#!/usr/bin/perl

{
  package a;
  
  sub new {
    my $invocation = shift();
    my $class = ref($invocation) || $invocation;
    my $self  = {};
    my $bless = bless($self, $class);
    return $bless;
  }

  sub a1 {
    my $self = shift();
    print "hi I'm a\n!";
  }
  
  sub a2 {
    my $self = shift();
    $self->a1();
  }
}
{
  package b;
  
  @ISA = qw(a);
  
  sub a1 {
    my $self = shift();
    print "hi I'm b\n";
  }
  
  1;
}

my $a = new a();
my $b = new b();

$b->a2();
$a->a2();