man > perl5380delta(1)

PERL5380DELTA(1)                  Perl Programmers Reference Guide                  PERL5380DELTA(1)

NAME
       perl5380delta - what is new for perl v5.38.0

DESCRIPTION
       This document describes differences between the 5.36.0 release and the 5.38.0 release.

Core Enhancements
   New "class" Feature
       A new experimental syntax is now available for defining object classes, where per-instance
       data is stored in "field" variables that behave like lexicals.

           use feature 'class';

           class Point
           {
               field $x;
               field $y;

               method zero { $x = $y = 0; }
           }

       This is described in more detail in perlclass.  Notes on the internals of its implementation
       and other related details can be found in perlclassguts.

       This remains a new and experimental feature, and is very much still under development. It
       will be the subject of much further addition, refinement and alteration in future releases.
       As it is experimental, it yields warnings in the "experimental::class" category.  These can
       be silenced by a "no warnings" statement.

           use feature 'class';
           no warnings 'experimental::class';

   Unicode 15.0 is supported
       See <https://www.unicode.org/versions/Unicode15.0.0/> for details.

   Deprecation warnings now have specific subcategories
       All deprecation warnings now have their own specific deprecation category which can be
       disabled individually. You can see a list of all deprecated features in perldeprecation, and
       in warnings. The following list is from warnings:

                +- deprecated ----+
                |                 |
                |                 +- deprecated::apostrophe_as_package_separator
                |                 |
                |                 +- deprecated::delimiter_will_be_paired
                |                 |
                |                 +- deprecated::dot_in_inc
                |                 |
                |                 +- deprecated::goto_construct
                |                 |
                |                 +- deprecated::smartmatch
                |                 |
                |                 +- deprecated::unicode_property_name
                |                 |
                |                 +- deprecated::version_downgrade

       It is still possible to disable all deprecation warnings in a single statement with

           no warnings 'deprecated';

       but now is possible to have a finer grained control. As has historically been the case these
       warnings are automatically enabled with

           use warnings;

   %{^HOOK} API introduced
       For various reasons it can be difficult to create subroutine wrappers for some of perls
       keywords. Any keyword which has an undefined prototype simply cannot be wrapped with a
       subroutine, and some keywords which perl permits to be wrapped are in practice very tricky to
       wrap.  For example "require" is tricky to wrap, it is possible but doing so changes the stack
       depth, and the standard methods of exporting assume that they will be exporting to a package
       at certain stack depth up the stack, and the wrapper will thus change where functions are
       exported to unless implemented with a great deal of care. This can be very awkward to deal
       with.

       Accordingly we have introduced a new hash called "%{^HOOK}" which is intended to facilitate
       such cases. When a keyword supports any kind of special hook then the hook will live in this
       new hash. Hooks in this hash will be named after the function they are called by, followed by
       two underbars and then the phase they are executed in, currently either before or after the
       keyword is executed.

       In this initial release we support two hooks "require__before" and "require__after". These
       are provided to make it easier to perform tasks before and after a require statement.

       See perlvar for more details.

   PERL_RAND_SEED
       Added a new environment variable "PERL_RAND_SEED" which can be used to cause a perl program
       which uses "rand" without using srand() explicitly or which uses srand() with no arguments to
       be repeatable.  See perlrun. This feature can be disabled at compile time by passing

           -Accflags=-DNO_PERL_RAND_SEED

       to Configure during the build process.

   Defined-or and logical-or assignment default expressions in signatures
       The default expression for a subroutine signature parameter can now be assigned using the
       "//=" or "||=" operators, to apply the defaults whenever the caller provided an undefined or
       false value (respectively), rather than simply when the parameter is missing entirely.  For
       more detail see the documentation in perlsub.

   @INC Hook Enhancements and $INC and INCDIR
       The internals for @INC hooks have been hardened to handle various edge cases and should no
       longer segfault or throw assert failures when hooks modify @INC during a require operation.
       As part of this we now ensure that any given hook is executed at most once during a require
       call, and that any duplicate directories do not trigger additional directory probes.

       To provide developers more control over dynamic module lookup, a new hook method "INCDIR" is
       now supported. An object supporting this method may be injected into the @INC array, and when
       it is encountered in the module search process it will be executed, just like how INC hooks
       are executed, and its return value used as a list of directories to search for the module.
       Returning an empty list acts as a no-op. Note that since any references returned by this hook
       will be stringified and used as strings, you may not return a hook to be executed later via
       this API.

       When an @INC hook (either "INC" or "INCDIR") is called during require, the $INC variable will
       be localized to be the value of the index of @INC that the hook came from. If the hook wishes
       to override what the "next" index in @INC should be it may update $INC to be one less than
       the desired index ("undef" is equivalent to -1). This allows an @INC hook to completely
       rewrite the @INC array and have perl restart its directory probes from the beginning of @INC.

       Blessed CODE references in @INC that do not support the "INC" or "INCDIR" methods will no
       longer trigger an exception, and instead will be treated the same as unblessed coderefs are,
       and executed as though they were an "INC" hook.

   Forbidden control flow out of "defer" or "finally" now detected at compile-time
       It is forbidden to attempt to leave a "defer" or "finally" block by means of control flow
       such as "return" or "goto". Previous versions of perl could only detect this when actually
       attempted at runtime.

       This version of perl adds compile-time detection for many cases that can be statically
       determined. This may mean that code which compiled successfully on a previous version of perl
       is now reported as a compile-time error with this one. This only happens in cases where it
       would have been an error to actually execute the code anyway; the error simply happens at an
       earlier time.

   Optimistic Eval in Patterns
       The use of "(?{ ... })" and "(??{ ... })" in a pattern disables various optimisations
       globally in that pattern. This may or may not be desired by the programmer. This release adds
       the "(*{ ... })" equivalent. The only difference is that it does not and will never disable
       any optimisations in the regex engine. This may make it more unstable in the sense that it
       may be called more or less times in the future, however the number of times it executes will
       truly match how the regex engine functions.  For example, certain types of optimisation are
       disabled when "(?{ ... })" is included in a pattern, so that patterns which are O(N) in
       normal use become O(N*N) with a "(?{ ... })" pattern in them. Switching to "(*{ ... })" means
       the pattern will stay O(N).

   REG_INF has been raised from 65,536 to 2,147,483,647
       Many regex quantifiers used to be limited to "U16_MAX" in the past, but are now limited to
       "I32_MAX", thus it is now possible to write "/(?:word){1000000}/" for example.  Note that
       doing so may cause the regex engine to run longer and use more memory.

   New API functions optimize_optree and finalize_optree
       There are two new API functions for operating on optree fragments, ensuring you can invoke
       the required parts of the optree-generation process that might otherwise not get invoked
       (e.g. when creating a custom LOGOP).  To get access to these functions, you first need to set
       a "#define" to opt-in to using these functions.

         #define PERL_USE_VOLATILE_API

       These functions are closely tied to the internals of how the interpreter works, and could be
       altered or removed at any time if other internal changes make that necessary.

   Some "goto"s are now permitted in "defer" and "finally" blocks
       Perl version 5.36.0 added "defer" blocks and permitted the "finally" keyword to also add
       similar behaviour to "try"/"catch" syntax.  These did not permit any "goto" expression within
       the body, as it could have caused control flow to jump out of the block.  Now, some "goto"
       expressions are allowed, if they have a constant target label, and that label is found within
       the block.

         use feature 'defer';

         defer {
           goto LABEL;
           print "This does not execute\n";
           LABEL: print "This does\n";
         }

   New regexp variable ${^LAST_SUCCESSFUL_PATTERN}
       This allows access to the last succesful pattern that matched in the current scope.  Many
       aspects of the regex engine refer to the "last successful pattern". The empty pattern reuses
       it, and all of the magic regex vars relate to it. This allows access to its pattern. The
       following code

           if (m/foo/ || m/bar/) {
               s//PQR/;
           }

       can be rewritten as follows

           if (m/foo/ || m/bar/) {
               s/${^LAST_SUCCESSFUL_PATTERN}/PQR/;
           }

       and it will do the exactly same thing.

