You are viewing the version of this documentation from Perl 5.35.9. This is a development version of Perl.



perldelta - what is new for perl v5.35.9


This document describes differences between the 5.35.8 release and the 5.35.9 release.

If you are upgrading from an earlier release such as 5.35.7, first read perl5358delta, which describes differences between 5.35.7 and 5.35.8.

Core Enhancements

Subroutine signatures are no longer experimental

Introduced in Perl version 5.20.0, and modified several times since, the subroutine signatures feature (use feature 'signatures') is now no longer considered experimental. It is now considered a stable language feature and is included in the :5.36 feature bundle, enabled automatically by use v5.36, and no longer prints a warning.

use v5.36;

sub add ($x, $y) {
  return $x + $y;

Despite this, certain elements of signatured subroutines remain experimental; see below.

@_ is now experimental within signatured subs

Even though subroutine signatures are now stable, use of the default arguments array (@_) with a subroutine that has a signature remains experimental, with its own warning category. Silencing the experimental::signatures warning category is not sufficient to dismiss this. The new warning is emitted with the category name experimental::args_array_with_signatures.

Any subroutine that has a signature and tries to make use of the defaults argument array or an element thereof (@_ or $_[INDEX]), either explicitly or implicitly (such as shift or pop with no argument) will provoke a warning at compile-time:

use v5.36;

sub f ($x, $y = 123) {
  say "The first argument is $_[0]";

Use of @_ in array element with signatured subroutine is experimental
at line 4.

The behaviour of code which attempts to do this is no longer specified, and may be subject to change in a future version.

The isa operator is no longer experimental

Introduced in Perl version 5.32.0, this operator has remained unchanged since then. The operator is now considered a stable language feature and is included in the :5.36 feature bundle, enabled automatically by use v5.36.

For more detail see "Class Instance Operator" in perlop.

-g command-line flag

A new command-line flag, -g, is available. It is a simpler alias for -0777.

For more information, see "-g" in perlrun.


Downgrading a use VERSION statement to below v5.11

Attempting to issue a second use VERSION statement that requests a version lower than v5.11 when an earlier statement that requested a version at least v5.11 has already been seen, will now print a deprecation warning.

For example:

use v5.14;
say "The say statement is permitted";
use v5.8;                               # This will print a warning
print "We must use print\n";

This is because of an intended related change to the interaction between use VERSION and use strict. If you specify a version >= 5.11, strict is enabled implicitly. If you request a version < 5.11, strict will become disabled even if you had previously written use strict. This was not the previous behaviour of use VERSION, which at present will track explicitly-enabled strictness flags independently.

Code which wishes to mix versions in this manner should use lexical scoping with block syntax to ensure that the differently versioned regions remain lexically isolated.

    use v5.14;
    say "The say statement is permitted";
    use v5.8;                           # No warning is emitted
    print "We must use print\n";

Modules and Pragmata

Updated Modules and Pragmata


New Diagnostics

New Warnings

Changes to Existing Diagnostics

Internal Changes


Perl 5.35.9 represents approximately 4 weeks of development since Perl 5.35.8 and contains approximately 8,700 lines of changes across 280 files from 22 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 3,000 lines of changes to 110 .pm, .t, .c and .h files.

Perl continues to flourish into its fourth decade thanks to a vibrant community of users and developers. The following people are known to have contributed the improvements that became Perl 5.35.9:

Branislav Zahradník, Christopher Yeleighton, Dagfinn Ilmari MannsÄker, Dave Cross, David Cantrell, Hugo van der Sanden, James E Keenan, James Raspass, Karl Williamson, Leon Timmermans, Max Maischein, Michiel Beijen, Nicholas Clark, Nicolas R., Paul Evans, Renee Baecker, Ricardo Signes, Sergey Zhmylove, TAKAI Kousuke, Tomasz Konojacki, Tony Cook, Yves Orton.

The list above is almost certainly incomplete as it is automatically generated from version control history. In particular, it does not include the names of the (very much appreciated) contributors who reported issues to the Perl bug tracker.

Many of the changes included in this version originated in the CPAN modules included in Perl's core. We're grateful to the entire CPAN community for helping Perl to flourish.

For a more complete list of all of Perl's historical contributors, please see the AUTHORS file in the Perl source distribution.

Reporting Bugs

If you find what you think is a bug, you might check the perl bug database at There may also be information at, the Perl Home Page.

If you believe you have an unreported bug, please open an issue at Be sure to trim your bug down to a tiny but sufficient test case.

If the bug you are reporting has security implications which make it inappropriate to send to a public issue tracker, then see "SECURITY VULNERABILITY CONTACT INFORMATION" in perlsec for details of how to report the issue.

Give Thanks

If you wish to thank the Perl 5 Porters for the work we had done in Perl 5, you can do so by running the perlthanks program:


This will send an email to the Perl 5 Porters list with your show of thanks.


The Changes file for an explanation of how to view exhaustive details on what changed.

The INSTALL file for how to build Perl.

The README file for general stuff.

The Artistic and Copying files for copyright information.