package Simple;
use vars qw ($AUTOLOAD);
use Carp;

{
my $version = "1.0.0";

# object data

my %_attr_data = 
  (
  "_debug" => [ 0, "r" ], 
  "_version" => [ $version, "r" ], 
  );

sub _accessible
  {
  my ($self, $attr, $mode) = @_;
  $_attr_data{$attr}[1] =~ /$mode/
  }

sub _default_for
  {
  my ($self, $attr) = @_;
  $_attr_data{$attr}[0];
  }

sub _standard_keys
  {
  keys %_attr_data;
  }

sub new
  {
  my ($caller, %arg) = @_;
  my $caller_is_obj = ref($caller);
  my $class = $caller_is_obj || $caller;
  my $self = bless {}, $class;
  foreach my $membername ( $self->_standard_keys() )
    {
    my ($argname) = ($membername =~ /^_(.*)/);
    if (exists $arg{$argname})
      { $self->{$membername} = $arg{$argname} }
    elsif ($caller_is_obj)
      { $self->{$membername} = $caller->{$membername} }
    else
      { $self->{$membername} = $self->_default_for($membername) }
    }
  return $self;
  }

sub yip
  {
  my ($self) = @_;
  print "yip!\n";
  }

sub AUTOLOAD
  {
  no strict "refs";
  my ($self, $newval) = @_;

  if ($AUTOLOAD =~ /.*::get(_\w+)/ && $self->_accessible($1,'r'))
    {
    my $attr_name = $1;
    *{$AUTOLOAD} = sub { return $_[0]->{$attr_name} };
    return $self->{$attr_name}
    }

  if ($AUTOLOAD =~ /.*::set(_\w+)/ && $self->_accessible($1,'rw'))
    {
    my $attr_name = $1;
    *{$AUTOLOAD} = sub { $_[0]->{$attr_name} = $_[1] };
    $self->{$1} = $newval;
    return
    }

  carp "no such method: $AUTOLOAD";
  }

sub DESTROY
  {
  }
}

1;

##</code><code>##

package Simple::Child;

use Carp;
use lib ".";
use Simple;
@ISA = qw (Simple);
use vars qw ($AUTOLOAD);

{
my %_attr_data = 
  (
  "_foo" => [ "bar", "rw" ],
  );

sub _accessible
  {
  my ($self, $attr, $mode) = @_;
  return $_attr_data{$attr}[1] =~ /$mode/ if exists $_attr_data{$attr};
  return $self->SUPER::_accessible($attr,$mode);
  }

sub _default_for
  {
  my ($self, $attr) = @_;
  return $_attr_data{$attr}[0] if exists $_attr_data{$attr};
  return $self->SUPER::_default_for($attr);
  }

sub _standard_keys
  {
  my ($self) = @_;
  ($self->SUPER::_standard_keys(), keys %_attr_data);
  }

sub yip
  {
  my ($self) = @_;
  print "yip! yip!\n";
  }
}

1;

##</code><code>##

#!/usr/bin/perl -w

use strict;
use lib ".";
use Simple::Child;

my $thingy = new Simple::Child;

print $thingy->get_foo . "\n" . $thingy->get_version . "\n";

$thingy->yip();