Object Oriented PERL Programming

In this article, we explore Object-Oriented Programming (OOP) in Perl, starting with the concepts of Packages and Modules for organizing and reusing code. We explain the syntax for creating custom Perl modules and introduce OOP principles, illustrating their real-life applications and benefits for code organization, maintainability, and reuse. Key OOP elements in Perl—objects, classes, blessing, constructors, destructors, methods, attributes, and inheritance—are demonstrated through coding examples. We also showcase the Moose.pm module, highlighting its expressive syntax and powerful features to simplify OOP development. Practical examples guide viewers in creating classes, objects, and writing modular, maintainable Perl code.

In this article we will cover the Object Oriented PERL through the below mentioned subtopics :

• Package & Module in PERL

• Package/Module Example

• Object Oriented Programming (OOP) Concept

• When to use OOP 

• Object/Class/Blessing/Constructor/Destructor/Methods/Inheritance

• Coding Example : Class & Object Creation in PERL

• Coding Example : Inheritance Class & Object Creation in PERL 

• Coding Example : Class & Object Creation in PERL using Moose.pm

Perl Package & Module :

• A namespace stores names of variables, subroutines, filehandles, and formats belonging to its scope. 

• Each namespace has its own symbol table, which is basically a hash table.

• Perl Namespaces are called "packages".

• The default namespace for any PERL program is main.

• Package declaration tells the compiler which namespace to prefix to our variables.

• A module is a package defined in a file whose name is the same as the package.

• All Perl modules are contained in global @INC array, which contains a list of library directories/paths.

• A module/package can be included in your program with use or require functions of PERL.

A Perl Module :

• A module is just a set of related functions in a library file! 

• Perl package with the same name as the file (FileName=SomeModule.pm). 

• File extension is .pm and NOT .pl

The module definition starts with : 

package SomeModule;  

use warning;

use strict;

# Code of this module goes here

# Subroutines 

# end of this module is declared by

1;  # don't forget to return a true value from the file

Usage of Custom Perl Module :

Keep the PM file in your current working directory

For any other directory , specify it in your .cshrc file & source it:

setenv PERL5LIB '/home/<userName>/PERL_Modules'

setenv PERLLIB '/home/<userName>/PERL_Modules'

Then use in your present myProg.pl as

use SomeModule;

or

require SomeModule;

or

require "SomeModule.pm";

Package/Module Example :

Here is how we create a PERL Module abc.pm :

And here is the example how we use it :

Object Oriented Concept :

• Most object systems share a number of common concepts.

• Understanding the concepts will make it much easier to read and write object-oriented code. 

• Perl's OO system is class-based. Class-based OO is fairly common. 

• It's used by Java, C++, C#, Python, Ruby, and many other languages. 

When to Use OOP ?

• The system being designed is large, or is likely to become large over time.

• The data can be put into obvious structures.

• There is prominent of inheritance and polymorphism.

• There is a piece of data on which many different operations are applied.

• You may need to perform the same general operations on related types of data, but with slight variations depending on the specific type of data the operations are applied to.

• Chances are there that you may add new data types later.

• The implementation of individual components of the system is likely to change over time.

• The system design is already object-oriented.

• Large numbers of other programmers from multi site will be using your code modules.

Objects :

• An object is a data structure that bundles together data and subroutines which operate on that data.

• An object's data is called attributes, and its subroutines are called methods.

• An object can be thought of as a noun (a person, a web service, a computer).

• An object represents a single discrete thing.

• For example, an object might represent a file. 

• The attributes for a file object might include its path, content, and last modification time. 

Class :

• A class defines the behavior of a category of objects.

• A class is a name for a category and a class also defines the behavior of objects in that category.

• A specific object is often referred to as an instance of a class.

In Perl, any package can be a class.

The difference between a package which is a class and one which isn't is based on how the package is used. Here's our "class declaration" for the File package: 

Blessing :

Most Perl objects are hashes, but an object can be an instance of any Perl data type (scalar, array, etc.). Turning a plain data structure into an object is done by blessing that data structure using Perl's bless function.

We sometimes say that an object has been "blessed into a class".

Constructor :

A constructor creates a new object belonging to a class. In Perl, a class's constructor is just another method, unlike some other languages, which provide syntax for constructors. Most Perl classes use new as the name for their constructor:

my $file = File→new(...);

Methods :

Method is a subroutine that operates on an object. 

In Perl, methods are simply subroutines that is defined inside a class's package. 

Methods are always written to receive the object as their first argument.

Attributes :

Each class can define its attributes. When we instantiate an object, we assign values to those attributes. For example, every File object has a path. Attributes are sometimes called properties.

Inheritance : 

Inheritance lets you create a specialized version of an existing class. Inheritance lets the new class reuse the methods and attributes of another class.

For example, we could create an File::MP3 class which inherits from File. An File::MP3 is-a more specific type of File. All mp3 files are files, but not all files are mp3 files.

We often refer to inheritance relationships as parent-child or super-class/subclass relationships. Sometimes we say that the child has an is-a relationship with its parent class.

File is a super-class of File::MP3, and File::MP3 is a subclass of File.

package File::MP3;

use parent 'File';

Overriding :

• Overriding methods and method resolution
• Inheritance allows two class to share code. By default, every method in the parent class is also available in the child. 
• The child can explicitly override a parent's method to provide its own implementation. 

Object Oriented PERL by Example :

So far we have walked through the theories , now we will do the object oriented programming using PERL .
In the below example we create the class "Student" . The "new" is the constructor and "DESTROY" is the destructor of the class.
We have three methods : setName , setSurname and setRoll to assign Name, Surname and Roll-No to each student.
The method "display" is to printout the rerecords of a student . 
Here goes the code :

In the below code we create two student objects from the above class :

Once we execute the code we get the below output :

Inheritance Example :

In the next code we will exemplify the Inheritance. Here the derived class is "intern" whose parent class is "student".

Here goes the inheritance class :

Now we create the objects of this class in the below example :
Once we execute the code we get the below output :

Creating Class Using Moose Package :

We have a PERL package , Moose.pm which is available from CPAN Network . We can use the module and create PERL objects in the easy way. Using moose we can declare the class i the below way.

 

And we can use it to create objects in the below fashion :

Once we execute the codes we get the below output :

The Moose.pm can be Installed in your Ubuntu System Easily . See the below Video :

The Entire Article is Well Narrated in the below video :

Courtesy : Image by Jae Rue from Pixabay