Kotlin Contracts sample

contracts.kt

import kotlin.contracts.ExperimentalContracts
import kotlin.contracts.InvocationKind
import kotlin.contracts.contract

class Foo {
  fun foo() {}
}

@ExperimentalContracts
inline fun Foo.bar(block: Foo.() -> Unit) {
  contract {
    callsInPlace(block, InvocationKind.AT_LEAST_ONCE)
  }
  block()
  this.foo()
}

@ExperimentalContracts
fun hoge(): Int {
  Foo().bar {
    return 1
  }
}