[feature request] BehaviorSubject to Signals migration

[ShacharHarshuv]

In the spirit of writing migration scripts to modernize Angular code, I want to propose the following script. Let me know if you think this is something that could fit the library.

The assumption here that everything that a BehaviorSubject is used for, a signal can be used instead, and I think it is possible to write a (relatively) robust script to do that migration. The script will:

• Replace member instantiation of new BehaviorSubject with signal, while keeping any used generics / inferred types.
• Replace .next with .set
• Rename the member if it ends with $
• Replace myValue$.value usages to myValue()
• Replace any other myValue$ with `toObservable(myValue)
  • caveat: it might not be in an injection context. A possible solution of it will be duplicating the member in instantiation so that we'll have both myValue as a signal and myValue$ as a stream. In that case, if there is no $ as a postfix, we'll have to add it.

[jdegand]

And convert .next to .set?

[ShacharHarshuv]

Yes, sorry. Added!

[eneajaho]

Hi, something is coming 🙌

Let's wait a little bit more 😬

[ShacharHarshuv]

Do you mean you are working on it, that Angular's core team is working on it, or that you think it's premature to add such a feature now?

[eneajaho]

I've been working on a prototype for myself to do these kinds of migration, but nothing ready yet.

[ShacharHarshuv]

Cool! I also thought that a next step could be converting something like that:

combineLatest({
  a: toObservable(this.a),
  b: toObservable(this.b),
})
.pipe(
  map(({a, b}) => this.a() + this.b()),
  distinctUntilChanged(), // ... and other operators that don't matter with signals like share etc
);

to

computed(() => this.a() + this.b());

Might be harder than I think but it feels like it could be possible.