here it is in separate files works fine:

[bobn@trc2:/home/bobn/misc]# cat subref.pl
#!/usr/bin/perl -w

use lib q/./;

use Collection;
use Sort;

my $collection = Collection->new({ 'sorter' => \&Sort::mysorter });

$collection->doit('here is something');

[bobn@trc2:/home/bobn/misc]# cat Collection.pm 
        package Collection;

        my $self = {}; 
        sub new
        {
                my ($class, $options) = @_;
                $self->{sorter} = $options->{sorter};
                bless $self, $class; 
        }

        sub doit
        {
                my ($self, $stuffToSort ) = @_;
                print "in doit: $stuffToSort\n";
                $self->{sorter}->($stuffToSort);
                print "in doit: $stuffToSort\n";
        }
        1;
[bobn@trc2:/home/bobn/misc]# cat Sort.pm 
package Sort;

sub mysorter
{
        print "in mysorter, @_\n";
} 
1;
[bobn@trc2:/home/bobn/misc]# ./subref.pl
in doit: here is something
in mysorter, here is something
in doit: here is something
[download]

All code given here is UNTESTED unless otherwise stated.

--Bob Niederman, http://bob-n.com