Kotlin generics

interface PacketTranscoder

open class Packet

class StringPacket(val body: String) : Packet()

interface PacketDecoder<out T : Packet> : PacketTranscoder {

    fun decode(client: String, buf: Array<String>): T

}

interface PacketEncoder<in T : Packet> : PacketTranscoder {

    fun encode(packet: T, buf: Array<String>)

}

class PacketHandler : PacketDecoder<StringPacket>, PacketEncoder<StringPacket> {
    override fun decode(client: String, buf: Array<String>) = StringPacket(buf[0])

    override fun encode(packet: StringPacket, buf: Array<String>) {
        buf[0] = packet.body
    }

}

fun main(args: Array<String>) {
    val inbuf = Array(1, { "test" })
    val p = PacketHandler()
    val packet = p.decode("", inbuf)
    val outBuf = Array(1, { "" })
    p.encode(packet, outBuf)
    assert(inbuf[0] == outBuf[0])
}