How to create custom Serializer for PersistentList?

[dennykurniawan48]

I have a list of classes and I need to save it into my datastore, probably related to issue #635.

The code is like so:

@Serializable
data class OrderData(
    @Serializable(with = CartData::class)
    val cartData: PersistentList<CartData> = persistentListOf()
)

and my subclass:

@Serializable
data class CartData(
    val price: double,
    val id: Int,
    val product_name: String,
    var qty: Int,
    val error: Boolean = false,
    val message: String = ""
)

But I got a warning when tried to serialize

@serializable(with = CartData::class)

Type mismatch.
Required:
KClass<out KSerializer<*>>
Found:
KClass

How to solve this problem? Thanks in advance.

[dennykurniawan48]

Got It the answer is in #1114

But get a new error:

error: incompatible types: Class<PersistentListSerializer> cannot be converted to Class<? extends KSerializer<?>>

Possibly related to bug #685

[sandwwraith]

If you're using KAPT, then it's #685

[simonalveteg]

I stumbled upon the same issue, and removing the type parameter from the class name and explicitly specifying a type for the rest solved it for me.

@Serializable
data class AppSettings(
    @Serializable(PersistentListSerializer::class)
    val favoriteApps: PersistentList<String> = persistentListOf()
)

@OptIn(ExperimentalSerializationApi::class)
@kotlinx.serialization.Serializer(forClass = PersistentList::class)
class PersistentListSerializer(private val dataSerializer: KSerializer<String>) : KSerializer<PersistentList<String>> {
    private class PersistentListDescriptor : SerialDescriptor by serialDescriptor<List<String>>() {
        @ExperimentalSerializationApi
        override val serialName: String = "kotlinx.serialization.immutable.persistentList"
    }
    override val descriptor: SerialDescriptor = PersistentListDescriptor()
    override fun serialize(encoder: Encoder, value: PersistentList<String>) {
        return ListSerializer(dataSerializer).serialize(encoder, value.toList())
    }
    override fun deserialize(decoder: Decoder): PersistentList<String> {
        return ListSerializer(dataSerializer).deserialize(decoder).toPersistentList()
    }
}

[realityexpander]

I stumbled upon the same issue, and removing the type parameter from the class name and explicitly specifying a type for the rest solved it for me.

@Serializable
data class AppSettings(
    @Serializable(PersistentListSerializer::class)
    val favoriteApps: PersistentList<String> = persistentListOf()
)

@OptIn(ExperimentalSerializationApi::class)
@kotlinx.serialization.Serializer(forClass = PersistentList::class)
class PersistentListSerializer(private val dataSerializer: KSerializer<String>) : KSerializer<PersistentList<String>> {
    private class PersistentListDescriptor : SerialDescriptor by serialDescriptor<List<String>>() {
        @ExperimentalSerializationApi
        override val serialName: String = "kotlinx.serialization.immutable.persistentList"
    }
    override val descriptor: SerialDescriptor = PersistentListDescriptor()
    override fun serialize(encoder: Encoder, value: PersistentList<String>) {
        return ListSerializer(dataSerializer).serialize(encoder, value.toList())
    }
    override fun deserialize(decoder: Decoder): PersistentList<String> {
        return ListSerializer(dataSerializer).deserialize(decoder).toPersistentList()
    }
}

So, you would have to create an individual custom serializer for each type of PersistentList, instead of using the generics?

[amustafa98]

So, you would have to create an individual custom serializer for each type of PersistentList, instead of using the generics?

[simonalveteg]

So, you would have to create an individual custom serializer for each type of PersistentList, instead of using the generics?

I suppose. I just needed it for one type of Persistent List, so for me that didn't matter, but a better solution should be possible

[realityexpander]

I don’t know how to make them generic, do you?

…

On Feb 21, 2023, at 5:23 PM, Simon Alveteg ***@***.***> wrote: So, you would have to create an individual custom serializer for each type of PersistentList, instead of using the generics? I suppose. I just needed it for one type of Persistent List, so for me that didn't matter, but a better solution should be possible — Reply to this email directly, view it on GitHub <#1908 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABHLEYWL52OLY54IJUTTFN3WYVE5TANCNFSM5T6TPGEA>. You are receiving this because you commented.

[simonalveteg]

I don't, the code I posted is a modified version of the code in this issue:
#1114
and I remember reading this medium article when I worked on the project that needed serialization:
https://medium.com/androiddevelopers/datastore-and-kotlin-serialization-8b25bf0be66c

You've probably seen both of those links before, but I'm afraid I can't be of more help than that

[realityexpander]

Idk... from what I can see its not clear to be that kotlinx serialization supports generics. But since I have no need for generic use case (its easy enough to make a serializer for each data class that I need in my app), Im going to end my investigations here, unless you have any better ideas? Best, Chris

…

On Feb 23, 2023, at 7:45 AM, Simon Alveteg ***@***.***> wrote: I don't, the code I posted is a modified version of the code in this issue: #1114 <#1114> and I remember reading this medium article when I worked on the project that needed serialization: https://medium.com/androiddevelopers/datastore-and-kotlin-serialization-8b25bf0be66c You've probably seen both of those links before, but I'm afraid I can't be of more help than that — Reply to this email directly, view it on GitHub <#1908 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABHLEYQ2XWFS7TNXTQZPTOLWY5SYFANCNFSM5T6TPGEA>. You are receiving this because you commented.