Kotlin examples of following/violation the Law of Demeter LoD (a.k.a. Principle of Least Knowledge PoLK)

kotlin-law-of-demeter.kt

/**
 * Kotlin examples of following/violation Law of Demeter LoD (a.k.a. Principle of Least Knowledge PoLK)
 *  
 * Law of Demeter for functions requires that a method m of an object O may only invoke the
 * methods of the following kinds of objects:
 * 1. O itself
 * 2. m's parameters
 * 3. Any objects created/instantiated within m
 * 4. O's direct component objects
 * 5. A global variable, accessible by O, in the scope of m
 *
 * Law of Demeter violation example: client.getOrder().getPrice()
 * Law of Demeter following principle: (LawOfDemeterInKotlin class below)
 */

val name:String = "John"

class LawOfDemeterInKotlin {
	private var basket: Basket? = null

	fun doSomething(order: Order) {

		// (1) it's okay to call class own methods
		run()

		// (2) it's okay to call methods on objects passed in to method
		val price = order.calculatePrice()

		// (3) it's okay to call methods on any objects created inside class
		basket = Basket()
		val item = basket?.getFirstItem()

		// (4) it's okay to call methods on any objects created inside method
		val component = Component()
		component.init()

		// (5) it's okay to call methods on global variables
		val userCode = name.toUpperCase()
	}

	fun run(){}
}

class Order(){
	fun calculatePrice(){}
}

class Basket {
	fun  getFirstItem() = "Banana"
}

class Component {
	fun init() {}
}