Security of Java takes a dangerous turn for the worse, experts say (ars technica)

Posted Sep 17, 2013 12:04 UTC (Tue) by HelloWorld (guest, #56129)
In reply to: Security of Java takes a dangerous turn for the worse, experts say (ars technica) by eru
Parent article: Security of Java takes a dangerous turn for the worse, experts say (ars technica)

That's the kind of workaround I was referring to, it breaks for non-trivial cases, for example when it's not known at compile time which function implementation a call will end up in.

scala> import scala.annotation.tailrec
import scala.annotation.tailrec

scala> class Test {
     |   @tailrec def apply { apply }
     | }
<console>:9: warning: method apply in class Test does nothing other than call itself recursively
         @tailrec def apply { apply }
                              ^
<console>:9: error: could not optimize @tailrec annotated method apply: it is neither private nor final so can be overridden
         @tailrec def apply { apply }
                      ^

It fails even for simple mutually recursive definitions:

scala> @tailrec def even(x: Int): Boolean = x == 0 || odd(x - 1); @tailrec def odd(x: Int): Boolean = x != 0 && even(x - 1)
<console>:10: error: @tailrec annotated method contains no recursive calls
       @tailrec def even(x: Int): Boolean = x == 0 || odd(x - 1); @tailrec def odd(x: Int): Boolean = x != 0 && even(x - 1)
                    ^
<console>:10: error: @tailrec annotated method contains no recursive calls
       @tailrec def even(x: Int): Boolean = x == 0 || odd(x - 1); @tailrec def odd(x: Int): Boolean = x != 0 && even(x - 1)

It's not just about tail *recursion* optimization, it's about general tail *call* optimization. JVM modifications are needed to make this kind of thing work.