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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.
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