privateExtensions.kt

class Platform {

    fun install(vararg module: Module) {
        module.forEach { mod -> mod.install() }
    }

    fun Module.install() {
        setup()
    }

    fun Module.modInitialMessage(message:String) {
        println(message)
    }
}


interface Module {
    fun Platform.setup()
}

class TeeModule : Module {
    override fun Platform.setup() = modInitialMessage("Installing tee...")
}

class CoffeeModule : Module {
    override fun Platform.setup() = modInitialMessage("Installing coffee...")
}



fun main(args: Array<String>) {

    TeeModule().install() // <-- Does Not Exist
    TeeModule().setup() // <-- Does Not Exist
	
    val platform = Platform()
    
    platform.install() // <--- OK
    platform.modInitialMessage() // <--- Does Not Exist

    platform.install(
        TeeModule(),
        CoffeeModule()
    )

    // ... ->
    //
    // Installing tee...
    // Installing coffee...
    //
    //
}