=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.27.6

=head1 DESCRIPTION

This document describes differences between the 5.27.5 release and the 5.27.6
release.

If you are upgrading from an earlier release such as 5.27.4, first read
L<perl5275delta>, which describes differences between 5.27.4 and 5.27.5.

=head1 Core Enhancements

=head2 Initialisation of aggregate state variables

A persistent lexical array or hash variable can now be initialized,
by an expression such as C<state @a = qw(x y z)>.  Initialization of a
list of persistent lexical variables is still not possible.

=head2 Full-size inode numbers

On platforms where inode numbers are of a type larger than perl's native
integer numerical types, L<stat|perlfunc/stat> will preserve the full
content of large inode numbers by returning them in the form of strings of
decimal digits.  Exact comparison of inode numbers can thus be achieved by
comparing with C<eq> rather than C<==>.  Comparison with C<==>, and other
numerical operations (which are usually meaningless on inode numbers),
work as well as they did before, which is to say they fall back to
floating point, and ultimately operate on a fairly useless rounded inode
number if the real inode number is too big for the floating point format.

=head1 Incompatible Changes

=head2 Yada-yada is now strictly a statement

By the time of its initial stable release in Perl 5.12, the C<...>
(yada-yada) operator was explicitly intended to serve as a statement,
not an expression.  However, the original implementation was confused
on this point, leading to inconsistent parsing.  The operator was
accidentally accepted in a few situations where it did not serve as a
complete statement, such as

    ... . "foo";
    ... if $a < $b;

The parsing has now been made consistent, permitting yada-yada only as
a statement.  Affected code can use C<do{...}> to put a yada-yada into
an arbitrary expression context.

=head2 Subroutines no longer need typeglobs

Perl 5.22.0 introduced an optimization allowing subroutines to be stored in
packages as simple sub refs, not requiring a full typeglob (thus
potentially saving large amounts of memeory).  However, the optimization
was flawed: it only applied to the main package.

This optimization has now been extended to all packages.  This may break
compatibility with introspection code that looks inside stashes and expects
everything in them to be a typeglob.

When this optimization happens, the typeglob still notionally exists, so
accessing it will cause the stash entry to be upgraded to a typeglob.  The
optimization does not apply to XSUBs or exported subroutines, and calling a
method will undo it, since method calls cache things in typeglobs.

(This change actually happened in perl 5.27.5 but was omitted from its perldelta.)

[perl #129916] [perl #132252]

=head2 Sort algorithm can no longer be specified

Since Perl 5.8, the L<sort> pragma has had subpragmata C<_mergesort>,
C<_quicksort>, and C<_qsort> that can be used to specify which algorithm
perl should use to implement the L<sort|perlfunc/sort> builtin.
This was always considered a dubious feature that might not last,
hence the underscore spellings, and they were documented as not being
portable beyond Perl 5.8.  These subpragmata have now been deleted,
and any attempt to use them is an error.  The L<sort> pragma otherwise
remains, and the algorithm-neutral C<stable> subpragma can be used to
control sorting behaviour.
[perl #119635]

=head1 Performance Enhancements

=over 4

=item *

Many string concatenation expressions are now considerably faster, due
to the introduction internally of a C<multiconcat> opcode which combines
multiple concatenations, and optionally a C<=> or C<.=>, into a single
action. For example, apart from retrieving C<$s>, C<$a> and C<$b>, this
whole expression is now handled as a single op:

    $s .= "a=$a b=$b\n"

As a special case, if the LHS of an assignment is a lexical variable or
C<my $s>, the op itself handles retrieving the lexical variable, which
is faster.

