5 perl5100delta - what is new for perl 5.10.0
9 This document describes the differences between the 5.8.8 release and
12 Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance
13 releases; they are not duplicated here and are documented in the set of
14 man pages named perl58[1-8]?delta.
16 =head1 Core Enhancements
18 =head2 The C<feature> pragma
20 The C<feature> pragma is used to enable new syntax that would break Perl's
21 backwards-compatibility with older releases of the language. It's a lexical
22 pragma, like C<strict> or C<warnings>.
24 Currently the following new features are available: C<switch> (adds a
25 switch statement), C<say> (adds a C<say> built-in function), and C<state>
26 (adds a C<state> keyword for declaring "static" variables). Those
27 features are described in their own sections of this document.
29 The C<feature> pragma is also implicitly loaded when you require a minimal
30 perl version (with the C<use VERSION> construct) greater than, or equal
31 to, 5.9.5. See L<feature> for details.
33 =head2 New B<-E> command-line switch
35 B<-E> is equivalent to B<-e>, but it implicitly enables all
36 optional features (like C<use feature ":5.10">).
38 =head2 Defined-or operator
40 A new operator C<//> (defined-or) has been implemented.
41 The following expression:
45 is merely equivalent to
53 can now be used instead of
55 $c = $d unless defined $c;
57 The C<//> operator has the same precedence and associativity as C<||>.
58 Special care has been taken to ensure that this operator Do What You Mean
59 while not breaking old code, but some edge cases involving the empty
60 regular expression may now parse differently. See L<perlop> for
63 =head2 Switch and Smart Match operator
65 Perl 5 now has a switch statement. It's available when C<use feature
66 'switch'> is in effect. This feature introduces three new keywords,
67 C<given>, C<when>, and C<default>:
70 when (/^abc/) { $abc = 1; }
71 when (/^def/) { $def = 1; }
72 when (/^xyz/) { $xyz = 1; }
73 default { $nothing = 1; }
76 A more complete description of how Perl matches the switch variable
77 against the C<when> conditions is given in L<perlsyn/"Switch statements">.
79 This kind of match is called I<smart match>, and it's also possible to use
80 it outside of switch statements, via the new C<~~> operator. See
81 L<perlsyn/"Smart matching in detail">.
83 This feature was contributed by Robin Houston.
85 =head2 Regular expressions
89 =item Recursive Patterns
91 It is now possible to write recursive patterns without using the C<(??{})>
92 construct. This new way is more efficient, and in many cases easier to
95 Each capturing parenthesis can now be treated as an independent pattern
96 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
97 "parenthesis number"). For example, the following pattern will match
98 nested balanced angle brackets:
102 ( # start capture buffer 1
103 < # match an opening angle bracket
105 (?> # don't backtrack over the inside of this group
106 [^<>]+ # one or more non angle brackets
107 ) # end non backtracking group
109 (?1) # recurse to bracket 1 and try it again
110 )* # 0 or more times.
111 > # match a closing angle bracket
112 ) # end capture buffer one
116 PCRE users should note that Perl's recursive regex feature allows
117 backtracking into a recursed pattern, whereas in PCRE the recursion is
118 atomic or "possessive" in nature. As in the example above, you can
119 add (?>) to control this selectively. (Yves Orton)
121 =item Named Capture Buffers
123 It is now possible to name capturing parenthesis in a pattern and refer to
124 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
125 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
126 syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
127 access the contents of the capture buffers.
129 Thus, to replace all doubled chars with a single copy, one could write
131 s/(?<letter>.)\k<letter>/$+{letter}/g
133 Only buffers with defined contents will be "visible" in the C<%+> hash, so
134 it's possible to do something like
136 foreach my $name (keys %+) {
137 print "content of buffer '$name' is $+{$name}\n";
