public function apply($perBatch = 50)
    {
        $this->iterated = $this->batches = $batches = 0;
        $that = $this;
        $it = $this->iterator;
        $callback = $this->callback;

        $batch = BatchBuilder::factory()
            ->createBatchesWith(new BatchSizeDivisor($perBatch))
            ->transferWith(new BatchClosureTransfer(function (array $batch) use ($that, $callback, &$batches, $it) {
                $batches++;
                $that->dispatch('iterator_batch.before_batch', array('iterator' => $it, 'batch' => $batch));
                call_user_func_array($callback, array($it, $batch));
                $that->dispatch('iterator_batch.after_batch', array('iterator' => $it, 'batch' => $batch));
            }))
            ->autoFlushAt($perBatch)
            ->build();

        $this->dispatch('iterator_batch.created_batch', array('batch' => $batch));

        foreach ($this->iterator as $resource) {
            $this->iterated++;
            $batch->add($resource);
        }

        $batch->flush();
        $this->batches = $batches;

        return $this->iterated;
    }