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1=encoding utf8
2
3=head1 NAME
4
7e7cfa2d 5perldelta - what is new for perl v5.17.6
e128ab2c 6
4eabcf70 7=head1 DESCRIPTION
6db9054f 8
7e7cfa2d 9This document describes differences between the 5.17.5 release and the 5.17.6
e08634c5 10release.
6db9054f 11
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12If you are upgrading from an earlier release such as 5.17.4, first read
13L<perl5175delta>, which describes differences between 5.17.4 and 5.17.5.
5faa50e9 14
5d8c8c8a 15=head1 Core Enhancements
4db91b87 16
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17=head2 Character name aliases may now include non-Latin1-range characters
18
19It is possible to define your own names for characters for use in
20C<\N{...}>, C<charnames::vianame()>, etc. These names can now be
21comprised of characters from the whole Unicode range. This allows for
22names to be in your native language, and not just English. Certain
23restrictions apply to the characters that may be used (you can't define
24a name that has punctuation in it, for example). See L<charnames/CUSTOM
25ALIASES>.
26
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27=head2 New hash function Murmurhash-32 (v3)
28
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29We have switched Perl's hash function to use Murmurhash-32, and added build
30support for several other hash functions. This new function is expected to
31perform equivalently to the old one for shorter strings and is faster,
32potentially twice as fast, for hashing longer strings.
86148eee 33
916c45d9 34=head1 Incompatible Changes
9c5f5e7a 35
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36=head2 An unknown character name in C<\N{...}> is now a syntax error
37
38Previously, it warned, and the Unicode REPLACEMENT CHARACTER was
39substituted. Unicode now recommends that this situation be a syntax
40error. Also, the previous behavior led to some confusing warnings and
41behaviors, and since the REPLACEMENT CHARACTER has no use other than as
42a stand-in for some unknown character, any code that has this problem is
43buggy.
44
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45=head2 Formerly deprecated characters in C<\N{}> character name aliases are now errors.
46
47Since v5.12.0, it has been deprecated to use certain characters in
48user-defined C<\N{...}> character names. These now cause a syntax
49error. For example, it is now an error to begin a name with a digit,
50such as in
51
52 my $undraftable = "\N{4F}"; # Syntax error!
53
54or to have commas anywhere in the name. See L<charnames/CUSTOM ALIASES>
55
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56=head2 Per process hash randomization
57
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58The seed used by Perl's hash function is now random. This means that the
59order which keys/values will be returned from functions like C<keys()>,
60C<values()>, and C<each()> will differ from run to run.
86148eee 61
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62This change was introduced to make Perl's hashes more robust to algorithmic
63complexity attacks, and also because we discovered that it exposes hash
64ordering dependency bugs and makes them easier to track down.
86148eee 65
1611045a 66Toolchain maintainers might want to invest in additional infrastructure to
0f773ca4 67test for things like this. Running tests several times in a row and then
1611045a 68comparing results will make it easier to spot hash order dependencies in
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69code. Authors are strongly encouraged not to expose the key order of
70Perl's hashes to insecure audiences.
1611045a 71
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72=head2 PERL_HASH_SEED enviornment variable now takes a hex value
73
74PERL_HASH_SEED no longer accepts an integer as a parameter, instead the
0f773ca4 75value is expected to be a binary string encoded in hex. This is to make
7a7a10c7 76the infrastructure support hash seeds of arbitrary lengths which might
0f773ca4 77exceed that of an integer. (SipHash uses a 16 byte seed).
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78
79=head2 Hash::Util::hash_seed() now returns a string
80
0f773ca4 81Hash::Util::hash_seed() now returns a string instead of an integer. This
7a7a10c7 82is to make the infrastructure support hash seeds of arbitrary lengths
0f773ca4 83which might exceed that of an integer. (SipHash uses a 16 byte seed).
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84
85=head2 Output of PERL_HASH_SEED_DEBUG has been changed
86
87The environment variable PERL_HASH_SEED_DEBUG now shows both the hash
88function perl was built with AND the seed, in hex in use for that process.
89Code parsing this output, should it exist, must change to accomodate the
0f773ca4 90new format. Example of the new format:
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91
92 $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
93 HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f
94
5d8c8c8a 95=head1 Performance Enhancements
45f11e9c 96
916c45d9 97=over 4
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98
99=item *
100
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101Lists of lexical variable declarations (C<my($x, $y)>) are now optimised
102down to a single op, and are hence faster than before.
0ace302a 103
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104=item *
105
106A new C preprocessor define NO_TAINT_SUPPORT was added that, if set, disables
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107Perl's taint support altogether. Using the -T or -t command line flags will
108cause a fatal error. Beware that both core tests as well as many a CPAN
109distribution's tests will fail with this change. On the upside, it provides
32209f41 110a small performance benefit due to reduced branching.
