Useful Scala snippets

FindNonexistentFile.scala

def newTempFile() = new File(IoTmpDir, "JavaTestTmp-"+random.nextLong())

/*
 * Tries 10 times to find a nonexistent file.
 * Uses Streams to lazily go through a range, generating a fresh
 * file each time.
 */
val dir = Stream.range(1,10)
  .map { newTempFile() }
  .find(!_.exists)
  .getOrElse(throw new IllegalStateException("Couldn't find unique filename!"))

/*
 * This form might be better, because it's using Iterator (which doesn't bother caching elements)
 * and directly creates a file generator rather than mapping onto a stream of numbers that aren't used.
 * The take() call doesn't evaluate anything in an Iterator, it just limits it to returning max 10 items.
 */
val dir = Iterator.continually { newTempFile() }.take(10)
  .find(!_.exists)
  .getOrElse(throw new IllegalStateException("Couldn't find unique filename!"))  

/* 
 * If you do not fear infinity's grasp, you could retry indefinitely.
 * If you expected to go through a large number of items, discarding all but one,
 * it may be better to use Iterator which doesn't keep previous items in memory.
 */
val dir = Stream.continually( newTempFile() )
  .find(!_.exists).get // It'll either return Some, or NEVER return. Careful!