Serializing Extensions

If we want data in our extension to be serializable and to be able to be saved and reloaded then we need to implement the SerializableExtension which itself also extends Extension.

Our extension now needs to override three methods, serialize(), deserialize(), and id():

class MyLevelExtension: SerializableExtension {
    var lastModifiedBlockPos: BlockPos? = null
    
    override fun serialize(output: ValueOutput) {
        output.storeNullable("last_modified_pos", BlockPos.CODEC, this.lastModifiedBlockPos)
    }
    
    override fun deserialize(input: ValueInput) {
        this.lastModifiedBlockPos = input.read("last_modified_pos", BlockPos.CODEC).getOrNull()
    }
    
    override fun id(): Identifier {
        return Identifier("example", "my_level_extension")
    }
    
    // ...
}

Registering these extensions are exactly the same, any class that can be extended will automatically handle calling the methods for serializing and deserializing your data.