   Locale category LC_NAME now supported on participating platforms
       On platforms that have the GNU extension "LC_NAME" category, you may now use it as the
       category parameter to "setlocale" in POSIX to set and query its locale.

Incompatible Changes
   readline() no longer clears the stream error and eof flags
       readline(), also spelled "<>", would clear the handle's error and eof flags after an error
       occurred on the stream.

       In nearly all cases this clear is no longer done, so the error and eof flags now properly
       reflect the status of the stream after readline().

       Since the error flag is no longer cleared calling close() on the stream may fail and if the
       stream was not explicitly closed, the implicit close of the stream may produce a warning.

       This has resulted in two main types of problems in downstream CPAN modules, and these may
       also occur in your code:

       •   If  your code reads to end of file, and then rebinds the handle to a new file descriptor,
           previously since the eof flag wasn't set you could continue to read from the stream.  You
           now need to clear the eof flag yourself with "$handle->clearerr()" to continue reading.

       •   If your code encounters an error on the stream while reading  with  readline()  you  will
           need  to  call  "$handle->clearerr"  to continue reading.  The one case this occurred the
           underlying file descriptor was marked non-blocking, so the read() system call was failing
           with "EAGAIN", which resulted in the error flag being set on the stream.

       The only case where error and eof flags continue to cleared on error is when reading from the
       child process for glob() in miniperl.  This allows it to correctly  report  errors  from  the
       child process on close().  This is unlikely to be an issue during normal perl development.

       [GH #20060 <https://github.com/Perl/perl5/issues/20060>]

   "INIT" blocks no longer run after an exit() in "BEGIN"
       "INIT"  blocks  will  no longer run after an exit() performed inside of a "BEGIN". This means
       that the combination of the "-v" option and the "-c" option  no  longer  executes  a  compile
       check as well as showing the perl version. The "-v" option executes an exit(0) after printing
       the version information inside of a "BEGIN" block, and the "-c" check is implemented by using
       "INIT" hooks, resulting in the "-v" option taking precedence.

       [GH        #1537        <https://github.com/Perl/perl5/issues/1537>]        [GH        #20181
       <https://github.com/Perl/perl5/issues/20181>]

   Syntax errors no longer produce "phantom error messages"
       Generally perl will continue parsing the source code even after encountering a compile error.
       In many cases this is helpful, for instance with misspelled variable names it is  helpful  to
       show  as  many examples of the error as possible. But in the case of syntax errors continuing
       often produces bizarre error messages and may  even  cause  segmentation  faults  during  the
       compile  process.  In  this  release  the  compiler  will  halt  at  the  first  syntax error
       encountered. This means that any code expecting to see the specific error messages we used to
       produce will be broken. The error that is emitted will be one of the diagnostics that used to
       be produced, but in some cases some messages that used to  be  produced  will  no  longer  be
       displayed.

       See "Changes to Existing Diagnostics" for more details.

   utf8::upgrade()
       Starting  in this release, if the input string is "undef", it remains "undef".  Previously it
       would be changed into a defined, zero-length string.

   Changes to "thread-safe" locales
       Perl 5.28 introduced "thread-safe" locales on systems  that  supported  them,  namely  modern
       Windows,  and systems supporting POSIX 2008 locale operations.  These systems accomplish this
       by having per-thread locales, while continuing to support the older global locale  operations
       for code that doesn't take the steps necessary to use the newer per-thread ones.

       It  turns  out  that  some POSIX 2008 platforms have or have had buggy implementations, which
       forced perl to not use them.  The "${^SAFE_LOCALES}" scalar  variable  contains  0  or  1  to
       indicate  whether or not the current platform is considered by perl to have a working thread-
       safe implementation.  Some implementations have been fixed already, but  FreeBSD  and  Cygwin
       have  been  newly  discovered to be sufficiently buggy that the thread-safe operations are no
       longer used by perl, starting in this release.  Hence, "${^SAFE_LOCALES}" is now 0 for  them.
       Older  versions  of perl can be configured to avoid these buggy implementations by adding the
       Configure option "-DNO_POSIX_2008_LOCALE".

       And v5.38 fixes a bug in all previous perls that led to locales not being fully  thread-safe.
       The  first  thread  that  finishes  caused the main thread (named "thread0") to revert to the
       global locale in effect  at  startup,  discarding  whatever  the  thread's  locale  had  been
       previously  set  to.   If  any  other  thread  had  switched  to the global locale by calling
       switch_to_global_locale() in XS code, those threads would all share the  global  locale,  and
       "thread0" would not be thread-safe.

Deprecations
   Use of "'" as a package name separator is deprecated
       Using "'" as package separator in a variable named in a double-quoted string has warned since
       5.28.   It  is now deprecated in both string interpolation and non-interpolated contexts, and
       will be removed in Perl 5.42.

   Switch and Smart Match operator
       The "switch" feature and the smartmatch operator, "~~",  were  introduced  in  v5.10.   Their
       behavior  was  significantly  changed  in v5.10.1.  When the "experiment" system was added in
       v5.18.0, switch and smartmatch were retroactively declared  experimental.   Over  the  years,
       proposals to fix or supplement the features have come and gone.

       In  v5.38.0,  we  are  declaring  the  experiment a failure.  Some future system may take the
       conceptual place of smartmatch, but it has not yet been designed or built.

       These features will be entirely removed from perl in v5.42.0.

Performance Enhancements
       •   Additional optree optimizations for common OP patterns. For example, multiple simple  OPs
           replaced  by  a  single streamlined OP, so as to be more efficient at runtime. [GH #19943
           <https://github.com/Perl/perl5/pull/19943>],                  [GH                  #20063
           <https://github.com/Perl/perl5/pull/20063>],                  [GH                  #20077
           <https://github.com/Perl/perl5/pull/20077>].

       •   Creating an anonymous sub no longer generates an "srefgen" op, the  reference  generation
           is   now   done  in  the  "anoncode"  or  "anonconst"  op,  saving  runtime.  [GH  #20290
           <https://github.com/Perl/perl5/pull/20290>]

Modules and Pragmata
   Updated Modules and Pragmata
       •   Added       the       is_tainted()       builtin       function.        [GH        #19854
           <https://github.com/Perl/perl5/issues/19854>]

       •   Added     the     export_lexically()     builtin     function    as    per    PPC    0020
           <https://github.com/Perl/PPCs/blob/main/ppcs/ppc0020-lexical-export.md>.    [GH    #19895
           <https://github.com/Perl/perl5/issues/19895>]

       •   Support   for   PPC   0018   <https://github.com/Perl/PPCs/blob/main/ppcs/ppc0018-module-
           true.md>, "use feature "module_true";" has been added to the default feature  bundle  for
           v5.38  and  later.  It  may  also be used explicitly. When enabled inside of a module the
           module does not need to return true explicitly, and in fact the return will be forced  to
           a simple true value regardless of what it originally was.

       •   Attribute::Handlers has been upgraded from version 1.02 to 1.03.

       •   attributes has been upgraded from version 0.34 to 0.35.

       •   autodie has been upgraded from version 2.34 to 2.36.

       •   B has been upgraded from version 1.83 to 1.88.

       •   B::Concise has been upgraded from version 1.006 to 1.007.

       •   B::Deparse has been upgraded from version 1.64 to 1.74.

       •   Benchmark has been upgraded from version 1.23 to 1.24.

       •   bignum has been upgraded from version 0.65 to 0.66.

       •   Carp has been upgraded from version 1.52 to 1.54.

