$keysort = $canonical ? sub { $a cmp $b } : undef;
 
        if ($self->{sort_by}) {
            $keysort = ref($self->{sort_by}) eq 'CODE' ? $self->{sort_by}
                     : $self->{sort_by} =~ /\D+/       ? $self->{sort_by}
                     : sub { $a cmp $b };
        }
 
        

 
sub sort_by {
    $_[0]->{sort_by} = defined $_[1] ? $_[1] : 1;
    $_[0];
}