Since I don't really know what you're doing, I've made minimal changes to your OPed code (but even so, please pay close attention to the Anonymonk's wise advice here and here). Try something like this:

c:\@Work\Perl>perl -wMstrict -le
"{ package ProcessData;
   ;;
   use warnings;
   use strict;
   use Carp qw(croak);
   ;;
   sub new {
     my ($pkg) = $_[0];
     bless {
       _dispatch_table => {},
       }, $pkg;
     }
   ;;
   sub add_subroutine {
     if($_[1] && $_[2]) {
       if(ref($_[2]) eq \"CODE\") {
         ${$_[0]->{_dispatch_table}}{$_[1]} = $_[2];
         }
       else {
         croak qq{non-CODE reference '$_[2]' passed to add_subroutine(
+)};
         }
       }
     else {
       croak \"Insufficient arguments passed to add_subroutine(). \";
       }
   }
   ;;
   sub process_data {
     my $self = shift;
     ;;
     die qq{no dispatch given} unless @_;
     my $dispatch = shift;
     die qq{unknown dispatch '$dispatch'}
       unless exists $self->{_dispatch_table}{$dispatch};
     ;;
     return $self->{_dispatch_table}{$dispatch}->(@_);
   }
   ;;
   sub process_locations {
     my $self = shift;
     return $self->process_data('locations', @_);
     }
   ;;
   }
 ;;
 use warnings;
 use strict;
 ;;
 my $pd = ProcessData->new();
 ;;
 $pd->add_subroutine('locations', \&get_locations);
 ;;
 $pd->process_locations(qw(here there everywhere));
 ;;
 sub get_locations { print qq{we got stuff: @_} }
"
we got stuff: here there everywhere
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