1PERL591DELTA(1) Perl Programmers Reference Guide PERL591DELTA(1)
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6 perl591delta - what is new for perl v5.9.1
7
9 This document describes differences between the 5.9.0 and the 5.9.1
10 development releases. See perl590delta for the differences between
11 5.8.0 and 5.9.0.
12
14 substr() lvalues are no longer fixed-length
15 The lvalues returned by the three argument form of substr() used to be
16 a "fixed length window" on the original string. In some cases this
17 could cause surprising action at distance or other undefined behaviour.
18 Now the length of the window adjusts itself to the length of the string
19 assigned to it.
20 The ":unique" attribute is only meaningful for globals
22 Now applying ":unique" to lexical variables and to subroutines will
23 result in a compilation error.
24
26 Lexical $_
27 The default variable $_ can now be lexicalized, by declaring it like
28 any other lexical variable, with a simple
29 my $_;
31 The operations that default on $_ will use the lexically-scoped version
33 of $_ when it exists, instead of the global $_.
34 In a "map" or a "grep" block, if $_ was previously my'ed, then the $_
36 inside the block is lexical as well (and scoped to the block).
37 In a scope where $_ has been lexicalized, you can still have access to
39 the global version of $_ by using $::_, or, more simply, by overriding
40 the lexical declaration with "our $_".
41 Tied hashes in scalar context
43 As of perl 5.8.2/5.9.0, tied hashes did not return anything useful in
44 scalar context, for example when used as boolean tests:
45 if (%tied_hash) { ... }
47 The old nonsensical behaviour was always to return false, regardless of
49 whether the hash is empty or has elements.
50 There is now an interface for the implementors of tied hashes to
52 implement the behaviour of a hash in scalar context, via the SCALAR
53 method (see perltie). Without a SCALAR method, perl will try to guess
54 whether the hash is empty, by testing if it's inside an iteration (in
55 this case it can't be empty) or by calling FIRSTKEY.
56 Formats
58 Formats were improved in several ways. A new field, "^*", can be used
59 for variable-width, one-line-at-a-time text. Null characters are now
60 handled correctly in picture lines. Using "@#" and "~~" together will
61 now produce a compile-time error, as those format fields are
62 incompatible. perlform has been improved, and miscellaneous bugs
63 fixed.
64 Stacked filetest operators
66 As a new form of syntactic sugar, it's now possible to stack up
67 filetest operators. You can now write "-f -w -x $file" in a row to mean
68 "-x $file && -w _ && -f _". See "-X" in perlfunc.
69
71 Benchmark
72 In "Benchmark", cmpthese() and timestr() now use the time
73 statistics of children instead of parent when the selected style is
74 'nop'.
75 Carp
77 The error messages produced by "Carp" now include spaces between
78 the arguments in function argument lists: this makes long error
79 messages appear more nicely in browsers and other tools.
80 Exporter
82 "Exporter" will now recognize grouping tags (such as ":name")
83 anywhere in the import list, not only at the beginning.
84 FindBin
86 A function "again" is provided to resolve problems where modules in
87 different directories wish to use FindBin.
88 List::Util
90 You can now weaken references to read only values.
91 threads::shared
93 "cond_wait" has a new two argument form. "cond_timedwait" has been
94 added.
95
97 "find2perl" now assumes "-print" as a default action. Previously, it
98 needed to be specified explicitly.
99 A new utility, "prove", makes it easy to run an individual regression
101 test at the command line. "prove" is part of Test::Harness, which users
102 of earlier Perl versions can install from CPAN.
103 The perl debugger now supports a "save" command, to save the current
105 history to a file, and an "i" command, which prints the inheritance
106 tree of its argument (if the "Class::ISA" module is installed.)
107
109 The documentation has been revised in places to produce more standard
110 manpages.
111 The long-existing feature of "/(?{...})/" regexps setting $_ and pos()
113 is now documented.
114
116 Sorting arrays in place ("@a = sort @a") is now optimized to avoid
117 making a temporary copy of the array.
118 The operations involving case mapping on UTF-8 strings (uc(), lc(),
120 "//i", etc.) have been greatly speeded up.
121 Access to elements of lexical arrays via a numeric constant between 0
123 and 255 is now faster. (This used to be only the case for global
124 arrays.)
125
127 UTF-8 bugs
128 Using substr() on a UTF-8 string could cause subsequent accesses on
129 that string to return garbage. This was due to incorrect UTF-8 offsets
130 being cached, and is now fixed.
131 join() could return garbage when the same join() statement was used to
133 process 8 bit data having earlier processed UTF-8 data, due to the
134 flags on that statement's temporary workspace not being reset
135 correctly. This is now fixed.
136 Using Unicode keys with tied hashes should now work correctly.
138 chop() and chomp() used to mangle UTF-8 strings. This has been fixed.
140 sprintf() used to misbehave when the format string was in UTF-8. This
142 is now fixed.
143 Threading bugs
145 Hashes with the ":unique" attribute weren't made read-only in new
146 threads. They are now.
147 More bugs
149 "$a .. $b" will now work as expected when either $a or $b is "undef".
150 Reading $^E now preserves $!. Previously, the C code implementing $^E
152 did not preserve "errno", so reading $^E could cause "errno" and
153 therefore $! to change unexpectedly.
154 "strict" wasn't in effect in regexp-eval blocks ("/(?{...})/").
