path: root/pod/perldelta.pod

=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.23.1

=head1 DESCRIPTION

This document describes differences between the 5.23.0 release and the 5.23.1
release.

If you are upgrading from an earlier release such as 5.22.0, first read
L<perl5230delta>, which describes differences between 5.22.0 and 5.23.0.

=head1 Core Enhancements

=head2 Integer shift (C<< << >> and C<< >> >>) now more explicitly defined

Negative shifts are reverse shifts: left shift becomes right shift,
and right shift becomes left shift.

Shifting by the number of bits in a native integer (or more) is zero,
except when the "overshift" is right shifting a negative value under
C<use integer>, in which case the result is -1 (arithmetic shift).

Until now negative shifting and overshifting have been undefined
because they have relied on whatever the C implementation happens
to do.  For example, for the overshift a common C behavior is
"modulo shift":

  1 >> 64 == 1 >> (64 % 64) == 1 >> 0 == 1  # Common C behavior.

  # And the same for <<, while Perl now produces 0 for both.

Now these behaviors are well-defined under Perl, regardless of what
the underlying C implementation does.  Note, however, that you cannot
escape the native integer width, you need to know how far left you
can go.  You can use for example:

  use Config;
  my $wordbits = $Config{uvsize} * 8;  # Or $Config{uvsize} << 3.

If you need a more bits on the left shift, you can use for example
the C<bigint> pragma, or the C<Bit::Vector> module from CPAN.

=head2 Postfix dereferencing is no longer experimental

Using the C<postderef> and C<postderef_qq> features no longer emits a
warning. Existing code that disables the C<experimental::postderef> warning
category that they previously used will continue to work. The C<postderef>
feature has no effect; all Perl code can use postfix dereferencing,
regardless of what feature declarations are in scope. The C<5.24> feature
bundle now includes the C<postderef_qq> feature.

=head2 printf and sprintf now allow reordered precision arguments

That is, C<< sprintf '|%.*2$|', 2, 3 >> now returns C<|002|>. This extends
the existing reordering mechanism (which allows reordering for arguments
that are used as format fields, widths, and vector separators).

=head1 Incompatible Changes

=head2 ASCII characters in variable names must now be all visible

It was legal until now on ASCII platforms for variable names to contain
non-graphical ASCII control characters (ordinals 0 through 31, and 127,
which are the C0 controls and C<DELETE>).  This usage has been
deprecated since v5.20, and as of now causes a syntax error.  The
variables these names referred to are special, reserved by Perl for
whatever use it may choose, now, or in the future.  Each such variable
has an alternative way of spelling it.  Instead of the single
non-graphic control character, a two character sequence beginning with a
caret is used, like C<$^]> and C<${^GLOBAL_PHASE}>.  Details are at
L<perlvar>.   It remains legal, though unwise and deprecated (raising a
deprecation warning), to use certain non-graphic non-ASCII characters in
variables names when not under S<C<use utf8>>.  No code should do this,
as all such variables are reserved by Perl, and Perl doesn't currently
define any of them (but could at any time, without notice).

=head2 The C<autoderef> feature has been removed

The experimental C<autoderef> feature (which allowed calling C<push>,
C<pop>, C<shift>, C<unshift>, C<splice>, C<keys>, C<values>, and C<each> on
a scalar argument) has been deemed unsuccessful. It has now been removed;
trying to use the feature (or to disable the C<experimental::autoderef>
warning it previously triggered) now yields an exception.

=head1 Deprecations

=head2 Module removals

XXX Remove this section if inapplicable.

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 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.

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

=head2 New Modules and Pragmata

=over 4

=item *

XXX

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

L<autodie> has been upgraded from version 2.28 to 2.29.

=item *

L<IPC::Open3> has been upgraded from version 1.18 to 1.19.

If a Perl exception was thrown from inside this module, the exception
C<IPC::Open3> threw to the callers of C<open3> would have an irrelevant
message derived from C<$!> which was in an undefined state, instead of the
C<$@> message which triggers the failure path inside C<open3>.

=item *

L<Unicode::Collate> has been upgraded from version 1.12 to 1.14.

=item *

L<Unicode::Normalize> has been upgraded from version 1.18 to 1.19.

=back

=head2 Removed Modules and Pragmata

=over 4

=item *

XXX

=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 C<printf> and C<sprintf> builtins are now more careful about the
warnings they emit: argument reordering now disables the "redundant
argument" warning in all cases; and invalid format strings are no longer
treated as absorbing arguments (so "redundant argument" warnings can
correctly be emitted by such code).

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item VMS

=over

=item *

The minimum supported version of VMS is now v7.3-2, released in 2003.  As a
side effect of this change, VAX is no longer supported as the terminal
release of OpenVMS VAX was v7.3 in 2001.

=back

=back

=head1 Internal Changes

=over 4

=item *

C<sv_catpvf> and related functions (including C<sv_vcatpvfn_flags> when
called with a C<va_list> rather than an array of SV pointers) have never
handled argument reordering. Attempts to reorder arguments now yield an
exception, rather than being silently ignored.

=back

=head1 Selected Bug Fixes

=over 4

=item *

A leak in the XS typemap caused one scalar to be leaked each time a C<FILE *>
or a C<PerlIO *> was C<OUTPUT:>ed or imported to Perl, since perl 5.000. These
particular typemap entries are thought to be extremely rarely used by XS
modules. [perl #124181]

=item *

C<alarm()> and C<sleep()> will now warn if the argument is a negative number
and return undef. Previously they would pass the negative value to the
underlying C function which may have set up a timer with a surprising value.

=back

=head1 Acknowledgements

XXX Generate this with:

  perl Porting/acknowledgements.pl v5.23.1..HEAD

=head1 Reporting Bugs

If you find what you think is a bug, you might check the articles recently
posted to the comp.lang.perl.misc newsgroup and 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 please send it
to perl5-security-report@perl.org.  This points to a closed subscription
unarchived mailing list, which includes all the core committers, who will be
able to help assess the impact of issues, figure out a resolution, and help
co-ordinate the release of patches to mitigate or fix the problem across all
platforms on which Perl is supported.  Please only use this address for
security issues in the Perl core, not for modules independently distributed on
CPAN.

=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