archon has asked for the wisdom of the Perl Monks concerning the following question:

basically, i want to instantiate an object of the base class (Foo).then i want to instantiate an object of the subclass (Foo::Bar). i want the subclass object to know about the object data of the superclass object.

for some reason, the following feels dirty to me.. can anyone suggest a better way?: 

package Foo;

use strict;

sub erf {
  my ($self) = shift;
  print $self->name();
}

sub new {
  my ($proto, $args) = @_;
  my $class = ref($proto) || $proto;
  my $self = {};
  if (ref($args) eq 'HASH') {
    if (exists $args->{'name'}) {
      $self->{'_name'} = $args->{'name'};
    } else {
      return undef;
    }
  } else {
    $self->{'_name'} = $args->name();
  }
  bless $self, $class;
  return $self;
}

sub name {
  my ($self) = shift;
  return $self->{'_name'};
}

package Foo::Bar;

use strict;

@Foo::Bar::ISA = qw/Foo/;

sub doit {
  my ($self) = shift;
  $self->erf();
}

package main;

use strict;

my %hash = (name => 'Homer');
my $foo = Foo->new(\%hash);
my $bar = Foo::Bar->new($foo);
$bar->doit();

[download]

Edit: 2001-03-03 by neshura

Replies are listed 'Best First'.
Re (tilly) 1: Inheriting object data
by tilly (Archbishop) on Feb 17, 2001 at 03:05 UTC
    Erm, I don't see why you want two objects. Just create an object in class Foo::Bar by calling the new method that it inherits from Foo.

    If you want to, you can actually give Foo::Bar a new() method which does some stuff and is a wrapper around SUPER::new (which is a "fake" method to get at your parent's new method).

[reply]

      i must be missing something.. i thought i _was_ creating an object in class Foo::Bar by calling the new method that it inherits from Foo. however, that thought seems incongruous with "I don't see why you want two objects." are you saying i don't want to create an object from the base class? i suppose that is an option.

      i am open to any solution that lets me use the subclass with the data that i fed the base class without having to give this data to the base class.

[reply]
        Just construct an object in Foo::Bar directly without making something in Foo first and pass it the data. That object "is-a" Foo as well.

        In other words my point is that the object you create in the base class Foo just seems to be a redundant object. It isn't used, it isn't necessary. I see no reason to not just lose it and then you have no problem left.

[reply]
Re: Inheriting object data
by coreolyn (Parson) on Feb 17, 2001 at 03:28 UTC

    You haven't ..instantiate an object of the subclass (Foo::Bar) I'm not seeing a bless in there anywhere. All you have is a function that has access to Foo's method's . (Which you already have in package main).There is no true OO inheritance or subclass in Foo::Bar.

    coreolyn

[reply]
[d/l]
[select]
      Erm, I think you misread the code. Foo::Bar inherits a perfectly good new() constructor from Foo, and that constructor uses the 2-argument form of bless correctly. Therefore you do indeed have a constructor for Foo::Bar.
[reply]

        Aw hell... You know we really need another voting catagory ++, --, & doh! Thanks for pointing out da error's of me ways :)

        coreolyn
[reply]

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