Understanding Inheritance in Perl

Object-oriented programming has very good and useful concept called inheritance. Inheritance simply means that properties and methods of a parent class will be available to the child classes. So you don't have to write the same code again and again, you can just inherit a parent class.

For example, we can have a class Employee, which inherits from Person. This is referred to as an "isa" relationship because an employee is a person. Perl has a special variable, @ISA, to help with this. @ISA governs (method) inheritance.

Following are the important points to be considered while using inheritance −

• Perl searches the class of the specified object for the given method or attribute, i.e., variable.
• Perl searches the classes defined in the object class's @ISA array.
• If no method is found in steps 1 or 2, then Perl uses an AUTOLOAD subroutine, if one is found in the @ISA tree.
• If a matching method still cannot be found, then Perl searches for the method within the UNIVERSAL class (package) that comes as part of the standard Perl library.
• If the method still has not found, then Perl gives up and raises a runtime exception.

So to create a new Employee class that will inherit methods and attributes from our Person class, we simply code as follows: Keep this code into Employee.pm.

#!/usr/bin/perl
package Employee;
use Person;
use strict;
our @ISA = qw(Person);       # inherits from Person

Now Employee Class has all the methods and attributes inherited from Person class and you can use them as follows: Use main.pl file to test it −

#!/usr/bin/perl
use Employee;
$object = new Employee( "Mohammad", "Saleem", 23234345);
# Get first name which is set using constructor.
$firstName = $object->getFirstName();
print "Before Setting First Name is : $firstName\n";
# Now Set first name using helper function.
$object->setFirstName( "Mohd." );
# Now get first name set by helper function.
$firstName = $object->getFirstName();
print "After Setting First Name is : $firstName\n";

When we execute above program, it produces the following result −

First Name is Mohammad
Last Name is Saleem
SSN is 23234345
Before Setting First Name is : Mohammad
Before Setting First Name is : Mohd.