path: root/pod/perl5151delta.pod

=encoding utf8

=head1 NAME

perl5151delta - what is new for perl v5.15.1

=head1 DESCRIPTION

This document describes differences between the 5.15.0 release and
the 5.15.1 release.

If you are upgrading from an earlier release such as 5.14.0, first read
L<perl5150delta>, which describes differences between 5.14.0 and
5.15.0.

=head1 Core Enhancements

=head2 C<splice()> doesn't warn when truncating

You can now limit the size of an array using C<splice(@a,MAX_LEN)> without
worrying about warnings.

=head2 The C<\$> prototype accepts any scalar lvalue

The C<\$> and C<\[$]> subroutine prototypes now accept any scalar lvalue
argument.  Previously they only accepted scalars beginning with C<$> and
hash and array elements.  This change makes them consistent with the way
the built-in C<read> and C<recv> functions (among others) parse their
arguments. This means that one can override the built-in functions with
custom subroutines that parse their arguments the same way.

=head2 You can now C<study> more than one string

The restriction that you can only have one C<study> active at a time has been
removed. You can now usefully C<study> as many strings as you want (until you
exhaust memory).

=head2 The Unicode C<Script_Extensions> property is now supported.

New in Unicode 6.0, this is an improved C<Script> property.  Details
are in L<perlunicode/Scripts>.

=head2 DTrace probes for interpreter phase change

The C<phase-change> probes will fire when the interpreter's phase
changes, which tracks the C<${^GLOBAL_PHASE}> variable. C<arg0> is
the new phase name; C<arg1> is the old one. This is useful mostly
for limiting your instrumentation to one or more of: compile time,
run time, destruct time.

=head2 New Pad API

Many new functions have been added to the API for manipulating lexical
pads.  See L<perlapi/Pad Data Structures> for more information.

=head1 Performance Enhancements

=over 4

=item *

The short-circuiting operators C<&&>, C<||>, and C<//>, when chained
(such as C<$a || $b || $c>), are now considerably faster to short-circuit,
due to reduced optree traversal.

=item *

The implementation of C<s///r> makes one fewer copy of the scalar's value.

=item *

If a studied scalar is C<split> with a regex, the engine will now take
advantage of the C<study> data.

=item *

C<study> now uses considerably less memory for shorter strings. Strings shorter
than 65535 characters use roughly half the memory than previously, strings
shorter than 255 characters use roughly one quarter of the memory.

=item *

Recursive calls to lvalue subroutines in lvalue scalar context use less
memory.

=back

=head1 Modules and Pragmata

=head2 New Modules and Pragmata

=over 4

=item *

The logic for parsing, merging, and dumping XS typemaps has been extracted
from C<ExtUtils::ParseXS> into a module of its own, L<ExtUtils::Typemaps>.
C<ExtUtils::Typemaps> offers an interface to typemap handling outside of
the scope of the XS compiler itself.

As a first use case of the improved API and extensibility, typemaps can now
be included inline in XS code with a HEREDOC-like syntax:

  TYPEMAP: <<END_TYPEMAP
  MyType	T_IV
  END_TYPEMAP

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

L<B::Deparse> has been upgrade from version 1.05 to 1.06.

It now correctly deparses interpolation of punctuation variables (like
C<@*>) that do not interpolate without braces [perl #93990].

=item *

L<CGI> has been upgraded from version 3.54 to version 3.55.

Things that may break your code:

C<url()> was fixed to return C<PATH_INFO> when it is explicitly requested
with either the C<path=E<gt>1> or C<path_info=E<gt>1> flag.

If your code is running under mod_rewrite (or compatible) and you are calling C<self_url()> or
you are calling C<url()> and passing C<path_info=E<gt>1>, These methods will actually be
returning C<PATH_INFO> now, as you have explicitly requested, or has C<self_url()>
has requested on your behalf.

The C<PATH_INFO> has been omitted in such URLs since the issue was introduced
in the 3.12 release in December, 2005.

This bug is so old your application may have come to depend on it or
workaround it. Check for application before upgrading to this release.

