An snippet of what I'm trying to do: ``` interface...

# announcements

[nyxcode]

An snippet of what I'm trying to do:

interface SerializationAdapter<T : Any> {
    fun serialize(obj: T, output: ByteBuf)
    fun deserialize(input: ByteBuf): T
}
data class PacketDeclaration<T : Packet>(val id: Int,
                                                                       val clazz: KClass<T>,
                                                                       val serializer: SerializationAdapter<T>)
interface PacketRegistry {
    fun <P : Packet> resolve(clazz: KClass<P>): PacketDeclaration<P>
}
fun serialize(byteBuf: ByteBuf, packet: Packet) {
    val registry = ...
    val dec = registry.resolve(packet::class)
   dec.serializer.serialize(packet, byteBuf)
   // ^^ Out-projected type 'SerializationAdapter<out Packet>' prohibits the use of 'public abstract fun serialize(obj: T, output: ByteBuf): Unit defined in de.nyxcode.dmn.protocol.SerializationAdapter
}

Any recommendations?

[diesieben07]

Add a type parameter <T : Packet> to serialize and make packet a T. Then add a parameter KClass<T>. Then make a 2nd version of serialize:
inline fun <reified T : Packet> serialize(buf: ByteBuf, packet: T) = serialize(buf, packet, T::class).

[diesieben07]

Of course this will only work if serialize is called with known values of T. If at the call-site for serialize you just have a Packet, then this won't help.

[nyxcode]

Interresting approach, thanks!

[nyxcode]

Just found out that this would work too:

(registry.resolve(msg::class) as PacketDeclaration<Packet>).serializer.serialize(msg, out)

[diesieben07]

That's avoiding it though and it's ugly 😛

[nyxcode]

:L Again, thanks for your help!

[diesieben07]

But I am not sure how to solve this better, either.

[groostav]

Out-projected type 'SerializationAdapter<out Packet>' prohibits the use of 'public abstract fun serialize(obj: T, output: ByteBuf): Unit defined in de.nyxcode.dmn.protocol.SerializationAdapter

this is a covariance warning, Its akin to you trying to writing

interface Vehicle; class Car: Vehicle; class Truck: Vehicle

val list: ArrayList<Vehicle> = newCarList() //returns ArrayList<Car>
list.add(new Truck()) //blam

If you change to

val list: ArrayList<out Vehicle> = ...

then the line

list.add(new Truck())

will fail with the same compiler error your seeing.

The type system is trying to tell you that it cannot be certain T is a Packet, and thus passing in a packet might cause heap pollution.

[groostav]

When working with dyanmic class instances I almost always simply drop the static type system's generics, reduce everything to star-projections, and then insert runtime type checks as appropriate. you might consider throwing in a couple assert(clazz.isInstance(paramOrReturnValue))

[nyxcode]

I agree - generics are a pain in the *. Also, I think that generics in Kotlin are even worse than in Java... Kotlin may have fixed the problem @groostav pointed out, but made it far harder to write generic code. Pretty sad, the rest of the language is awesome.. '_'