In general, the more the expression includes a mix of constant strings and
variable expressions, the longer the expression, and the more it mixes
together non-utf8 and utf8 strings, the more marked the performance
improvement. For example on a C<x86_64> system, this code has been
benchmarked running four times faster:

    my $s;
    my $a = "ab\x{100}cde";
    my $b = "fghij";
    my $c = "\x{101}klmn";

    for my $i (1..10_000_000) {
        $s = "\x{100}wxyz";
        $s .= "foo=$a bar=$b baz=$c";
    }

In addition, C<sprintf> expressions which have a constant format
containing only C<%s> and C<%%> format elements, and which have a fixed
number of arguments, are now also optimised into a C<multiconcat> op.

=item *

Subroutines in packages no longer need to be stored in typeglobs, saving
large amounts of memory.  See L</Subroutines no longer need typeglobs>
under L</Incompatible Changes>, above.

=back

=head1 Modules and Pragmata

Key highlights in this release across several modules:

=head2 Removal of use vars

The usage of C<use vars> has been discouraged since the introduction of C<our> in
Perl 5.6.0. Where possible the usage of this pragma has now been removed from
the Perl source code.

This had a slight effect (for the better) on the output of WARNING_BITS in B::Deparse.

=head2 Use of DynaLoader changed to XSLoader in many modules

XSLoader is more modern, and most modules already require perl 5.6 or greater, so
no functionality is lost by switching. In some cases, we have also made changes to
the local implementation that may not be reflected in the version on CPAN due
to a desire to maintain more backwards compatibility.

=head2 Updated Modules and Pragmata

=over 4

=item *

L<Attribute::Handlers> has been upgraded from version 1.00 to 1.01.

=item *

L<attributes> has been upgraded from version 0.31 to 0.32.

=item *

L<B> has been upgraded from version 1.70 to 1.72.

=item *

L<B::Concise> has been upgraded from version 1.002 to 1.003.

=item *

L<B::Deparse> has been upgraded from version 1.43 to 1.45.

=item *

L<base> has been upgraded from version 2.26 to 2.27.

=item *

L<blib> has been upgraded from version 1.06 to 1.07.

=item *

L<Carp> has been upgraded from version 1.43 to 1.44.

If a package on the call stack contains a constant named C<ISA>, Carp no
longer throws a "Not a GLOB reference" error.

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.074 to 2.075.

This addresses a security vulnerability in older versions of the 'zlib' library
(which is bundled with Compress-Raw-Zlib).

=item *

L<Config::Extensions> has been upgraded from version 0.01 to 0.02.

=item *

L<Devel::PPPort> has moved from cpan-first to perl-first maintenance

Primary responsibility for the code in Devel::PPPort has moved into core perl.
In a practical sense there should be no change except that hopefully it will
stay more up to date with changes made to symbols in perl, rather than needing
to be updated after the fact.

=item *

L<DynaLoader> has been upgraded from version 1.42 to 1.44.

=item *

L<experimental> has been upgraded from version 0.016 to 0.017.

=item *

L<ExtUtils::CBuilder> has been upgraded from version 0.280228 to 0.280229.

=item *

L<ExtUtils::Embed> has been upgraded from version 1.34 to 1.35.

=item *

L<ExtUtils::Miniperl> has been upgraded from version 1.06 to 1.07.

=item *

L<ExtUtils::ParseXS> has been upgraded from version 3.35 to 3.36.

=item *

L<ExtUtils::Typemaps> has been upgraded from version 3.35 to 3.36.

=item *

L<ExtUtils::XSSymSet> has been upgraded from version 1.3 to 1.4.

=item *

L<fields> has been upgraded from version 2.23 to 2.24.

=item *

L<File::Copy> has been upgraded from version 2.32 to 2.33.  It will now use
Time::HiRes utime where available (perl #132401).

=item *

L<File::Spec> has been upgraded from version 3.68 to 3.70.

=item *

L<File::stat> has been upgraded from version 1.07 to 1.08.

=item *

L<FileCache> has been upgraded from version 1.09 to 1.10.

=item *

L<Filter::Simple> has been upgraded from version 0.94 to 0.95.

