NAME

Perl::Critic::Policy::Compatibility::ConstantPragmaHash - new enough "constant" module for multiple constants

DESCRIPTION

This policy is part of the "Perl::Critic::Pulp" add-on. It requires that when you use the hash style multiple constants of "use constant" that you explicitly declare either Perl 5.8 or "constant" 1.03 or higher.

    use constant { AA => 1, BB => 2 };       # bad

    use 5.008;
    use constant { CC => 1, DD => 2 };       # ok

    use constant 1.03;
    use constant { EE => 1, FF => 2 };       # ok

    use constant 1.03 { GG => 1, HH => 2 };  # ok

The idea is to keep you from using the multi-constant feature in code which might run on Perl 5.6, or might in principle still run there. On that basis this policy is under the "compatibility" theme (see "POLICY THEMES" in Perl::Critic).

If you declare "constant 1.03" then the code can still run on Perl 5.6 and perhaps earlier if the user gets a suitably newer "constant" module from CPAN. Or of course for past compatibility just don't use the hash style at all!

Details

A version declaration must be before the first multi-constant, so it's checked before the multi-constant is attempted and gives an obscure error.

    use constant { X => 1, Y => 2 };       # bad
    use 5.008;

A "require" for the perl version is not enough since "use constant" is at "BEGIN" time, before plain code.

    require 5.008;                         # doesn't run early enough
    use constant { X => 1, Y => 2 };       # bad

But a "require" within a "BEGIN" block is ok (a past style, still found occasionally).

    BEGIN { require 5.008 }
    use constant { X => 1, Y => 2 };       # ok

    BEGIN {
      require 5.008;
      and_other_setups ...;
    }
    use constant { X => 1, Y => 2 };       # ok

Currently "ConstantPragmaHash" pays no attention to any conditionals within the "BEGIN", it assumes any "require" there always runs. It could be tricked by some obscure tests but hopefully anything like that is rare or does the right thing anyway.

A quoted version number like

    use constant '1.03';    # no good

is no good, only a bare number is recognised by "use" and acted on by ConstantPragmaHash. A string like that goes through to "constant" as if a name to define (which you'll see it objects to as soon as you try run it).

Drawbacks

Explicitly adding required version numbers in the code can be irritating, especially if other things you're doing only run on 5.8 up anyway. But declaring what code needs is accurate, it allows maybe for backports of modules, and explicit versions can be grepped out to create or check Makefile.PL or Build.PL prereqs.

As always if you don't care about this or if you only ever use Perl 5.8 anyway then you can disable "ConstantPragmaHash" from your .perlcriticrc in the usual way (see "CONFIGURATION" in Perl::Critic),

    [-Compatibility::ConstantPragmaHash]

HOME PAGE

<http://user42.tuxfamily.org/perl-critic-pulp/index.html>

COPYRIGHT

Perl-Critic-Pulp is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

Perl-Critic-Pulp is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.