Oh, well, whatever you want, as specifically as you expect is what to do. If the XMLin() will always return a HashRef for your data, then specify that. Otherwise something like \my $moo; can be considered valid XML in your object layer. Better to catch problems early. I think you can | (OR) stuff together too if you need to consider ArrayRef as well. I'm not even sure if XML::Simple allows for that. While we're on the topic XML::Simple is not really anyone's friend except in the most predictable and unchanging use. See Examples where XML::Simple is the optimal choice? and Stepping up from XML::Simple to XML::LibXML.