Extending an Object in Perl

Question

I've got a base object called RuleObject and an object that inherits from that called RuleObjectString. I have a new method in RuleObjectString that I want to call in my code that uses that object. But I get the error. 'Can't locate object method "compare" via package "RuleObject" at ./testobject.pl line 10.' But I'm not creating a RuleObject. I'm creating a RuleObjectString. What am I doing wrong here?

testobject.pl

  1 #! /usr/bin/perl
  2
  3 use strict;
  4
  5 use RuleObjectString;
  6
  7 my $s = RuleObjectString->new();
  8 $s->value('stuff goes here');
  9
 10 if ($s->compare('stuff')){
 11         print "MATCH!\n";
 12 }else{
 13         print "no match :(\n";
 14 }

RuleObject.pm

package RuleObject;

our @ISA = qw/Exporter/;
our @EXPORT = qw/new/;

use strict;

sub new{
        my $class = shift;

        my $self;
        $self->{value} = undef;

        bless $self;
        return $self;
}

sub value{
        my $self = shift;
        my $value = shift;
        if ($value){
                $self->{value} = $value;
        }else{
                return $self->{value};
        }
}

RuleObjectString.pm

package RuleObjectString;

our @ISA = qw/RuleObject/;
our @EXPORT = qw/compare/;

use strict;

sub compare{
        my $self = shift;
        my $compareto = shift;

        return $self->value() =~ /$compareto/;
}

Answer 1

I think jmcneirney is on the right track. In your RuleObject constructor, you say

bless $self;

which is the same as

bless $self, __PACKAGE__;

or

bless $self, 'RuleObject'

but what you want is for the object to blessed as a RuleObjectString. So what you want to do is say

bless $self, $class

Now

RuleObject->new()
RuleObjectString->new()

will both call the same constructor, but the object returned by the first call will be blessed as a RuleObject and the second object will be blessed as a RuleObjectString.

Answer 2

This is 2012, so you should consider using proper OOP solutions instead of reinventing the wheel all over again.

By using Moose, the solution would look something like this (untested):

RuleObject.pm

package RuleObject;
use Moose;

has 'value' => ( isa => 'Str', is => 'rw', required => 0, default => '' );

1;

RuleObjectString.pm

package RuleObjectString;
use Moose;

extends 'RuleObject';

sub compare {
    my $self      = shift;
    my $compareto = shift;

    return $self->value =~ /$compareto/;
}

1;

Simple! :)