sub can
{
    my ($class, $name) = @_;

    return if $name eq 'constant';
    my ($error, $val) = constant($name);

    return if $error;
    my $sub = sub () { $val };

    {
        no strict 'refs';
        *{ $class . '::' . $name } = $sub;
    }

    return $sub;
}