Programming Perl, 3rd Edition

Object Construction

All objects are references, but not all references are objects. A reference won't work as an object unless its referent is specially marked to tell Perl what package it belongs to. The act of marking a referent with a package name--and therefore, its class, since a class is just a package--is known as blessing. You can think of the blessing as turning a reference into an object, although it's more accurate to say that it turns the reference into an object reference.

The bless function takes either one or two arguments. The first argument is a reference and the second is the package to bless the referent into. If the second argument is omitted, the current package is used.

$obj = { };                 # Get reference to anonymous hash.
bless($obj);                # Bless hash into current package.
bless($obj, "Critter");     # Bless hash into class Critter.

Here we've used a reference to an anonymous hash, which is what people usually use as the data structure for their objects. Hashes are extremely flexible, after all. But allow us to emphasize that you can bless a reference to anything you can make a reference to in Perl, including scalars, arrays, subroutines, and typeglobs. You can even bless a reference to a package's symbol table hash if you can think of a good reason to. (Or even if you can't.) Object orientation in Perl is completely orthogonal to data structure.

Once the referent has been blessed, calling the built-in ref function on its reference returns the name of the blessed class instead ...