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Monthly Archives: September 2007

Writing configurable Perl::Critic Policies.

As of Perl::Critic 1.07, I would like to discourage the creation of constructors for Policies. Instead, I would encourage the use of P::C::Policy::initialize_if_enabled(). The reasoning is twofold.

One, this allows initialization to be deferred to the point where we know that the policy is going to be used. P::C::PolicyFactory always instantiates every Policy that it can find. It is up to the P::C::Config object to filter that set down. Primarily, this is an issue for Policies which dynamically load other modules.

Two, this method enables the Policy to decide for itself whether it should be enabled. This means that a Policy that depends upon a module that might not be present can remove itself from the set that violates() gets called on, thus speeding things up because it isn’t being called on every PPI::Element.

This originated from Chris Dolan’s work on the Perl Foundation grant to create the remaining Policies that can be implemented that enforce one of the ideas in PBP. Specifically, for Documentation::PodSpelling, but this change has been made to all the configurable core Policies. In particular, this helps CodeLayout::RequireTidyCode.

Differences from a constructor other than the obvious first parameter:

  1. The configuration is passed in as a hashref and not a hash an instance of Perl::Critic::PolicyConfig (corrected 2009/5/16).
  2. initialize_if_enabled() returns a boolean specifying whether the Policy should be enabled.

This is how the two above policies bow out.

This post originally appeared at use.perl.org.

Lesson of the day: Readonly, Exporter, and subroutine sigils

They don’t get along.

As of the recent 1.07 release, Perl::Critic, has started using Readonly to be more more self-compliant with Perl Best Practices. We had been avoiding use of constant for the reasons described in the book, but had not been willing to add the Readonly dependency until now.

The Perl::Critic coding standard has been to use sigils for subroutines in @EXPORT_OK, etc. and import lists, but Exporter treats them as optional. And, in fact, there’s code that strips them off (line 47 in v5.58). I haven’t figured out the commonality, but in a few environments, this fails spectacularly. Once we removed the subroutine sigils from everywhere, the problems have gone.

Explicitness: 0, Keyboard laziness: 1.

This post originally appeared at use.perl.org.