The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.


Perl::Critic::Policy::Subroutines::ProhibitExcessComplexity - Minimize complexity by factoring code into smaller subroutines.


This Policy is part of the core Perl::Critic distribution.


All else being equal, complicated code is more error-prone and more expensive to maintain than simpler code. The first step towards managing complexity is to establish formal complexity metrics. One such metric is the McCabe score, which describes the number of possible paths through a subroutine. This Policy approximates the McCabe score by summing the number of conditional statements and operators within a subroutine. Research has shown that a McCabe score higher than 20 is a sign of high-risk, potentially untestable code. See for some discussion about the McCabe number and other complexity metrics.

The usual prescription for reducing complexity is to refactor code into smaller subroutines. Mark Dominus book "Higher Order Perl" also describes callbacks, recursion, memoization, iterators, and other techniques that help create simple and extensible Perl code.


The maximum acceptable McCabe can be set with the max_mccabe configuration item. Any subroutine with a McCabe score higher than this number will generate a policy violation. The default is 20. An example section for a .perlcriticrc:

  max_mccabe = 30


  "Everything should be made as simple as possible, but no simpler."

                                                  -- Albert Einstein

Complexity is subjective, but formal complexity metrics are still incredibly valuable. Every problem has an inherent level of complexity, so it is not necessarily optimal to minimize the McCabe number. So don't get offended if your code triggers this Policy. Just consider if there might be a simpler way to get the job done.


Jeffrey Ryan Thalhammer <>


Copyright (c) 2005-2011 Imaginative Software Systems. All rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of this license can be found in the LICENSE file included with this module.