Entity and Player Extensions

Entity and player extensions need additional behavior because they can be re-constructed when travelling between dimensions, respawning, or converting to other entity types. In these cases we need to effectively transfer our extension to the new entity.

Both EntityExtension and PlayerExtension implement TransferableEntityExtension which defines a transfer method to override. EntityExtensions require you to override this method, PlayerExtensions however have a default implementation which is to transfer the extension as-is. This can be done because the PlayerExtension doesn't hold a reference to the ServerPlayer object itself but the ServerGamePacketListenerImpl which holds a reference to the current player.

Here's an example:

class MyEntityExtension(entity: Entity): EntityExtension(entity) {
    var persistentData = 0
    var transientData = 0

    override fun transfer(
        entity: Entity,
        reason: EntityTransferReason,
        delayed: DelayedActions
    ): Extension {
        val transferred = MyEntityExtension(entity)
        transferred.persistentData = this.persistentData
        return transferred
    }
}