gears

val valid: UserId = findUserIdByEmail(email) val invalid1: UserId = findUserIdByEmail("bar") // error: can't use String as Email val invalid2: UserId = 123 // error: can't use Int as UserId 3. Union types (Scala 3). You can emulate them in Java/Kotlin with Sealed Types but it's much more verbose. type JsonScalar = String | Int | Boolean type Json = JsonScalar | Map[String, JsonScalar] | List[JsonScalar] // Makes writing functions that take multiple argument types much easier: def handle(it: String | Int | Boolean): Unit = ... 4. Context-oriented programming with "given/using" in Scala 3 and "context-receivers" in Kotlin. This one is harder to explain succinctly but essentially it allows you to decorate methods/classes with required "contextual" args. Instead of passing them as regular function arguments, you must invoke the function inside of an "environment"/"context" where the requirements are satisfied. This makes threading dependencies through your code much easier, and eliminates the need for dependency injection frameworks in many cases. interface Logger { fun log(message: String) } object ConsoleLogger : Logger { override fun log(message: String) = println(message) } ctx(Logger) fun doSomething(): Int { log("Hello") return 42 } fun main() { val logger = ConsoleLogger with (logger) { doSomething() } } 5. First-class support for asynchronous programming. With "suspend" in Kotlin and a current prototype being done in Scala 3: - REPO: https://github.com/lampepfl/async | SLIDES: https://github.com/lampepfl/async/blob/main/scalar-slides.pd... | YOUTUBE TALK: https://www.youtube.com/watch?v=0Fm0y4K4YO8 6. Passing arguments by name, rather than positionally. fun doSomething(a: Int, b: Int, c: Int): Int = ... doSomething(a = 1, b = 2, c = 3) 7. Tuples (Scala). They're like anonymous data classes/records. val t: (Int, String) = (1, "foo") val (a, b) = t