How does Perl polymorphism work?

Question

I am unable to figure out an explanation on how polymorphism works in Perl. I understand what polymorphism means but I am trying to figure out how it internally works within perl. Can someone point me to some documentation that explains it. All the google searches I have done gives me examples of what polymorphism is in perl but not how perl makes it work.

Answer 1

When a method is invoked on an object or class, Perl looks to see if that method is provided directly by the class itself.

Because classes are simply Perl packages, it is simply a matter of looking for the existence of a subroutine &Class::method.

If no such subroutine is found, Perl examines the @ISA array in the same package (i.e. @Class::ISA) which contains a list of base classes for the class, and does the same check for every package/class that appears in there.

Each of those classes in turn may also have an @ISA array, so the search is recursive.

Finally, if the method is found nowhere by this method, Perl looks in a special package UNIVERSAL for a subroutine &UNIVERSAL::method.

A failure at this point goes on to invoke the AUTOLOAD system, but that is really beyond the principle of polymorphism.

A failure to find a suitable matching method anywhere raises an exception.