Update Module::CoreList for 5.35.10

[perl5.git] / pod / perldelta.pod

=encoding utf8

=head1 NAME

[ this is a template for a new perldelta file.  Any text flagged as XXX needs
to be processed before release. ]

perldelta - what is new for perl v5.35.10

=head1 DESCRIPTION

This document describes differences between the 5.35.9 release and the 5.35.10
release.

If you are upgrading from an earlier release such as 5.35.8, first read
L<perl5359delta>, which describes differences between 5.35.8 and 5.35.9.

=head1 Notice

XXX Any important notices here

=head1 Core Enhancements

XXX New core language features go here.  Summarize user-visible core language
enhancements.  Particularly prominent performance optimisations could go
here, but most should go in the L</Performance Enhancements> section.

=head2 New function C<builtin::trim>

This function treats its argument as a string, returning the result of
removing all white space at its beginning and ending.  See
L<builtin/trim>

=head2 Variable length lookbehind is mostly no longer considered experimental.

Prior to this release any form of variable length lookbehind was
considered experimental. With this release the experimental status has
been reduced to cover only lookbehind that contains capturing parenthesis.
This is because it is not clear if

    "aaz"=~/(?=z)(?<=(a|aa))/

should match and leave $1 equaling "a" or "aa". Currently it will match
the longest possible alternative, "aa". We are confident that the overall
construct will now match only when it should, we are not confident that we
will keep the current "longest match" behavior.

=head2 Added 'builtin::indexed'

A new function has been added to the C<builtin> package, called C<indexed>.
It returns a list twice as big as its argument list, where each item is
preceeded by its index within that list. This is primarily useful for using
the new C<foreach> syntax with multiple iterator variables to iterate over
an array or list, while also tracking the index of each item:

    use builtin 'indexed';

    foreach my ($index, $val) (indexed @array) {
        ...
    }

=head2 Added experimental feature 'extra_paired_delimiters'

Perl traditionally has allowed just four pairs of string/pattern
delimiters: S<C<( )>> S<C<{ }>> S<C<[ ]>> and S<C<< < > >>>, all in the
ASCII range.  Unicode has hundreds more possibilities, and using this
feature enables many of them.  When enabled, you can say S<C<qr« »>> for
example, or S<C<use utf8; <q𝄃string𝄂>>.  See
L<feature/The 'extra_paired_delimiters' feature> for
details.

=head1 Security

XXX Any security-related notices go here.  In particular, any security
vulnerabilities closed should be noted here rather than in the
L</Selected Bug Fixes> section.

[ List each security issue as a =head2 entry ]

=head1 Incompatible Changes

XXX For a release on a stable branch, this section aspires to be:

    There are no changes intentionally incompatible with 5.XXX.XXX
    If any exist, they are bugs, and we request that you submit a
    report.  See L</Reporting Bugs> below.

[ List each incompatible change as a =head2 entry ]

=head1 Deprecations

Using any of the characters enabled by
L</Added experimental feature 'extra_paired_delimiters'> as a
non-paired string delimiter is now deprecated.

=head2 Module removals

XXX Remove this section if not applicable.

The following modules will be removed from the core distribution in a
future release, and will at that time need to be installed from CPAN.
Distributions on CPAN which require these modules will need to list them as
prerequisites.

The core versions of these modules will now issue C<"deprecated">-category
warnings to alert you to this fact.  To silence these deprecation warnings,
install the modules in question from CPAN.

Note that these are (with rare exceptions) fine modules that you are encouraged
to continue to use.  Their disinclusion from core primarily hinges on their
necessity to bootstrapping a fully functional, CPAN-capable Perl installation,
not usually on concerns over their design.

=over

=item XXX

XXX Note that deprecated modules should be listed here even if they are listed
as an updated module in the L</Modules and Pragmata> section.

=back

[ List each other deprecation as a =head2 entry ]

=head1 Performance Enhancements

XXX Changes which enhance performance without changing behaviour go here.
There may well be none in a stable release.

[ List each enhancement as an =item entry ]

=over 4

=item *

Large hashes no longer allocate their keys from the shared string table.

