Epigraph for 5.21.5

[perl5.git] / pod / perldelta.pod

=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.21.5

=head1 DESCRIPTION

This document describes differences between the 5.21.4 release and the 5.21.5
release.

If you are upgrading from an earlier release such as 5.21.3, first read
L<perl5214delta>, which describes differences between 5.21.3 and 5.21.4.

=head1 Core Enhancements

=head2 New double-diamond operator

C<<< <<>> >>> is like C<< <> >> but uses three-argument C<open> to open
each file in @ARGV.  So each element of @ARGV is an actual file name, and
"|foo" won't be treated as a pipe open.

=head2 Aliasing via reference

Variables and subroutines can now be aliased by assigning to a reference:

    \$c = \$d;
    \&x = \&y;

Or by using a backslash before a C<foreach> iterator variable, which is
perhaps the most useful idiom this feature provides:

    foreach \%hash (@array_of_hash_refs) { ... }

This feature is experimental and must be enabled via C<use feature
'refaliasing'>.  It will warn unless the C<experimental::refaliasing>
warnings category is disabled.

See L<perlref/Assigning to References>

=head2 Perl now supports POSIX 2008 locale currency additions.

On platforms that are able to handle POSIX.1-2008, the
hash returned by
L<C<POSIX::localeconv()>|perllocale/The localeconv function>
includes the international currency fields added by that version of the
POSIX standard.  These are
C<int_n_cs_precedes>,
C<int_n_sep_by_space>,
C<int_n_sign_posn>,
C<int_p_cs_precedes>,
C<int_p_sep_by_space>,
and
C<int_p_sign_posn>.

=head2 Packing infinity or not-a-number into a character is now fatal

Before, when trying to pack infinity or not-a-number into a
(signed) character, Perl would warn, and assumed you tried to
pack C<< 0xFF >>; if you gave it as an argument to C<< chr >>,
C<< U+FFFD >> was returned. 

But now, all such actions (C<< pack >>, C<< chr >>, and C<< print '%c' >>)
result in a fatal error.

=head2 Inf and NaN

Many small improvements, bug fixes and added test cases for dealing 
with math related to infinity and not-a-number.

=head1 Security

=head2 Perl is now compiled with -fstack-protector-strong if available

Perl has been compiled with the anti-stack-smashing option
C<-fstack-protector> since 5.10.1.  Now Perl uses the newer variant
called C<-fstack-protector-strong>, if available.  (This was added
already in 5.21.4.)

=head1 Deprecations

=head2 Use of multiple /x regexp modifiers

It is now deprecated to say something like any of the following:

    qr/foo/xx;
    /(?xax:foo)/;
    use re qw(/amxx);

That is, now C<x> should only occur once in any string of contiguous
regular expression pattern modifiers.  We do not believe there are any
occurrences of this in all of CPAN.  This is in preparation for a future
Perl release having C</xx> mean to allow white-space for readability in
bracketed character classes (those enclosed in square brackets:
C<[...]>).

=head1 Performance Enhancements

=over 4

=item *

C<length> is up to 20% faster for non-magical/non-tied scalars containing a
string if it is a non-utf8 string or if C<use bytes;> is in scope.

=item *

Non-magical/non-tied scalars that contain only a floating point value and are
on most Perl builds with 64 bit integers now use 8-32 less bytes of memory
depending on OS.

=item *

In C<@array = split>, the assignment can be optimized away with C<split>
writing directly to the array.  This optimisation was happening only for
package arrays other than @_ and only
sometimes.  Now this optimisation happens
almost all the time.

=item *

C<join> is now subject to constant folding.  Moreover, C<join> with a
scalar or constant for the separator and a single-item list to join is
simplified to a stringification.  The separator doesn't even get evaluated.

=item *

C<qq(@array)> is implemented using two ops: a stringify op and a join op.
If the qq contains nothing but a single array, the stringification is
optimized away.

