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]

SEE ALSO

       Perl::Critic::Pulp, Perl::Critic,
       Perl::Critic::Policy::Compatibility::ConstantLeadingUnderscore,
       Perl::Critic::Policy::ValuesAndExpressions::ProhibitConstantPragma,
       Perl::Critic::Policy::Modules::RequirePerlVersion

       constant, "Constant Functions" in perlsub

HOME PAGE

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

COPYRIGHT

       Copyright 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2019, 2021 Kevin
       Ryde

       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.

       You should have received a copy of the GNU General Public License along with Perl-Critic-
       Pulp.  If not, see <http://www.gnu.org/licenses/>.

perl v5.32.1                         Perl::Critic::Policy::Compatibility::ConstantPragmaHash(3pm)