inheritance

[Peter Scott]

At 03:51 PM 2/19/03 -0800, nkuipers wrote:
>Hello,
>
>I've been playing around with inheritance and I've got a question.  Let's say
>the parent class is called BIO::Basic and the child class is called
>BIO::Annotate, and each class is in a separate file.
>
>Parent constructor is as follows:
>
>sub new {
>         my $caller = shift;
>         my $type = ref($caller) || $caller;
>         my $self = { id       => 'no value',
>                      desc     => 'no value',
>                      seq      => 'no value',
>                      alphabet => 'no value',
>                      profile  => {},
>                      @_ };
>.
>.
>.
>bless $self, $type;
>}
>
>Child constructor is as follows:
>
>sub new {
>         my $type = shift;
>         my $self = {};
>         $self->{bogus_key} = BIO::Basic->new(@_);
>         bless $self, $type;
>}
>
>If I just call $self = BIO::Basic->new(@_), then Annotate objects cannot use
>Basic methods.  Addition of the {super} key in Annotate's self allows access
>to Basic methods in the driver script, as in:
>
>$annotate_object->{bogus_key}->parent_method();
>
>Am I missing something here?  Isn't there a simpler way?  I guess I'm used to
>the inheritance of java.  I got the above approach from
>
>http://www.perldoc.com/perl5.6/pod/perlbot.html


The problem with learning from a Baog O' Tricks page is that some 
fundamentals got glossed over.  (Get Conway's book.)  In this case 
you've missed the way that inheritance is done in Perl using @ISA.  (In 
fact, perlbot ought to be updated to use "use base", which is better.)

Inheritance is easier, much easier.  Here's the child:

package BIO::Annotate;
use strict;
use warnings;
use base qw(BIO::Basic);

sub new {
   my $caller = shift;
   my type = ref($caller) || $caller;
   my $self = $caller->SUPER::new(@_);
   # anything else you want to do with $self
   return $self;
}

SUPER is documented in perlobj.

What you did is object "delegation".  There is a raging controversy 
among O-O purists about when the best time to use this is.  But it's 
not what you were looking for.

--
Peter Scott
Pacific Systems Design Technologies
http://www.perldebugged.com/