Internals of implicit value classes

[Jasper-M]

Hi,

I was trying to understand more about how implicit value classes allow extension methods without boxing, so I tried looking into the bytecode that got generated.

Now there are a few lines there (in bold) of which I don't really understand the purpose. I'm guessing the empty class names have something to do with this being a REPL session, but I still don't understand why `2` has to be passed to some method before the actual extension method is called.

scala> implicit class IntExt(private val i: Int) extends AnyVal {

     |   def ext(o: Int) = i - o

     | }

defined class IntExt

scala> class Foo{ def foo(i: Int) = 2 ext i }

defined class Foo

scala> :javap Foo

  public int foo(int);

    descriptor: (I)I

    flags: ACC_PUBLIC

    Code:

      stack=3, locals=2, args_size=2

         0: getstatic     #13                 // Field IntExt$.MODULE$:LIntExt$;

         3: getstatic     #18                 // Field .MODULE$:L;

         6: iconst_2

         7: invokevirtual #21                 // Method .IntExt:(I)I

        10: iload_1

        11: invokevirtual #25                 // Method IntExt$.ext$extension:(II)I

        14: ireturn

Also, is it necessary that equals$extension and hashCode$extension methods get generated in IntExt$?

Best,

Jasper