How to do basic inheritance in Perl OO?

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

plz explain it, if this makes any sense, i hope u'll understand what im trying to do here.

package AGENT;

sub new
{
  ....
}

sub Callme
{
  ....
}

1;
[download]

package TOOLS;

use AGENT;

sub new : AGENT::new # should initialize the AGENT::new
{
  ....
}

sub Callme
{
  ....
}

1;
[download]


use TOOLS;

my $tools = new TOOLS;

$tools->SUPER::Callme(); # it should call the AGENT::Callme
$tools->Callme();
[download]

Does perl has SUPER to call the base class if i ahave to packages in one perl module
sorry for type errors.

2006-11-11 Retitled by g0n, as per Monastery guidelines
Original title: 'Advanced OOP'

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Re: How to do basic inheritance in Perl OO? by Joost (Canon) on Nov 06, 2006 at 18:58 UTC
`my $tools = new TOOLS; $tools->SUPER::Callme(); # it should call the AGENT::Callme $tools->Callme();` [download] If you need to do this outside of the TOOLS package, you're doing something very wrong. The code that's using the $tools object should not need to know or care what $tool's inheritance chain is. If your TOOL's Callme() cannot work without also using AGENT::Callme(), then you should set it up so that AGENT::Callme is called automatically from TOOL::Callme, not rely on the user to do it for you. Same goes for new(). `package TOOLS; sub new { my ($package) = @_; my $self = $package->SUPER::new(); # do other stuff, or remove this whole sub if # you're not acutally doing anything in this # method and let AGENT's new() method do all the work. return $self; } sub Callme { my ($self) = @_; $self->SUPER::Callme(); # do stuff. }` [download] As explained by someone else above, you can't (and shouldn't) use SUPER outside of the package that is the subclass. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re: How to do basic inheritance in Perl OO? by samtregar (Abbot) on Nov 06, 2006 at 18:37 UTC
There's a number of problems in your code. First off, as has already been pointed out, you need to set @ISA to establish inheritence, either directly or with 'use base'. Second - this isn't valid Perl syntax: `sub new : AGENT::new` I don't know what you thought that would do, but I doubt it's going to help! Finally, this won't work in most cases: `$tools->SUPER::Callme();` In Perl, SUPER only works inside the sub-class's package. It looks like it should be evaluating $tool's @ISA but in fact it's evaluating @__PACKAGE__::ISA. In most cases this is what you want since you don't usually allow clients to skip up the inheritence tree, but in your example that would appear to be the case. I suggest you slow down and pick up a good book on object-oriented Perl - "Programming Perl" or "Object Oriented Perl" are both good. You need to learn the basics before you start free-stylin'. -sam	[reply] [d/l] [select]
Re: How to do basic inheritance in Perl OO? by Sidhekin (Priest) on Nov 06, 2006 at 18:22 UTC
You want `use base 'AGENT';` or something like `@TOOLS::ISA = ('AGENT');` `use AGENT;` on its own just loads (if necessary) and imports from (if any exports exist in) AGENT. Update: Yikes, that's @ISA, not @isa, of course. `print "Just another Perl ${\(trickster and hacker)},"` The Sidhekin proves Sidhe did it!	[reply] [d/l] [select]