       •   Class::Struct has been upgraded from version 0.66 to 0.68.

       •   Compress::Raw::Bzip2 has been upgraded from version 2.103 to 2.204_001.

       •   Compress::Raw::Zlib has been upgraded from version 2.105 to 2.204_001.

       •   Config::Perl::V has been upgraded from version 0.33 to 0.36.

       •   CPAN has been upgraded from version 2.33 to 2.36.

       •   Data::Dumper has been upgraded from version 2.184 to 2.188.

       •   DB_File has been upgraded from version 1.857 to 1.858.

       •   Devel::Peek has been upgraded from version 1.32 to 1.33.

       •   Devel::PPPort has been upgraded from version 3.68 to 3.71.

       •   Digest::MD5 has been upgraded from version 2.58 to 2.58_01.

       •   Digest::SHA has been upgraded from version 6.02 to 6.04.

       •   DynaLoader has been upgraded from version 1.52 to 1.54.

       •   Encode has been upgraded from version 3.17 to 3.19.

       •   encoding::warnings has been upgraded from version 0.13 to 0.14.

       •   Env has been upgraded from version 1.05 to 1.06.

       •   Errno has been upgraded from version 1.36 to 1.37.

       •   experimental has been upgraded from version 0.028 to 0.031.

       •   ExtUtils::CBuilder has been upgraded from version 0.280236 to 0.280238.

       •   ExtUtils::Install has been upgraded from version 2.20 to 2.22.

       •   ExtUtils::MakeMaker has been upgraded from version 7.64 to 7.70.

       •   ExtUtils::Miniperl has been upgraded from version 1.11 to 1.13.

       •   ExtUtils::ParseXS has been upgraded from version 3.45 to 3.51.

       •   ExtUtils::PL2Bat has been upgraded from version 0.004 to 0.005.

       •   ExtUtils::Typemaps has been upgraded from version 3.45 to 3.51.

       •   feature has been upgraded from version 1.72 to 1.82.

       •   File::Basename has been upgraded from version 2.85 to 2.86.

       •   File::Copy has been upgraded from version 2.39 to 2.41.

       •   File::Find has been upgraded from version 1.40 to 1.43.

       •   File::Glob has been upgraded from version 1.37 to 1.40.

       •   File::Spec has been upgraded from version 3.84 to 3.89.

       •   File::stat has been upgraded from version 1.12 to 1.13.

       •   FileHandle has been upgraded from version 2.03 to 2.05.

       •   Filter::Util::Call has been upgraded from version 1.60 to 1.64.

       •   GDBM_File has been upgraded from version 1.23 to 1.24.

       •   Getopt::Long has been upgraded from version 2.52 to 2.54.

       •   Hash::Util has been upgraded from version 0.28 to 0.30.

       •   HTTP::Tiny has been upgraded from version 0.080 to 0.083.

       •   I18N::Langinfo has been upgraded from version 0.21 to 0.22.

       •   IO has been upgraded from version 1.50 to 1.52.

       •   IO-Compress has been upgraded from version 2.106 to 2.204.

       •   IO::Socket::IP has been upgraded from version 0.41 to 0.41_01.

           On  DragonflyBSD,  detect  setsockopt()  not  actually  clearing  "IPV6_V6ONLY" even when
           setsockopt()            returns            success.             [cpan             #148293
           <https://rt.cpan.org/Ticket/Display.html?id=148293>]

       •   IO::Zlib has been upgraded from version 1.11 to 1.14.

       •   JSON::PP has been upgraded from version 4.07 to 4.16.

       •   libnet has been upgraded from version 3.14 to 3.15.

       •   Locale::Maketext has been upgraded from version 1.31 to 1.33.

       •   Math::BigInt has been upgraded from version 1.999830 to 1.999837.

       •   Math::BigInt::FastCalc has been upgraded from version 0.5012 to 0.5013.

       •   Math::BigRat has been upgraded from version 0.2621 to 0.2624.

       •   Math::Complex has been upgraded from version 1.5902 to 1.62.

       •   Memoize has been upgraded from version 1.03_01 to 1.16.

       •   MIME::Base64 has been upgraded from version 3.16 to 3.16_01.

       •   Module::CoreList has been upgraded from version 5.20220520 to 5.20230520.

       •   mro has been upgraded from version 1.26 to 1.28.

       •   NDBM_File has been upgraded from version 1.15 to 1.16.

       •   Net::Ping has been upgraded from version 2.74 to 2.76.

       •   ODBM_File has been upgraded from version 1.17 to 1.18.

       •   Opcode has been upgraded from version 1.57 to 1.64.

       •   overload has been upgraded from version 1.35 to 1.37.

       •   parent has been upgraded from version 0.238 to 0.241.

       •   PerlIO::via::QuotedPrint has been upgraded from version 0.09 to 0.10.

       •   Pod::Checker has been upgraded from version 1.74 to 1.75.

       •   Pod::Html has been upgraded from version 1.33 to 1.34.

       •   Pod::Usage has been upgraded from version 2.01 to 2.03.

       •   podlators has been upgraded from version 4.14 to 5.01.

       •   POSIX has been upgraded from version 2.03 to 2.13.

       •   re has been upgraded from version 0.43 to 0.44.

       •   Safe has been upgraded from version 2.43 to 2.44.

       •   Scalar::Util has been upgraded from version 1.62 to 1.63.

       •   SDBM_File has been upgraded from version 1.15 to 1.17.

       •   Socket has been upgraded from version 2.033 to 2.036.

       •   Storable has been upgraded from version 3.26 to 3.32.

       •   Sys::Hostname has been upgraded from version 1.24 to 1.25.

       •   Term::Cap has been upgraded from version 1.17 to 1.18.

       •   Test::Simple has been upgraded from version 1.302190 to 1.302194.

       •   Text::Balanced has been upgraded from version 2.04 to 2.06.

       •   threads has been upgraded from version 2.27 to 2.36.

       •   threads::shared has been upgraded from version 1.64 to 1.68.

       •   Tie::File has been upgraded from version 1.06 to 1.07.

       •   Time::HiRes has been upgraded from version 1.9770 to 1.9775.

       •   Time::Piece has been upgraded from version 1.3401 to 1.3401_01.

       •   Unicode::Normalize has been upgraded from version 1.31 to 1.32.

       •   UNIVERSAL has been upgraded from version 1.14 to 1.15.

       •   User::grent has been upgraded from version 1.03 to 1.04.

       •   User::pwent has been upgraded from version 1.01 to 1.02.

       •   utf8 has been upgraded from version 1.24 to 1.25.

       •   warnings has been upgraded from version 1.58 to 1.65.

       •   XS::APItest has been upgraded from version 1.22 to 1.32.

       •   XSLoader has been upgraded from version 0.31 to 0.32.

Documentation
   New Documentation
       perlclass

       Describes the new "class" feature.

       perlclassguts

       Describes the internals of the new "class" feature.

   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:

       perlapi

       •   Documented "hv_ksplit"

       •   Documented "hv_name_set"

       •   "hv_store" and "hv_stores" documentation have been greatly improved.

       •   Documented "gv_autoload_pv"

       •   Documented "gv_autoload_pvn"

       •   Documented "gv_autoload_sv"

       •   Documented "gv_name_set"

       •   Documented "start_subparse"

       •   Documented "SV_CHECK_THINKFIRST_COW_DROP"

       •   Documented "SV_CHECK_THINKFIRST"

       •   Documented "SvPV_shrink_to_cur"

       •   Documented "save_aelem"

       •   Documented "save_aelem_flags"

       •   Documented "save_helem"

       •   Documented "save_helem_flags"

       perldeprecation

       •   Added information about unscheduled deprecations and their categories.

       •   Added category information for existing scheduled deprecations.