=item *

C<our $var> and C<our($s,@a,%h)> in void context are no longer evaluated at
run time.  Even a whole sequence of C<our $foo;> statements will simply be
skipped over.  The same applies to C<state> variables.

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<attributes> has been upgraded from version 0.23 to 0.24.

Avoid reading beyond the end of a buffer. [perl #122629]

=item *

L<B> has been upgraded from version 1.51 to 1.52.

=item *

L<B::Concise> has been upgraded from version 0.993 to 0.994.

Null ops that are part of the execution chain are now given sequence
numbers.

Private flags for nulled ops are now dumped with mnemonics as they would be
for the non-nulled counterparts.

L<B::Deparse> has been upgraded from version 1.28 to 1.29.

Parenthesised arrays in lists passed to C<\> are now correctly deparsed
with parentheses (e.g., C<\(@a, (@b), @c)> now retains the parentheses
around @b), this preserving the flattening behaviour of referenced
parenthesised arrays.  Formerly, it only worked for one array: C<\(@a)>.

C<local our> is now deparsed correctly, with the C<our> included.

C<for($foo; !$bar; $baz) {...}> was deparsed without the C<!> (or C<not>).
This has been fixed.

Core keywords that conflict with lexical subroutines are now deparsed with
the C<CORE::> prefix.

C<foreach state $x (...) {...}> now deparses correctly with C<state> and
not C<my>.

C<our @array = split(...)> now deparses correctly with C<our> in those
cases where the assignment is optimized away.

=item *

L<B::Debug> has been upgraded from version 1.21 to 1.22.

=item *

L<B::Deparse> has been upgraded from version 1.28 to 1.29.

=item *

L<Compress::Raw::Bzip2> has been upgraded from version 2.064 to 2.066.

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.065 to 2.066.

=item *

L<CPAN::Meta> has been upgraded from version 2.142060 to 2.142690.

=item *

L<DynaLoader> has been upgraded from version 1.26 to 1.27.

Remove dl_nonlazy global if unused in Dynaloader. [perl #122926]

=item *

L<Errno> has been upgraded from version 1.20_04 to 1.21.

=item *

L<experimental> has been upgraded from version 0.010 to 0.012.

=item *

L<ExtUtils::CBuilder> has been upgraded from version 0.280219 to 0.280220.

=item *

L<ExtUtils::Miniperl> has been upgraded from version 1.02 to 1.03.

=item *

L<Fcntl> has been upgraded from version 1.11 to 1.13.

Add support for the Linux pipe buffer size fcntl() commands.

=item *

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

=item *

L<File::Find> has been upgraded from version 1.28 to 1.29.

Slightly faster module loading time.

=item *

L<File::Spec> has been upgraded from version 3.50 to 3.51.

=item *

L<HTTP::Tiny> has been upgraded from version 0.049 to 0.050.

=item *

The IO-Compress set of modules has been upgraded from version 2.064 to 2.066.

=item *

L<JSON::PP> has been upgraded from version 2.27203 to 2.27300.

=item *

The libnet collection of modules has been upgraded from version 1.27 to 3.02.

Support for IPv6 and SSL to Net::FTP, Net::NNTP, Net::POP3 and Net::SMTP.

Improvements in Net::SMTP authentication.

=item *

L<Module::CoreList> has been upgraded from version 5.20140920 to 5.20141020.

Updated to cover the latest releases of Perl.

=item *

L<Opcode> has been upgraded from version 1.28 to 1.29.

=item *

The PathTools module collection has been upgraded from version 3.50 to 3.51.

Slightly faster module loading time.

=item *

L<perlfaq> has been upgraded from version 5.0150045 to version 5.0150046.
[perl #123008]

=item *

L<POSIX> has been upgraded from version 1.43 to 1.45.

POSIX::tmpnam() now produces a deprecation warning.  [perl #122005]

=item *

L<re> has been upgraded from version 0.26 to 0.27.

=item *

L<Socket> has been upgraded from version 2.015 to 2.016.

=item *

L<Test::Simple> has been upgraded from version 1.001006 to 1.001008.

