perldelta tweaks on the shift.

[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 v5.23.1

=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 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.

[ List each enhancement as a =head2 entry ]

=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 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

=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

XXX Any deprecated features, syntax, modules etc. should be listed here.

=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 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 a =item entry ]

=over 4

=item *

XXX

=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.

[ 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 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

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.

=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">

=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 *

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 Utility Changes

XXX Changes to installed programs such as F<perlbug> 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 a =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.

[ List each test improvement as a =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 a =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 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

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 a =item entry ]

=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

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 a =item entry ]

=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]

=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 a =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 has died, we've added a short obituary
here.

=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