What's the idiomatic equivalent in Scala for C#'s event

Question

In C#, classes and interfaces can have events:

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:

Minimal boilerplate code
Single publisher, multiple subscribers
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.

this may be helpful: http://stackoverflow.com/questions/6814246/in-scala-how-would-i-combine-event-driven-programming-with-a-functional-approac — daryal, Jan 24 '13 at 14:23

score 2 · Accepted Answer · edited May 23 '17 at 12:25

2

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

Take a look at this answer for implementation.

edited May 23 '17 at 12:25

Community

1
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answered Jan 24 '13 at 14:24

senia

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How does saying "don't use the observer problem" help the OP in the slightest (in terms of actually answering his question)? – Kirk Woll Jan 24 '13 at 14:34
1

I'm guessing that "don't do it like that at all, do it in some related way" is what senia means. – Jesper Jan 24 '13 at 14:37
@KirkWoll : OP upvoted the answer, must be doing something right =) – FMM Jan 24 '13 at 16:10
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@om-nom-nom I'll let you figure that one out. – FMM Jan 24 '13 at 20:45
@FMM oh, that talk in the third person totally messed me up :-) – om-nom-nom Jan 24 '13 at 20:47

score 2 · Answer 2 · edited Feb 27 '17 at 17:58

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)

edited Feb 27 '17 at 17:58

myuce

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answered Jan 24 '13 at 14:29

Ph0en1x

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From the question: "I'm not looking for an implementation of C# events in Scala." – FMM Jan 24 '13 at 14:55
2

Please, if you post a link, provide at least basic excerpt: as the time goes on, page may become unavailable and future reader wouldn't have any direction to dig into. – om-nom-nom Jan 24 '13 at 20:34

What's the idiomatic equivalent in Scala for C#'s event

2 Answers2