Class delegation

Let's rewrite the CalculatorMachine class in Kotlin:

class CalculatorMachine(private val delegate: Calculator): Calculator by delegate

That's it. Now you can use the CalculatorMachine class written in Kotlin similarly to the version written in Java:

fun main (args: Array<String>) {
    CalculatorMachine(CalculatorBrain())
}

You can see that the compiler generates the same bytecode for the Kotlin version of the CalculatorMachine class as for the Java version:

public final class delegation/kotlin/CalculatorMachine implements delegation/Calculator  {

    private final Ldelegation/Calculator; delegate

    public <init>(Ldelegation/Calculator;)V
    @Lorg/jetbrains/annotations/NotNull;() // invisible, parameter 0
L0
    ALOAD 1
LDC "delegate"
INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull (Ljava/lang/Object;Ljava/lang/String;)V
    L1
    LINENUMBER 6 L1
    ALOAD 0
INVOKESPECIAL java/lang/Object.<init> ()V
            ALOAD 0
ALOAD 1
PUTFIELD...