140 The C<%-> hash is a bit more complete, since it will contain array refs
141 holding values from all capture buffers similarly named, if there should
144 C<%+> and C<%-> are implemented as tied hashes through the new module
145 C<Tie::Hash::NamedCapture>.
147 Users exposed to the .NET regex engine will find that the perl
148 implementation differs in that the numerical ordering of the buffers
149 is sequential, and not "unnamed first, then named". Thus in the pattern
151 /(A)(?<B>B)(C)(?<D>D)/
153 $1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
154 $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
155 would expect. This is considered a feature. :-) (Yves Orton)
157 =item Possessive Quantifiers
159 Perl now supports the "possessive quantifier" syntax of the "atomic match"
160 pattern. Basically a possessive quantifier matches as much as it can and never
161 gives any back. Thus it can be used to control backtracking. The syntax is
162 similar to non-greedy matching, except instead of using a '?' as the modifier
163 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
164 quantifiers. (Yves Orton)
166 =item Backtracking control verbs
168 The regex engine now supports a number of special-purpose backtrack
169 control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
170 and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
172 =item Relative backreferences
174 A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
175 safer form of back-reference notation as well as allowing relative
176 backreferences. This should make it easier to generate and embed patterns
177 that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
181 The functionality of Jeff Pinyan's module Regexp::Keep has been added to
182 the core. In regular expressions you can now use the special escape C<\K>
183 as a way to do something like floating length positive lookbehind. It is
184 also useful in substitutions like:
188 that can now be converted to
192 which is much more efficient. (Yves Orton)
194 =item Vertical and horizontal whitespace, and linebreak
196 Regular expressions now recognize the C<\v> and C<\h> escapes that match
197 vertical and horizontal whitespace, respectively. C<\V> and C<\H>
198 logically match their complements.
200 C<\R> matches a generic linebreak, that is, vertical whitespace, plus
201 the multi-character sequence C<"\x0D\x0A">.
203 =item Optional pre-match and post-match captures with the /p flag
205 There is a new flag C</p> for regular expressions. Using this
206 makes the engine preserve a copy of the part of the matched string before
207 the matching substring to the new special variable C<${^PREMATCH}>, the
208 part after the matching substring to C<${^POSTMATCH}>, and the matched
209 substring itself to C<${^MATCH}>.
211 Perl is still able to store these substrings to the special variables
212 C<$`>, C<$'>, C<$&>, but using these variables anywhere in the program
213 adds a penalty to all regular expression matches, whereas if you use
214 the C</p> flag and the new special variables instead, you pay only for
215 the regular expressions where the flag is used.
217 For more detail on the new variables, see L<perlvar>; for the use of
218 the regular expression flag, see L<perlop> and L<perlre>.
224 say() is a new built-in, only available when C<use feature 'say'> is in
225 effect, that is similar to print(), but that implicitly appends a newline
226 to the printed string. See L<perlfunc/say>. (Robin Houston)
230 The default variable C<$_> can now be lexicalized, by declaring it like
231 any other lexical variable, with a simple
235 The operations that default on C<$_> will use the lexically-scoped
236 version of C<$_> when it exists, instead of the global C<$_>.
238 In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
239 C<$_> inside the block is lexical as well (and scoped to the block).
241 In a scope where C<$_> has been lexicalized, you can still have access to
242 the global version of C<$_> by using C<$::_>, or, more simply, by
243 overriding the lexical declaration with C<our $_>. (Rafael Garcia-Suarez)
245 =head2 The C<_> prototype
247 A new prototype character has been added. C<_> is equivalent to C<$> but
248 defaults to C<$_> if the corresponding argument isn't supplied (both C<$>
249 and C<_> denote a scalar). Due to the optional nature of the argument,
250 you can only use it at the end of a prototype, or before a semicolon.
252 This has a small incompatible consequence: the prototype() function has
253 been adjusted to return C<_> for some built-ins in appropriate cases (for
254 example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
256 =head2 UNITCHECK blocks
258 C<UNITCHECK>, a new special code block has been introduced, in addition to
259 C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
261 C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
262 are always executed at the transition between the compilation and the
263 execution of the main program, and thus are useless whenever code is
264 loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
265 just after the unit which defined them has been compiled. See L<perlmod>
266 for more information. (Alex Gough)
268 =head2 New Pragma, C<mro>
270 A new pragma, C<mro> (for Method Resolution Order) has been added. It
271 permits to switch, on a per-class basis, the algorithm that perl uses to
272 find inherited methods in case of a multiple inheritance hierarchy. The
273 default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
274 available: the C3 algorithm. See L<mro> for more information.