=item *

L<threads::shared> has been upgraded from version 1.46 to 1.47.

=item *

L<warnings> has been upgraded from version 1.26 to 1.28.

=item *

L<XSLoader> has been upgraded from version 0.17 to 0.18.

Allow XSLoader to load modules from a different namespace.
[perl #122455]

=back

=head1 Documentation

=head2 Changes to Existing Documentation

=head3 L<perlrecharclass>

=over 4

=item *

Clarifications have been added to L<perlrecharclass/Character Ranges>
to the effect that Perl guarantees that C<[A-Z]>, C<[a-z]>, C<[0-9]> and
any subranges thereof in regular expression bracketed character classes
are guaranteed to match exactly what a naive English speaker would
expect them to match, even on platforms (such as EBCDIC) where special
handling is required to accomplish this.

=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 New Diagnostics

=head3 New Errors

=over 4

=item *

L<Cannot chr %f|perldiag/"Cannot chr %f">

=item *

L<Cannot compress %f in pack|perldiag/"Cannot compress %f in pack">

=item *

L<Cannot pack %f with '%c'|perldiag/"Cannot pack %f with '%c'">

=item *

L<Cannot print %f with '%c'|perldiag/"Cannot printf %f with '%c'">

=back

=head2 Changes to Existing Diagnostics

=over 4

=item *

'"my" variable &foo::bar can't be in a package' has been reworded to say
'subroutine' instead of 'variable'.

=back

=head1 Testing

=over 4

=item *

Some regular expression tests are written in such a way that they will
run very slowly if certain optimizations break. These tests have been
moved into new files, F<< t/re/speed.t >> and F<< t/re/speed_thr.t >>,
and are run with a C<< watchdog() >>.

=back

=head1 Platform Support

=head2 Regained Platforms

IRIX and Tru64 platforms are working again.
(Some C<make test> failures remain.)

=head2 Platform-Specific Notes

=over 4

=item EBCDIC

Special handling is required on EBCDIC platforms to get C<qr/[i-j]/> to
match only C<"i"> and C<"j">, since there are 7 characters between the
code points for C<"i"> and C<"j">.  This special handling had only been
invoked when both ends of the range are literals.  Now it is also
invoked if any of the C<\N{...}> forms for specifying a character by
name or Unicode code point is used instead of a literal.  See
L<perlrecharclass/Character Ranges>.

=back

=head1 Internal Changes

=over 4

=item *

SVs of type SVt_NV are now bodyless when a build configure and platform allow
it, specifically C<sizeof(NV) <= sizeof(IV)>. The bodyless trick is the same one
as for IVs since 5.9.2, but for NVs, unlike IVs, is not guaranteed on all
platforms and build configurations.

=item *

The C<$DB::single>, C<$DB::signal> and C<$DB::trace> now have set and
get magic that stores their values as IVs and those IVs are used when
testing their values in C<pp_dbstate>.  This prevents perl from
recursing infinity if an overloaded object is assigned to any of those
variables. [perl #122445]

=item *

C<Perl_tmps_grow> which is marked as public API but undocumented has been
removed from public API. If you use C<EXTEND_MORTAL> macro in your XS code to
preextend the mortal stack, you are unaffected by this change.

=item *

C<cv_name>, which was introduced in 5.21.4, has been changed incompatibly.
It now has a flags field that allows the caller to specify whether the name
should be fully qualified.  See L<perlapi/cv_name>.

=item *

Internally Perl no longer uses the C<SVs_PADMY> flag.  C<SvPADMY()> now
returns a true value for anything not marked PADTMP.  C<SVs_PADMY> is now
defined as 0.

=item *

The macros SETsv and SETsvUN have been removed. They were no longer used
in the core since commit 6f1401dc2a, and have not been found present on
CPAN.

=item *

The C<< SvFAKE >> bit (unused on HVs) got informally reserved by
David Mitchell for future work on vtables.

