val list = listOf("hello" to "world", "hello" to "world2", "bla" to "quz")
val result = list.groupingBy { it.first }.fold(null as String?) { acc, elem -> acc ?: elem.second }

fun mapKeysOrReturnNullIfAnyNulls(keys: Array<out String>, f: (s: String) -> String?): List<String>? = try {
    keys.map { f.invoke(it) }.requireNoNulls().toList()
} catch (e: IllegalArgumentException) {
    null
}

request.session().attribute('flash')[key] = [requests: 1, value: value]

class Hi(val something : String, val filter : (String) -> Boolean = {true}){

    fun letsHaveSomeFun() : String? {
        when(filter(something)){
            true-> return something
            false -> return null
        }
    }

}

val user = User("Bertrand").apply{
    userName = "Alice"
    addFriend("Bob")
}

also

return call().ignore{ //no it or this here }

List(1,2) match {
  case x :: xs => println(x + " " + xs)
  case _ => println("")
}

val clazz = ((Int) -> Int)::class

Regex

java.util.regex.Pattern

val pattern = "[0-9]+".toPattern()
val matcher = pattern.matcher(string).region(startIndex, string.length)
if (matcher.lookingAt()) { ... }

try {
    myObject.theField
} catch(t: Throwable) {
    log.error("theField is null")
}