277 Note that, due to changes in the implementation of class hierarchy search,
278 code that used to undef the C<*ISA> glob will most probably break. Anyway,
279 undef'ing C<*ISA> had the side-effect of removing the magic on the @ISA
280 array and should not have been done in the first place. Also, the
281 cache C<*::ISA::CACHE::> no longer exists; to force reset the @ISA cache,
282 you now need to use the C<mro> API, or more simply to assign to @ISA
283 (e.g. with C<@ISA = @ISA>).
285 =head2 readdir() may return a "short filename" on Windows
287 The readdir() function may return a "short filename" when the long
288 filename contains characters outside the ANSI codepage. Similarly
289 Cwd::cwd() may return a short directory name, and glob() may return short
290 names as well. On the NTFS file system these short names can always be
291 represented in the ANSI codepage. This will not be true for all other file
292 system drivers; e.g. the FAT filesystem stores short filenames in the OEM
293 codepage, so some files on FAT volumes remain unaccessible through the
296 Similarly, $^X, @INC, and $ENV{PATH} are preprocessed at startup to make
297 sure all paths are valid in the ANSI codepage (if possible).
299 The Win32::GetLongPathName() function now returns the UTF-8 encoded
300 correct long file name instead of using replacement characters to force
301 the name into the ANSI codepage. The new Win32::GetANSIPathName()
302 function can be used to turn a long pathname into a short one only if the
303 long one cannot be represented in the ANSI codepage.
305 Many other functions in the C<Win32> module have been improved to accept
306 UTF-8 encoded arguments. Please see L<Win32> for details.
308 =head2 readpipe() is now overridable
310 The built-in function readpipe() is now overridable. Overriding it permits
311 also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
312 Moreover, it now defaults to C<$_> if no argument is provided. (Rafael
315 =head2 Default argument for readline()
317 readline() now defaults to C<*ARGV> if no argument is provided. (Rafael
320 =head2 state() variables
322 A new class of variables has been introduced. State variables are similar
323 to C<my> variables, but are declared with the C<state> keyword in place of
324 C<my>. They're visible only in their lexical scope, but their value is
325 persistent: unlike C<my> variables, they're not undefined at scope entry,
326 but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)
328 To use state variables, one needs to enable them by using
332 or by using the C<-E> command-line switch in one-liners.
333 See L<perlsub/"Persistent Private Variables">.
335 =head2 Stacked filetest operators
337 As a new form of syntactic sugar, it's now possible to stack up filetest
338 operators. You can now write C<-f -w -x $file> in a row to mean
339 C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
341 =head2 UNIVERSAL::DOES()
343 The C<UNIVERSAL> class has a new method, C<DOES()>. It has been added to
344 solve semantic problems with the C<isa()> method. C<isa()> checks for
345 inheritance, while C<DOES()> has been designed to be overridden when
346 module authors use other types of relations between classes (in addition
347 to inheritance). (chromatic)
349 See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
353 Formats were improved in several ways. A new field, C<^*>, can be used for
354 variable-width, one-line-at-a-time text. Null characters are now handled
355 correctly in picture lines. Using C<@#> and C<~~> together will now
356 produce a compile-time error, as those format fields are incompatible.
357 L<perlform> has been improved, and miscellaneous bugs fixed.
359 =head2 Byte-order modifiers for pack() and unpack()
361 There are two new byte-order modifiers, C<E<gt>> (big-endian) and C<E<lt>>
362 (little-endian), that can be appended to most pack() and unpack() template
363 characters and groups to force a certain byte-order for that type or group.
364 See L<perlfunc/pack> and L<perlpacktut> for details.
368 You can now use C<no> followed by a version number to specify that you
369 want to use a version of perl older than the specified one.
371 =head2 C<chdir>, C<chmod> and C<chown> on filehandles
373 C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
374 filenames, if the system supports respectively C<fchdir>, C<fchmod> and
375 C<fchown>, thanks to a patch provided by Gisle Aas.
379 C<$(> and C<$)> now return groups in the order where the OS returns them,
380 thanks to Gisle Aas. This wasn't previously the case.
