strict "refs" has no influence whatsoever on method calls.

It's probably failing on $s->{_classes}, but we'd have to see the calling code to know for sure.

If I comment out the line the for loop, the script exits without error. But here is the calling code:

  $s->_run_chain('_run_processes');
[download]

$PM = "Perl Monk's";
$MCF = "Most Clueless Friar Abbot Bishop Pontiff Deacon Curate Priest Vicar";
$nysus = $PM . ' ' . $MCF;
Click here if you love Perl Monks

Then $s is probably a class name, not an object.

Based on our previous conversations, I will guess that you want to call every implementation of a method in the inheritance tree instead of only the most-specific?

There is probably a module on CPAN somewhere for this, and perhaps another monk will be able to cite it, but I do not know. I suggest trying: (untested)

sub _run_chain {
  my $s = shift;
  my $sub = shift;
  for my $r ( @{ $s->{_classes} }  ) {
    $s->($r.'::'.$sub) if $s->can($r.'::'.$sub);
  }
}
[download]

This will override the method search to directly call each method. Because Perl is a highly dynamic language, I have removed the no strict and expect that this will not contain a symref.

Your problem was not in this code at all — it was looking up $sub as a class method for each $r and then, finding that a sub by that name does indeed exist in that package, invoking it as a class method even though it is written as an instance method. You have been actually calling into File::Collector::Date::Classifie...::$sub and that is where the error is occurring. I think that running your code under the debugger would give you a nice backtrace showing the successful call and the unsuccessful dereference. (Simply run the script with perl -d and type c at the prompt to let the program run.)

And another comment on OO design: subclass relationships and the package hierarchy are independent in Perl. It might make more sense to have a File::Collector::Sorter::Date::ByMonth mixin class that groups files by month, or your sorting classes may all make more sense somewhere in your application's local package hierarchy.

What is the value of $s ?

It's a big hairy object. I have the expected values for $r and $sub.

$PM = "Perl Monk's";
$MCF = "Most Clueless Friar Abbot Bishop Pontiff Deacon Curate Priest Vicar";
$nysus = $PM . ' ' . $MCF;
Click here if you love Perl Monks

That's what you think it is. What your error message says is it's the string "File::Collector::Date::Classifie"...