       •   Added smartmatch and apostrophe as a package separator deprecation data.

       perlintern

       •   Documented "save_pushptr"

       •   Documented "save_scalar_at"

       •   Entries  have  been  added  to perlguts for the new "newAV_alloc_x", "newAV_alloc_xz" and
           *_simple functions.

       •   References to the now-defunct PrePAN service have been  removed  from  perlcommunity  and
           perlmodstyle.

       •   A section on symbol naming has been added to perlhacktips.

       •   perlexperiment has been edited to properly reference the warning categories for the defer
           block modifier and extra paired delimiters for quote-like operators.

       perlexperiment

       •   Smartmatch  has  been moved from experimental status to deprecated status.  Unfortunately
           the experiment did not work out.

       perlfunc

       •   Some wording improvements have been made for the "ucfirst", "push", "unshift" and "bless"
           functions, as well as additional examples added.

       perlhacktips

       •   A new section, "Writing safer macros" in perlhacktips has been added to discuss  pitfalls
           and solutions to using C macros in C and XS code.

       •   A  new  section,  "Choosing good symbol names" in perlhacktips, has been added to discuss
           unexpected gotchas with names.

       perlop

       •   Document the behavior of matching the empty pattern better and specify  its  relationship
           to the new "${^LAST_SUCCESSFUL_PATTERN}" properly.

       perlvar

       •   Added  a  section  on  "Scoping Rules of Regex Variables", and other wording improvements
           made throughout.

       •   Added information on the new "%{^HOOK}" interface,  and  the  new  "require__before"  and
           "require__after" hooks which it exposes.

       •   Correct   information   on   the   regex   variables   "${^PREMATCH}",   "${^MATCH}"  and
           "${^POSTMATCH}",  all  of  which  were  incorrectly  documented  due  to  an   oversight.
           Specifically they only work properly after a regex operation that used the /p modifier to
           enable them.

       •   Added   information  on  the  new  regex  variable  "${^LAST_SUCCESSFUL_PATTERN}",  which
           represents the pattern of the last successful regex match in scope.

Diagnostics
       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

       •   A  new  syntax  error has been added for the error that a "catch" block does not have its
           required variable declaration. See catch block requires a (VAR)

       •   Too many nested BEGIN blocks, maximum of %d allowed

       •   Execution of %s aborted due to compilation errors.

       •   Can't locate object method "INC", nor "INCDIR" nor string overload via package "%s" %s in
           @INC

       •   Attempt to bless into a class

           (F) You are attempting to call "bless" with a package name that is a  new-style  "class".
           This is not necessary, as instances created by the constructor are already in the correct
           class.  Instances cannot be created by other means, such as "bless".

       •   Cannot assign :param(%s) to field %s because that name is already in use

           (F)  An  attempt  was made to apply a parameter name to a field, when the name is already
           being used by another field in the same class, or one of its parent classes.  This  would
           cause a name clash so is not allowed.

       •   Cannot create class %s as it already has a non-empty @ISA

           (F)  An  attempt  was  made  to  create a class out of a package that already has an @ISA
           array, and the array is not empty.  This is not permitted, as it would lead  to  a  class
           with inconsistent inheritance.

       •   Cannot invoke a method of "%s" on an instance of "%s"

           (F)  You  tried to directly call a "method" subroutine of one class by passing in a value
           that is an instance of a different class.  This is not permitted, as the method would not
           have access to the correct instance fields.

       •   Cannot invoke method on a non-instance

           (F) You tried to directly call a "method" subroutine of a class by  passing  in  a  value
           that  is  not  an instance of that class.  This is not permitted, as the method would not
           then have access to its instance fields.

       •   Cannot '%s' outside of a 'class'

           (F) You attempted to use one of the keywords that  only  makes  sense  inside  a  "class"
           definition, at a location that is not inside such a class.

       •   Cannot reopen existing class "%s"

           (F) You tried to begin a "class" definition for a class that already exists.  A class may
           only have one definition block.

       •   Can't bless an object reference

           (F)  You  attempted  to  call  "bless"  on  a  value that already refers to a real object
           instance.

       •   can't convert empty path

           (F) On Cygwin, you called a path conversion function with an empty path.  Only  non-empty
           paths are legal.

       •   Class already has a superclass, cannot add another

           (F)  You  attempted  to  specify  a  second  superclass for a "class" by using the ":isa"
           attribute, when one is already specified.  Unlike classes  whose  instances  are  created
           with  "bless",  classes  created  via  the  "class"  keyword  cannot  have  more than one
           superclass.

       •   Class attribute %s requires a value

           (F) You specified an attribute for a class that would require a value  to  be  passed  in
           parentheses,  but did not provide one.  Remember that whitespace is not permitted between
           the attribute name and its value; you must write this as

               class Example::Class :attr(VALUE) ...

       •   Class :isa attribute requires a class but "%s" is not one

           (F) When creating a subclass using the "class" ":isa"  attribute,  the  named  superclass
           must also be a real class created using the "class" keyword.

       •   Field already has a parameter name, cannot add another

           (F)  A  field  may  have  at  most  one application of the ":param" attribute to assign a
           parameter name to it; once applied a second one is not allowed.

       •   Field attribute %s requires a value

           (F) You specified an attribute for a field that would require a value  to  be  passed  in
           parentheses,  but did not provide one.  Remember that whitespace is not permitted between
           the attribute name and its value; you must write this as

               field $var :attr(VALUE) ...

       •   Field %s is not accessible outside a method

           (F) An attempt was made to access a field variable of a class from  code  that  does  not
           appear  inside the body of a "method" subroutine.  This is not permitted, as only methods
           will have access to the fields of an instance.

       •   Field %s of "%s" is not accessible in a method of "%s"

           (F) An attempt was made to access a field variable of a class, from a method  of  another
           class  nested  inside  the  one that actually defined it.  This is not permitted, as only
           methods defined by a given class are permitted to access fields of that class.

       •   Only scalar fields can take a :param attribute

           (F) You tried to apply the ":param" attribute to an array or hash field.  Currently  this
           is not permitted.

       •   Required parameter '%s' is missing for %s constructor

           (F)  You  called the constructor for a class that has a required named parameter, but did
           not pass that parameter at all.

       •   Unexpected characters while parsing class :isa attribute: %s

           (F) You tried to specify something other than  a  single  class  name  with  an  optional
           trailing  version  number as the value for a "class" ":isa" attribute.  This confused the
           parser.

       •   Unrecognized class attribute %s

           (F) You attempted to add a named attribute to a "class" definition,  but  perl  does  not
           recognise the name of the requested attribute.

       •   Unrecognized field attribute %s

           (F)  You  attempted  to  add a named attribute to a "field" definition, but perl does not
           recognise the name of the requested attribute.

       •   ${^HOOK}{%s} may only be a CODE reference or undef

       •   Attempt to set unknown hook '%s' in %{^HOOK}

       •   Missing or undefined argument to %s via %{^HOOK}{require__before}

       •   Too many capture groups (limit is %d) in regex m/%s/

       New Warnings

       •   Unknown locale category %d

           This is a shortened form of an already existing diagnostic, for use when there is no  new
           locale being switched to.  The previous diagnostic was misleading in such circumstances.

       •   Locale '%s' is unsupported, and may crash the interpreter.

       •   Treating %s::INIT block as BEGIN block as workaround

       •   Filehandle STD%s reopened as %s only for input

       •   %s on BEGIN block ignored

       •   ADJUST is experimental

           (S  experimental::class)  This warning is emitted if you use the "ADJUST" keyword of "use
           feature 'class'".  This keyword is currently experimental and its behaviour may change in
           future releases of Perl.

       •   class is experimental

           (S experimental::class) This warning is emitted if you use the "class"  keyword  of  "use
           feature 'class'".  This keyword is currently experimental and its behaviour may change in
           future releases of Perl.

