Example of the Builder pattern using Kotlin

shipBuilding.kt

class Ship {
  var name: String = ""
  var crewSize: Int = 0
  var numMasts: Int = 0

  override fun toString(): String {
    return "Ship { Name: $name, Num masts: $numMasts Crew Size: $crewSize}"
  }
}

class Builder {

  constructor(init: Builder.() -> Unit) {
    init()
  }

  private var shipInfo: ShipInfo? = null
  private var title: String = ""

  fun setTitle(newTitle: String) {
    title = newTitle
  }

  fun configure(init: ShipInfo.() -> Unit) {
    shipInfo = ShipInfo().apply { init() }
  }

  fun build(): Ship {
    val ship = Ship()

    ship.name = title

    shipInfo?.apply {
      ship.crewSize = crewSize
      ship.numMasts = numMasts
    }

    return ship
  }

  class ShipInfo {
    var crewSize: Int = 0
    var numMasts: Int = 0
  }
}

fun main() {
  val builder = Builder {
    setTitle("Bonnie Lassie")
    configure {
      crewSize = 10
      numMasts = 2
    }
  }

  println(builder.build())
}