Perl inheritance through ISA - perl

Question

Question regarding inheritance in Perl using #ISA:
Input - 3 files: one is a main script, two containing parent & child packages, correspondingly:
main:
#!/usr/bin/perl
use child qw(parent_or_child_function srictly_parent_function);
parent_or_child_function();
srictly_parent_function();
parent.pm:
package parent;
sub srictly_parent_function
{
print "this is strictly parent function\n";
}
sub parent_or_child_function
{
print "this is parent function which can be inherited\n";
}
1;
child.pm:
package child;
our #ISA = 'parent';
use Exporter qw(import);
#EXPORT_OK = qw(parent_or_child_function srictly_parent_function);
sub parent_or_child_function
{
print "this is child function that replaced parent's\n";
}
1;
Output is:
$main
this is child function that replaced parent's
Undefined subroutine &child::srictly_parent_function called at main line 6.
What am I doing wrong? I understand that child package doesn't have strictly_parent_function , but shouldn't child's #ISA package be searched for it?

Answer 1

Firstly, make parent actually an object.
package parent;
use strict;
use warnings;
# Constructor
sub new {
my ($proto) = #_;
my $class = ref($proto) || $proto;
my $self = {};
# Bless is what casts $self (instance of this class) as an object
return bless($self, $class);
}
sub srictly_parent_function {
my ($self) = #_;
print "this is strictly parent function\n";
}
sub parent_or_child_function {
my ($self) = #_;
print "this is parent function which can be inherited\n";
}
1;
Then with parent as an object, child can inherit
package child;
use strict;
use warnings;
# I prefer use base, as it's safer than pushing classes into #ISA
# See http://docstore.mik.ua/orelly/perl2/prog/ch31_03.htm)
use base qw(parent);
sub parent_or_child_function {
my ($self) = #_;
print "this is child function that replaced parent's\n";
}
# To give an example for accessing variables from a class.
my $variable = "WHATEVER";
sub get_variable { return $variable;}
1;
Then to test your code:
perl -e "use child; $object = child->new(); $object->parent_or_child_function();"
or to script it up properly;
# Load up child class
use child qw();
# Invoke constructor to create an instance of the class
my $object = child->new();
# Invoke function from child class
$object->parent_or_child_function();
# Get Variable
$object->get_variable();