       •   Method %s redefined

           (W redefine) You redefined a method.  To suppress this warning, say

               {
                  no warnings 'redefine';
                  *name = method { ... };
               }

       •   Odd number of elements in hash field initialization

           (W misc) You specified an odd number of elements to initialise a hash field of an object.
           Hashes  are  initialised  from a list of key/value pairs so there must be a corresponding
           value to every key.  The final missing value will be filled in with undef instead.

       •   Old package separator "'" deprecated

           (W deprecated, syntax) You used the old package separator "'" in a  variable,  subroutine
           or package name.  Support for the old package separator will be removed in Perl 5.40.

       •   field is experimental

           (S  experimental::class)  This  warning is emitted if you use the "field" keyword of "use
           feature 'class'".  This keyword is currently experimental and its behaviour may change in
           future releases of Perl.

       •   method is experimental

           (S experimental::class) This warning is emitted if you use the "method" keyword  of  "use
           feature 'class'".  This keyword is currently experimental and its behaviour may change in
           future releases of Perl.

       •   Can't call destructor for 0x%p in global destruction

   Changes to Existing Diagnostics
       •   The  compiler will now stop parsing on the first syntax error it encounters. Historically
           the compiler would attempt to "skip past" the error and continue parsing so that it could
           list multiple errors. For things like undeclared variables under strict this makes sense.
           For syntax errors however it has been found that continuing tends to result in a storm of
           unrelated or bizarre errors that mostly just obscure the true error. In extreme cases  it
           can even lead to segfaults and other incorrect behavior.

           Therefore  we  have reformed the continuation logic so that the parse will stop after the
           first seen syntax error. Semantic errors like undeclared  variables  will  not  stop  the
           parse,  so  you  may still see multiple errors when compiling code. However if there is a
           syntax error it will be the last error message reported by perl and  all  of  the  errors
           that you see will be something that actually needs to be fixed.

       •   Error  messages  that  output  class or package names have been modified to output double
           quoted strings with various characters escaped so as to make the exact value clear  to  a
           reader.  The  exact  rules  on  which  characters  are  escaped  may change over time but
           currently are that printable ASCII codepoints, with the exception of  """  and  "\",  and
           unicode word characters whose codepoint is over 255 are output raw, and any other symbols
           are  escaped  much as Data::Dumper might escape them, using "\n" for newline and "\"" for
           double quotes, etc. Codepoints in the range 128-255 are always escaped as they can  cause
           trouble on unicode terminals when output raw.

           In older versions of perl the one liner

               $ perl -le'"thing\n"->foo()'

           would  output  the  following  error message exactly as shown here, with text spread over
           multiple lines because the "\n" would be emitted as a raw newline character:

               Can't locate object method "foo" via package "thing
               " (perhaps you forgot to load "thing
               "?) at -e line 1.

           As of this release we would output this instead (as one line):

               Can't locate object method "foo" via package "thing\n"
                 (perhaps you forgot to load "thing\n"?) at -e line 1.

           Notice the newline in the package name has been quoted and escaped, and  thus  the  error
           message  is  a  single  line.  The  text  is  shown  here  wrapped  to two lines only for
           readability.

       •   When package or class names in errors are very large the middle excess  portion  will  be
           elided from the message. As of this release error messages will show only up to the first
           128  characters and the last 128 characters in a package or class name in error messages.
           For example

            $ perl -le'("Foo" x 1000)->new()'

           will output the following as one line:

            Can't locate object method "new" via package "FooFooFooFooFooFooFoo
            FooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFoo
            FooFooFooFooFooFooFooFooFooFooFooFooFooFo"..."oFooFooFooFooFooFooFoo
            FooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFoo
            FooFooFooFooFooFooFooFooFooFooFooFooFoo" (perhaps you forgot to load
            "FooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFoo
            FooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFo"...
            "oFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFoo
            FooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFooFoo"?)
            at -e line 1.

           Notice the  "prefix"..."suffix"  form of the package name  in  this  case.   In  previous
           versions  of perl the complete string would have been shown making the error message over
           6k long and there was no upper limit on the length of the error message at  all.  If  you
           accidentally  used  a 1MB string as a class name then the error message would be over 2MB
           long. In this perl the upper limit should be around 2k  when  eliding  and  escaping  are
           taken into account.

       •   Removed "Complex regular subexpression recursion limit (%d) exceeded"

           The  regular expresion engine has not used recursion in some time. This warning no longer
           makes sense.

           See [GH #19636 <https://github.com/Perl/perl5/pull/19636>].

       •   Various warnings that used to produce parenthesized hints  underneath  the  main  warning
           message  and after its "location data" were chanaged to put the hint inline with the main
           message. For instance:

            Bareword found where operator expected at -e line 1, near "foo bar"
                (Do you need to predeclare foo?)

           will now look like this but as one line:

            Bareword found where operator expected (Do you need to predeclare
            foo?) at -e line 1, near "foo bar"

           as a result such warnings will no longer trigger $SIG{__WARN__} twice, and the hint  will
           be visible when fatal warnings is in effect.

       •   The  error  message  that  is produced when a "require" or "use" statement fails has been
           changed. It used to contain the words "@INC contains:", and it used to show the state  of
           @INC  *after* the require had completed and failed. The error message has been changed to
           say "@INC entries checked:" and to reflect the actual  directories  or  hooks  that  were
           executed during the require statement. For example:

               perl -e'push @INC, sub {@INC=()}; eval "require Frobnitz"
                   or die $@'
               Can't locate Frobnitz.pm in @INC (you may need to install the
               Frobnitz module) (@INC contains:) at (eval 1) line 1.

           Will change to (with some output elided for clarity):

               perl -e'push @INC, sub {@INC=()}; eval "require Frobnitz"
                   or die $@'
               Can't locate Frobnitz.pm in @INC (you may need to install the
               Frobnitz module) (@INC entries checked:
               .../site_perl/5.38.0/x86_64-linux .../site_perl/5.38.0
               .../5.38.0/x86_64-linux .../5.38.0 CODE(0x562745e684b8))
               at (eval 1) line 1.

           thus  showing  the  actual  directories checked. Code that checks for "@INC contains:" in
           error messages should be hardened against any future wording changes between the @INC and
           ":", for instance use "qr/\@INC[  \w]+:/"  instead  of  using  "qr/\@INC  contains:/"  or
           "qr/\@INC  entries  checked:/"  in  tests  as  this will ensure both forward and backward
           compatibility.

       •   Old package separator used in string

           This diagnostic is now also part of the "deprecated" category.

       •   given is deprecated replaces "given is experimental".

       •   when is deprecated replaces "when is experimental".

       •   Smartmatch is deprecated replaces "Smartmatch is experimental".

Configuration and Compilation
       •   "make -j6 minitest" could fail due to a  build  conflict  in  building  "$(MINIPERL_EXE)"
           between    the    main    make    process    and    a    child   process.    [GH   #19829
           <https://github.com/Perl/perl5/issues/19829>]

       •   Properly populate osvers on Dragonfly BSD when the hostname isn't set.

       •   Fix typos for C99 macro name "PRIX64".

       •   Remove ancient and broken GCC for VMS support

       •   Remove vestigial reference to "/VAXC" qualifier

       •   Remove sharedperl option on VMS

       •   VMS now has mkostemp

       •   "Configure"  now  properly  handles  quoted  elements  outputted  by  gcc.   [GH   #20606
           <https://github.com/Perl/perl5/issues/20606>]

       •   "Configure"  probed  for  the  return  type  of  malloc()  and  free() by testing whether
           declarations  for  those  functions  produced  a  function   type   mismatch   with   the
           implementation.  On Solaris, with a C++ compiler, this check always failed, since Solaris
           instead  imports malloc() and free() from "std::" with "using" for C++ builds.  Since the
           return types of malloc() and free() are well defined by the C standard, skip probing  for
           them.   "Configure" command-line arguments and hints can still override these type in the
           unlikely case that is needed.  [GH #20806 <https://github.com/Perl/perl5/issues/20806>]

Testing
       Tests were added and changed to reflect the other additions  and  changes  in  this  release.
       Furthermore, these significant changes were made:

       •   Unicode normalization tests have been added.

