use strict;

package Foo;

sub new {
	my $class = shift;
	my $self = bless {}, $class;
	$self->_init;
	return $self;
}

sub _init {
	my $self = shift;
	$self->{important_flag} = 1;
}

package Foo::Bar;
use base 'Foo';

sub new {
	my $class = shift;
	my $self = $class->SUPER::new(@_);
	$self->_init('har har har');
	return $self;
}

sub _init {
	my $self = shift;
	$self->{ext_prop} = $_[0];
}

package main;
use Data::Dumper;

my $foo = Foo->new;
my $bar = Foo::Bar->new;
print Dumper([$foo, $bar]);

__END__

$VAR1 = [
          bless( {
                   'important_flag' => 1
                 }, 'Foo' ),
          bless( {
                   'ext_prop' => 'har har har'
                 }, 'Foo::Bar' )
        ];