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perldelta - what is new for perl v5.35.4


This document describes differences between the 5.35.3 release and the 5.35.4 release.

If you are upgrading from an earlier release such as 5.35.2, first read perl5353delta, which describes differences between 5.35.2 and 5.35.3.

Core Enhancements

defer blocks

This release adds support for defer blocks, which are blocks of code prefixed by the defer modifier. They provide a section of code which runs at a later time, during scope exit.

For more information, see "defer blocks" in perlsyn.

Unicode 14.0 is supported

See https://www.unicode.org/versions/Unicode14.0.0/ for details.

SIGFPE no longer deferred

Floating-point exceptions are now delivered immediately, in the same way as other "fault"-like signals such as SIGSEGV. This means one has at least a chance to catch such a signal with a $SIG{FPE} handler, e.g. so that die can report the line in perl that triggered it.

Stable boolean tracking

The "true" and "false" boolean values, often accessed by constructions like !!0 and !!1, as well as being returned from many core functions and operators, now remember their boolean nature even through assignment into variables. The new function isbool() in Scalar::Util can check whether a value has boolean nature.

This is likely to be useful when interoperating with other languages or data-type serialisation, among other places.

Incompatible Changes

There are no changes intentionally incompatible with 5.35.3. If any exist, they are bugs, and we request that you submit a report. See "Reporting Bugs" below.

Performance Enhancements

  • We now probe for compiler support for C11 thread local storage, and where available use this for "implicit context" for XS extensions making API calls for a threaded Perl build. This requires fewer function calls at the C level than POSIX thread specific storage. We continue to use the the pthreads approach if the C11 approach is not available.

    Configure run with the defaults will build an unthreaded Perl (which is slightly faster), but most operating systems ship a threaded Perl.

Modules and Pragmata

Updated Modules and Pragmata

  • attributes has been upgraded from version 0.33 to 0.34.

  • B has been upgraded from version 1.82 to 1.83.

  • B::Deparse has been upgraded from version 1.57 to 1.58.

  • Devel::Peek has been upgraded from version 1.31 to 1.32.

  • Exporter has been upgraded from version 5.76 to 5.77.

  • ExtUtils::ParseXS has been upgraded from version 3.43 to 3.44.

  • ExtUtils::Typemaps has been upgraded from version 3.43 to 3.44.

  • feature has been upgraded from version 1.67 to 1.68.

  • Hash::Util::FieldHash has been upgraded from version 1.22 to 1.23.

  • IO has been upgraded from version 1.47 to 1.48.

  • Module::CoreList has been upgraded from version 5.20210820 to 5.20210920.

  • mro has been upgraded from version 1.25_001 to 1.26.

  • Opcode has been upgraded from version 1.53 to 1.54.

  • Pod::Html has been upgraded from version 1.32 to 1.33.

  • Scalar::Util has been upgraded from version 1.56 to 1.56_001.

  • Storable has been upgraded from version 3.24 to 3.25.

  • Text::Tabs has been upgraded from version 2021.0804 to 2021.0814.

  • Text::Wrap has been upgraded from version 2021.0804 to 2021.0814.

  • threads::shared has been upgraded from version 1.63 to 1.64.

  • Unicode::Collate has been upgraded from version 1.30 to 1.31. Experimental support for EBCDIC has been added.

  • Unicode::UCD has been upgraded from version 0.77 to 0.78.

  • UNIVERSAL has been upgraded from version 1.13 to 1.14.

  • warnings has been upgraded from version 1.53 to 1.54.

  • XS::APItest has been upgraded from version 1.18 to 1.19.

  • XS::Typemap has been upgraded from version 0.18 to 0.19.


Changes to Existing Documentation

We have attempted to update the documentation to reflect the changes listed in this document. If you find any we have missed, open an issue at https://github.com/Perl/perl5/issues.

Additionally, the following selected changes have been made:


  • Updated to discourage the use of the /d regexp modifier.


The following additions or changes have been made to diagnostic output, including warnings and fatal error messages. For the complete list of diagnostic messages, see perldiag.

New Diagnostics

New Errors

  • Can't "%s" out of a defer block

    (F) An attempt was made to jump out of the scope of a defer block by using a control-flow statement such as return, goto or a loop control. This is not permitted.

New Warnings

  • defer is experimental

    (S experimental::defer) The defer block modifier is experimental. If you want to use the feature, disable the warning with no warnings 'experimental::defer', but know that in doing so you are taking the risk that your code may break in a future Perl version.

Changes to Existing Diagnostics

"unexpected constant lvalue entersub entry via type/targ %d:%d" now has a panic prefix

This makes it consistent with other checks of internal consistency when compiling a subroutine.

Removed a number of diagnostics

Commit 6a3871b339 removes many diagnostics that have been removed from the perl core across many years.

Platform-Specific Notes

keys %ENV on VMS returns consistent results

On VMS entries in the %ENV hash are loaded from the OS environment on first access, hence the first iteration of %ENV requires the entire environment to be scanned to find all possible keys. This initialisation had always been done correctly for full iteration, but previously was not happening for %ENV in scalar context, meaning that scalar %ENV would return 0 if called before any other %ENV access, or would only return the count of keys accessed if there had been no iteration.

These bugs are now fixed - %ENV and keys %ENV in scalar context now return the correct result - the count of all keys in the environment.

Internal Changes

  • Perl_ptr_table_clear has been deleted. This has been marked as deprecated since v5.14.0 (released in 2011), and is not used by any code on CPAN.

  • Added new boolean macros and functions. See "Stable boolean tracking" for related information and perlapi for documentation.

    • sv_setbool

    • sv_setbool_mg

    • SvIsBOOL

  • Added 4 missing functions for dealing with RVs:

    • sv_setrv_noinc

    • sv_setrv_noinc_mg

    • sv_setrv_inc

    • sv_setrv_inc_mg

  • xs_handshake()'s two failure modes now provide distinct messages.


Perl 5.35.4 represents approximately 4 weeks of development since Perl 5.35.3 and contains approximately 64,000 lines of changes across 540 files from 19 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 49,000 lines of changes to 310 .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 5.35.4:

Aristotle Pagaltzis, Chris 'BinGOs' Williams, Dagfinn Ilmari Mannsåker, Dan Book, David Mitchell, Felipe Gasper, Hugo van der Sanden, James E Keenan, Karen Etheridge, Karl Williamson, Matthew Horsfall, Nicholas Clark, Paul Evans, Richard Leach, TAKAI Kousuke, Todd Rinaldo, Tomasz Konojacki, Tomoyuki Sadahiro, Tony Cook, Unicode Consortium.

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 https://github.com/Perl/perl5/issues. There may also be information at http://www.perl.org/, the Perl Home Page.

If you believe you have an unreported bug, please open an issue at https://github.com/Perl/perl5/issues. 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.