       •   t/test.pl: Add ability to cancel an watchdog timer

Platform Support
   Discontinued Platforms
       Ultrix
           Support  code for DEC Ultrix has been removed.  Ultrix was the native Unix-like operating
           system for various Digital Equipment Corporation machines.   Its  final  release  was  in
           1995.

   Platform-Specific Notes
       DragonflyBSD
           Skip   tests   to   workaround   an   apparent   bug   in   setproctitle().   [GH  #19894
           <https://github.com/Perl/perl5/issues/19894>]

       FreeBSD
           FreeBSD no longer  uses  thread-safe  locale  operations,  to  avoid  a  bug  in  FreeBSD
           <https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=265950>

           Replace    the    first    part    of    archname    with    "uname    -p"   [GH   #19791
           <https://github.com/Perl/perl5/issues/19791>]

       Solaris
           Avoid  some  compiler  and  compilation  issues  on  NetBSD/Solaris  from  regexec.c  and
           regcomp.c.

       Synology
           Update Synology Readme for DSM 7.

       Windows
           Fix win32 memory alignment needed for gcc-12 from vmem.h.

           utimes()  on  Win32  would  print  a message to stderr if it failed to convert a supplied
           "time_t" to to a "FILETIME".  [GH #19668 <https://github.com/Perl/perl5/issues/19668>]

           In some cases, timestamps returned by stat() and lstat() failed to take  daylight  saving
           time  into  account.  [GH #20018 <https://github.com/Perl/perl5/issues/20018>] [GH #20061
           <https://github.com/Perl/perl5/issues/20061>]

           stat()     now     works     on     "AF_UNIX"     socket     files.       [GH      #20204
           <https://github.com/Perl/perl5/issues/20204>]

           readlink()  now returns the "PrintName" from a symbolic link reparse point instead of the
           "SubstituteName", which should make it better match the name the link was  created  with.
           [GH #20271 <https://github.com/Perl/perl5/pull/20271>]

           lstat()  on Windows now returns the length of the link target as the size of the file, as
           it does on POSIX systems.  [GH #20476 <https://github.com/Perl/perl5/issues/20476>]

           symlink() on Windows now replaces any "/" in the target with "\", since Windows does  not
           recognise "/" in symbolic links.  The reverse translation is not done by readlink().  [GH
           #20506 <https://github.com/Perl/perl5/issues/20506>]

           symlink() where the target was an absolute path to a directory was incorrectly created as
           a file symbolic link.  [GH #20533 <https://github.com/Perl/perl5/issues/20533>]

           "POSIX::dup2"      no      longer      creates     broken     sockets.     [GH     #20920
           <https://github.com/Perl/perl5/issues/20920>]

           Closing    a    busy    pipe    could    cause    Perl    to     hang.     [GH     #19963
           <https://github.com/Perl/perl5/issues/19963>]

Internal Changes
       •   Removed many deprecated C functions.

           These       have       been      deprecated      for      a      long      time.      See
           <https://github.com/perl/perl5/commit/7008caa915ad99e650acf2aea40612b5e48b7ba2>   for   a
           full list.

       •   "get_op_descs",  "get_op_names", "get_opargs", "get_no_modify" and "get_ppaddr" have been
           marked deprecated.

       •   "hv_free_ent" has been marked as internal API.

       •   "save_pushptr", "save_pushptrptr", and "save_pushi32ptr" have  been  marked  as  internal
           API.

       •   New  bool  related  functions  and macros have been added to complement the new bool type
           introduced in 5.36:

           The functions are:

           "newSVbool(const bool bool_val)"
           newSV_true()
           newSV_false()
           "sv_set_true(SV *sv)"
           "sv_set_false(SV *sv)"
           "sv_set_bool(SV *sv, const bool bool_val)"

           The macros are:

           SvIandPOK(sv)
           SvIandPOK_off(sv)
           "SvIandPOK_on"
       •   Perl  is  no  longer  manipulating   the   "environ"   array   directly.   The   variable
           "PL_use_safe_putenv"  has been removed and "PERL_USE_SAFE_PUTENV" is always defined. This
           means XS modules can now call "setenv" and  "putenv"  without  causing  segfaults.  [perl
           #19399 <https://github.com/Perl/perl5/issues/19399>]

       •   Internal  C  API functions are now hidden with "__attribute__((hidden))" on the platforms
           that support it. This means they  are  no  longer  callable  from  XS  modules  on  those
           platforms.

           It  should  be noted that those functions have always been hidden on Windows. This change
           merely     brings     that     to     the     other     platforms.      [perl      #19655
           <https://github.com/Perl/perl5/pull/19655>]

       •   New formatting symbols were added for printing values declared as "U32" or "I32":

           I32df -- Like %d
           U32of -- Like %o
           U32uf -- Like %u
           U32xf -- Like %x
           U32Xf -- Like %X

           These  are  used  in  the  same way already existing similar symbols, such as "IVdf", are
           used.  See "I/O Formats" in perlapi.

       •   new 'HvHasAUX' macro

       •   regexec.c: Add some branch predictions reorder conds

       •   locale: Change macro name to be C conformant

       •   Rename the "PADNAMEt_*" constants to "PADNAMEf_*"

       •   Changes all the API macros that retrieve a PV into a call to an inline function so as  to
           evaluate the parameter just once.

       •   regexec.c: multiple code refactor to make the code more readable

       •   perl.h:  Change  macro  name  to  be  C  conformant (remove leading _ from NOT_IN_NUMERIC
           macros)

       •   regcomp.h: add new "BITMAP_BIT" macro in  addition  to  the  existing  "BITMAP_BYTE"  and
           "BITMAP_TEST" ones.

       •   Create   new   regnode   type   ANYOFH.    populate_ANYOF_from_invlist   was  renamed  to
           populate_bitmap_from_invlist

       •   regex: Refactor bitmap vs non-bitmap of qr/[]/

       •   regcomp.c: add new functions to convert from an inversion list  to  a  bitmap  (and  vice
           versa) "populate_bitmap_from_invlist" and "populate_invlist_from_bitmap".

       •   Add  newAVav()  to create an AV from an existing AV.  Add newAVhv() to create an AV using
           keys and values from an existing HV.

       •   Fix definition of "Perl_atof".

       •   Fix undefined behavior with overflow related "OPTIMIZE_INFTY" and delta in regcomp.c.

       •   Fix regnode pointer alignment issue in regcomp.h.

       •   The  "CVf_METHOD"  CV  flag  and  associated  "CvMETHOD"  macro  has  been   renamed   to
           "CVf_NOWARN_AMBIGUOUS"   and   "CvNOWARN_AMBIGUOUS".  This  closer  reflects  its  actual
           behaviour (it suppresses a warning that would  otherwise  be  generated  about  ambiguous
           names),  in  order to be less confusing with "CvIsMETHOD", which indicates that a CV is a
           "method" subroutine relating to the "class" feature.

       •   The "OPf_SPECIAL" flag is no longer set on the "OP_ENTERSUB" op constructed to  call  the
           "VERSION",  "import"  and  "unimport"  methods as part of a "use" statement and attribute
           application, nor when assigning to an ":lvalue" subroutine.

       •   A new CV flag "CVf_REFCOUNTED_ANYSV" has been added, which indicates that the  CV  is  an
           XSUB  and  stores  an  SV  pointer  in  the  "CvXSUBANY.any_sv"  union  field.  Perl core
           operations such as cloning or destroying the CV will maintain the reference count of  the
           pointed-to SV, destroying it when required.

