Programming Perl, 3rd Edition

Perl's Object System

Perl doesn't provide any special syntax for defining objects, classes, or methods. Instead, it reuses existing constructs to implement these three concepts.^[1]

Here are some simple definitions that you may find reassuring:

An object is simply a reference...er, a referent.

Since references let individual scalars represent larger collections of data, it shouldn't be a surprise that references are used for all objects. Technically, an object isn't the reference proper--it's really the referent that the reference points at. This distinction is frequently blurred by Perl programmers, however, and since we feel it's a lovely metonymy, we will perpetuate the usage here when it suits us.^[2]

A class is simply a package.

A package serves as a class by using the package's subroutines to execute the class's methods, and by using the package's variables to hold the class's global data. Often, a module is used to hold one or more classes.

A method is simply a subroutine.

You just declare subroutines in the package you're using as the class; these will then be used as the class's methods. Method invocation, a new way to call subroutines, passes an extra argument: the object or package used for invoking the method.

^[1] Now there's an example of software reuse for you!

^[2] We prefer linguistic vigor over mathematical rigor. Either you will agree or you won't.