OOD overriding problem

[whn]

Dear experts,

Below is small pieces of OO perl codes. The calling sequence is not what I expected.

Base Class (base.pm):

package base;

use strict;
use warnings;

sub new {
  my ($obj, $testArgs, $prodName) = @_;
  print "In base.pm..new()\n";
  my $class = ref($obj) || $obj;
  my $this  = {};
  bless $this, $class;
  return $this;
}

sub basePrepare {
  my ($this) = @_;
  print "In base.pm..basePrepare(), calling subroutine1()\n";
  $this->subroutine1();
};

sub subroutine1 {
  my ($this) = @_;
  print "In base.pm..subroutine1()\n";
}

1;
[

Derived class (derived.pm):

package derived;

use strict;
use warnings;
use lib './';
use base;
our @ISA = "base";

sub new {
  my ($obj, $testArgs) = @_;
  print "In derived.pm..new()\n";
  my $class = ref($obj) || $obj;
  my $this  = base->new();
  bless $this, $class;
  return $this;
}

sub prepare {
  my ($this) = @_;
  print "In derived.pm..prepare(), calling subroutine1()\n";
  $this->subroutine1();
};

sub subroutine1 {
  my ($this) = @_;
  print "In derived.pm..subroutine1()\n";
}

1;

And the main codes (test.pl):

#! /usr/bin/perl

use strict;
use warnings;
use derived;

my $obj = derived->new();
print "$0..To call base.pm..basePrepare()\n";
$obj->basePrepare();
print "$0..To call derived.pm..prepare()\n";
$obj->prepare();
exit;

Test run:

% ./test.pl
In derived.pm..new()
In base.pm..new()
./test.pl..To call base.pm..basePrepare()
In base.pm..basePrepare(), calling subroutine1()
[COLOR=red][b]In derived.pm..subroutine1()[/b][/color]
./test.pl..To call derived.pm..prepare()
In derived.pm..prepare(), calling subroutine1()
In derived.pm..subroutine1()

My question:

I expect that base.pm..basePrepare() would call base.pm..subroutine1(). However, it actually calls In derived.pm..subroutine1() instead.

Could someone please tell me
1) whether my understanding is incorrect?
OR
2) whether my implementation is incorrect?

Many thanks!!

 

[1DMF]

You're constructor in the derived module looks strange to me.

you're making $this = a reference to another object and then blessing it as it's own object?

That's not how I inherit a superclass's attributes, i use this...

sub new {
    
    # class variable
    my $class = shift;

    # instantiate superclass helper object
    my $helper = MySuperClass->new();
    
    # object attributes
    my $self = {
       
        THIS_ATTRIBUTE => 'a value',             
        [b]%{$helper}[/b]             
        
    };
     
    # Bless the data structure, making it a true object
    bless ($self,$class);

    # Return the object to the calling program.
    return $self;
}

But i'm not sure that will sort out the method call issue.

This looks like an overriding issue, i don't beleive perl handles overloading/ridding per sae , so input arguments don't create overloading, as it would in other languages.

The instantiated object is 'derived' and it contains a subroutine1 , I guess perl sees that and so runs it.

If you want a particular function to run from the superclass via the @ISA system array, make sure it isn't called the same in any other module that makes up the entire object.

That's what I'd do at least to test if it resolves the issue.

Then you can look into how perl handles overriding (or perhaps doesn't) and at least give you an angle to come at it from!

Just my pennies worth, hope it helps.





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[whn]

Thank you, DMF. I need a bit more time to digest it.

Thanks again.