Can this kind of interface marked as @Immutable? ```interface ColorSpec { @Composable operat...

# compose

[Berkeli Alashov]

Can this kind of interface marked as @Immutable?

interface ColorSpec {
    @Composable
    operator fun invoke(): Color

    companion object {
        fun fromColor(lightVariant: Color, darkVariant: Color): ColorSpec = object : ColorSpec {
            @Composable
            override fun invoke(): Color = if (Theme.isDarkTheme) darkVariant else lightVariant
        }
    }
}

[itnoles]

https://developer.android.com/reference/kotlin/androidx/compose/runtime/Immutable

[Berkeli Alashov]

I checked that already, also https://medium.com/androiddevelopers/jetpack-compose-stability-explained-79c10db270c8. Properties of ColorSpec don't change, but @Composable invoke() can produce different results (depending on Theme.isDarkTheme, which is backed by value in CompositionLocalProvider).

[Adam Powell]

@Stable is probably more semantically correct but the way you've set things up here it won't help you much since you're not defining equals for the objects returned from your utility. Different but equivalent objects can't skip recomposition if you don't implement equals

[Berkeli Alashov]

So if I make fromColor return a data class that implements ColorSpec, then I still should use @Stable?

[Adam Powell]

That'd be one way to do it

[Berkeli Alashov]

I don't get why use @Stable instead of @Immutable then..

[Adam Powell]

If you have an interface that can be implemented by others then stable keeps the contract less strict but compose will give you the same skipping behavior either way

[Berkeli Alashov]

Gotcha. Does adding @immutable to extending data classes will improve skipping behavior?

[Adam Powell]

I'd assume it inherits the interface's stability since otherwise it wouldn't meet the is-a contract, but I'd need to check. Most data classes will get the compiler plugin to infer the class as stable anyway though

[Adam Powell]

At least data classes like the one you listed here where the only properties are Color or something else that's known stable

[Adam Powell]

To be clear, compose treats @Immutable and @Stable in exactly the same way for skipping behavior

[Berkeli Alashov]

^ didn't know that, I thought it would be different

[Adam Powell]

Not currently, anyway