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111
112B<Do not enable this unless you know exactly what you are getting yourself
113into.>
32209f41 114
5d8c8c8a 115=back
5faa50e9 116
5d8c8c8a 117=head1 Modules and Pragmata
5faa50e9 118
916c45d9 119=head2 Updated Modules and Pragmata
4cc02608 120
916c45d9 121=over 4
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122
123=item *
124
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125L<Carp> has been upgraded from version 1.27 to 1.28.
126
127Carp is no longer confused when C<caller> returns undef for a package that
128has been deleted.
129
130=item *
131
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132L<CPAN> has been upgraded from version 1.98 to 1.99_51.
133
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134=item *
135
136L<DynaLoader> has been upgraded from version 1.16 to 1.17.
137
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138=item *
139
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140L<Env> has been upgraded from version 1.03 to 1.04.
141
142Its SPLICE implementation no longer misbehaves in list context.
143
144=item *
145
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146L<Module::CoreList> has been upgraded from version 2.77 to 2.78.
147
148=item *
149
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150L<Tie::Hash::NamedCapture> has been upgraded from version 0.08 to 0.09.
151
5d8c8c8a 152=back
5f877a7f 153
5d8c8c8a 154=head2 Changes to Existing Documentation
1ea91bbe 155
c9ac5216 156=head3 L<perlref>
5faa50e9 157
5d8c8c8a 158=over 4
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159
160=item *
161
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162C<*foo{NAME}> and C<*foo{PACKAGE}>, which have existed since perl 5.005,
163are now documented.
5faa50e9 164
916c45d9 165=back
9c5f5e7a 166
5d8c8c8a 167=head1 Platform Support
4db91b87 168
5d8c8c8a 169=head2 Discontinued Platforms
4db91b87 170
5d8c8c8a 171=over 4
4db91b87 172
739a0b84 173=item EPOC
4db91b87 174
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175Support code relating to EPOC has been removed. EPOC was a family of
176operating systems developed by Psion for mobile devices. It was the
177predecessor of Symbian. The port was last updated in April 2002.
4db91b87 178
5d8c8c8a 179=back
5faa50e9 180
5d8c8c8a 181=head2 Platform-Specific Notes
5faa50e9 182
5d8c8c8a 183=over 4
5faa50e9 184
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185=item VMS
186
187Where possible, the case of filenames and command-line arguments is now
188preserved by enabling the CRTL features C<DECC$EFS_CASE_PRESERVE> and
189C<DECC$ARGV_PARSE_STYLE> at start-up time. The latter only takes effect
190when extended parse is enabled in the process from which Perl is run.
191
6998fcfc 192=item WinCE
5faa50e9 193
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194Building on WinCE is now possible once again, although more work is required
195to fully restore a clean build.
5faa50e9 196
5d8c8c8a 197=back
5faa50e9 198
5d8c8c8a 199=head1 Internal Changes
5faa50e9 200
5d8c8c8a 201=over 4
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202
203=item *
204
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205The private Perl_croak_no_modify has had its context parameter removed. It is
206now has a void prototype. Users of the public API croak_no_modify remain
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207unaffected.
208
209=item *
210
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211Copy-on-write (shared hash key) scalars are no longer marked read-only.
212C<SvREADONLY> returns false on such an SV, but C<SvIsCOW> still returns
213true.
90814a4e 214
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215=item *
216
0f773ca4 217A new op type, C<OP_PADRANGE> has been introduced. The perl peephole
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218optimiser will, where possible, substitute a single padrange op for a
219pushmark followed by one or more pad ops, and possibly also skipping list
0f773ca4 220and nextstate ops. In addition, the op can carry out the tasks associated
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221with the RHS of a my(...) = @_ assignment, so those ops may be optimised
222away too.
223
5d8c8c8a 224=back
31c15ce5 225
5d8c8c8a 226=head1 Selected Bug Fixes
4db91b87 227
5d8c8c8a 228=over 4
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229
230=item *
231
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232Uninitialized warnings mentioning hash elements would only mention the
233element name if it was not in the first bucket of the hash, due to an
234off-by-one error.
235
236=item *
237
238A regular expression optimizer bug could cause multiline "^" to behave
239incorrectly in the presence of line breaks, such that
240C<"/\n\n" =~ m#\A(?:^/$)#im> would not match [perl #115242].
241
242=item *
243
244Failed C<fork> in list context no longer currupts the stack.
245C<@a = (1, 2, fork, 3)> used to gobble up the 2 and assign C<(1, undef, 3)>
246if the C<fork> call failed.
247
248=item *
249
250Numerous memory leaks have been fixed, mostly involving tied variables that
251die, regular expression character classes and code blocks, and syntax
252errors.
253
254=item *
255
256Assigning a regular expression (C<${qr//}>) to a variable that happens to
257hold a floating point number no longer causes assertion failures on
258debugging builds.
