=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.17.6

=head1 DESCRIPTION

This document describes differences between the 5.17.5 release and the 5.17.6
release.

If you are upgrading from an earlier release such as 5.17.4, first read
L<perl5175delta>, which describes differences between 5.17.4 and 5.17.5.

=head1 Core Enhancements

=head2 Character name aliases may now include non-Latin1-range characters

It is possible to define your own names for characters for use in
C<\N{...}>, C<charnames::vianame()>, etc.  These names can now be
comprised of characters from the whole Unicode range.  This allows for
names to be in your native language, and not just English.  Certain
restrictions apply to the characters that may be used (you can't define
a name that has punctuation in it, for example).  See L<charnames/CUSTOM
ALIASES>.

=head2 New hash function Murmurhash-32 (v3)

We have switched Perl's hash function to use Murmurhash-32, and added build
support for several other hash functions.  This new function is expected to
perform equivalently to the old one for shorter strings and is faster,
potentially twice as fast, for hashing longer strings.

=head1 Incompatible Changes

=head2 An unknown character name in C<\N{...}> is now a syntax error

Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
substituted.  Unicode now recommends that this situation be a syntax
error.  Also, the previous behavior led to some confusing warnings and
behaviors, and since the REPLACEMENT CHARACTER has no use other than as
a stand-in for some unknown character, any code that has this problem is
buggy.

=head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.

Since v5.12.0, it has been deprecated to use certain characters in
user-defined C<\N{...}> character names.  These now cause a syntax
error.  For example, it is now an error to begin a name with a digit,
such as in

 my $undraftable = "\N{4F}";    # Syntax error!

or to have commas anywhere in the name.  See L<charnames/CUSTOM ALIASES>

=head2 Per process hash randomization

The seed used by Perl's hash function is now random.  This means that the
order which keys/values will be returned from functions like C<keys()>,
C<values()>, and C<each()> will differ from run to run.

This change was introduced to make Perl's hashes more robust to algorithmic
complexity attacks, and also because we discovered that it exposes hash
ordering dependency bugs and makes them easier to track down.

Toolchain maintainers might want to invest in additional infrastructure to
test for things like this.  Running tests several times in a row and then
comparing results will make it easier to spot hash order dependencies in
code.  Authors are strongly encouraged not to expose the key order of
Perl's hashes to insecure audiences.

=head2 PERL_HASH_SEED enviornment variable now takes a hex value

PERL_HASH_SEED no longer accepts an integer as a parameter, instead the
value is expected to be a binary string encoded in hex.  This is to make
the infrastructure support hash seeds of arbitrary lengths which might
exceed that of an integer.  (SipHash uses a 16 byte seed).

=head2 Hash::Util::hash_seed() now returns a string

Hash::Util::hash_seed() now returns a string instead of an integer.  This
is to make the infrastructure support hash seeds of arbitrary lengths
which might exceed that of an integer.  (SipHash uses a 16 byte seed).

=head2 Output of PERL_HASH_SEED_DEBUG has been changed

The environment variable PERL_HASH_SEED_DEBUG now shows both the hash
function perl was built with AND the seed, in hex in use for that process.
Code parsing this output, should it exist, must change to accomodate the
new format.  Example of the new format:

    $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
    HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f

=head1 Performance Enhancements

=over 4

=item *

Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
down to a single op, and are hence faster than before.

=item *

A new C preprocessor define NO_TAINT_SUPPORT was added that, if set, disables
Perl's taint support altogether.  Using the -T or -t command line flags will
cause a fatal error.  Beware that both core tests as well as many a CPAN
distribution's tests will fail with this change.  On the upside, it provides
a small performance benefit due to reduced branching.

B<Do not enable this unless you know exactly what you are getting yourself
into.>

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<Carp> has been upgraded from version 1.27 to 1.28.

Carp is no longer confused when C<caller> returns undef for a package that
has been deleted.

=item *

L<CPAN> has been upgraded from version 1.98 to 1.99_51.

=item *

L<DynaLoader> has been upgraded from version 1.16 to 1.17.

=item *

L<Env> has been upgraded from version 1.03 to 1.04.

Its SPLICE implementation no longer misbehaves in list context.

=item *

L<Module::CoreList> has been upgraded from version 2.77 to 2.78.

=item *

L<Tie::Hash::NamedCapture> has been upgraded from version 0.08 to 0.09.

