Delegates: Difference between revisions

=={{header|Scala}}==

{{Out}}Best seen running in your browser either by [https://scalafiddle.io/sf/cCYD9tQ/0 ScalaFiddle (ES aka JavaScript, non JVM)] or [https://scastie.scala-lang.org/2TWYJifpTuOVhrAfWP51oA Scastie (remote JVM)].

<lang Scala>trait Thingable {

def thing: String

}

class Delegator {

var delegate: Thingable = _

def operation: String = if (delegate == null) "default implementation"

else delegate.thing

}

class Delegate extends Thingable {

override def thing = "delegate implementation"

}

// Example usage

// Memory management ignored for simplification

object DelegateExample extends App {

val a = new Delegator

assert(a.operation == "default implementation")

// With a delegate:

val d = new Delegate

a.delegate = d

assert(a.operation == "delegate implementation")

// Same as the above, but with an anonymous class:

a.delegate = new Thingable() {

override def thing = "anonymous delegate implementation"

}

assert(a.operation == "anonymous delegate implementation")

}</lang>

empty: default implementation

NonDelegate: default implementation

Delegate: delegate implementation