In Scala, can I call Source.reset() on resources read from the classpath?

Question

Suppose I have a jarfile on my classpath. In that jarfile I have a file afile.txt.

I need to iterate on that file twice, once to count the lines and once to parse it. This is what I did:

val source = Source.fromInputStream(/*some magic to get the resource's InputStream*/)
source.getLines.foreach (/*count the lines*/)
source.getLines.reset.foreach (/*do something interesting*/)

But this doesn't work. In the debugger it looks like the call to reset() returns an empty iterator. The code above works fine when the Source refers to a file on the filesystem instead of on the classpath.

Am I doing something wrong, or is this a bug in Scala's io library?

Answer 1

I think this is a bug is the Scala library. I had a quick look at Source.scala in 2.8 trunk and reset seems to return a new wrapper around the original input stream which would have no content left after the first pass. I think it should throw an exception. I can't think of a straightforward way you could reset an arbitrary input stream.

I think you can simply call val source2 = Source.fromInputStream and read again, as it seems reset does not do more than that.