using Scala 2.10.1 Value Types in Java

Question

I am updating my 2.9.* project to 2.10. I have several classes for fundamental types (angles, lengths, etc) that seem like they are perfect candidates for value types. Unf

Answer 1

Scala compiler turns value classes into their unboxed type, which eliminates their cost for runtime. Inspecting the compiled class file for Angle, you'll see:

public static double Zero();

So from Java's point of view, Angle.Zero returns a double; it's not aware of the semantics of Scala's value classes.

Angle's own methods, such as degrees, get compiled into a) a static extension method that takes in the unboxed value (double) b) an instance method:

public static double degrees$extension(double);
public double degrees();

Which means the latter can still be called on an instance of Angle in Java:

Angle a = new Angle(0);
Assert.assertEquals(a.degrees(), 0, 1E-9);