=item *

L<Hash::Util::FieldHash> has been upgraded from version 1.19 to 1.20.

=item *

L<I18N::Langinfo> has been upgraded from version 0.14 to 0.15.

=item *

L<I18N::LangTags> has been upgraded from version 0.42 to 0.43.

=item *

The libnet distribution has been upgraded from version 3.10 to 3.11.

=item *

L<Locale::Maketext> has been upgraded from version 1.28 to 1.29.

=item *

L<Module::CoreList> has been upgraded from version 5.20171020 to 5.20171120.

=item *

L<Net::Ping> has been upgraded from version 2.55 to 2.62.

=item *

L<ODBM_File> has been upgraded from version 1.14 to 1.15.

=item *

L<Opcode> has been upgraded from version 1.40 to 1.41.

=item *

L<Pod::Html> has been upgraded from version 1.2202 to 1.2203.

=item *

L<POSIX> has been upgraded from version 1.78 to 1.80.

=item *

L<re> has been upgraded from version 0.35 to 0.36.

=item *

L<SelfLoader> has been upgraded from version 1.24 to 1.25.

=item *

L<Socket> has been upgraded from version 2.020_03 to 2.020_04.

=item *

L<sort> has been upgraded from version 2.03 to 2.04.

=item *

L<Storable> has been upgraded from version 2.64 to 2.65.

=item *

L<Test> has been upgraded from version 1.30 to 1.31.

=item *

L<Test::Simple> has been upgraded from version 1.302103 to 1.302111.

=item *

L<threads> has been upgraded from version 2.18 to 2.19.

=item *

L<Tie::Array> has been upgraded from version 1.06 to 1.07.

=item *

L<Tie::StdHandle> has been upgraded from version 4.4 to 4.5.

=item *

L<Time::gmtime> has been upgraded from version 1.03 to 1.04.

=item *

L<Time::HiRes> has been upgraded from version 1.9746 to 1.9747.

=item *

L<Time::localtime> has been upgraded from version 1.02 to 1.03.

=item *

L<Unicode::Collate> has been upgraded from version 1.19 to 1.23.

=item *

L<Unicode::Normalize> has been upgraded from version 1.25 to 1.26.

=item *

L<User::grent> has been upgraded from version 1.01 to 1.02.

=item *

L<User::pwent> has been upgraded from version 1.00 to 1.01.

=item *

L<VMS::DCLsym> has been upgraded from version 1.08 to 1.09.

=item *

L<VMS::Stdio> has been upgraded from version 2.42 to 2.44.

=item *

L<warnings> has been upgraded from version 1.37 to 1.38.

=item *

L<XS::Typemap> has been upgraded from version 0.15 to 0.16.

=item *

L<XSLoader> has been upgraded from version 0.27 to 0.28.

=back

=head1 Documentation

=head2 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, send email
to L<perlbug@perl.org|mailto:perlbug@perl.org>.

Additionally, the following selected changes have been made:

=over 4

=item * L<perldiag/Variable length lookbehind not implemented in regex m/%s/>

This now gives more ideas as to workarounds to the issue that was
introduced in Perl 5.18 (but not documented explicitly in its perldelta)
for the fact that some Unicode C</i> rules cause a few sequences such as

 (?<!st)

to be considered variable length, and hence disallowed.

=item * "Use of state $_ is experimental" in L<perldiag>

This entry has been removed, as the experimental support of this construct was
removed in perl 5.24.0.

=item *

The section on reference counting in L<perlguts> has been heavily revised,
to describe references in the way a programmer needs to think about them
rather than in terms of the physical data structures.

=item *

The section "Truth and Falsehood" in L<perlsyn> has been removed from
that document, where it didn't belong, and merged into the existing
paragraph on the same topic in L<perldata>.

