sub Instance_Var ($) {
    my $package=__PACKAGE__;
    my ($var)=@_;
    my $accessor_name = "$package\::$var";
    my $acc = sub {
        my $t = shift;
        $t->{$var}=$_[0] if @_;
        $t->{$var};
    };

    # Now install our anonymous subroutine as $package::$var
    no strict 'refs';
    *{ $accessor_name } = $acc;
}