259
260=item *
261
262Assigning a regular expression to a scalar containing a number no longer
263causes subsequent nummification to produce random numbers.
264
265=item *
266
267Assigning a regular expression to a magic variable no longer wipes away the
268magic. This is a regression from 5.10.
269
270=item *
271
272Assigning a regular expression to a blessed scalar no longer results in
273crashes. This is also a regression from 5.10.
274
275=item *
276
277Regular expression can now be assigned to tied hash and array elements with
278flattening into strings.
279
280=item *
281
282Nummifying a regular expression no longer results in an uninitialized
283warning.
284
285=item *
286
287Negative array indices no longer cause EXISTS methods of tied variables to
288be ignored. This is a regression from 5.12.
289
290=item *
291
292Negative array indices no longer result in crashes on arrays tied to
293non-objects.
294
295=item *
296
297C<$x = "(?{})"; /a++(?{})+$x/x> no longer erroneous produces an error (just
298a warning, as expected). This was broken in 5.17.1.
299
300=item *
301
302C<$byte_overload .= $utf8> no longer results in doubly-encoded UTF8 if the
303left-hand scalar happened to have produced a UTF8 string the last time
304overloading was invoked.
305
306=item *
307
308C<goto &sub> now uses the current value of @_, instead of using the array
309the subroutine was originally called with. This means
310C<local @_ = (...); goto &sub> now works [perl #43077].
311
312=item *
313
314If a debugger is invoked recursively, it no longer stomps on its own
315lexical variables. Formerly under recursion all calls would share the same
316set of lexical variables [perl #115742].
2d9cd31f 317
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318=item *
319
320C<*_{ARRAY}> returned from a subroutine no longer spontaneously
321becomes empty.
322
5d8c8c8a 323=back
4db91b87 324
916c45d9 325=head1 Acknowledgements
05bee12a 326
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327Perl 5.17.6 represents approximately 5 weeks of development since Perl 5.17.5
328and contains approximately 79,000 lines of changes across 460 files from 30
329authors.
330
331Perl continues to flourish into its third decade thanks to a vibrant community
332of users and developers. The following people are known to have contributed the
333improvements that became Perl 5.17.6:
334
335Alexandr Ciornii, Brian Fraser, Chris 'BinGOs' Williams, Craig A. Berry,
336Dagfinn Ilmari Mannsåker, Daniel Dragan, David Golden, David Mitchell, Dominic
337Hargreaves, Eric Brine, Father Chrysostomos, Florian Ragwitz, Hugo van der
338Sanden, James E Keenan, Jerry D. Hedden, Jesse Luehrs, Karl Williamson, Lukas
339Mai, Nicholas Clark, Paul Johnson, Reini Urban, Ricardo Signes, Ruslan Zakirov,
340Shlomi Fish, Steffen Müller, Steve Hay, Tom Wyant, Tony Cook, Vadim Konovalov,
341Yves Orton.
342
343The list above is almost certainly incomplete as it is automatically generated
344from version control history. In particular, it does not include the names of
345the (very much appreciated) contributors who reported issues to the Perl bug
346tracker.
347
348Many of the changes included in this version originated in the CPAN modules
349included in Perl's core. We're grateful to the entire CPAN community for
350helping Perl to flourish.
351
352For a more complete list of all of Perl's historical contributors, please see
353the F<AUTHORS> file in the Perl source distribution.
29cf780c 354
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355=head1 Reporting Bugs
356
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357If you find what you think is a bug, you might check the articles recently
358posted to the comp.lang.perl.misc newsgroup and the perl bug database at
359http://rt.perl.org/perlbug/ . There may also be information at
360http://www.perl.org/ , the Perl Home Page.
44691e6f 361
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362If you believe you have an unreported bug, please run the L<perlbug> program
363included with your release. Be sure to trim your bug down to a tiny but
364sufficient test case. Your bug report, along with the output of C<perl -V>,
365will be sent off to perlbug@perl.org to be analysed by the Perl porting team.
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366
367If the bug you are reporting has security implications, which make it
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368inappropriate to send to a publicly archived mailing list, then please send it
369to perl5-security-report@perl.org. This points to a closed subscription
370unarchived mailing list, which includes all the core committers, who will be
371able to help assess the impact of issues, figure out a resolution, and help
f9001595 372co-ordinate the release of patches to mitigate or fix the problem across all
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373platforms on which Perl is supported. Please only use this address for
374security issues in the Perl core, not for modules independently distributed on
375CPAN.
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376
377=head1 SEE ALSO
378
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379The F<Changes> file for an explanation of how to view exhaustive details on
380what changed.
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381
382The F<INSTALL> file for how to build Perl.
383
384The F<README> file for general stuff.
385
386The F<Artistic> and F<Copying> files for copyright information.
387
388=cut