CODEWITHSUNDEEP
scala
K J
K J

Reputation: 4743

Scala: Another usage of underscore?

I'm looking into the scala actors library, and there I found the following code:

private[scheduler] trait TerminationMonitor { 
    _: IScheduler =>

    protected var activeActors = 0 
    ...

The question is what is the meaning of _: IScheduler => is here?
I'm new to Scala and it confuses me that there are so many different meanings with the underscore.

Thanks for your help in advance!

Upvotes: 3

Views: 233

Answers (1)

Debilski
Debilski

Reputation: 67828

This usage of the underscore is similar to those:

someElem match {
  case _: String => doSomething()
}

val k = (_: Int) => "This does not use the Int argument."

val (m, _, o) = (1,2,3)

It is a syntactic placeholder for an identifier (variable) which is immediately discarded afterwards.

In your example, the naming of the self-type is therefore being avoided. (But since the self-type reference is always accessible as this, it would be equivalent to writing this: IScheduler => in that special case.)

Upvotes: 5

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