Question

Here at work most people use Java, while I am working with Scala. We have decided to gather some common classes in an library which will be written in Java. Now I want to add some pseudo-functional programming to the library, take a look at the following:

java:

public interface Func<A, R> {
    public R f(a A);
}

public AClass {
    public <R> ArrayList<R> myMethod(
                             Func<String, R> func
    ) {
        // ...
    }
}

usage in java:

AClass ac = new AClass();
ArrayList<String> al = ac.myMethod(
                            new Func<String, String> (
                                public String f(String s) {
                                    return s + "!";
                                }
                            })

The above is not exactly exiting (more like daunting actually, from a scala perspective). Is there any way to summon some scala magic to be able to do something like the following in scala:

var ac = new ACLass
var al = ac.myMethod(str => str + "!")             // alternative 1
al = ac.myMethod { case: str:String => str + "!" } // alternative 2

I messed around with implicits for a while but couldn’t get things sorted out =P.

Answer 1

With implicit conversions:

object FuncConversions {
  implicit def func2function[A,R]( fn: (A) => R ) =
    new Func[A,R] {
      def f(a: A) = fn(a)
    }
}

Don’t forget to import the conversion in your scope:

import FuncConversions._

You can also implement the opposite conversion.