=back

=head2 Changes to Existing Documentation

=head3 L<perlref>

=over 4

=item *

C<*foo{NAME}> and C<*foo{PACKAGE}>, which have existed since perl 5.005,
are now documented.

=back

=head1 Platform Support

=head2 Discontinued Platforms

=over 4

=item EPOC

Support code relating to EPOC has been removed.  EPOC was a family of
operating systems developed by Psion for mobile devices.  It was the
predecessor of Symbian.  The port was last updated in April 2002.

=back

=head2 Platform-Specific Notes

=over 4

=item VMS

Where possible, the case of filenames and command-line arguments is now
preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
C<DECC$ARGV_PARSE_STYLE> at start-up time.  The latter only takes effect
when extended parse is enabled in the process from which Perl is run.

=item WinCE

Building on WinCE is now possible once again, although more work is required
to fully restore a clean build.

=back

=head1 Internal Changes

=over 4

=item *

The private Perl_croak_no_modify has had its context parameter removed.  It is
now has a void prototype.  Users of the public API croak_no_modify remain
unaffected.

=item *

Copy-on-write (shared hash key) scalars are no longer marked read-only.
C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
true.

=item *

A new op type, C<OP_PADRANGE> has been introduced.  The perl peephole
optimiser will, where possible, substitute a single padrange op for a
pushmark followed by one or more pad ops, and possibly also skipping list
and nextstate ops.  In addition, the op can carry out the tasks associated
with the RHS of a my(...) = @_ assignment, so those ops may be optimised
away too.

=back

=head1 Selected Bug Fixes

=over 4

=item *

Uninitialized warnings mentioning hash elements would only mention the
element name if it was not in the first bucket of the hash, due to an
off-by-one error.

=item *

A regular expression optimizer bug could cause multiline "^" to behave
incorrectly in the presence of line breaks, such that
C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].

=item *

Failed C<fork> in list context no longer currupts the stack.
C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
if the C<fork> call failed.

=item *

Numerous memory leaks have been fixed, mostly involving tied variables that
die, regular expression character classes and code blocks, and syntax
errors.

=item *

Assigning a regular expression (C<${qr//}>) to a variable that happens to
hold a floating point number no longer causes assertion failures on
debugging builds.

=item *

Assigning a regular expression to a scalar containing a number no longer
causes subsequent nummification to produce random numbers.

=item *

Assigning a regular expression to a magic variable no longer wipes away the
magic.  This is a regression from 5.10.

=item *

Assigning a regular expression to a blessed scalar no longer results in
crashes.  This is also a regression from 5.10.

=item *

Regular expression can now be assigned to tied hash and array elements with
flattening into strings.

=item *

Nummifying a regular expression no longer results in an uninitialized
warning.

=item *

Negative array indices no longer cause EXISTS methods of tied variables to
be ignored.  This is a regression from 5.12.

=item *

Negative array indices no longer result in crashes on arrays tied to
non-objects.

=item *

C<$x = "(?{})"; /a++(?{})+$x/x> no longer erroneous produces an error (just
a warning, as expected).  This was broken in 5.17.1.

=item *

C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF8 if the
left-hand scalar happened to have produced a UTF8 string the last time
overloading was invoked.

=item *

C<goto &sub> now uses the current value of @_, instead of using the array
the subroutine was originally called with.  This means
C<local @_ = (...); goto &sub> now works [perl #43077].

=item *

If a debugger is invoked recursively, it no longer stomps on its own
lexical variables.  Formerly under recursion all calls would share the same
set of lexical variables [perl #115742].

=item *

C<*_{ARRAY}> returned from a subroutine no longer spontaneously
becomes empty.

=back

=head1 Acknowledgements

Perl 5.17.6 represents approximately 5 weeks of development since Perl 5.17.5
and contains approximately 79,000 lines of changes across 460 files from 30
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 5.17.6:

Alexandr Ciornii, Brian Fraser, Chris 'BinGOs' Williams, Craig A. Berry,
Dagfinn Ilmari Mannsåker, Daniel Dragan, David Golden, David Mitchell, Dominic
Hargreaves, Eric Brine, Father Chrysostomos, Florian Ragwitz, Hugo van der
Sanden, James E Keenan, Jerry D. Hedden, Jesse Luehrs, Karl Williamson, Lukas
Mai, Nicholas Clark, Paul Johnson, Reini Urban, Ricardo Signes, Ruslan Zakirov,
Shlomi Fish, Steffen Müller, Steve Hay, Tom Wyant, Tony Cook, Vadim Konovalov,
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 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