Examples of affected method calls:

  $q->url(-absolute => 1, -query => 1, -path_info => 1 )
  $q->url(-path=>1)
  $q->url(-full=>1,-path=>1)
  $q->url(-rewrite=>1,-path=>1)
  $q->self_url();

=item *

L<CPANPLUS> has been upgraded from version 0.9105 to version 0.9108

=item *

L<Compress::Raw::Bzip2> has been upgraded from version 2.035 to version 2.037

=item *

L<Compress::Raw::Zlib> has been upgraded from version 2.035 to version 2.037

Added offset parameter to CRC32

=item *

L<Compress::Zlib> has been upgraded from version 2.035 to version 2.037

IO::Compress::Zip and IO::Uncompress::Unzip now have support for LZMA (method 14).
There is a fix for a CRC issue in IO::Compress::Unzip and it supports Streamed
Stored context now. And fixed a Zip64 issue in
IO::Compress::Zip when the content size was exactly 0xFFFFFFFF.

=item *

L<Cwd> has been upgraded from version 3.36 to 3.37, to address an
incompatibility with the EPIC debugger.

=item *

L<ExtUtils::MakeMaker> has been upgraded from version 6.57_05 to version 6.58

=item *

L<ExtUtils::ParseXS> has been upgraded from version 2.2210 to 3.00_01.

Much of L<ExtUtils::ParseXS>, the module behind the XS compiler C<xsubpp>,
was rewritten and cleaned up. It has been made somewhat more extensible
and now finally uses strictures.

The typemap logic has been moved into a separate module,
L<ExtUtils::Typemaps>.  See L</New Modules and Pragmata>, above.

=item *

L<HTTP::Tiny> has been upgraded from version 0.012 to version 0.013.

Added support for using C<$ENV{http_proxy}> to set the default proxy host.

=item *

L<IPC::Cmd> has been upgraded from version 0.70 to version 0.72

Capturing of command output (both C<STDOUT> and C<STDERR>) is now supported
using L<IPC::Open3> on MSWin32 without requiring L<IPC::Run>.

=item *

L<Locale::Codes> has been upgraded from version 3.16 to version 3.17

Added Language Extension codes (langext) and Language Variation codes
(langvar) as defined in the IANA language registry.

Added language codes from ISO 639-5

Added language/script codes from the IANA language subtag
registry

Fixed an uninitialized value warning.  RT 67438

Fixed the return value for the all_XXX_codes and all_XXX_names functions.  RT 69100

Reorganized modules to move Locale::MODULE to Locale::Codes::MODULE to
allow for cleaner future additions.  The original four modules (Locale::Language,
Locale::Currency, Locale::Country, Locale::Script) will continue to work, but
all new sets of codes will be added in the Locale::Codes namespace.

=item *

L<Math::BigInt::FastCalc> has been upgraded from version 0.28 to version 0.29.

The XS code is now compiled with C<PERL_NO_GET_CONTEXT>, which will aid
performance under ithreads.

=item *

L<Module::CoreList> has been upgraded from version 2.51 to 2.54.

Some extraneous (and erroneous) entries have been removed
[rt.cpan.org #69108].

The C<corelist> utility now understands the C<-r> option for
displaying Perl release dates.

=item *

L<Pod::Perldoc> has been upgraded from version 3.15_05 to 3.15_06.

The B<-v> option now fetches the right section for C<$0>.

=item *

L<Pod::Simple> has been upgraded from version 3.16 to version 3.18

=item *

L<Unicode::Collate> has been upgraded from version 0.76 to version 0.77

Applied [perl #93470] silencing compiler warnings with -Wwrite-strings

=item *

L<Win32API::File> has been upgraded from version 0.1101 to version 0.1200

Added SetStdHandle and GetStdHandle functions

=item *

L<attributes> has been upgraded from version 0.14 to 0.15, as part of the
lvalue attribute warnings fix.  See L</Selected Bug Fixes>, below.

=item *

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

It now knows how to find descriptions for diagnostic messages ending with a
dot, instead getting confused by it.

=item *

L<threads> has been upgraded from version 1.83 to 1.84

An unused variable was removed from the XS code.

