package Food::Product;
use strict;
use LEOCHARRE::Class2; # you do this your way
use vars qw/$errstr/;
__PACKAGE__->make_accessor_setget(qw/isle stock errst/);

sub new {
   my($class,$arg)=@_;
   $arg 
      or $errstr = "Missing valid arg"
      and return;
   return { name => $arg }, $class;
}

sub sell {
   my($self,$count)=@_;
   $count 
      or $self->errstr('missing how much to sell ammount')
      and return;

   my $now = $self->stock
      or $self->errstr('no stock left to sell from')
      and return;

   my $left_over = ( $now - $count ) ... some other rationalle
   $self->stock($left_over);
}