       •   A  new  API  function  ""Perl_localeconv""  in  perlapi  is  added.   This is the same as
           "POSIX::localeconv" (returning a hash of the localeconv() fields), but directly  callable
           from XS code.

       •   A  new  API  function, ""Perl_langinfo8"" in perlapi is added.  This is the same as plain
           ""Perl_langinfo"" in perlapi, but with an extra  parameter  that  allows  the  caller  to
           simply and reliably know if the returned string is UTF-8.

       •   We  have  introduced  a  limit  on  the  number  of nested "eval EXPR"/"BEGIN" blocks and
           "require"/"BEGIN" (and thus "use" statements as well) to prevent C stack overflows.  This
           variable  can  also  be  used  to forbid "BEGIN" blocks from executing during "eval EXPR"
           compilation.  The  limit  defaults  to  1000  but  can  be  overridden  by  setting   the
           "${^MAX_NESTED_EVAL_BEGIN_BLOCKS}" variable. The default itself can be changed at compile
           time with

               -Accflags='-DPERL_MAX_NESTED_EVAL_BEGIN_BLOCKS_DEFAULT=12345'

           Note  that  this  value  relates  to  the  size  of  your  C  stack  and if you choose an
           inappropriately large value Perl may segfault, be conservative about what you choose.

       •   A new magic type "PERL_MAGIC_extvalue" has been added. This is  available  for  use  like
           "PERL_MAGIC_ext",  but  is  a  value  magic:  upon localization the new value will not be
           magical.

       •   The SSNEW(), SSNEWt(), SSNEWa() and SSNEWat() APIs now return  a  "SSize_t"  value.   The
           SSPTR()  and  SSPTRt()  macros  now  expect  a  "SSize_t"  parameter, and enforce that on
           debugging builds.  [GH #20411 <https://github.com/Perl/perl5/issues/20411>]

       •   Filenames in cops are now refcounted under threads.  Under threads we  were  copying  the
           filenames  into  each opcode. This is because in theory opcodes created in one thread can
           be destroyed in another.  The change adds a new struct/type "RCPV", which is a refcounted
           string using shared memory. This is implemented in such a way that code  that  previously
           used a char * can continue to do so, as the refcounting data is located a specific offset
           before the char * pointer itself.

       •   Added  "HvNAMEf"  and  "HvNAMEf_QUOTEDPREFIX"  special formats. They take an "HV *" as an
           argument and use HvNAME() and related macros to determine the  string,  its  length,  and
           whether it is utf8.

       •   The underlying "Perl_dowantarray" function implementing the long-deprecated "GIMME" macro
           has  been  marked  as  deprecated, so that use of the macro emits a compile-time warning.
           "GIMME" has been documented as deprecated in favour of "GIMME_V" since Perl  v5.6.0,  but
           had not previously issued a warning.

       •   The API function "utf8_length" in perlapi is now more efficient.

       •   Added SAVERCPV() and SAVEFREERCPV() for better support for working with "RCPV" (reference
           counted  string/pointer  value)  structures  which currently are used in opcodes to share
           filename and warning bit data in a memory efficient manner.

       •   Added MORTALSVFUNC_SV() and MORTALDESTRUCTOR_SV()  macros,  which  make  it  possible  to
           create  a  destructor  which  is fired at the end of the current statement. This uses the
           "PERL_MAGIC_destruct" magic to use "free" magic to trigger an action when a  variable  is
           freed. The action can be specified as a C function or as a Perl code reference.

       •   Added  the  "%{^HOOK}"  api  and  related "PERL_MAGIC_hook" and "PERL_MAGIC_hookelem" for
           providing ways to hook selected perl functions  which  for  one  reason  or  another  are
           problematic to wrap with a customized subroutine.

       •   Added  support  for "${^HOOK}{require__before}" which can be used to rewrite the filename
           that "require" will try to load, and also to block  "require"  from  loading  a  specific
           module,  even  via  fully  qualified filename. The hook can also be used to perform "pre-
           require" and "post-require" actions.

       •   Added support for "${^HOOK}{require__after}" which can be used to track what modules have
           been required after the fact.

       •   Regular expression opcodes (regops) now use a standardized  structure  layout  that  uses
           unions  to expose data in different format. This means it should be much easier to extend
           or modify regops to use more memory.  This has been used to make a number of regops track
           how many parens they contain.

Selected Bug Fixes
       •   Avoid recursion and stack overflow parsing 'pack' template

           [GH #16319 <https://github.com/Perl/perl5/issues/16319>]

       •   An eval() as the last statement in a regex code block could trigger an interpreter panic;
           e.g.

               /(?{ ...; eval {....}; })/

           [GH #19680 <https://github.com/Perl/perl5/issues/19680>]

       •   Disabling the "bareword_filehandles" feature no longer treats "print Class->method" as an
           error.  [GH #19704 <https://github.com/Perl/perl5/issues/19704>]

       •   When a Perl  subroutine  tail-calls  an  XS  subroutine  using  "goto  &xs_sub",  the  XS
           subroutine  can  now  correctly  determine its calling context.  Previously it was always
           reported as scalar.

           In addition, where the Perl subroutine is freed at the same time:

               sub foo { *foo = sub {}; goto &xs_sub }

           this formerly could lead to crashes if the XS  subroutine  tried  to  use  the  value  of
           "PL_op", since this was being set to NULL. This is now fixed.

           [GH #19936 <https://github.com/Perl/perl5/issues/19936>]

       •   setsockopt()  now  uses the mechanism added in 5.36 to better distinguish between numeric
           and   string   values   supplied    as    the    "OPTVAL"    parameter.     [GH    #18761
           <https://github.com/Perl/perl5/issues/18761>]

       •   4-argument  select()  now  rejects  strings with code points above 255. Additionally, for
           code points 128-255, this operator will now always give the corresponding  octet  to  the
           OS, regardless of how Perl stores such code points in memory. (Previously Perl leaked its
           internal        string       storage       to       the       OS.)       [GH       #19882
           <https://github.com/Perl/perl5/issues/19882>]

       •   Fix    panic    issue    from    "val    {}     inside     /(?{...})/"     [GH     #19390
           <https://github.com/Perl/perl5/issues/19390>]

       •   Fix    multiple    compiler    warnings    from    regexp.c,    locale.c    [GH    #19915
           <https://github.com/Perl/perl5/issues/19915>]

       •   Fix a bug with querying locales on platforms that  don't  have  "LC_NUMERIC"  [GH  #19890
           <https://github.com/Perl/perl5/issues/19890>]

       •   Prevent undefined behaviour in S_maybe_multideref().

       •   Avoid signed integer overflow in "use integer" ops.

       •   Avoid adding an offset to a NULL pointer in "hv_delete_common".

       •   PerlIO::get_layers will now accept IO references too

           Previously  it would only take glob references or names of globs. Now it will also accept
           IO references.

       •   Fixes to memory handling for "PL_splitstr":

           •   If a thread was created the allocated string would be freed twice.

           •   If two "-F" switches were supplied the memory allocated for the first switch wouldn't
               be freed.

       •   Correctly handle "OP_ANONCODE" ops generated by  CPAN  modules  that  don't  include  the
           OPf_REF      flag      when      propagating      lvalue     context.      [GH     #20532
           <https://github.com/Perl/perl5/pull/20532>]

       •   POSIX::strxfrm now uses the "LC_CTYPE" locale category to specify its collation, ignoring
           any differing "LC_COLLATE".  It doesn't make sense for a string  to  be  encoded  in  one
           locale  (say,  ISO-8859-6,  Arabic)  and to collate it based on another (like ISO-8859-7,
           Greek).  Perl assumes  that  the  current  "LC_CTYPE"  locale  correctly  represents  the
           encoding, and collates accordingly.

