput<any>>(v1: O1, v2: O2, v3: O3, v4: O4, v5: O5, v6: O6): Observable<ObservedValueOf<O1> | ObservedValueOf<O2> | ObservedValueOf<O3> | ObservedValueOf<O4> | ObservedValueOf<O5> | ObservedValueOf<O6>>;
-export function concat<O extends ObservableInput<any>>(...observables: O[]): Observable<ObservedValueOf<O>>;
-/** @deprecated Use {@link scheduled} and {@link concatAll} (e.g. `scheduled([o1, o2, o3], scheduler).pipe(concatAll())`) */
-export function concat<O extends ObservableInput<any>>(...observables: (O | SchedulerLike)[]): Observable<ObservedValueOf<O>>;
-export function concat<R>(...observables: ObservableInput<any>[]): Observable<R>;
-/** @deprecated Use {@link scheduled} and {@link concatAll} (e.g. `scheduled([o1, o2, o3], scheduler).pipe(concatAll())`) */
-export function concat<R>(...observables: (ObservableInput<any> | SchedulerLike)[]): Observable<R>;
+export function concat<A extends ObservableInput<any>[]>(...observables: A): Observable<ObservedValuesFromArray<A>>;
+
 /* tslint:enable:max-line-length */
 /**
  * Creates an output Observable which sequentially emits all values from given
@@ -127,17 +117,13 @@ export function concat<R>(...observables: (ObservableInput<any> | SchedulerLike)
  * @see {@link concatMap}
  * @see {@link concatMapTo}
  *
- * @param {ObservableInput} input1 An input Observable to concatenate with others.
- * @param {ObservableInput} input2 An input Observable to concatenate with others.
+ * @param input1 An input Observable to concatenate with others.
+ * @param input2 An input Observable to concatenate with others.
  * More than one input Observables may be given as argument.
- * @param {SchedulerLike} [scheduler=null] An optional {@link SchedulerLike} to schedule each
+ * @param scheduler An optional {@link SchedulerLike} to schedule each
  * Observable subscription on.
- * @return {Observable} All values of each passed Observable merged into a
- * single Observable, in order, in serial fashion.
- * @static true
- * @name concat
- * @owner Observable
  */
-export function concat<O extends ObservableInput<any>, R>(...observables: Array<O | SchedulerLike>): Observable<ObservedValueOf<O> | R> {
-  return concatAll<R>()(of(...observables) as Observable<ObservedValueOf<O>>);
+export function concat<O extends ObservableInput<any>>(...observables: Array<O | SchedulerLike>): Observable<ObservedValueOf<O>> {
+  // The cast with `as` below is due to the SchedulerLike, once this is removed, it will no longer be a problem.
+  return concatAll<ObservedValueOf<O>>()(of(...observables) as Observable<ObservedValueOf<O>>);
 }

src/internal/operators/concat.ts

@@ -25,5 +25,5 @@ export function concat<T, R>(...observables: Array<ObservableInput<any> | Schedu
  * @deprecated Deprecated in favor of static {@link concat}.
  */
 export function concat<T, R>(...observables: Array<ObservableInput<any> | SchedulerLike>): OperatorFunction<T, R> {
-  return (source: Observable<T>) => source.lift.call(concatStatic(source, ...observables));
+  return (source: Observable<T>) => source.lift.call(concatStatic(source, ...(observables as any[])));
 }