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Kevin Ryde


Perl::Critic::Policy::CodeLayout::RequireTrailingCommaAtNewline - comma at end of list at newline


This policy is part of the Perl::Critic::Pulp add-on. It asks you to put a comma at the end of a list etc when it ends with a newline,

    @array = ($one,
              $two     # bad

    @array = ($one,
              $two,    # ok

This makes no difference to how the code runs, so the policy is low priority and under the "cosmetic" theme (see "POLICY THEMES" in Perl::Critic).

The idea is to make it easier when editing the code since you don't have to remember to add a comma to a preceding item when extending or re-arranging lines.

If the closing bracket is on the same line as the last element then no comma is required. It can be be present if desired, but is not required.

    $hashref = { abc => 123,
                 def => 456 };   # ok

Parens around an expression are not a list, so nothing is demanded in for instance

    $foo = (
            + 2        # ok, an expression not a list

But a single element paren expression is a list when it's in an array assignment or a function or method call.

    @foo = (
            + 2        # bad, list of one value

    @foo = (
            + 2,       # ok

Return Statement

A return statement with a single value is considered an expression so a trailing comma is not required.

    return ($x
            + $y    # ok

Whether such code is a single-value expression or a list of only one value depends on how the function is specified. There's nothing in the text (nor even at runtime) which would say for sure.

It's handy to included parens around a single-value expression to make it clear some big arithmetic is all part of the return, especially if you can't remember precedence levels. In such an expression a newline before the final ")" can help keep a comment together with a term for a cut and paste, or not lose a paren if commenting the last line, etc. So for now the policy is lenient. Would an option be good though?

Here Documents

An exception is made for a single expression ending with a here-document. This is slightly experimental, and might become an option, but the idea is that a newline is necessary for a here-document within parens and so shouldn't demand a comma.

    foo(<<HERE      # ok
    some text

This style is a little unusual but some people like the whole here-document at the place its string result will expand. If the code is all on one line (see "<<EOF" in perlop) then trailing comma considerations don't apply. But both forms work and so are a matter of personal preference.

    some text

Multiple values still require a final comma. Multiple values suggests a list and full commas guards against forgetting to add a comma if extending or rearranging.

        <<HERE      # bad


If you don't care about trailing commas like this you can as always disable from .perlcriticrc in the usual way (see "CONFIGURATION" in Perl::Critic),



except_function_calls (boolean, default false)

If true then function calls and method calls are not checked, allowing for instance

    foo (
      2     # ok under except_function_calls

The idea is that if foo() takes only two arguments then you don't want to write a trailing comma as it might suggest something more could be added.

Whether you write calls spread out this way is a matter of personal preference. If you do then enable except_function_calls with the following in your .perlcriticrc file,



Perl::Critic::Pulp, Perl::Critic, Perl::Critic::Policy::CodeLayout::RequireTrailingCommas

Other Ways to Do It

This policy is a variation of CodeLayout::RequireTrailingCommas. That policy doesn't apply to function calls or hashref constructors, and you may find its requirement for a trailing comma in even one-line lists like @x=(1,2,) too much.




Copyright 2009, 2010, 2011, 2012, 2013, 2014, 2015 Kevin Ryde

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