156
158 A new deprecation warning, Deprecated use of my() in false conditional,
159 has been added, to warn against the use of the dubious and deprecated
160 construct
161 my $x if 0;
163 See perldiag.
165 The fatal error DESTROY created new reference to dead object is now
167 documented in perldiag.
168 A new error, %ENV is aliased to %s, is produced when taint checks are
170 enabled and when *ENV has been aliased (and thus doesn't reflect the
171 program's environment anymore.)
172
174 These news matter to you only if you either write XS code or like to
175 know about or hack Perl internals (using Devel::Peek or any of the
176 "B::" modules counts), or like to run Perl with the "-D" option.
177 Reordering of SVt_* constants
179 The relative ordering of constants that define the various types of
180 "SV" have changed; in particular, "SVt_PVGV" has been moved before
181 "SVt_PVLV", "SVt_PVAV", "SVt_PVHV" and "SVt_PVCV". This is unlikely to
182 make any difference unless you have code that explicitly makes
183 assumptions about that ordering. (The inheritance hierarchy of "B::*"
184 objects has been changed to reflect this.)
185 Removal of CPP symbols
187 The C preprocessor symbols "PERL_PM_APIVERSION" and
188 "PERL_XS_APIVERSION", which were supposed to give the version number of
189 the oldest perl binary-compatible (resp. source-compatible) with the
190 present one, were not used, and sometimes had misleading values. They
191 have been removed.
192 Less space is used by ops
194 The "BASEOP" structure now uses less space. The "op_seq" field has been
195 removed and replaced by two one-bit fields, "op_opt" and "op_static".
196 "opt_type" is now 9 bits long. (Consequently, the "B::OP" class doesn't
197 provide an "seq" method anymore.)
198 New parser
200 perl's parser is now generated by bison (it used to be generated by
201 byacc.) As a result, it seems to be a bit more robust.
202
204 "Configure" now invokes callbacks regardless of the value of the
205 variable they are called for. Previously callbacks were only invoked in
206 the "case $variable $define)" branch. This change should only affect
207 platform maintainers writing configuration hints files.
208 The portability and cleanliness of the Win32 makefiles has been
210 improved.
211
213 There are still a couple of problems in the implementation of the
214 lexical $_: it doesn't work inside "/(?{...})/" blocks and with regard
215 to the reverse() built-in used without arguments. (See the TODO tests
216 in t/op/mydef.t.)
217 Platform Specific Problems
219 The test ext/IPC/SysV/t/ipcsysv.t may fail on OpenBSD. This hasn't been
220 diagnosed yet.
221 On some configurations on AIX 5, one test in lib/Time/Local.t fails.
223 When configured with long doubles, perl may fail tests 224-236 in
224 t/op/pow.t on the same platform.
225 For threaded builds, ext/threads/shared/t/wait.t has been reported to
227 fail some tests on HP-UX 10.20.
228
230 This is a non-exhaustive, non-ordered, non-contractual and non-
231 definitive list of things to do (or nice to have) for perl 5.10.0 :
232 Clean up and finish support for assertions. See assertions.
234 Reimplement the mechanism of lexical pragmas to be more extensible. Fix
236 current pragmas that don't work well (or at all) with lexical scopes or
237 in run-time eval(STRING) ("sort", "re", "encoding" for example). MJD
238 has a preliminary patch that implements this.
239 Fix (or rewrite) the implementation of the "/(?{...})/" closures.
241 Conversions from byte strings to UTF-8 currently map high bit
243 characters to Unicode without translation (or, depending on how you
244 look at it, by implicitly assuming that the byte strings are in
245 Latin-1). As perl assumes the C locale by default, upgrading a string
246 to UTF-8 may change the meaning of its contents regarding character
247 classes, case mapping, etc. This should probably emit a warning (at
248 least).
249 Introduce a new special block, UNITCHECK, which is run at the end of a
251 compilation unit (module, file, eval(STRING) block). This will
252 correspond to the Perl 6 CHECK. Perl 5's CHECK cannot be changed or
253 removed because the O.pm/B.pm backend framework depends on it.
254 Study the possibility of adding a new prototype character, "_", meaning
256 "this argument defaults to $_".
257 Make the peephole optimizer optional.
259 Allow lexical aliases (maybe via the syntax "my \$alias = \$foo".
261 Fix the bugs revealed by running the test suite with the "-t" switch
263 (via "make test.taintwarn").
264 Make threads more robust.
266 Make "no 6" and "no v6" work (opposite of "use 5.005", etc.).
268 A test suite for the B module would be nice.
270 A ponie.
272
274 If you find what you think is a bug, you might check the articles
275 recently posted to the comp.lang.perl.misc newsgroup and the perl bug
276 database at http://bugs.perl.org/ . There may also be information at
277 http://www.perl.org/ , the Perl Home Page.
278 If you believe you have an unreported bug, please run the perlbug
280 program included with your release. Be sure to trim your bug down to a
281 tiny but sufficient test case. Your bug report, along with the output
282 of "perl -V", will be sent off to perlbug@perl.org to be analysed by
283 the Perl porting team.
284
286 The Changes file for exhaustive details on what changed.
287 The INSTALL file for how to build Perl.
289 The README file for general stuff.
291 The Artistic and Copying files for copyright information.
293perl v5.10.1 2009-02-12 PERL591DELTA(1)