ngOnDestroy not fired when service is provided using useFactory

[colinkahn]

I'm submitting a ... (check one with "x")

[ ] bug report => search github for a similar issue or PR before submitting
[x] feature request
[ ] support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior
When you provide a service using useFactory, ngOnDestroy will never be called.

Expected behavior
Regardless of how you provide the service, ngOnDestroy should get called if it is a method on the service.

Minimal reproduction of the problem with instructions
https://plnkr.co/edit/aUaz6ewyM3m5JorsAoCO?p=preview

1. Open the console.
2. Click the "Create Component" button one or many times
3. After a 2 second delay the component will be destroyed, but no console output will be seen.
4. If you replace useFactory with useClass the problem goes away and you'll see output.

What is the motivation / use case for changing the behavior?
There are many cases, main motivator is that this isn't intuitive.

Please tell us about your environment:

• Angular version: 2.4.8

• Browser: Chrome 56.0.2924.87

• Language: TypeScript 2.0

• Node (for AoT issues): node --version =

[DzmitryShylovich]

it's by design. there's no way to know if returned by the factory object has ngOnDestroy or not.

[colinkahn]

As a user useClass, useValue, and useFactory would seem to all just be different ways to achieve the same result. I think this should be a feature if it's not possible in the current implementation.

[colinkahn]

A few other related examples showing that even useClass doesn't always work:

https://plnkr.co/edit/eIs7pjvldhcFrMmaJ4IV?p=preview

In that version I'm providing an abstract class and using useClass to specify a concrete version. ngOnDestroy is never called.

https://plnkr.co/edit/G7vLIvA1nz1dBoJ4sPcW?p=preview

Similar to the above, but using an OpaqueToken.

As far as I can tell the only time ngOnDestroy does work is if you use one of these (I believe they're equivalent):

[
  {
    provide: X,
    useClass: X,
  },
  // OR
  X,
]

[SonyStone]

I have simuler issue with Factory providers from this gide:

https://angular.io/guide/dependency-injection#factory-providers

Minimal reproduction of the problem with instructions
https://stackblitz.com/edit/angular-service-factory-issue?file=src%2Fapp%2Ftest.service.ts

• Click the "toggle" button one or many times
  Test 1 Service will be created and destroyed. Test 2 Service will be created and never destroyed.

[simeyla]

I can't believe it doesn't work with an InjectionToken (used to be OpaqueToken).
That was very unexpected!

I need to unsubscribe to some observables in my service - I ended up having to inject a 'SubscriptionManager' service to my component and had the dependent service use that.

I suppose in future maybe it's better to have the component call init on the service (to return Subscription instance) and then track the subscriptions in the component.

[lloydaf]

@simeyla do you have any gists to demonstrate using a subscription manager?