PS_11_Perl - Object-Oriented Perl

Object-Oriented Perl

In Perl, modules and object-oriented programming go hand in hand. Not all modules are written in an object-oriented fashion, but most are. A couple of definitions are warranted here:

· An object is simply a referenced thingy that happens to know which class it

belongs to.

· A class is simply a package that happens to provide methods to deal with objects.

· A method is simply a subroutine that expects an object reference (or a package name, for class methods) as its first argument.

To create an object (or instance of a class), use the class constructor. Usually the class constructor will be a function named “new,” but may be called “Create” for some Win32 modules. For example,

$tri = new Triangle::Right (side1=>3, side2=>4);

The constructor takes a list of arguments describing the properties of the object to be created (see the documentation of the module in question to determine what these should be) and returns a reference to the created object.

An example of a class constructor (internal to the module) is shown below:

package critter; # declare the name of the package

sub new {

my $class = shift; # Get class name

my $self = {}; # Initialize the object to nothing

bless $self, $class; # Declare object to be part of class

$self->_initialize();# Do other initializations

return $self;

}

Methods (subroutines expecting an object reference as their first argument) may be invoked in two ways:

Packagename->constructor(args)->method_name(args)

Or:

$object = Packagename->constructor(args);

$object->method_name(args);

Methods are simply declared subroutines in the package source file.