Kotlin: how to limit scope within a block?

Question

In Java one can use curly braces to delineate a block of code with its own scope:

void f() {
  {
    int x = 1
    // do something with x
  }

  // x not visible here anymore
}

How is this done in Kotlin?

Answer 1

You can use run for this purpose:

inline fun <R> run(block: () -> R): R (source)
Calls the specified function block and returns its result.

_kotlin.run

fun f() {
    run {
        val x = 1
        // do something with x
    }
    // x not visible here anymore
}

This is an inline function (like many other language construct-like functions in Kotlin), so performance-wise it's equivalent to the Java code.

---

{} doesn't work since it creates a lambda (which is never actually invoked, so it does nothing). You could call it immediately ({ foo }()) with the overhead of creating a lambda, or create an inline function that does this for you - which is exactly what run does.