sub foo : get
{
  my $self = shift;
  return $self->{_foo};
}

sub foo : set
{
  my $self  = shift;
  my $value = shift;
  
  die "foo is a integer field!\n"
    unless $value =~ /[+-]?[0-9]+/;
  
  $self->{_foo} = $value;
}