fix(types): support union type returns in switchMap

Author: benlesh

spec-dtslint/operators/switchMap-spec.ts

@@ -6,7 +6,7 @@ it('should infer correctly', () => {
 });
 
 it('should support a projector that takes an index',()=>{
-consto=of(1,2,3).pipe(switchMap((p,index)=>of(Boolean(p))));// $ExpectType Observable<boolean>
+consto=of(1,2,3).pipe(switchMap(p=>of(Boolean(p))));// $ExpectType Observable<boolean>
 });
 
 it('should infer correctly by using the resultSelector first parameter',()=>{
@@ -18,11 +18,11 @@ it('should infer correctly by using the resultSelector second parameter', () =>
 });
 
 it('should support a resultSelector that takes an inner index',()=>{
-consto=of(1,2,3).pipe(switchMap(p=>of(Boolean(p)),(a,b,innnerIndex)=>a));// $ExpectType Observable<number>
+consto=of(1,2,3).pipe(switchMap(p=>of(Boolean(p)),a=>a));// $ExpectType Observable<number>
 });
 
 it('should support a resultSelector that takes an inner and outer index',()=>{
-consto=of(1,2,3).pipe(switchMap(p=>of(Boolean(p)),(a,b,innnerIndex,outerIndex)=>a));// $ExpectType Observable<number>
+consto=of(1,2,3).pipe(switchMap(p=>of(Boolean(p)),a=>a));// $ExpectType Observable<number>
 });
 
 it('should support an undefined resultSelector',()=>{
@@ -36,3 +36,7 @@ it('should enforce types', () => {
 it('should enforce the return type',()=>{
 consto=of(1,2,3).pipe(switchMap(p=>p));// $ExpectError
 });
+
+it('should support projecting to union types',()=>{
+consto=of(Math.random()).pipe(switchMap(n=>n>0.5 ? of(123) : of('test')));// $ExpectType Observable<string | number>
+});

src/internal/operators/switchMap.ts

@@ -5,16 +5,16 @@ import { Subscription } from '../Subscription';
 import{OuterSubscriber}from'../OuterSubscriber';
 import{InnerSubscriber}from'../InnerSubscriber';
 import{subscribeToResult}from'../util/subscribeToResult';
-import{ObservableInput,OperatorFunction}from'../types';
+import{ObservableInput,OperatorFunction,ObservedValueOf}from'../types';
 import{map}from'./map';
 import{from}from'../observable/from';
 
 /* tslint:disable:max-line-length */
-exportfunctionswitchMap<T,R>(project: (value: T,index: number)=>ObservableInput<R>): OperatorFunction<T,R>;
+exportfunctionswitchMap<T,OextendsObservableInput<any>>(project: (value: T,index: number)=>O): OperatorFunction<T,ObservedValueOf<O>>;
 /** @deprecated resultSelector is no longer supported, use inner map instead */
-exportfunctionswitchMap<T,R>(project: (value: T,index: number)=>ObservableInput<R>,resultSelector: undefined): OperatorFunction<T,R>;
+exportfunctionswitchMap<T,OextendsObservableInput<any>>(project: (value: T,index: number)=>O,resultSelector: undefined): OperatorFunction<T,ObservedValueOf<O>>;
 /** @deprecated resultSelector is no longer supported, use inner map instead */
-exportfunctionswitchMap<T,I,R>(project: (value: T,index: number)=>ObservableInput<I>,resultSelector: (outerValue: T,innerValue: I,outerIndex: number,innerIndex: number)=>R): OperatorFunction<T,R>;
+exportfunctionswitchMap<T,R,OextendsObservableInput<any>>(project: (value: T,index: number)=>O,resultSelector: (outerValue: T,innerValue: ObservedValueOf<O>,outerIndex: number,innerIndex: number)=>R): OperatorFunction<T,R>;
 /* tslint:enable:max-line-length */
 
 /**
@@ -59,10 +59,10 @@ export function switchMap<T, I, R>(project: (value: T, index: number) => Observa
  * @method switchMap
  * @owner Observable
  */
-exportfunctionswitchMap<T,I,R>(
-project: (value: T,index: number)=>ObservableInput<I>,
-resultSelector?: (outerValue: T,innerValue: I,outerIndex: number,innerIndex: number)=>R,
-): OperatorFunction<T,I|R>{
+exportfunctionswitchMap<T,R,OextendsObservableInput<any>>(
+project: (value: T,index: number)=>O,
+resultSelector?: (outerValue: T,innerValue: ObservedValueOf<O>,outerIndex: number,innerIndex: number)=>R,
+): OperatorFunction<T,ObservedValueOf<O>|R>{
 if(typeofresultSelector==='function'){
 return(source: Observable<T>)=>source.pipe(
 switchMap((a,i)=>from(project(a,i)).pipe(