The same internal datatype (C<PVHV>) is used for all of

=over 4

=item *

Symbol tables

=item *

Objects (by default)

=item *

Associative arrays

=back

The shared string table was originally added to improve performance for blessed
hashes used as objects, because every object instance has the same keys, so it
is an optimisation to share memory between them. It also makes sense for symbol
tables, where derived classes will have the same keys (typically method names),
and the OP trees built for method calls can also share memory. The shared
string table behaves roughly like a cache for hash keys.

But for hashes actually used as associative arrays - mapping keys to values -
typically the keys are not re-used in other hashes. For example, "seen" hashes
are keyed by object IDs (or addresses), and logically these keys won't repeat
in other hashes.

Storing these "used just once" keys in the shared string table increases CPU
and RAM use for no gain. For such keys the shared string table behaves as a
cache with a 0% hit rate. Storing all the keys there increases the total size
of the shared string table, as well as increasing the number of times it is
resized as it grows. B<Worse> - in any environment that has "copy on write"
memory for child process (such as a pre-forking server), the memory pages used
for the shared string table rapidly need to be copied as the child process
manipulates hashes. Hence if most of the shared string table is such keys that
are used only in one place, there is no benefit from re-use within the perl
interpreter, but a high cost due to more pages for the OS to copy.

The perl interpreter now disables shared hash keys for "large" hashes (that are
neither objects nor symbol tables). "Large" is a heuristic - currently the
heuristic is that sharing is disabled when adding a key to a hash triggers
allocation of more storage, and the hash has more than 42 keys.

This B<might> cause slightly increased memory usage for programs that create
(unblessed) data structures that contain multiple large hashes that share the
same keys. But generally our testing suggests that for the specific cases
described it is a win, and other code is unaffected.

=back

=head1 Modules and Pragmata

XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
go here.  If Module::CoreList is updated, generate an initial draft of the
following sections using F<Porting/corelist-perldelta.pl>.  A paragraph summary
for important changes should then be added by hand.  In an ideal world,
dual-life modules would have a F<Changes> file that could be cribbed.

The list of new and updated modules is modified automatically as part of
preparing a Perl release, so the only reason to manually add entries here is if
you're summarising the important changes in the module update. (Also, if the
manually-added details don't match the automatically-generated ones, the
release manager will have to investigate the situation carefully.)

[ Within each section, list entries as an =item entry ]

=head2 New Modules and Pragmata

=over 4

=item *

XXX Remove this section if not applicable.

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

L<XXX> has been upgraded from version A.xx to B.yy.

If there was something important to note about this change, include that here.

=back

=head2 Removed Modules and Pragmata

=over 4

=item *

XXX

=back

=head1 Documentation

XXX Changes to files in F<pod/> go here.  Consider grouping entries by
file and be sure to link to the appropriate page, e.g. L<perlfunc>.

=head2 New Documentation

XXX Changes which create B<new> files in F<pod/> go here.

=head3 L<XXX>

XXX Description of the purpose of the new file here

=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, open an issue
at L<https://github.com/Perl/perl5/issues>.

XXX Changes which significantly change existing files in F<pod/> go here.
However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
section.

Additionally, the following selected changes have been made:

=head3 L<XXX>

=over 4

=item *

XXX Description of the change here

=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>.

XXX New or changed warnings emitted by the core's C<C> code go here.  Also
include any changes in L<perldiag> that reconcile it to the C<C> code.

=head2 New Diagnostics

XXX Newly added diagnostic messages go under here, separated into New Errors
and New Warnings

=head3 New Errors

=over 4

=item *

XXX L<message|perldiag/"message">

=item *

L<Wide character in $0|perldiag/"Wide character in %s">

Attempts to put wide characters into the program name (C<$0>) now
provoke this warning.

=back

=head3 New Warnings

=over 4

=item *

XXX L<message|perldiag/"message">

=back

=head2 Changes to Existing Diagnostics

XXX Changes (i.e. rewording) of diagnostic messages go here

=over 4

=item *

XXX Describe change here

=item * New 'scalar' category for "Useless use of sort in scalar context"

When C<sort> is used in scalar context, it provokes a warning that this is not
useful. This warning used to be in the C<void> category. A new category for
warnings about scalar context has now been added, called C<scalar>.