382 =head2 Recursive sort subs
384 You can now use recursive subroutines with sort(), thanks to Robin Houston.
386 =head2 Exceptions in constant folding
388 The constant folding routine is now wrapped in an exception handler, and
389 if folding throws an exception (such as attempting to evaluate 0/0), perl
390 now retains the current optree, rather than aborting the whole program.
391 Without this change, programs would not compile if they had expressions that
392 happened to generate exceptions, even though those expressions were in code
393 that could never be reached at runtime. (Nicholas Clark, Dave Mitchell)
395 =head2 Source filters in @INC
397 It's possible to enhance the mechanism of subroutine hooks in @INC by
398 adding a source filter on top of the filehandle opened and returned by the
399 hook. This feature was planned a long time ago, but wasn't quite working
400 until now. See L<perlfunc/require> for details. (Nicholas Clark)
402 =head2 New internal variables
406 =item C<${^RE_DEBUG_FLAGS}>
408 This variable controls what debug flags are in effect for the regular
409 expression engine when running under C<use re "debug">. See L<re> for
412 =item C<${^CHILD_ERROR_NATIVE}>
414 This variable gives the native status returned by the last pipe close,
415 backtick command, successful call to wait() or waitpid(), or from the
416 system() operator. See L<perlvar> for details. (Contributed by Gisle Aas.)
418 =item C<${^RE_TRIE_MAXBUF}>
420 See L</"Trie optimisation of literal string alternations">.
422 =item C<${^WIN32_SLOPPY_STAT}>
424 See L</"Sloppy stat on Windows">.
430 C<unpack()> now defaults to unpacking the C<$_> variable.
432 C<mkdir()> without arguments now defaults to C<$_>.
434 The internal dump output has been improved, so that non-printable characters
435 such as newline and backspace are output in C<\x> notation, rather than
438 The B<-C> option can no longer be used on the C<#!> line. It wasn't
439 working there anyway, since the standard streams are already set up
440 at this point in the execution of the perl interpreter. You can use
441 binmode() instead to get the desired behaviour.
445 The copy of the Unicode Character Database included in Perl 5 has
446 been updated to version 5.0.0.
450 MAD, which stands for I<Miscellaneous Attribute Decoration>, is a
451 still-in-development work leading to a Perl 5 to Perl 6 converter. To
452 enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
453 obtained perl isn't binary compatible with a regular perl 5.10, and has
454 space and speed penalties; moreover not all regression tests still pass
455 with it. (Larry Wall, Nicholas Clark)
457 =head2 kill() on Windows
459 On Windows platforms, C<kill(-9, $pid)> now kills a process tree.
460 (On Unix, this delivers the signal to all processes in the same process
463 =head1 Incompatible Changes
465 =head2 Packing and UTF-8 strings
467 The semantics of pack() and unpack() regarding UTF-8-encoded data has been
468 changed. Processing is now by default character per character instead of
469 byte per byte on the underlying encoding. Notably, code that used things
470 like C<pack("a*", $string)> to see through the encoding of string will now
471 simply get back the original $string. Packed strings can also get upgraded
472 during processing when you store upgraded characters. You can get the old
473 behaviour by using C<use bytes>.
475 To be consistent with pack(), the C<C0> in unpack() templates indicates
476 that the data is to be processed in character mode, i.e. character by
477 character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
478 the packed string is processed in its UTF-8-encoded Unicode form on a byte
479 by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
480 between pack() and unpack().
482 Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
483 respectively character and byte modes.
485 C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
486 specified encoding mode, honoring parens grouping. Previously, parens were
489 Also, there is a new pack() character format, C<W>, which is intended to
490 replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
491 the strings internal representation. C<W> represents unsigned (logical)
492 character values, which can be greater than 255. It is therefore more
493 robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
494 values outside the range 0..255, and not respect the string encoding).
496 In practice, that means that pack formats are now encoding-neutral, except
499 For consistency, C<A> in unpack() format now trims all Unicode whitespace
500 from the end of the string. Before perl 5.9.2, it used to strip only the
501 classical ASCII space characters.
