Hello folks, question can someone help/point to docs me understand why this does not work? Thanks in...

# serialization

[George]

Hello folks, question can someone help/point to docs me understand why this does not work? Thanks in advance for any answers !

@file:UseSerializers(UrlSerializer::class)

// using serializer explicitly works
val url = URL("<https://test>")
val protobytes = ProtoBuf.encodeToByteArray(UrlSerializer, url)
val result = ProtoBuf.decodeFromByteArray(UrlSerializer, protobytes)

// use file serializer, this fails
shouldThrow<SerializationException> {
    val protobytes2 = ProtoBuf.encodeToByteArray(url)
    val result2: URL = ProtoBuf.decodeFromByteArray(protobytes)
    println(result2)
}

// use typealias serializer, this also fails
shouldThrow<SerializationException> {
    val url2: UrlAsString = url
    val protobytes2 = ProtoBuf.encodeToByteArray(url)
    val result2: UrlAsString = ProtoBuf.decodeFromByteArray(protobytes)
    println(result2)
}

// using inside data class works (like in the guide)
@Serializable
data class TestUrl(val value: URL)

val testUrl = TestUrl(url)
val proto = ProtoBuf.encodeToByteArray(testUrl)
val resultUrl: TestUrl = ProtoBuf.decodeFromByteArray(proto)
println(resultUrl)

In case, when using file serializer or global how come it throws: cannot find serializer for URL ?

[George]

Serializer:

public typealias UrlAsString = @Serializable(UrlSerializer::class) URL

public object UrlSerializer : KSerializer<URL> {
    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("URL", PrimitiveKind.STRING)

    override fun serialize(encoder: Encoder, value: URL) {
        encoder.encodeString(value.toExternalForm())
    }

    override fun deserialize(decoder: Decoder): URL {
        return URL(decoder.decodeString())
    }
}

[ephemient]

@file:UseSerializers only affects the use of URL in @Serializable classes. it's not persisted anywhere that the reified helper can look up (and it doesn't know what file you're in). also typealiases don't really exist after being substituted so that's not surprising.