=back

=head1 Utility Changes

XXX Changes to installed programs such as F<perldoc> and F<xsubpp> go here.
Most of these are built within the directory F<utils>.

[ List utility changes as a =head2 entry for each utility and =item
entries for each change
Use L<XXX> with program names to get proper documentation linking. ]

=head2 L<XXX>

=over 4

=item *

XXX

=back

=head1 Configuration and Compilation

XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
go here.  Any other changes to the Perl build process should be listed here.
However, any platform-specific changes should be listed in the
L</Platform Support> section, instead.

[ List changes as an =item entry ].

=over 4

=item *

XXX

=back

=head1 Testing

XXX Any significant changes to the testing of a freshly built perl should be
listed here.  Changes which create B<new> files in F<t/> go here as do any
large changes to the testing harness (e.g. when parallel testing was added).
Changes to existing files in F<t/> aren't worth summarizing, although the bugs
that they represent may be covered elsewhere.

XXX If there were no significant test changes, say this:

Tests were added and changed to reflect the other additions and changes
in this release.

XXX If instead there were significant changes, say this:

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

[ List each test improvement as an =item entry ]

=over 4

=item *

XXX

=back

=head1 Platform Support

XXX Any changes to platform support should be listed in the sections below.

[ Within the sections, list each platform as an =item entry with specific
changes as paragraphs below it. ]

=head2 New Platforms

XXX List any platforms that this version of perl compiles on, that previous
versions did not.  These will either be enabled by new files in the F<hints/>
directories, or new subdirectories and F<README> files at the top level of the
source tree.

=over 4

=item XXX-some-platform

XXX

=back

=head2 Discontinued Platforms

XXX List any platforms that this version of perl no longer compiles on.

=over 4

=item XXX-some-platform

XXX

=back

=head2 Platform-Specific Notes

XXX List any changes for specific platforms.  This could include configuration
and compilation changes or changes in portability/compatibility.  However,
changes within modules for platforms should generally be listed in the
L</Modules and Pragmata> section.

=over 4

=item XXX-some-platform

XXX

=back

=head1 Internal Changes

XXX Changes which affect the interface available to C<XS> code go here.  Other
significant internal changes for future core maintainers should be noted as
well.

[ List each change as an =item entry ]

=over 4

=item *

XXX

=item *

C<sv_dump> (and L<Devel::Peek>’s C<Dump> function) now escapes high-bit
octets in the PV as hex rather than octal. Since most folks understand hex
more readily than octal, this should make these dumps a bit more legible.
This does B<not> affect any other diagnostic interfaces like C<pv_display>.

=back

=head1 Selected Bug Fixes

XXX Important bug fixes in the core language are summarized here.  Bug fixes in
files in F<ext/> and F<lib/> are best summarized in L</Modules and Pragmata>.

[ List each fix as an =item entry ]

=over 4

=item *

XXX

=back

=head1 Known Problems

XXX Descriptions of platform agnostic bugs we know we can't fix go here.  Any
tests that had to be C<TODO>ed for the release would be noted here.  Unfixed
platform specific bugs also go here.

[ List each fix as an =item entry ]

=over 4

=item *

XXX

=back

=head1 Errata From Previous Releases

=over 4

=item *

XXX Add anything here that we forgot to add, or were mistaken about, in
the perldelta of a previous release.

=back

=head1 Obituary

XXX If any significant core contributor or member of the CPAN community has
died, add a short obituary here.

=head1 Acknowledgements

XXX Generate this with:

  perl Porting/acknowledgements.pl v5.35.9..HEAD

=head1 Reporting Bugs

If you find what you think is a bug, you might check the perl bug database
at L<https://github.com/Perl/perl5/issues>.  There may also be information at
L<http://www.perl.org/>, the Perl Home Page.

If you believe you have an unreported bug, please open an issue at
L<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
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