=encoding utf8

=head1 NAME

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 Core Enhancements

=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
preceded 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 Performance Enhancements

=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

=head2 Updated Modules and Pragmata

=over 4

=item *

L<Attribute::Handlers> has been upgraded from version 1.01 to 1.02.

=item *

L<B::Deparse> has been upgraded from version 1.62 to 1.63.

=item *

L<DB_File> has been upgraded from version 1.856 to 1.857.

=item *

L<Devel::PPPort> has been upgraded from version 3.64 to 3.68.

=item *

L<experimental> has been upgraded from version 0.027 to 0.028.

=item *

L<ExtUtils::ParseXS> has been upgraded from version 3.44 to 3.45.

=item *

L<ExtUtils::Typemaps> has been upgraded from version 3.44 to 3.45.

=item *

L<feature> has been upgraded from version 1.70 to 1.71.

=item *

L<File::Spec> has been upgraded from version 3.83 to 3.84.

=item *

L<GDBM_File> has been upgraded from version 1.22 to 1.23.

=item *

L<Module::CoreList> has been upgraded from version 5.20220220 to 5.20220320.

=item *

L<Opcode> has been upgraded from version 1.56 to 1.57.

=item *

L<Scalar::Util> has been upgraded from version 1.61 to 1.62.

=item *

L<Test::Simple> has been upgraded from version 1.302188 to 1.302190.

=item *

L<warnings> has been upgraded from version 1.57 to 1.58.

=item *

L<XS::APItest> has been upgraded from version 1.21 to 1.22.

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

=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 New Diagnostics

=head3 New Errors

=over 4

=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

=head2 Changes to Existing Diagnostics

=over 4

=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 Internal Changes

=over 4

=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 Acknowledgements

Perl 5.35.10 represents approximately 4 weeks of development since Perl
5.35.9 and contains approximately 15,000 lines of changes across 300 files
from 26 authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 6,900 lines of changes to 190 .pm, .t, .c and .h files.

Perl continues to flourish into its fourth decade thanks to a vibrant
community of users and developers. The following people are known to have
contributed the improvements that became Perl 5.35.10:

Bernd, Brad Barden, Chad Granum, cuishuang, Curtis Poe, Dagfinn Ilmari
Mannsåker, Daniel Laügt, Felipe Gasper, Graham Knop, Hugo van der Sanden,
James E Keenan, Karl Williamson, Leon Timmermans, Matthew Horsfall, Michiel
Beijen, Nicholas Clark, Nicolas R, Paul Evans, Renee Baecker, Ricardo
Signes, Richard Leach, Sawyer X, Sisyphus, Steve Hay, TAKAI Kousuke, Yves
Orton.

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

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

For a more complete list of all of Perl's historical contributors, please
see the 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://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
