I would like to ++ this node, but I won't. And my reason is that I find this node sloppy and occasionally gives bad advice, and it also doesn't follow its own advice.

Besides the good points made by Aristotle and gjb I have a couple of my own:

• Documentation references
  This being a very dense tutorial, the perhaps most important missing thing is references to further reading. I would also like to see some sort of reference to documents, nodes, benchmarks, or something else that backs up certain statements. If this was done, the author would've found out what aragorn pointed out.
• &-style subroutine calls
  The code always have the ampersand in subroutine calls. This is definately not to recommend. The first line of code in the node almost made me not read further, since it uses &testA without parentheses. But then I remembered that it was about optimizations and since this form of subroutine call was explicitly made available as an optimization feature, I thought it might be intentional. But I doubt it, since it was done without any comment on it, and the ampersand is used throughout the whole node.
• Shows but doesn't explain
  It tries to teach references in five seconds. This is bad, imho. References is something that should be understood before used, but this thread doesn't explain them at all. It just says how to use them. This can (and will) encourage people to use techniques they don't understand, and that will undoubtedly lead to unholy code. A simple reference to perlreftut would have been very nice to see here, so people know where to read up on the subject after getting a little demostration on how and why you might want to use them.
• foreach my $Key ( keys %{$rf_h} ) {
  Wasn't the point to not have to copy the whole (large) hash? Here the keys are copied anyway. For large hashes, this has a memory impact. A simple test on w2k gave me a memory difference of about 4.5 MB for a hash with 100000 five char long keys. In this case it would be preferable to do

    my $h;
    while ($h = each %$rf_h) { ... }
  [download]

  which doesn't have any significant efficiency loss speed-wise (about 3% according to my preliminary benchmark).
• open (FLHD,"$0") ;
  Where is the check? What are the quotes doing there?
• my $fl_data ; 1 while( sysread(FLHD, $fl_data , 1024*8 , length($fl_data) ) ) ;
  On first iteration $fl_data will be undef, and length(undef) emits warning. A side-note: perhaps you want to make sure that sysread() failed due to eof and nothing else? This is checked through the return value of sysread().
• while (my $line = <FLHD>) {
  Wasn't lexicals like this one supposed to be outside the loop, per own suggestion?

ihb

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