Feature: allow inject() to be used in constructor

I'm submitting a...


[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Performance issue
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
[ ] Other... Please describe:

Current behavior

All the dependencies must be injected in constructor:

@Injectable()
export class MyService {
  constructor(private myOtherSerivice: MyOtherService) {}
}

Expected behavior

Allow to use inject() function when object is constructed, for example:

@Injectable()
export class MyService {
  private myOtherSerivice: MyOtherService = inject(MyOtherService);
}

Minimal reproduction of the problem with instructions

N/A

What is the motivation / use case for changing the behavior?

Imagine You have an abstract class which is extended by many services or components.
Then You want to change it which requires adding a new dependency.
When injecting via constructor You would have modify EVERY class that inherits it.

Environment


Angular version: 6.0.3

Actually it is possible to inject Injector and call its get-methods in your parent constructor.

@kemsky

@kemsky I know but it feels like a hack and You still need to inject Injector which may require a change in existing code base. With inject() approach it would be possible to create (as a library) decorator that uses reflections or create TypeScript transformer to achieve something like this:

@Injectable()
export class MyService {
  @Autowire() private myOtherSerivice: MyOtherService;
}

@kemsky

@kemsky This is more about consistency, using inject() is already supported at service constructor (with module-level provider):

https://stackblitz.com/edit/angular-dergtr?file=src%2Fapp%2Fapp.component.ts

This is indeed the correct behavior with current default provider semantics. Given this pattern is mostly about consumer-side usage, so it's should not be restricted to default provider, but also constructor of component, directive, pipe and directive provider should be supported as well.

Given Ivy is going to be fully context-based (instead of call stack-based), I guess this will be supported in Ivy by default (haven't checked yet).

EDIT: have a quick look at current Ivy codes, which should indeed work for most scenarios as long as powered by factory ~~method~~ function property of ngXXXDef, like:

class SomeDirective {
  constructor(directive: DirectiveA) {}

  static ngDirectiveDef = defineDirective({
    type: SomeDirective,
    factory: () => new SomeDirective(directiveInject(DirectiveA))
  });
}

So the constructor would always share the same context of the factory.

Given this is already the case in Ivy, should be reasonable to bring it (back?) to view engine.

EDIT Again for Ivy: one thing possibly needs to be noticed is the inconsistency between inject and directiveInject, the private services like ElementRef, ViewContainerRef would not be available in inject (by default).

Likely this behavior would be fixed by #23330, which would make inject() for directives different than inject() for application-wide services.

@vicb

Seems a little hard for current view engine, I'd suggest just waiting for Ivy.

@vicb Possibly add a fixed by Ivy tag for better tracking?

I think this should really be fixed because right now DI behaviour is inconsistent.

If a service that is provided in @Component tries to inject ViewContainerRef it will not get it unless the component itself injects it.

Repro: https://stackblitz.com/edit/angular-jxyoet

REMOVED.

@trotyl

@trotyl I do not think I am able to create a PR since I have not enough knowledge of how DI resolution mechanics are implemented.

I hope that in Ivy this will be fixed tho (#23330).

@trotyl

@trotyl Correct me if I'm wrong, but wouldn't simple change in StaticInjector be sufficient?
Just wrap get() method body with something like this:

const former = setCurrentInjector(this);
try {
  // body
} finally {
  setCurrentInjector(former);
}

@dawidgarus

@dawidgarus Static injector, module injector and node injector are mostly unrelated, and what used in a normal application are only module injector and node injector, not static injector.

Also, the creation of Component, Directive, Pipe, NgModule is not the job of any injector.

Hopefully ivy will make everything simpler, because right now contributing to angular core by an outsider is, for all intents and purposes, impossible. Is there a public document which describes in details how angular internals work? For example what ngfactory file structure is exactly?

Hopefully ivy will make everything simpler

This is going to be a built-in feature in Ivy and no need to worry about.

because right now contributing to angular core by an outsider is, for all intents and purposes, impossible

I guess it's not a good idea to ask another outsider then.

Just a heads up that we kicked off a community voting process for your feature request. There are 20 days until the voting process ends.

Find more details about Angular's feature request process in our documentation.

Thank you for submitting your feature request! Looks like during the polling process it didn't collect a sufficient number of votes to move to the next stage.

We want to keep Angular rich and ergonomic and at the same time be mindful about its scope and learning journey. If you think your request could live outside Angular's scope, we'd encourage you to collaborate with the community on publishing it as an open source package.

You can find more details about the feature request process in our documentation.

Closing as a duplicate of #34425 (they are the same underlying request)

Wow, injection via decorators sounds great! Just out of curiosity: since I still won't be able to get the cdr on demand I'd need to inject it (via decorator) in all of my components. Could this have a noticable performance impact? Or is it like No, the CDR exists anyway for every component, you wouldn't even be able to measure it?

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Feature: allow inject() to be used in constructor #25039

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Feature: allow inject() to be used in constructor #25039

Description

I'm submitting a...

Current behavior

Expected behavior

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

Environment

Activity

kemsky commented on Jul 23, 2018

dawidgarus commented on Jul 23, 2018

trotyl commented on Jul 24, 2018

trotyl commented on Jul 27, 2018

gund commented on Jul 27, 2018

trotyl commented on Jul 27, 2018

gund commented on Jul 27, 2018

dawidgarus commented on Jul 27, 2018

trotyl commented on Jul 30, 2018

dawidgarus commented on Jul 30, 2018

trotyl commented on Jul 30, 2018

angular-robot commented on Jun 4, 2021

angular-robot commented on Jun 25, 2021

alxhub commented on May 4, 2022

angelaki commented on May 5, 2022

angular-automatic-lock-bot commented on Jun 5, 2022

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