对于C＃的事件，Scala中惯用的等价物是什么

Question

In C#, classes and interfaces can have event s:

public class Foo
{
    public event Action SomethingHappened;

    public void DoSomething()
    {
        // yes, i'm aware of the potential NRE
        this.SomethingHappened();
    }
}

This facilitates a push-based notification with minimal boilerplate code, and enables a multiple-subscriber model so that many observers can listen to the event:

var foo = new Foo();
foo.SomethingHappened += () => Console.WriteLine("Yay!");
foo.DoSomething();  // "Yay!" appears on console. 

Is there an equivalent idiom in Scala? What I'm looking for is:

1. Minimal boilerplate code
2. Single publisher, multiple subscribers
3. Attach/detach subscribers

Examples of its use in Scala documentation would be wonderful. I'm not looking for an implementation of C# events in Scala. Rather, I'm looking for the equivalent idiom in Scala.

Answer 1

Idiomatic way for scala is not to use observer pattern. See Deprecating the Observer Pattern .

Take a look at this answer for implementation.

Answer 2

This is a nice article how to implement C# events in Scala Think it could be really helpful.

Base event class;

class Event[T]() {

  private var invocationList : List[T => Unit] = Nil

  def apply(args : T) {
    for (val invoker <- invocationList) {
      invoker(args)
    }
  }

  def +=(invoker : T => Unit) {
    invocationList = invoker :: invocationList
  }

  def -=(invoker : T => Unit) {
    invocationList = invocationList filter ((x : T => Unit) => (x != invoker))
  }

}

and usage;

val myEvent = new Event[Int]()

val functionValue = ((x : Int) => println("Function value called with " + x))
myEvent += functionValue
myEvent(4)
myEvent -= functionValue
myEvent(5)