Programming Perl, 3rd Edition

Efficiency

While most of the work of programming may be simply getting your program working properly, you may find yourself wanting more bang for the buck out of your Perl program. Perl's rich set of operators, data types, and control constructs are not necessarily intuitive when it comes to speed and space optimization. Many trade-offs were made during Perl's design, and such decisions are buried in the guts of the code. In general, the shorter and simpler your code is, the faster it runs, but there are exceptions. This section attempts to help you make it work just a wee bit better.

If you want it to work a lot better, you can play with the Perl compiler backend described in Chapter 18, or rewrite your inner loop as a C extension as illustrated in Chapter 21.

Note that optimizing for time may sometimes cost you in space or programmer efficiency (indicated by conflicting hints below). Them's the breaks. If programming was easy, they wouldn't need something as complicated as a human being to do it, now would they?

Time Efficiency

• Use hashes instead of linear searches. For example, instead of searching through @keywords to see if $_ is a keyword, construct a hash with:

  my %keywords;
  for (@keywords) {
      $keywords{$_}++;
  }

  Then you can quickly tell if $_ contains a keyword by testing $keyword{$_} for a nonzero value.

• Avoid subscripting when a foreach or list operator will do. Not only is subscripting an extra operation, but if your subscript variable happens to be in floating point ...