Kodebits Day 48: Delegation By Keyword

What does this print?

interface Calc {
  fun add(a: Int, b: Int): Int
}
class Base : Calc {
  override fun add(
    a: Int, b: Int
  ) = a + b
}
class Wrap(c: Calc) : Calc by c
fun main() {
  println(Wrap(Base()).add(2, 5))
}

Try it in the online Kotlin Playground →

[spoiler title="Solution"]

Answer:

7

Explanation:

by keyword delegates interface implementation to another object.

[/spoiler]

Further Reading

• Utilize Control Flow in Kotlin
• Leverage Kotlin Functions & Lambdas