with

with is a non-extension function that can access members of its argument concisely: you can omit the instance name when referring to its members.

class Configuration(var host: String, var port: Int) 

fun main() {
    val configuration = Configuration(host = "127.0.0.1", port = 9000) 

    with(configuration) {
        println("$host:$port")
    }

    // instead of:
    println("${configuration.host}:${configuration.port}")    
}