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POWhy does Perl::Critic dislike using shift to populate subroutine variables?
 

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  1. POWhy does Perl::Critic dislike using shift to populate subroutine variables?
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    <p>Lately, I've decided to start using <a href="http://search.cpan.org/perldoc?Perl::Critic" rel="nofollow noreferrer">Perl::Critic</a> more often on my code. After programming in Perl for close to 7 years now, I've been settled in with most of the Perl best practices for a long while, but I know that there is always room for improvement. One thing that has been bugging me though is the fact that <a href="http://search.cpan.org/perldoc?Perl::Critic" rel="nofollow noreferrer">Perl::Critic</a> doesn't like the way I unpack @_ for subroutines. As an example:</p> <pre><code>sub my_way_to_unpack { my $variable1 = shift @_; my $variable2 = shift @_; my $result = $variable1 + $variable2; return $result; } </code></pre> <p>This is how I've always done it, and, as its been discussed on both PerlMonks and Stack Overflow, its <a href="https://stackoverflow.com/questions/1328411/is-shift-evil-for-processing-perl-subroutine-parameters">not necessarily evil</a> either.</p> <p>Changing the code snippet above to...</p> <pre><code>sub perl_critics_way_to_unpack { my ($variable1, $variable2) = @_; my $result = $variable1 + $variable2; return $result; } </code></pre> <p>...works too, but I find it harder to read. I've also read Damian Conway's book <a href="http://oreilly.com/catalog/9780596001735" rel="nofollow noreferrer">Perl Best Practices</a> and I don't really understand how my preferred approach to unpacking falls under his suggestion to avoid using <code>@_</code> directly, as <a href="http://search.cpan.org/perldoc?Perl::Critic" rel="nofollow noreferrer">Perl::Critic</a> implies. I've always been under the impression that Conway was talking about nastiness such as:</p> <pre><code>sub not_unpacking { my $result = $_[0] + $_[1]; return $result; } </code></pre> <p>The above example is bad and hard to read, and I would never ever consider writing that in a piece of production code.</p> <p>So in short, why does <a href="http://search.cpan.org/perldoc?Perl::Critic" rel="nofollow noreferrer">Perl::Critic</a> consider my preferred way bad? Am I really committing a heinous crime unpacking by using shift?</p> <p>Would this be something that people other than myself think should be brought up with the <a href="http://search.cpan.org/perldoc?Perl::Critic" rel="nofollow noreferrer">Perl::Critic</a> maintainers?</p>
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    1. COAt a guess, Perl::Critic doesn't like it because it works using "magic," such as `shift` operating on `@_` when no variable is specified. It would help to know which Perl::Critic rule wants to change this, though.
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    2. COAs an aside, if you use the list form of assignment, then Komodo Edit/IDE can tell you the arguments to a subroutine.
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    3. COThanks Brad, I didn't realize that. I'm an old ViM user so usually I ignore what Komodo Edit is putting in front of me, but I've always wondered how that worked.
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