Basic Extensions

To create a basic extension we just need to create a class that implements the Extension interface:

kotlin

class MyExtension: Extension {

}

From here we can add any fields that we want to store in our extension:

kotlin

class MyExtension: Extension {
    var foo: String = "example"
    var bar: Int = 0xDEADBEEF
    var baz: Identifier = Identifier("modid", "path")
}

We then need to register our extension to the type that we want to extend. Currently, arcade supports extending ServerPlayer, Entity, ServerLevel, and PlayerTeam. Each of which have an event which we can hook into to add our extension:

kotlin

class MyExtension: Extension {
    // ...
    companion object {
        // Call this from your mod initializer
        internal fun registerEvents() {
            GlobalEventHandler.Server.register<LevelExtensionEvent> {
                it.addExtension(MyExtension())
            }
        }
    }
}

Typically, we want to always register our extension to a class meaning there will never be an instance of the class without the extension.

To then access our extension we can use the getExtension utility extension functions defined in ExtensionUtils, but a nicer way to access your extension is to define an extension property:

kotlin

class MyExtension: Extension {
    // ...
    companion object {
        @JvmStatic // If we want to access the extension from Java
        val ServerLevel.myExtension: MyExtension
            get() = this.getExtension()
        
        // ...
    }
}

fun foo(level: ServerLevel) {
    // Using the getExtension function
    val a = level.getExtension<MyExtension>()
    // Using our extension property, which is nicer
    val b = level.myExtension
}

It may also be useful for our extension to have context of its owner. When registering your extension the event will provide access to the owner, you can pass this reference into your extension, except extensions for entities and players which work slightly differently. This will be covered in the Entities and Players Section.

We can also register other events to update our extension, lets for example say we wanted to keep track of the last modified block position in our world:

kotlin

class MyLevelExtension: Extension {
    var lastModifiedBlockPos: BlockPos? = null

    companion object {
        val ServerLevel.myExtension: MyLevelExtension
            get() = this.getExtension()

        internal fun registerEvents() {
            GlobalEventHandler.Server.register<LevelExtensionEvent> { event ->
                event.addExtension(MyLevelExtension())
            }
            GlobalEventHandler.Server.register<LevelBlockChangedEvent> { (level, pos, _, _) ->
                level.myExtension.lastModifiedBlockPos = pos
            }
        }
    }
}

Basic Extensions ​

Basic Extensions