wrong mulitpass

gistfile1.txt

// Copyright Shunsuke Sogame 2008-2009.
// Distributed under the terms of an MIT-style license.


package mada.iter


/**
 * Contains utility methods operating on multi-pass iterables.
 */
object MultiPass {
    /**
     * Creates from <code>Iterable</code>.
     */
    def elements[A](it: Iterable[A]): MultiPassIterator[A] = new MultiPassIterator[A] {
        private var c: Iterable[A] = it.projection
        private var i = c.elements
        override def hasNext = i.hasNext
        override def next = { c = Iterables.drop(c, 1); i.next } // drop is O(n)!!
        override def clone = elements(c)
    }
}


/**
 * Placed only because of "academic" reason.
 * This is equivalent to STL ForwardIterator, but practically unusable
 * because JVM triggers heap-allocation every cloning of iterator.
 * In JVM, ForwardRange algorithms is implemented by <code>Vector</code>.
 * (This strategy has already been taken in <code>java.util.regex</code>.)
 * As a result, you have to copy <code>Iterable</code> into <code>Vector</code>.
 */
trait MultiPassIterator[+A] extends Iterator[A] {
    override def clone: MultiPassIterator[A] = throw new CloneNotSupportedException
}