=back

=head2 Removed Modules and Pragmata

=over 4

=item *

Perl 4-era .pl libraries

Perl used to bundle a handful of library files that predate Perl 5. Most of
these files, which have been deprecated since version 5.14.0, have now been
removed. If your code still relies on these libraries, you can install them
again from L<Perl4::CoreLibs> on CPAN.

=back

=head1 Documentation

=head2 New Documentation

=head3 L<perldtrace>

L<perldtrace> describes Perl's DTrace support, listing the provided probes
and gives examples of their use.

=head3 L<perl5141delta>

The delta file for Perl 5.14.1 has been copied to blead.

=head2 Changes to Existing Documentation

=over 4

=item *

L<perlxs> was extended with documentation on inline typemaps.

=item *

L<perlref> has a new L<Circular References|perlref/Circular References>
section explaining how circularities may not be freed and how to solve that
with weak references.

=item *

The documentation for smart match in L<perlsyn> has been corrected for the
case of C<undef> on the left-hand side.  The list of different smart match
behaviours had an item in the wrong place.

=item *

Parts of L<perlapi> were clarified, and Perl equivalents of some C
functions have been added as an additional mode of exposition.

=item *

A few parts of L<perlre> and L<perlrecharclass> were clarified.

=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 L<Invalid version format|perldiag/"Invalid version format (%s)">
error message now says "negative version number" within the parentheses,
rather than "non-numeric data", for negative numbers.

=item *

The two warnings
L<Possible attempt to put comments in qw() list|perldiag/"Possible attempt to put comments in qw() list">
and
L<Possible attempt to separate words with commas|perldiag/"Possible attempt to separate words with commas">
are no longer mutually exclusive: the same C<qw> construct may produce
both.

=item *

Warnings that mention the names of lexical (C<my>) variables with Unicode
characters in them now respect the presence or absence of the C<:utf8>
layer on the output handle, instead of outputting UTF8 regardless.  Also,
the correct names are included in the strings passed to C<$SIG{__WARN__}>
handlers, rather than the raw UTF8 bytes.

=back

=head1 Testing

=over 4

=item *

F<t/run/dtrace.t> was added to test Perl's DTrace support. This
test will only be run if your Perl was built with C<-Dusedtrace>
and if calling C<dtrace> actually lets you instrument code. This
generally requires being run as root, so this test file is primarily
intended for use by the dtrace subcommittee of p5p.

=item *

F<t/win32/runenv.t> was added to test aspects of Perl's environment
variable handling on MSWin32 platforms.  Previously, such tests were
skipped on MSWin32 platforms.

=item *

Some bitrot has been fixed in the miniperl test suite, so that it now
nearly passes.  The minitest is normally only run when building the
full perl fails, so it was liable to fall into disrepair making it a
less useful debugging tool.  When it is fully passing it is hoped to
start including it in regular smoke tests, so that future bitrot will
be quickly detected.

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=head3 Windows

=over

=item *

On Windows 7, 2008 and Vista, C<@INC> is now always properly populated
based on the value of PERL5LIB set in the environment.  Previously,
values of PERL5LIB longer than 32766 bytes were skipped when C<@INC>
was being populated.  Tests for environment handling were
also added (see L</Testing> section).  Fixes
L<RT #87322|https://rt.perl.org/rt3/Public/Bug/Display.html?id=87322>.

=back

=head1 Internal Changes

=over 4

=item *

The experimental C<fetch_cop_label> function has been renamed to
C<cop_fetch_label>.

=item *

The C<cop_store_label> function has been added to the API, but is
experimental.

=back

=head1 Selected Bug Fixes

=over 4

=item *

Applying the :lvalue attribute to subroutine that is already defined does
not work properly, as the attribute changes the way the sub is compiled.
Hence, Perl 5.12 began warning when an attempt is made to apply the
attribute to an already defined sub.  In such cases, the attribute is
discarded.

But the change in 5.12 missed the case where custom attributes are also
present: that case still silently and ineffectively applied the attribute.
That omission has now been corrected.  C<sub foo :lvalue :Whatever> (when
C<foo> is already defined) now warns about the :lvalue attribute, and does
not apply it.

