Abstract Class in Perl OOP

Perl Object Oriented Programming – Part 11

Perl Course

Foreword: In this part of the series I talk about what is known as abstract class and abstract method in Perl.

By: Chrysanthus Date Published: 26 Sep 2015

Introduction

This is part 11 of my series, Perl Object Oriented Programming. In this part of the series I talk about what is known as abstract class and abstract method in Perl. You should have read the previous parts of the series before reaching here; this is a continuation.

Abstract Method
An abstract method is a method in the parent class that does not have the method body. The method body is given to the overriding method in the derived class. The method should be used only in the derived class; it should not be used in the parent class.

Abstract Class
An abstract class is one having an abstract method. An abstract class is normally not useful. However I give the reason for the coding of abstract classes below. It is the derived classes that are usually used. Read and try the following program:

use strict;

    {package Calculator;

        sub new
            {
                my $class = $_[0];
                bless {}, $class;
            }

        sub add;
    }

    {package ChildCalculator;

        @ChildCalculator::ISA = ("Calculator");

        sub add
            {
                my $sum = $_[1] + $_[2];
                return $sum;
            }
    }

    my $childObj = ChildCalculator->new();
    my $result = $childObj->add(2,3);
    print $result;

In the program, the add() method is the abstract method and the parent class is the abstract class. In the parent class description above, the add() method declaration, does not have the parentheses.

When the add() function is called by the instantiated object, $_[0] is the reference to the object (not used above),  $_[1] is the first argument (e.g. 2 above) and $_[2] is the second argument (e.g. 3 above).

Reason for Abstract Class
You may write a class today; you know the method, but you have not yet decided on the method implementation. In that case you create the abstract class. In future you implement the method. In some cases, the method might even be implemented by a different person. It is also possible that with time, the implementation code may be changed; in that case, the (super) class structure is left intact and not affected.

That is it for this part of the series.

Chrys

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