           Also, embedded "NUL" characters are now allowed in the input.

           If  locale collation is not enabled on the platform ("LC_COLLATE"), the input is returned
           unchanged.

       •   Double FETCH during stringification of tied scalars returning an overloaded  object  have
           been  fixed.  The  FETCH method should only be called once, but prior to this release was
           actually called twice.  [GH #20574 <https://github.com/Perl/perl5/pull/20574>]

       •   Writing to a magic variables associated with the selected output handle, $^, $~, $=, "$-"
           and $%, no longer crashes perl if the IO object has been cleared from the selected output
           handle. [GH #20733 <https://github.com/Perl/perl5/issues/20733>]

       •   Redefining a "use constant" list constant with "use constant" now properly  warns.   This
           changes  the  behaviour  of  "use  constant"  but  is  a  core  change,  not  a change to
           constant.pm.  [GH #20742 <https://github.com/Perl/perl5/issues/20742>]

       •   Redefining a "use constant" list constant with an  empty  prototype  constant  sub  would
           result in an assertion failure.  [GH #20742 <https://github.com/Perl/perl5/issues/20742>]

       •   Fixed  a  regression  where the "INC" method for objects in @INC would not be resolved by
           "AUTOLOAD", while it was in 5.36.  The "INCDIR" method for  objects  in  @INC  cannot  be
           resolved   by   "AUTOLOAD"   as  "INC"  would  have  been  resolved  first.   [GH  #20665
           <https://github.com/Perl/perl5/issues/20665>]

       •   $SIG{__DIE__} will now be  called  from  eval  when  the  code  dies  during  compilation
           regardless  of  how it dies. This means that code expecting to be able to upgrade $@ into
           an object will be called consistently. In earlier versions of  perl  $SIG{__DIE__}  would
           not  be  called  for  certain  compilation errors, for instance undeclared variables. For
           other errors it might be called if there were more than a certain number of  errors,  but
           not if there were less. Now you can expect that it will be called in every case.

       •   Compilation  of  code  with errors used to inconsistently stop depending on the count and
           type of errors encountered. The intent was that after 10 errors compilation  would  halt,
           but  bugs in this logic meant that certain types of error would be counted, but would not
           trigger the threshold check to stop compilation. Other errors would.  With  this  release
           after at most 10 errors compilation will terminate, regardless of what type of error they
           were.

           Note that you can change the maximum count by defining "PERL_STOP_PARSING_AFTER_N_ERRORS"
           to be something else during the configuration process. For instance

               ./Configure ... -Accflags='-DPERL_STOP_PARSING_AFTER_N_ERRORS=100'

           would allow up to 100 errors.

       •   The  API function "my_snprintf" in perlapi now prints a non-dot decimal point if the perl
           code it ultimately is called from is in the scope of  "use  locale"  and  the  locale  in
           effect calls for that.

       •   A  number  of  bugs  related to capture groups in quantified groups in regular expression
           have been fixed, especially in alternations. For example in a pattern like:

                   "foobazfoobar" =~ /((foo)baz|foo(bar))+/

           the regex variable $2 will not be "foo" as it once was, it will be undef.

       •   Bugs with regex backreference operators that are inside of  a  capture  group  have  been
           fixed. For instance:

               "xa=xaaa" =~ /^(xa|=?\1a){2}\z/

           will now correctly not match. [GH #10073 <https://github.com/Perl/perl5/issues/10073>]

       •   SSGROW()  and SSCHECK() have been reworked to ensure that the requested space is actually
           allocated. SSCHECK() is now an alias for SSGROW().

Acknowledgements
       Perl 5.38.0 represents approximately 12 months of development since Perl 5.36.0 and  contains
       approximately 290,000 lines of changes across 1,500 files from 100 authors.

       Excluding  auto-generated  files,  documentation  and release tools, there were approximately
       190,000 lines of changes to 970 .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 5.38.0:

       Alex, Alexander Nikolov, Alex Davies, Andreas  König,  Andrew  Fresh,  Andrew  Ruthven,  Andy
       Lester,  Aristotle  Pagaltzis,  Arne  Johannessen,  A.  Sinan Unur, Bartosz Jarzyna, Bart Van
       Assche, Benjamin Smith, Bram, Branislav Zahradník, Brian Greenfield, Bruce Gray, Chad Granum,
       Chris 'BinGOs' Williams, chromatic, Clemens Wasser, Craig A. Berry, Dagfinn Ilmari Mannsåker,
       Dan Book, danielnachun,  Dan  Jacobson,  Dan  Kogai,  David  Cantrell,  David  Golden,  David
       Mitchell, E. Choroba, Ed J, Ed Sabol, Elvin Aslanov, Eric Herman, Felipe Gasper, Ferenc Erki,
       Firas  Khalil Khana, Florian Weimer, Graham Knop, Håkon Hægland, Harald Jörg, H.Merijn Brand,
       Hugo van der Sanden, James E Keenan, James Raspass, jkahrman,  Joe  McMahon,  Johan  Vromans,
       Jonathan  Stowe,  Jon  Gentle,  Karen  Etheridge,  Karl Williamson, Kenichi Ishigaki, Kenneth
       Ölwing, Kurt Fitzner, Leon Timmermans, Li Linjie, Loren Merritt,  Lukas  Mai,  Marcel  Telka,
       Mark  Jason  Dominus,  Mark  Shelor, Matthew Horsfall, Matthew O. Persico, Mattia Barbon, Max
       Maischein, Mohammad S Anwar, Nathan Mills, Neil  Bowers,  Nicholas  Clark,  Nicolas  Mendoza,
       Nicolas  R,  Paul  Evans,  Paul  Marquess,  Peter  John Acklam, Peter Levine, Philippe Bruhat
       (BooK), Reini Urban, Renee Baecker, Ricardo Signes, Richard Leach, Russ Allbery, Scott Baker,
       Sevan Janiyan, Sidney Markowitz, Sisyphus, Steve Hay, TAKAI  Kousuke,  Todd  Rinaldo,  Tomasz
       Konojacki, Tom Stellard, Tony Cook, Tsuyoshi Watanabe, Unicode Consortium, vsfos, Yves Orton,
       Zakariyya Mughal, Zefram, 小鸡.

       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:

           perlthanks

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

SEE ALSO
       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.

perl v5.38.2                                 2026-06-12                             PERL5380DELTA(1)
perl5380delta(1)
NAME DESCRIPTION Core Enhancements
New "class" Feature Unicode 15.0 is supported Deprecation warnings now have specific subcategories %{^HOOK} API introduced Defined-or and logical-or assignment default expressions in signatures @INC Hook Enhancements and $INC and INCDIR Forbidden control flow out of "defer" or "finally" now detected at compile-time Optimistic Eval in Patterns REG_INF has been raised from 65,536 to 2,147,483,647 New API functions optimize_optree and finalize_optree Some "goto"s are now permitted in "defer" and "finally" blocks New regexp variable ${^LAST_SUCCESSFUL_PATTERN} Locale category LC_NAME now supported on participating platforms
Incompatible Changes
readline() no longer clears the stream error and eof flags "INIT" blocks no longer run after an exit() in "BEGIN" Syntax errors no longer produce "phantom error messages" Changes to "thread-safe" locales
Deprecations
Use of "'" as a package name separator is deprecated Switch and Smart Match operator
Performance Enhancements Modules and Pragmata
Updated Modules and Pragmata
Documentation
New Documentation Changes to Existing Documentation
Diagnostics
New Diagnostics Changes to Existing Diagnostics
Configuration and Compilation Testing Platform Support
Discontinued Platforms Platform-Specific Notes
Internal Changes Selected Bug Fixes Acknowledgements Reporting Bugs Give Thanks SEE ALSO

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