Disassembling Scala code

Question

How can I disassemble Scala code? Can it be done without first building the Jar and decompiling the resulting .class files? Is there an alternative, faster way to do this?

For Python there is dis which can be used as follows:

def myfunc(alist):
    return len(alist)

>>> dis.dis(myfunc)
  2           0 LOAD_GLOBAL              0 (len)
              3 LOAD_FAST                0 (alist)
              6 CALL_FUNCTION            1
              9 RETURN_VALUE

Answer 1

You know you can do this in the REPL:

scala> def foo[A](xs: Seq[A]) = xs.size
foo: [A](xs: Seq[A])Int

scala> :javap foo
  Size 714 bytes
...
public <A extends java/lang/Object> int foo(scala.collection.Seq<A>);
  flags: ACC_PUBLIC
  Code:
    stack=1, locals=2, args_size=2
     0: aload_1       
     1: invokeinterface #20, 1 // InterfaceMethod scala/collection/Seq.size:()I
     6: ireturn       
...

You have crawl a bit through the output because it contains the outer module and many more information.