I'm trying to determine whether it's appropriate t...

# compose

[Doug McCluer]

I'm trying to determine whether it's appropriate to annotate a type I've defined with @Stable . The docs say:

When applied to a class or an interface, `Stable` indicates that the following must be true:
1. The result of `equals` will always return the same result for the same two instances.
2. When a public property of the type changes, composition will be notified.
3. All public property types are stable.

• For #1, I'm familiar with how equals works and can answer this.
• Regarding #2, I'm less sure, because I don't know how notification works under the hood. Is it safe to assume that if a public property changes in such a way that using equals would evaluate false when comparing the before and after, then that means composition will always be notified about the change?

[Melody Horn]

i’m hardly an expert, but my assumption would be that if your type is immutable, no public properties can change, so 2 holds, and if your type has some public mutable property that is ignored by equals, it needs to be backed by a MutableState for 2 to hold

[Melody Horn]

presumably there are ways other than MutableState to tie into the composition notification system, but that’s the most common as far as i know

[Doug McCluer]

@Melody Horn thanks for the reply.
And if every property is not ignored by equals, then can I assume #2 is met?

[jw]

No. The system needs to know when to even call equals which is what the notification mechanism internal to MutableState provides.

[Doug McCluer]

@jw I see. So every property in the type needs to be a MutableState (or possibly some other Compose-based item). Thank you!

[jw]

It needs to be backed by MutableState, not necessary MutableState itself.

[Melody Horn]

if every property is used in equals then 1 means your class needs to be fully immutable

[Zach Klippenstein (he/him) [MOD]]

Technically it needs to be backed by a StateObject, not necessarily MutableState (eg SnapshotStateList is the former not the latter)

[Zach Klippenstein (he/him) [MOD]]

If you really want to dig in, more info here

[Doug McCluer]

oh, nice - I'll give that a read!

[Colton Idle]

FWIW, and I know I'm no JW or ZK but if it helps... I've helped ship over 10 apps using compose to production. Ranging from 1M users to 100M on the play store. I have used the @Stable annotation exactly 0 times 😅

There's probably valid use cases for it, but I try to keep my composables simple and follow jim sprochs best practices for compose and weve never had issues. my approach of not worrying about stability unless a measurable issue arises was further validated when compose strong skipping mode was unveiled https://developer.android.com/develop/ui/compose/performance/stability/strongskipping

[Zach Klippenstein (he/him) [MOD]]

yea unless you're measuring and have proof that instability is causing performance issues, no point