503 =head2 Byte/character count feature in unpack()
505 A new unpack() template character, C<".">, returns the number of bytes or
506 characters (depending on the selected encoding mode, see above) read so far.
508 =head2 The C<$*> and C<$#> variables have been removed
510 C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
511 modifiers, has been removed.
513 The deprecated C<$#> variable (output format for numbers) has been
516 Two new severe warnings, C<$#/$* is no longer supported>, have been added.
518 =head2 substr() lvalues are no longer fixed-length
520 The lvalues returned by the three argument form of substr() used to be a
521 "fixed length window" on the original string. In some cases this could
522 cause surprising action at distance or other undefined behaviour. Now the
523 length of the window adjusts itself to the length of the string assigned to
526 =head2 Parsing of C<-f _>
528 The identifier C<_> is now forced to be a bareword after a filetest
529 operator. This solves a number of misparsing issues when a global C<_>
530 subroutine is defined.
534 The C<:unique> attribute has been made a no-op, since its current
535 implementation was fundamentally flawed and not threadsafe.
537 =head2 Effect of pragmas in eval
539 The compile-time value of the C<%^H> hint variable can now propagate into
540 eval("")uated code. This makes it more useful to implement lexical
543 As a side-effect of this, the overloaded-ness of constants now propagates
548 A bareword argument to chdir() is now recognized as a file handle.
549 Earlier releases interpreted the bareword as a directory name.
552 =head2 Handling of .pmc files
554 An old feature of perl was that before C<require> or C<use> look for a
555 file with a F<.pm> extension, they will first look for a similar filename
556 with a F<.pmc> extension. If this file is found, it will be loaded in
557 place of any potentially existing file ending in a F<.pm> extension.
559 Previously, F<.pmc> files were loaded only if more recent than the
560 matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
563 =head2 $^V is now a C<version> object instead of a v-string
565 $^V can still be used with the C<%vd> format in printf, but any
566 character-level operations will now access the string representation
567 of the C<version> object and not the ordinals of a v-string.
568 Expressions like C<< substr($^V, 0, 2) >> or C<< split //, $^V >>
569 no longer work and must be rewritten.
571 =head2 @- and @+ in patterns
573 The special arrays C<@-> and C<@+> are no longer interpolated in regular
574 expressions. (Sadahiro Tomoyuki)
576 =head2 $AUTOLOAD can now be tainted
578 If you call a subroutine by a tainted name, and if it defers to an
579 AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
582 =head2 Tainting and printf
584 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
585 reject any tainted format argument. (Rafael Garcia-Suarez)
587 =head2 undef and signal handlers
589 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
590 equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
592 =head2 strictures and dereferencing in defined()
594 C<use strict 'refs'> was ignoring taking a hard reference in an argument
595 to defined(), as in :
599 if (defined $$x) {...}
601 This now correctly produces the run-time error C<Can't use string as a
602 SCALAR ref while "strict refs" in use>.
604 C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
605 'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
606 (C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
609 =head2 C<(?p{})> has been removed
611 The regular expression construct C<(?p{})>, which was deprecated in perl
612 5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
614 =head2 Pseudo-hashes have been removed
616 Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
617 pragma remains here, but uses an alternate implementation.)
619 =head2 Removal of the bytecode compiler and of perlcc
621 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
622 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
623 experimental tools have never worked reliably, and, due to the lack of
624 volunteers to keep them in line with the perl interpreter developments, it
625 was decided to remove them instead of shipping a broken version of those.
626 The last version of those modules can be found with perl 5.9.4.
628 However the B compiler framework stays supported in the perl core, as with
629 the more useful modules it has permitted (among others, B::Deparse and
632 =head2 Removal of the JPL
634 The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.
636 =head2 Recursive inheritance detected earlier
638 Perl will now immediately throw an exception if you modify any package's
639 C<@ISA> in such a way that it would cause recursive inheritance.
641 Previously, the exception would not occur until Perl attempted to make
642 use of the recursive inheritance while resolving a method or doing a
643 C<$foo-E<gt>isa($bar)> lookup.
645 =head2 warnings::enabled and warnings::warnif changed to favor users of modules
647 The behaviour in 5.10.x favors the person using the module;
648 The behaviour in 5.8.x favors the module writer;
650 Assume the following code:
652 main calls Foo::Bar::baz()
653 Foo::Bar inherits from Foo::Base
654 Foo::Bar::baz() calls Foo::Base::_bazbaz()
655 Foo::Base::_bazbaz() calls: warnings::warnif('substr', 'some warning
658 On 5.8.x, the code warns when Foo::Bar contains C<use warnings;>
659 It does not matter if Foo::Base or main have warnings enabled
660 to disable the warning one has to modify Foo::Bar.
