5 perldelta - what is new for perl v5.17.6
9 This document describes differences between the 5.17.5 release and the 5.17.6
12 If you are upgrading from an earlier release such as 5.17.4, first read
13 L<perl5175delta>, which describes differences between 5.17.4 and 5.17.5.
15 =head1 Core Enhancements
17 =head2 Character name aliases may now include non-Latin1-range characters
19 It is possible to define your own names for characters for use in
20 C<\N{...}>, C<charnames::vianame()>, etc. These names can now be
21 comprised of characters from the whole Unicode range. This allows for
22 names to be in your native language, and not just English. Certain
23 restrictions apply to the characters that may be used (you can't define
24 a name that has punctuation in it, for example). See L<charnames/CUSTOM
27 =head2 New hash function Murmurhash-32 (v3)
29 We have switched Perl's hash function to use Murmurhash-32, and added build
30 support for several other hash functions. This new function is expected to
31 perform equivalently to the old one for shorter strings and is faster,
32 potentially twice as fast, for hashing longer strings.
34 =head1 Incompatible Changes
36 =head2 An unknown character name in C<\N{...}> is now a syntax error
38 Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
39 substituted. Unicode now recommends that this situation be a syntax
40 error. Also, the previous behavior led to some confusing warnings and
41 behaviors, and since the REPLACEMENT CHARACTER has no use other than as
42 a stand-in for some unknown character, any code that has this problem is
45 =head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.
47 Since v5.12.0, it has been deprecated to use certain characters in
48 user-defined C<\N{...}> character names. These now cause a syntax
49 error. For example, it is now an error to begin a name with a digit,
52 my $undraftable = "\N{4F}"; # Syntax error!
54 or to have commas anywhere in the name. See L<charnames/CUSTOM ALIASES>
56 =head2 Per process hash randomization
58 The seed used by Perl's hash function is now random. This means that the
59 order which keys/values will be returned from functions like C<keys()>,
60 C<values()>, and C<each()> will differ from run to run.
62 This change was introduced to make Perl's hashes more robust to algorithmic
63 complexity attacks, and also because we discovered that it exposes hash
64 ordering dependency bugs and makes them easier to track down.
66 Toolchain maintainers might want to invest in additional infrastructure to
67 test for things like this. Running tests several times in a row and then
68 comparing results will make it easier to spot hash order dependencies in
69 code. Authors are strongly encouraged not to expose the key order of
70 Perl's hashes to insecure audiences.
72 =head2 PERL_HASH_SEED enviornment variable now takes a hex value
74 PERL_HASH_SEED no longer accepts an integer as a parameter, instead the
75 value is expected to be a binary string encoded in hex. This is to make
76 the infrastructure support hash seeds of arbitrary lengths which might
77 exceed that of an integer. (SipHash uses a 16 byte seed).
79 =head2 Hash::Util::hash_seed() now returns a string
81 Hash::Util::hash_seed() now returns a string instead of an integer. This
82 is to make the infrastructure support hash seeds of arbitrary lengths
83 which might exceed that of an integer. (SipHash uses a 16 byte seed).
85 =head2 Output of PERL_HASH_SEED_DEBUG has been changed
87 The environment variable PERL_HASH_SEED_DEBUG now shows both the hash
88 function perl was built with AND the seed, in hex in use for that process.
89 Code parsing this output, should it exist, must change to accomodate the
90 new format. Example of the new format:
92 $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
93 HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f
95 =head1 Performance Enhancements
101 Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
102 down to a single op, and are hence faster than before.
106 A new C preprocessor define NO_TAINT_SUPPORT was added that, if set, disables
107 Perl's taint support altogether. Using the -T or -t command line flags will
108 cause a fatal error. Beware that both core tests as well as many a CPAN
109 distribution's tests will fail with this change. On the upside, it provides
110 a small performance benefit due to reduced branching.
112 B<Do not enable this unless you know exactly what you are getting yourself
117 =head1 Modules and Pragmata
119 =head2 Updated Modules and Pragmata
125 L<Carp> has been upgraded from version 1.27 to 1.28.
127 Carp is no longer confused when C<caller> returns undef for a package that
132 L<CPAN> has been upgraded from version 1.98 to 1.99_51.
136 L<DynaLoader> has been upgraded from version 1.16 to 1.17.
140 L<Env> has been upgraded from version 1.03 to 1.04.
142 Its SPLICE implementation no longer misbehaves in list context.
146 L<Module::CoreList> has been upgraded from version 2.77 to 2.78.
150 L<Tie::Hash::NamedCapture> has been upgraded from version 0.08 to 0.09.
154 =head2 Changes to Existing Documentation
162 C<*foo{NAME}> and C<*foo{PACKAGE}>, which have existed since perl 5.005,
167 =head1 Platform Support
169 =head2 Discontinued Platforms
175 Support code relating to EPOC has been removed. EPOC was a family of
176 operating systems developed by Psion for mobile devices. It was the
177 predecessor of Symbian. The port was last updated in April 2002.
181 =head2 Platform-Specific Notes
187 Where possible, the case of filenames and command-line arguments is now
188 preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
189 C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
190 when extended parse is enabled in the process from which Perl is run.
194 Building on WinCE is now possible once again, although more work is required
195 to fully restore a clean build.