=item *

The description of the C<x> operator in L<perlop> has been clarified.  [perl #132460]

=item *

L<perluniprops> has been updated to note that C<\p{Word}> now includes
code points matching the C<\p{Join_Control}> property.  The change to
the property was made in Perl 5.18, but not documented until now.  There
are currently only two code points that match this property U+200C (ZERO
WIDTH NON-JOINER) and U+200D (ZERO WIDTH JOINER).

=item *

The entry for C<$+> in perlvar has been expanded upon to describe handling of
multiply-named capturing groups.

=item *

L<perlop> has been updated to note that C<qw>'s whitespace rules differ from that of
C<split>'s in that only ASCII whitespace is used.

=item *

L<POSIX> has been updated with some more cautions about using locale-specific
functions in threaded applications.

=back

=head1 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 L<perldiag>.

=head2 Changes to Existing Diagnostics

=over 4

=item *

The diagnostic C<Initialization of state variables in list context
currently forbidden> has changed to C<Initialization of state variables
in list currently forbidden>, because list-context initialization of
single aggregate state variables is now permitted.

=back

=head1 Utility Changes

=head2 L<perlbug>

=over 4

=item *

C<--help> and C<--version> options have been added.

=back

=head1 Configuration and Compilation

=over 4

=item C89 requirement

Perl has been documented as requiring a C89 compiler to build since October
1998.  A variety of simplifications have now been made to Perl's internals to
rely on the features specified by the C89 standard. We believe that this
internal change hasn't altered the set of platforms that Perl builds on, but
please report a bug if Perl now has new problems building on your platform.

=item New probes

=over 2

=item HAS_BUILTIN_ADD_OVERFLOW

=item HAS_BUILTIN_MUL_OVERFLOW

=item HAS_BUILTIN_SUB_OVERFLOW

=item HAS_THREAD_SAFE_NL_LANGINFO_L

=item HAS_LOCALECONV_L

=item HAS_MBRLEN

=item HAS_MBRTOWC

=item HAS_MEMRCHR

=item HAS_NANOSLEEP

=item HAS_STRNLEN

=item HAS_STRTOLD_L

=item I_WCHAR

=back

=back

=head1 Packaging

For the past few years we have released perl using three different archive
formats: bzip (C<.bz2>), LZMA2 (C<.xz>) and gzip (C<.gz>). Since xz compresses
better and decompresses faster, and gzip is more compatible and uses less memory,
we have dropped the C<.bz2> archive format with this release.
(If this poses a problem, do let us know; see L</Reporting Bugs>, below.)

=head1 Platform Support

=head2 Discontinued Platforms

=over 4

=item PowerUX / Power MAX OS

Compiler hints and other support for these apparently long-defunct platforms has been removed.

=back

=head2 Platform-Specific Notes

=over 4

=item Windows

Visual C++ compiler version detection has been improved to work on non-English
language systems.

=back

=head1 Internal Changes

=over 4

=item *

A new optimisation phase has been added to the compiler,
C<optimize_optree()>, which does a top-down scan of a complete optree
just before the peephole optimiser is run. This phase is not currently
hookable.

=item *

An C<OP_MULTICONCAT> op has been added. At C<optimize_optree()> time, a
chain of C<OP_CONCAT> and C<OP_CONST> ops, together optionally with an
C<OP_STRINGIFY> and/or C<OP_SASSIGN>, are combined into a single
C<OP_MULTICONCAT> op. The op is of type C<UNOP_AUX>, and the aux array
contains the argument count, plus a pointer to a constant string and a set
of segment lengths. For example with

    my $x = "foo=$foo, bar=$bar\n";

the constant string would be C<"foo=, bar=\n"> and the segment lengths
would be (4,6,1). If the string contains characters such as C<\x80>, whose
representation changes under utf8, two sets of strings plus lengths are
precomputed and stored.