662 On 5.10.0 and newer, the code warns when main contains C<use warnings;>
663 It does not matter if Foo::Base or Foo::Bar have warnings enabled
664 to disable the warning one has to modify main.
666 =head1 Modules and Pragmata
668 =head2 Upgrading individual core modules
670 Even more core modules are now also available separately through the
671 CPAN. If you wish to update one of these modules, you don't need to
672 wait for a new perl release. From within the cpan shell, running the
673 'r' command will report on modules with upgrades available. See
674 C<perldoc CPAN> for more information.
676 =head2 Pragmata Changes
682 The new pragma C<feature> is used to enable new features that might break
683 old code. See L</"The C<feature> pragma"> above.
687 This new pragma enables to change the algorithm used to resolve inherited
688 methods. See L</"New Pragma, C<mro>"> above.
690 =item Scoping of the C<sort> pragma
692 The C<sort> pragma is now lexically scoped. Its effect used to be global.
694 =item Scoping of C<bignum>, C<bigint>, C<bigrat>
696 The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
697 lexically scoped. (Tels)
701 The C<base> pragma now warns if a class tries to inherit from itself.
704 =item C<strict> and C<warnings>
706 C<strict> and C<warnings> will now complain loudly if they are loaded via
707 incorrect casing (as in C<use Strict;>). (Johan Vromans)
711 The C<version> module provides support for version objects.
715 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
716 that used C<Carp> routines without having loaded it at compile time might
717 need to be adjusted; typically, the following (faulty) code won't work
718 anymore, and will require parentheses to be added after the function name:
722 Carp::confess 'argh';
726 C<less> now does something useful (or at least it tries to). In fact, it
727 has been turned into a lexical pragma. So, in your modules, you can now
728 test whether your users have requested to use less CPU, or less memory,
729 less magic, or maybe even less fat. See L<less> for more. (Joshua ben
740 C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
741 whenever an ASCII character string containing high-bit bytes is implicitly
742 converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
743 perls, its effect is global.
747 C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
748 you what versions of core modules ship with any versions of Perl 5. It
749 comes with a command-line frontend, C<corelist>.
753 C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
754 C<Math::BigInt::Calc>.
758 C<Compress::Zlib> is an interface to the zlib compression library. It
759 comes with a bundled version of zlib, so having a working zlib is not a
760 prerequisite to install it. It's used by C<Archive::Tar> (see below).
764 C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
768 C<Archive::Tar> is a module to manipulate C<tar> archives.
772 C<Digest::SHA> is a module used to calculate many types of SHA digests,
773 has been included for SHA support in the CPAN module.
777 C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
781 C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
782 provides support for I<field hashes>: hashes that maintain an association
783 of a reference with a value, in a thread-safe garbage-collected way.
784 Such hashes are useful to implement inside-out objects.
788 C<Module::Build>, by Ken Williams, has been added. It's an alternative to
789 C<ExtUtils::MakeMaker> to build and install perl modules.
793 C<Module::Load>, by Jos Boumans, has been added. It provides a single
794 interface to load Perl modules and F<.pl> files.
798 C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
799 modules as loaded or unloaded.
803 C<Package::Constants>, by Jos Boumans, has been added. It's a simple
804 helper to list all constants declared in a given package.
808 C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
809 This module provides low-level access to Win32 system API calls for
814 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
815 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
816 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
817 gracefully degrades when the later isn't present.
821 C<Params::Check> implements a generic input parsing/checking mechanism. It
826 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
830 C<Object::Accessor> provides an interface to create per-object accessors.
834 C<Module::Pluggable> is a simple framework to create modules that accept
835 pluggable sub-modules.
