package Parent;

sub new {
    my $invocant = shift;
    my $class = ref($invocant) || $invocant;
    my $self = {};
    bless $self, $class;
    $self->init(@_);
    return $self;
}

sub init {
    return; # or die to force child class to do something here
}

package Child;
use base qw(Parent);

sub init {
    # do child specific stuff;
}