=item *

Direct access to L<C<PL_keyword_plugin>|perlapi/PL_keyword_plugin> is not
safe in the presence of multithreading. A new
L<C<wrap_keyword_plugin>|perlapi/wrap_keyword_plugin> function has been
added to allow XS modules to safely define custom keywords even when
loaded from a thread, analogous to L<C<PL_check>|perlapi/PL_check> /
L<C<wrap_op_checker>|perlapi/wrap_op_checker>.

=back

=head1 Selected Bug Fixes

=over 4

=item *

C<stat()>, C<lstat()>, and file test operators now fail if given a
filename containing a nul character, in the same way that C<open()>
already fails.

=item *

C<stat()>, C<lstat()>, and file test operators now reliably set C<$!> when
failing due to being applied to a closed or otherwise invalid file handle.

=item *

File test operators for Unix permission bits that don't exist on a
particular platform, such as C<-k> (sticky bit) on Windows, now check that
the file being tested exists before returning the blanket false result,
and yield the appropriate errors if the argument doesn't refer to a file.

=item *

The in-place reverse optimisation now correctly strengthens weak
references using the L<C<sv_rvunweaken()>|perlapi/sv_rvunweaken>
API function.

=item *

Fixed a read before buffer when parsing a range starting with C<\N{}>
at the beginning of the character set for the transliteration
operator.  [perl #132245]

=item *

Fixed a leaked SV when parsing an empty C<\N{}> at compile-time.
[perl #132245]

=item *

Calling C<do $path> on a directory or block device now yields a meaningful
error code in C<$!>.  [perl #125774]

=item *

Regexp substitution using an overloaded replacement value that provides
a tainted stringification now correctly taints the resulting string.
[perl #115266]

=item *

Lexical sub declarations in C<do> blocks such as C<do { my sub lex; 123 }>
could corrupt the stack, erasing items already on the stack in the
enclosing statement.  This has been fixed.  [perl #132442]

=back

=head1 Errata From Previous Releases

=over 4

=item *

L</Subroutines no longer need typeglobs> under L</Incompatible Changes>, above,
was made for perl 5.27.5 but was mistakenly omitted from its perldelta.

=back

=head1 Acknowledgements

Perl 5.27.6 represents approximately 4 weeks of development since Perl 5.27.5
and contains approximately 110,000 lines of changes across 1,100 files from 30
authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 20,000 lines of changes to 430 .pm, .t, .c and .h files.

Perl continues to flourish into its third decade thanks to a vibrant community
of users and developers. The following people are known to have contributed the
improvements that became Perl 5.27.6:

Aaron Crane, Andrew Fresh, Ask Bjöern Hansen, Chris 'BinGOs' Williams, Craig
A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, David Cantrell, David
Mitchell, Dominic Hargreaves, Father Chrysostomos, Harald Jörg, H.Merijn
Brand, James E Keenan, Jarkko Hietaniemi, J. Nick Koston, John Lightsey, Karen
Etheridge, Karl Williamson, Lukas Mai, Matthew Horsfall, Nicolas R., Paul
Marquess, Sawyer X, Slaven Rezic, Steve Hay, Todd Rinaldo, Tony Cook, Yves
Orton, Zefram.

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 F<AUTHORS> file in the Perl source distribution.

=head1 Reporting Bugs

If you find what you think is a bug, you might check the perl bug database
at L<https://rt.perl.org/> .  There may also be information at
L<http://www.perl.org/> , the Perl Home Page.

If you believe you have an unreported bug, please run the L<perlbug> program
included with your release.  Be sure to trim your bug down to a tiny but
sufficient test case.  Your bug report, along with the output of C<perl -V>,
will be sent off to perlbug@perl.org to be analysed by the Perl porting team.

If the bug you are reporting has security implications which make it
inappropriate to send to a publicly archived mailing list, then see
L<perlsec/SECURITY VULNERABILITY CONTACT INFORMATION>
for details of how to report the issue.

=head1 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 C<perlthanks> program:

    perlthanks

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

=head1 SEE ALSO

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

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=cut