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fix(typescript): Update typings for race to support proper return types #4465

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Jan 14, 2019
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fix(typescript): Update typings for race to support proper return types #4465

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fix(typescript): Update typings for race to support proper return types
benlesh Jan 11, 2019
7d5e8a5
fixup! fix(typescript): Update typings for race to support proper ret…
benlesh Jan 11, 2019
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42 changes: 38 additions & 4 deletions spec-dtslint/observables/race-spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -2,17 +2,51 @@ import { race, of } from 'rxjs';

it('should infer correctly with 1 parameter', () => {
const a = of(1);
const res = race(a); // $ExpectType Observable<number>
const o = race(a); // $ExpectType Observable<number>
});

it('should infer correctly with multiple parameters of the same type', () => {
const a = of(1);
const b = of(2);
const res = race(a, b); // $ExpectType Observable<number>
const o = race(a, b); // $ExpectType Observable<number>
});

it('should not support multiple parameters with different type', () => {
it('should support 2 parameters with different types', () => {
const a = of(1);
const b = of('a');
const res = race(a, b); // $ExpectError
const o = race(a, b); // $ExpectType Observable<string> | Observable<number>
});

it('should support 3 parameters with different types', () => {
const a = of(1);
const b = of('a');
const c = of(true);
const o = race(a, b, c); // $ExpectType Observable<string> | Observable<number> | Observable<boolean>
});

it('should support 4 parameters with different types', () => {
const a = of(1);
const b = of('a');
const c = of(true);
const d = of([1, 2, 3]);
const o = race(a, b, c, d); // $ExpectType Observable<string> | Observable<number> | Observable<boolean> | Observable<number[]>
});

it('should support 5 parameters with different types', () => {
const a = of(1);
const b = of('a');
const c = of(true);
const d = of([1, 2, 3]);
const e = of(['blah']);
const o = race(a, b, c, d, e); // $ExpectType Observable<string> | Observable<number> | Observable<boolean> | Observable<number[]> | Observable<string[]>
});

it('should return {} for 6 or more arguments of different types', () => {
const a = of(1);
const b = of('a');
const c = of(true);
const d = of([1, 2, 3]);
const e = of(['blah']);
const f = of({ foo: 'bar' });
const o = race(a, b, c, d, e, f); // $ExpectType Observable<{}>
});
15 changes: 12 additions & 3 deletions src/internal/observable/race.ts
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Expand Up @@ -9,9 +9,18 @@ import { OuterSubscriber } from '../OuterSubscriber';
import { InnerSubscriber } from '../InnerSubscriber';
import { subscribeToResult } from '../util/subscribeToResult';

// tslint:disable:max-line-length
export function race<A, B>(a: Observable<A>, b: Observable<B>): Observable<A> | Observable<B>;
export function race<A, B, C>(a: Observable<A>, b: Observable<B>, c: Observable<C>): Observable<A> | Observable<B> | Observable<C>;
export function race<A, B, C, D>(a: Observable<A>, b: Observable<B>, c: Observable<C>, d: Observable<D>): Observable<A> | Observable<B> | Observable<C> | Observable<D>;
export function race<A, B, C, D, E>(a: Observable<A>, b: Observable<B>, c: Observable<C>, d: Observable<D>, e: Observable<E>): Observable<A> | Observable<B> | Observable<C> | Observable<D> | Observable<E>;
// tslint:enable:max-line-length

export function race<T>(observables: Array<Observable<T>>): Observable<T>;
export function race<T>(observables: Array<Observable<any>>): Observable<T>;
export function race<T>(...observables: Array<Observable<T> | Array<Observable<T>>>): Observable<T>;
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@cartant cartant Jan 11, 2019 •
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I don't understand why

export function race<T>(...observables: Array<Observable<T> | Array<Observable<T>>>): Observable<T>;

needs to be an overload signature. I can see why it is the implementation signature, but why it needs to be an overload baffles me. Don't the others handle the scenarios that are bundled into this signature?

Do we really need to keep this already-existing signature? Can it be removed?

LGTM, otherwise.

export function race(...observables: Observable<any>[]): Observable<{}>;

/**
* Returns an Observable that mirrors the first source Observable to emit an item.
*
Expand All @@ -38,14 +47,14 @@ export function race<T>(...observables: Array<Observable<T> | Array<Observable<T
* @name race
* @owner Observable
*/
export function race<T>(...observables: Array<Observable<any> | Array<Observable<any>>>): Observable<T> {
export function race<T>(...observables: (Observable<any>[] | Observable<any>)[]): Observable<T> {
// if the only argument is an array, it was most likely called with
// `race([obs1, obs2, ...])`
if (observables.length === 1) {
if (isArray(observables[0])) {
observables = <Array<Observable<any>>>observables[0];
observables = observables[0] as Observable<any>[];
} else {
return <Observable<any>>observables[0];
return observables[0] as Observable<T>;
}
}

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