Is there an easy way to write something like ```@Serializable data class Foo( val date: @Seriali...

# serialization

[CLOVIS]

Is there an easy way to write something like

@Serializable
data class Foo(
    val date: @SerializeAsUnixSeconds Instant,
)

where it would serialize as

data class Foo(
    val date: Int, // number of seconds since UNIX epoch
)

?

I know I could create a custom serializer for Foo , but there are many classes and fields where I need this and I don't want to create custom serializers for all of them.

(same question for serializing a Duration as an Int number of seconds)

[CLOVIS]

Found https://github.com/Kotlin/kotlinx-datetime/issues/181

I guess something like

val date: @Serializable(with = UnixSecondsSerializer::class) Instant,

?

[hfhbd]

@Serializable(with = UnixSecondsSerializer::class) val date: Instant,

[hfhbd]

https://youtrack.jetbrains.com/issue/KT-57012/Support-typealias-for-annotation-with-constant-values

[CLOVIS]

Ah, I see

[ephemient]

the annotation works on the property or the type, both result in the same serializer

[ephemient]

as such you can also

typealias SerializableInstant = @Serializable(with = SerializeAsUnixSeconds::class) Instant

@Serializable
data class Foo(
    val date: SerializableInstant, 
)

[hfhbd]

Oh, that’s nice too know 👀

[curioustechizen]

TIL that you can typealias annotations like that

[ephemient]

it's in the docs: https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serializers.md#specifying-a-serializer-globally-using-a-typealias

[Sebastian Schuberth]

Also https://github.com/Kantis/ks3 might have something for your needs.

[Emil Kantis]

InstantAsLong should do the trick if you try out ks3 🙂

[CLOVIS]

Am I right that ks3 would need to be an api dependency? I think serializers need to be visible on the place where serialization happens, which is most likely in downstream code

[Emil Kantis]

I can't tell for sure, I haven't tried using it that way. If you end up trying it out please let me know 😄

[CLOVIS]

I know that it was a problem in ktmongo.opensavvy.dev: I initially implemented the serializers as internal but then you get weird serialization errors

[Sebastian Schuberth]

I just checked via https://github.com/autonomousapps/dependency-analysis-gradle-plugin, and it seems to be fine with having ks3 an an implementation dependency in my project.

[Emil Kantis]

Thx for the confirmation @Sebastian Schuberth