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Question

gt <https developer android com reference kotlin androidx compose runtime Immutable> the doc of ` Immutable` said that data classes that only contain val properties that do not have custom getters can safely be marked as Immutable if the types of properties are either primitive types or also Immutable I thought the data class with val properties should have been treated as Stable or Immutable by Compiler isn t it if I don t annotate `Person` with ` Immutable` means the `PersonView` can t skip the unnecessary Recomposition

Albert Chang · Answer

If the types of val properties are all known to be stable the compiler will infer the class as stable

Peng Wang · Answer

so the ` Immutable` of `Person` in the sample doesn t make any sense right <https developer android com reference kotlin androidx compose runtime Immutable>

Paul Woitaschek · Answer

Stable = Immutable The compiler would infer it as stable but not as immutable

Paul Woitaschek · Answer

Also all this implies that you enabled compose for that module So if you consume a class that is located in a module that does not have the compose plugin applied the stability will not be inferred at all

Peng Wang · Answer

In terms of smart recomposition what s the difference between Immutable and Stable

Albert Chang · Answer

Actually Stable == Immutable <https kotlinlang slack com archives CJLTWPH7S p1626966996282200 thread ts=1626898531 198700 amp cid=CJLTWPH7S|https kotlinlang slack com archives CJLTWPH7S p1626966996282200 thread ts=1626898531 198700 amp cid=CJLTWPH7S>

Albert Chang · Answer

The compiler can infer the stability but it doesn t make manually marking classes pointless You can see that all classes that are stable are manually marked in the framework Marking a class ensures its stability and there are also some cases where the compiler can t infer the stability

Paul Woitaschek · Answer

Oh that s interesting

Paul Woitaschek · Answer

I so wished I didn t need to mark everything containing a list or a platform class as stable

Peng Wang · Answer

I m used to using data class to define my UiState but I ve never marked `Immutable` and also I rarely see it in other people s code What I want to know is whether `Immutable` should always be marked for data class even if it is stable What is the bad case if don t mark it for the data class < Albert Chang>

Paul Woitaschek · Answer

He already quoted that stable has the same effect as Immutable If it can t be inferred as stable it will cause recompositons

Peng Wang · Answer

the the `Person` of official sample is stable itself right why it still needs to be marked as `Immutable`

Paul Woitaschek · Answer

It s correct to mark it as Immutable but it s not necessary But if I understand correctly there is a distinction in the definition of immutable and stable that might be used one day by compose

hfhbd · Answer

Sooo if you have another module containing only data classes in your project without compose do you still need to mark them manually or apply the compose plugin

Albert Chang · Answer

You need to apply compose compiler plugin Even if you mark them manually if you don t apply the compiler plugin they will still be treated as unstable in other modules