L<attributes.pm|attributes> has likewise been updated to warn and not apply
the attribute.

=item *

The remaining discrepancies between explicit and implicit return from
lvalue subroutines have been resolved.  They mainly involved which error
message to display when a read-only value is returned in lvalue context.
Also, returning a PADTMP (the result of most built-ins, like C<index>) in
lvalue context is now forbidden for explicit return, as it always has been
for implicit return.  This is not a regression from 5.14, as all the cases
in which it could happen where previously syntax errors.

=item *

Explicitly returning a tied C<my> variable from an lvalue subroutine in
list lvalue context used to clear the variable before the assignment could
happen.  This is something that was missed when explicit return was made to
work in 5.15.0.

=item *

A minor memory leak, introduced in 5.15.0, has been fixed.  It would occur
when a hash is freed that has had its current iterator deleted
[perl #93454].

=item *

The C<prototype> function no longer dies for the C<__FILE__>, C<__LINE__>
and C<__PACKAGE__> directives.  It now returns an empty-string prototype
for them, because they are syntactically very similar to nullary functions
like C<time>.

=item *

C<prototype> now returns C<undef> for all overridable infix operators,
such as C<eq>, which are not callable in any way resembling functions.
It used to return incorrect prototypes for some and die for others
[perl #94984].

=item *

A bug affecting lvalue context propagation through nested lvalue subroutine
calls has been fixed.  Previously, returning a value in nested rvalue
context would be treated as lvalue context by the inner subroutine call,
resulting in some values (such as read-only values) being rejected.

=item *

Some core bugs affecting L<Hash::Util> have been fixed: locking a hash
element that is a glob copy no longer causes subsequent assignment to it to
corrupt the glob, and unlocking a hash element that holds a copy-on-write
scalar no longer causes modifications to that scalar to modify other
scalars that were sharing the same string buffer.

=item *

C<when> blocks are now capable of returning variables declared inside the
enclosing C<given> block [perl #93548].

=item *

A problem with context propagation when a C<do> block is an argument to
C<return> has been fixed.  It used to cause C<undef> to be returned in
some cases of a C<return> inside an C<if> block which itself is followed by
another C<return>.

=item *

Calling C<index> with a tainted constant no longer causes constants in
subsequently compiled code to become tainted [perl #64804].

=item *

Use of lexical (C<my>) variables in code blocks embedded in regular
expressions will no longer result in memory corruption or crashes.

Nevertheless, these code blocks are still experimental, as there are still
problems with the wrong variables being closed over (in loops for instance)
and with abnormal exiting (e.g., C<die>) causing memory corruption.

=item *

The C<SvIsCOW> C macro now returns false for read-only copies of typeglobs,
such as those created by:

  $hash{elem} = *foo;
  Hash::Util::lock_value %hash, 'elem';

It used to return true.

=item *

Assignment to C<$^A> (the format output accumulator) now recalculates
the number of lines output.

=item *

The regexp optimiser no longer crashes on debugging builds when merging
fixed-string nodes with inconvenient contents.

=back

=head1 Acknowledgements

Perl 5.15.1 represents approximately 5 weeks of development since Perl 5.15.0
and contains approximately 220,000 lines of changes across 650 files from 37
authors.

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 5.15.1:

Abhijit Menon-Sen, Alan Haggai Alavi, Brian Fraser, Brian Greenfield, Chris
'BinGOs' Williams, Claes Jacobsson, Craig A. Berry, Dave Rolsky, David Golden,
David Mitchell, Dee Newcum, Eric Brine, Father Chrysostomos, Florian Ragwitz,
Gerard Goossen, H.Merijn Brand, Hojung Yoon, James E Keenan, Jesse Luehrs,
Jesse Vincent, John Peacock, Karl Williamson, Keith Thompson, Leon Brocard,
Matthew Horsfall, Nicholas Clark, Niko Tyni, Phil Monsen, Reini Urban, Ricardo
Signes, Robin Barker, Sam Kimbrel, Shawn M Moore, Shlomi Fish, Steffen Müller,
Vincent Pit, Zefram.

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 http://rt.perl.org/perlbug/ .  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