Converting AVMetadataObject to AVMetadataMachineReadableCodeObject

I'm currently writing an app that can scan various types of barcodes. I've got my inputs and output set up and it's calling the DidOutputMetadataObjects on my delegate. When I ToString the AVMetadatObject that comes back, I get:

type "org.gs1.EAN-13", bounds { 0.5,0.2 0.0x0.7 }, corners { 0.5,1.0 0.5,1.0 0.5,0.2 0.5,0.2 }, time 1043428851375166, stringValue "0123456789104"

which is exactly what I would expect. However, I cannot cast the AVMetadataObject to AVMetadataMachineReadableCodeObject as the former is the parent of the later. I need to get an AVMetadataMachineReadableCodeObject so that I can get access to the stringValue property. Any suggestions? What is the appropriate way to obtain this information?

Thanks in advance.