For the sake of clarity, I oversimplified some of the facts about objects. Here are a few of the gorier details:

•  Every example I gave of a constructor was a class method. But object methods can be constructors, too, if the class was written to work that way: $new = $old->copy, $node_y = $node_x->new_subnode, or the like.

•  I’ve given the impression that there’s two kinds of methods: object methods and class methods. In fact, the same method can be both, because the distinction has to do only with how it parses parameters.

•  The term "object value" isn’t something you’ll find used much anywhere else. It’s just my shorthand for what would properly be called an "object reference" or "reference to a blessed item". In fact, people usually say "object" when they properly mean a reference to that object.

•  I mentioned creating objects with constructors, but I didn’t mention destroying them with destructors — a destructor is a kind of method that you call to tidy up the object once you’re done with it, and want it to neatly go away (close connections, delete temporary files, free up memory, and so on). But because of the way Perl handles memory, most modules don’t require destructors.

•  I said that class method syntax has to have the class name, as in $session = Net::FTP->new($host). Actually, you can instead use any expression that returns a class name: $ftp_class = 'Net::FTP'; $session = $ftp_class->new($host). Moreover, instead of the method name for object- or class-method calls, you can use a scalar holding the method name: $foo->$method($host). In practice, these formulations are rarely useful.

Finally, to learn about objects from the perspective of writing your own classes, see the perltoot documentation, or Damian Conway’s exhaustive and clear book Object Oriented Perl (Manning Publications 1999, ISBN 1-884777-79-1).