=item *

The C<sv_catpvn_flags> function accepts C<SV_CATBYTES> and C<SV_CATUTF8>
flags, which specify whether the appended string is bytes or utf8,
respectively.

=item *

A new opcode class, C<< METHOP >> has been introduced, which holds
class/method related info needed at runtime to improve performance
of class/object method calls.

C<< OP_METHOD >> and C<< OP_METHOD_NAMED >> are moved from being
C<< UNOP/SVOP >> to being C<< METHOD >>.

=back

=head1 Selected Bug Fixes

=over 4

=item *

Locking and unlocking values via L<Hash::Util> or C<Internals::SvREADONLY>
no longer has any effect on values that are read-only to begin.
Previously, unlocking such values could result in crashes, hangs or
other erratic behaviour.

=item *

The internal C<looks_like_number> function (which L<Scalar::Util> provides
access to) began erroneously to return true for "-e1" in 5.21.4, affecting
also C<-'-e1'>.  This has been fixed.

=item *

The flip-flop operator (C<..> in scalar context) would return the same
scalar each time, unless the containing subroutine was called recursively.
Now it always returns a new scalar.  [perl #122829]

=item *

Some unterminated C<(?(...)...)> constructs in regular expressions would
either crash or give erroneous error messages.  C</(?(1)/> is one such
example.

=item *

C<pack "w", $tied> no longer calls FETCH twice.

=item *

List assignments like C<($x, $z) = (1, $y)> now work correctly if $x and $y
have been aliased by C<foreach>.

=item *

Some patterns including code blocks with syntax errors, such as
C</ (?{(^{})/>, would hang or fail assertions on debugging builds.  Now
they produce errors.

=item *

An assertion failure when parsing C<sort> with debugging enabled has been
fixed.  [perl #122771]

=item *

C<*a = *b; @a = split //, $b[1]> could do a bad read and produce junk
results.

=item *

In C<() = @array = split>, the C<() => at the beginning no longer confuses
the optimizer, making it assume a limit of 1.

=item *

Fatal warnings no longer prevent the output of syntax errors.
[perl #122966]

=item *

Fixed a NaN double to long double conversion error on VMS. For quiet NaNs
(and only on Itanium, not Alpha) negative infinity instead of NaN was
produced. 

=item *

Fixed the issue that caused C<< make distclean >> to leave files behind
that shouldn't. [perl #122820]

=item *

AIX now sets the length in C<< getsockopt >> correctly. [perl #120835],
[rt #91183], [rt #85570].

=item *

During the pattern optimization phase, we no longer recurse into
GOSUB/GOSTART when not SCF_DO_SUBSTR. This prevents the optimizer
to run "forever" and exhaust all memory. [perl #122283]

=item *

F<< t/op/crypt.t >> now performs SHA-256 algorithm if the default one
is disabled. [perl #121591]

=item *

Fixed an off-by-one error when setting the size of shared array.
[perl #122950]

=item *

Fixed a bug that could cause perl to execute an infinite loop during
compilation. [perl #122995]

=back

=head1 Acknowledgements

Perl 5.21.5 represents approximately 4 weeks of development since Perl 5.21.4
and contains approximately 40,000 lines of changes across 530 files from 33
authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 29,000 lines of changes to 390 .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 5.21.5:

Aaron Crane, Abigail, Alberto Simões, Andrew Fresh, Chris 'BinGOs' Williams,
Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, David Mitchell, Doug
Bell, Ed J, Father Chrysostomos, George Greer, Graham Knop, James E Keenan,
Jarkko Hietaniemi, Karen Etheridge, Karl Williamson, Leon Timmermans, Lukas
Mai, Niko Tyni, Peter Martini, Petr Písař, Rafael Garcia-Suarez, Reini Urban,
Ricardo Signes, Shlomi Fish, Steve Hay, syber, Tony Cook, Vincent Pit, Yves
Orton, Ævar Arnfjörð Bjarmason.

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 articles recently
posted to the comp.lang.perl.misc newsgroup and the perl bug database at
https://rt.perl.org/ .  There may also be information at
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