199 =head1 Internal Changes
205 The private Perl_croak_no_modify has had its context parameter removed. It is
206 now has a void prototype. Users of the public API croak_no_modify remain
211 Copy-on-write (shared hash key) scalars are no longer marked read-only.
212 C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
217 A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
218 optimiser will, where possible, substitute a single padrange op for a
219 pushmark followed by one or more pad ops, and possibly also skipping list
220 and nextstate ops. In addition, the op can carry out the tasks associated
221 with the RHS of a my(...) = @_ assignment, so those ops may be optimised
226 =head1 Selected Bug Fixes
232 Uninitialized warnings mentioning hash elements would only mention the
233 element name if it was not in the first bucket of the hash, due to an
238 A regular expression optimizer bug could cause multiline "^" to behave
239 incorrectly in the presence of line breaks, such that
240 C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
244 Failed C<fork> in list context no longer currupts the stack.
245 C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
246 if the C<fork> call failed.
250 Numerous memory leaks have been fixed, mostly involving tied variables that
251 die, regular expression character classes and code blocks, and syntax
256 Assigning a regular expression (C<${qr//}>) to a variable that happens to
257 hold a floating point number no longer causes assertion failures on
262 Assigning a regular expression to a scalar containing a number no longer
263 causes subsequent nummification to produce random numbers.
267 Assigning a regular expression to a magic variable no longer wipes away the
268 magic. This is a regression from 5.10.
272 Assigning a regular expression to a blessed scalar no longer results in
273 crashes. This is also a regression from 5.10.
277 Regular expression can now be assigned to tied hash and array elements with
278 flattening into strings.
282 Nummifying a regular expression no longer results in an uninitialized
287 Negative array indices no longer cause EXISTS methods of tied variables to
288 be ignored. This is a regression from 5.12.
292 Negative array indices no longer result in crashes on arrays tied to
297 C<$x = "(?{})"; /a++(?{})+$x/x> no longer erroneous produces an error (just
298 a warning, as expected). This was broken in 5.17.1.
302 C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF8 if the
303 left-hand scalar happened to have produced a UTF8 string the last time
304 overloading was invoked.
308 C<goto &sub> now uses the current value of @_, instead of using the array
309 the subroutine was originally called with. This means
310 C<local @_ = (...); goto &sub> now works [perl #43077].
314 If a debugger is invoked recursively, it no longer stomps on its own
315 lexical variables. Formerly under recursion all calls would share the same
316 set of lexical variables [perl #115742].
320 C<*_{ARRAY}> returned from a subroutine no longer spontaneously
325 =head1 Acknowledgements
327 Perl 5.17.6 represents approximately 5 weeks of development since Perl 5.17.5
328 and contains approximately 79,000 lines of changes across 460 files from 30
331 Perl continues to flourish into its third decade thanks to a vibrant community
332 of users and developers. The following people are known to have contributed the
333 improvements that became Perl 5.17.6:
335 Alexandr Ciornii, Brian Fraser, Chris 'BinGOs' Williams, Craig A. Berry,
336 Dagfinn Ilmari Mannsåker, Daniel Dragan, David Golden, David Mitchell, Dominic
337 Hargreaves, Eric Brine, Father Chrysostomos, Florian Ragwitz, Hugo van der
338 Sanden, James E Keenan, Jerry D. Hedden, Jesse Luehrs, Karl Williamson, Lukas
339 Mai, Nicholas Clark, Paul Johnson, Reini Urban, Ricardo Signes, Ruslan Zakirov,
340 Shlomi Fish, Steffen Müller, Steve Hay, Tom Wyant, Tony Cook, Vadim Konovalov,
343 The list above is almost certainly incomplete as it is automatically generated
344 from version control history. In particular, it does not include the names of
345 the (very much appreciated) contributors who reported issues to the Perl bug
348 Many of the changes included in this version originated in the CPAN modules
349 included in Perl's core. We're grateful to the entire CPAN community for
350 helping Perl to flourish.
352 For a more complete list of all of Perl's historical contributors, please see
353 the F<AUTHORS> file in the Perl source distribution.
355 =head1 Reporting Bugs
357 If you find what you think is a bug, you might check the articles recently
358 posted to the comp.lang.perl.misc newsgroup and the perl bug database at
359 http://rt.perl.org/perlbug/ . There may also be information at
360 http://www.perl.org/ , the Perl Home Page.
362 If you believe you have an unreported bug, please run the L<perlbug> program
363 included with your release. Be sure to trim your bug down to a tiny but
364 sufficient test case. Your bug report, along with the output of C<perl -V>,
365 will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
367 If the bug you are reporting has security implications, which make it
368 inappropriate to send to a publicly archived mailing list, then please send it
369 to perl5-security-report@perl.org. This points to a closed subscription
370 unarchived mailing list, which includes all the core committers, who will be
371 able to help assess the impact of issues, figure out a resolution, and help
372 co-ordinate the release of patches to mitigate or fix the problem across all
373 platforms on which Perl is supported. Please only use this address for
374 security issues in the Perl core, not for modules independently distributed on
379 The F<Changes> file for an explanation of how to view exhaustive details on
382 The F<INSTALL> file for how to build Perl.
384 The F<README> file for general stuff.
386 The F<Artistic> and F<Copying> files for copyright information.