839 C<Module::Load::Conditional> provides simple ways to query and possibly
840 load installed modules.
844 C<Time::Piece> provides an object oriented interface to time functions,
845 overriding the built-ins localtime() and gmtime().
849 C<IPC::Cmd> helps to find and run external commands, possibly
854 C<File::Fetch> provide a simple generic file fetching mechanism.
858 C<Log::Message> and C<Log::Message::Simple> are used by the log facility
863 C<Archive::Extract> is a generic archive extraction mechanism
864 for F<.tar> (plain, gzipped or bzipped) or F<.zip> files.
868 C<CPANPLUS> provides an API and a command-line tool to access the CPAN
873 C<Pod::Escapes> provides utilities that are useful in decoding Pod
874 EE<lt>...E<gt> sequences.
878 C<Pod::Simple> is now the backend for several of the Pod-related modules
883 =head2 Selected Changes to Core Modules
887 =item C<Attribute::Handlers>
889 C<Attribute::Handlers> can now report the caller's file and line number.
892 All interpreted attributes are now passed as array references. (Damian
897 C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
898 with plugins. (Joshua ben Jore)
902 It's now possible to access the lexical pragma hints (C<%^H>) by using the
903 method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
904 can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
909 As the old 5005thread threading model has been removed, in favor of the
910 ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
911 be used in old code only. It has been removed from the default list of
916 =head1 Utility Changes
922 The Perl debugger can now save all debugger commands for sourcing later;
923 notably, it can now emulate stepping backwards, by restarting and
924 rerunning all bar the last command from a saved command history.
926 It can also display the parent inheritance tree of a given class, with the
931 C<ptar> is a pure perl implementation of C<tar> that comes with
936 C<ptardiff> is a small utility used to generate a diff between the contents
937 of a tar archive and a directory tree. Like C<ptar>, it comes with
942 C<shasum> is a command-line utility, used to print or to check SHA
943 digests. It comes with the new C<Digest::SHA> module.
947 The C<corelist> utility is now installed with perl (see L</"New modules">
952 C<h2ph> and C<h2xs> have been made more robust with regard to
955 C<h2xs> implements a new option C<--use-xsloader> to force use of
956 C<XSLoader> even in backwards compatible modules.
958 The handling of authors' names that had apostrophes has been fixed.
960 Any enums with negative values are now skipped.
964 C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
965 option to run I<all> tests.
969 C<find2perl> now assumes C<-print> as a default action. Previously, it
970 needed to be specified explicitly.
972 Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
973 C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
978 C<config_data> is a new utility that comes with C<Module::Build>. It
979 provides a command-line interface to the configuration of Perl modules
980 that use Module::Build's framework of configurability (that is,
981 C<*::ConfigData> modules that contain local configuration information for
982 their parent modules.)
986 C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, a
987 helper for CPANPLUS operation, has been added too, but isn't intended for
992 C<cpan2dist> is a new utility that comes with CPANPLUS. It's a tool to
993 create distributions (or packages) from CPAN modules.
997 The output of C<pod2html> has been enhanced to be more customizable via
998 CSS. Some formatting problems were also corrected. (Jari Aalto)
1002 =head1 New Documentation
1004 The L<perlpragma> manpage documents how to write one's own lexical
1005 pragmas in pure Perl (something that is possible starting with 5.9.4).
1007 The new L<perlglossary> manpage is a glossary of terms used in the Perl
1008 documentation, technical and otherwise, kindly provided by O'Reilly Media,
1011 The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
1012 Perl regular expression engine.
1014 The L<perlreapi> manpage describes the interface to the perl interpreter
1015 used to write pluggable regular expression engines (by Ævar Arnfjörð
1018 The L<perlunitut> manpage is a tutorial for programming with Unicode and
1019 string encodings in Perl, courtesy of Juerd Waalboer.
1021 A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
1024 The L<perlcommunity> manpage gives a description of the Perl community
1025 on the Internet and in real life. (Edgar "Trizor" Bering)
1027 The L<CORE> manual page documents the C<CORE::> namespace. (Tels)
1029 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
1032 =head1 Performance Enhancements
1034 =head2 In-place sorting
1036 Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
1037 making a temporary copy of the array.
