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Perl-Version-Bumper-0.277
⭐ Starred 3 / Perl::Version::Bumper::Rationale

NAME

Perl::Version::Bumper::Rationale - or: How I Learned to Stop Worrying and Love the Bump

TL;DR:

Forget about use strict; use warnings;, just use VERSION;!

use VERSION

use VERSION lexically enables all features available in the requested version as defined by the feature pragma, disabling any features not in the requested version's feature bundle.

Feature bundles:

  • enable new, stable features;

  • disable old, deprecated features;

  • have a lexical effect.

    (Meaning that a use VERSION at the top of the file will apply to the entire file)

Line 0 vs. Line 1

Perl has an extreme focus on backwards compatibility. A sensibly-written Perl script produced in the year 2001 should work just fine on a Perl published in 2026.

When reading a file, starting from line 0, perl starts in "compatibility-mode" (this is the :default feature bundle). This is roughly equivalent to Perl as it was in version 5.008.

Contrary to many other programming languages, Perl requires the developer to opt in to the new features of the languague.

You can do this on line 1, simply by writing (for example):

use v5.36;

Which is equivalent to:

require v5.36;
use strict;
use warnings;
use feature 'say';
use feature 'state';
use feature 'current_sub';
use feature 'fc';
use feature 'lexical_subs';
use feature 'signatures';
use feature 'isa';
use feature 'bareword_filehandles';
use feature 'bitwise';
use feature 'evalbytes';
use feature 'postderef_qq';
use feature 'unicode_eval';
use feature 'unicode_strings';
no feature 'indirect';
no feature 'multidimensional';

As time passes, and more features are added to the language, picking a more recent version gets you a better Perl.

Unfeatures

The :default feature bundle only enables backwards-compatibility features. These are ancient Perl features that were eventually deemed undesirable, and that can be disabled (via the no feature pragma). These are also called "unfeatures".

They started to appear in Perl v5.32 (indirect), and started being disabled in the v5.36 feature bundle. As time went on, more unfeatures were added (or removed, depending on how you look at it).

As soon as a new unfeature is created, the :default bundle implicitly includes it.

Three Steps Summary

  1. Pick a version of the Perl language that is the most suited for your use case.

  2. Add the appropriate use VERSION line at the top of all of your Perl programs and modules.

    (Starting with version 1.154 (October 2024), Perl::Critic won't count this as a violation of Perl::Critic::Policy::Modules::RequireExplicitPackage.)

  3. Profit!

Picking a Perl version

There are different use cases, which can lead to choosing a different feature bundle for your project.

Personal code

For personal code, you can basically pick whatever version the operating system you plan to run your code on provides. Or whichever version supports your pet feature.

Company code

Private or company code is only limited by the version of Perl used internally. It might be the stock perl from the operating system selected by the organization. It might be a perl compiled specifically for that purpose.

Given how easy it is to compile your own Perl, internal company or personal code can actually run on the bleeding edge!

Open source Perl application

Know your target. Pick a version of Perl that is packaged by default with the currently supported releases of the operating system you target.

Given that the last two versions of Perl are officially maintained, you can expect the current version of you operating system to ship with a fairly recent version of Perl (that is, either the latest stable release, or the one before that).

For Windows, that's basically the latest version of Strawberry Perl (https://strawberryperl.com/).

CPAN modules

Again, know your target. As explained above, any recent operating system will be at most two versions behind.

At the Perl Toolchain Summit 2023 in Lyon, the toolchain authors agreed that: "No new release of a distribution in the Perl toolchain will specify a minimum perl prerequisite version (whether configure, build, runtime, or test) that has been available for less than ten years."

Most CPAN modules do not need to be more extreme than toolchain ones.

There are valid exceptions, though: Perl::Version::Bumper, for example, is written in the v5.10 dialect of Perl, for maximal utility. The point is to help developers make the jump from really ancient versions of Perl to more modern ones.

REFERENCES

AUTHOR

Philippe Bruhat (BooK) <book@cpan.org>.

COPYRIGHT

Copyright 2024-2026 Philippe Bruhat (BooK), all rights reserved.

LICENSE

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.