package UnderScore;
use Carp;
sub TIESCALAR {
    my $class = shift;
    my $dummy;
    return bless \$dummy => $class;
} 
sub FETCH { croak "Read access to \$_ forbidden"  } 
sub STORE { croak "Write access to \$_ forbidden" } 
sub unimport { tie($_, _     _PACKAGE_     _) }
sub import { untie $_ } 
tie($_, _     _PACKAGE_     _) unless tied $_;
1;