Scala-Java interop, issue with overloading of methods (Array and varargs)

Question

I have a Scala class which has two overloaded set methods, one with an Array param and the other with varargs. I want to call these methods from Java side, I am facing some issues due to overloading and/or boxing/unboxing. It would be helpful if someone can explain the reason behind the issue I'm facing and/or suggest workarounds.

Scala class

class Sample {
  def set[S](values: Array[S]): Unit = {
    println("Array overload")
  }


  @varargs
  def set[S](value: S, values: S*): Unit = {
    println("Varargs overload")
  }
}

Call from Java

 public static void main(String[] args) {
        Sample sample = new Sample();

        Boolean[] array = {true, false};
        Boolean boxed = true;
        boolean primitive = true;

        // works for array
        sample.set(array); // should call Array-overload, calls Array-overload


        // doesn't work for single element varargs
        sample.set(boxed); // should call varargs-overload, calls Array-overload instead
        sample.set(primitive); // should call varargs-overload, calls Array-overload instead

        // works for multiple varargs
        sample.set(boxed, boxed); // should call varargs-overload, varargs-overload is called
        sample.set(primitive, primitive); // should call varargs-overload, varargs-overload is called


    }

Thanks, I forgot to add that in sample, will correct that. But the problem remains, varargs overload doesn't get called when method is called with single element. — Dollyg
– Dollyg, Commented Feb 12, 2020 at 18:26
Java and Scala overload resolution works differently. There are tickets where this stumps everyone. — som-snytt
– som-snytt, Commented Feb 12, 2020 at 18:45

som-snytt · Accepted Answer · 2020-02-12 22:23:12Z

3

I guess it's because Scala results in

public <S extends java.lang.Object> void set(java.lang.Object);

instead of

<S extends java.lang.Object> void set(S[]);

I have no idea if that has to do with covariance of Arrays or what. (Edit: why generic array is erased to Object: Scala: arrays and type erasure)

Edit: Scala 3 output doesn't compile under Java at this time, probably because it hasn't forward-ported Scala 2 improvements.

edited Feb 12, 2020 at 22:23

answered Feb 12, 2020 at 19:53

som-snytt

39.6k2 gold badges49 silver badges133 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Scala-Java interop, issue with overloading of methods (Array and varargs)

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related