# third option:
sub process {
 my ($data, $filter) = @_;

 # lengthy calculations with $data here ... 
 # in that length calculation you have to decide
 # if you continue with your calculation:

 if ($filter) {
   for (@$data){
     if ($filter->($_)) {
       push @$data, other_lengthy_calculation($_);
     }
   }
 }
 else {
   for (@$data){
     push @$data, other_lengthy_calculation($_);
   }
 }

[download]
Sure, it involves more lines (12 now instead of ~8 lines), but why you would deliberately want to throw a costly sub call in a loop? If @$data is huge and $filter is usually empty, using '$filter = sub {1;}' could quickly become a bottleneck.

I agree with the OP, use of a sub {1;} to avoid 'undefined' doesn't make much sense (to me anyway), unless the application interface guarantees that parameter to be a sub reference all the time. But that's not clear from the code snippet.

In reply to Re^4: what is sub {1;} by ruzam
in thread what is sub {1;} by mlgvalt

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