1039 Likewise, C<reverse sort ...> is now optimized to sort in reverse,
1040 avoiding the generation of a temporary intermediate list.
1042 =head2 Lexical array access
1044 Access to elements of lexical arrays via a numeric constant between 0 and
1045 255 is now faster. (This used to be only the case for global arrays.)
1047 =head2 XS-assisted SWASHGET
1049 Some pure-perl code that perl was using to retrieve Unicode properties and
1050 transliteration mappings has been reimplemented in XS.
1052 =head2 Constant subroutines
1054 The interpreter internals now support a far more memory efficient form of
1055 inlineable constants. Storing a reference to a constant value in a symbol
1056 table is equivalent to a full typeglob referencing a constant subroutine,
1057 but using about 400 bytes less memory. This proxy constant subroutine is
1058 automatically upgraded to a real typeglob with subroutine if necessary.
1059 The approach taken is analogous to the existing space optimisation for
1060 subroutine stub declarations, which are stored as plain scalars in place
1061 of the full typeglob.
1063 Several of the core modules have been converted to use this feature for
1064 their system dependent constants - as a result C<use POSIX;> now takes about
1067 =head2 C<PERL_DONT_CREATE_GVSV>
1069 The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
1070 in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
1071 from creating an empty scalar with every new typeglob. See L<perl589delta>
1074 =head2 Weak references are cheaper
1076 Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
1077 Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
1078 happens at program exit, it may be skipped completely.
1080 =head2 sort() enhancements
1082 Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
1083 and to speed up some cases.
1085 =head2 Memory optimisations
1087 Several internal data structures (typeglobs, GVs, CVs, formats) have been
1088 restructured to use less memory. (Nicholas Clark)
1090 =head2 UTF-8 cache optimisation
1092 The UTF-8 caching code is now more efficient, and used more often.
1095 =head2 Sloppy stat on Windows
1097 On Windows, perl's stat() function normally opens the file to determine
1098 the link count and update attributes that may have been changed through
1099 hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up
1100 stat() by not performing this operation. (Jan Dubois)
1102 =head2 Regular expressions optimisations
1106 =item Engine de-recursivised
1108 The regular expression engine is no longer recursive, meaning that
1109 patterns that used to overflow the stack will either die with useful
1110 explanations, or run to completion, which, since they were able to blow
1111 the stack before, will likely take a very long time to happen. If you were
1112 experiencing the occasional stack overflow (or segfault) and upgrade to
1113 discover that now perl apparently hangs instead, look for a degenerate
1114 regex. (Dave Mitchell)
1116 =item Single char char-classes treated as literals
1118 Classes of a single character are now treated the same as if the character
1119 had been used as a literal, meaning that code that uses char-classes as an
1120 escaping mechanism will see a speedup. (Yves Orton)
1122 =item Trie optimisation of literal string alternations
1124 Alternations, where possible, are optimised into more efficient matching
1125 structures. String literal alternations are merged into a trie and are
1126 matched simultaneously. This means that instead of O(N) time for matching
1127 N alternations at a given point, the new code performs in O(1) time.
1128 A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune
1129 this optimization. (Yves Orton)
1131 B<Note:> Much code exists that works around perl's historic poor
1132 performance on alternations. Often the tricks used to do so will disable
1133 the new optimisations. Hopefully the utility modules used for this purpose
1134 will be educated about these new optimisations.
1136 =item Aho-Corasick start-point optimisation
1138 When a pattern starts with a trie-able alternation and there aren't
1139 better optimisations available, the regex engine will use Aho-Corasick
1140 matching to find the start point. (Yves Orton)
1144 =head1 Installation and Configuration Improvements
1146 =head2 Configuration improvements
1150 =item C<-Dusesitecustomize>
1152 Run-time customization of @INC can be enabled by passing the
1153 C<-Dusesitecustomize> flag to Configure. When enabled, this will make perl
1154 run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
1155 then be set up to add additional entries to @INC.
1157 =item Relocatable installations
1159 There is now Configure support for creating a relocatable perl tree. If
1160 you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
1161 everything else in %Config) can be optionally located via the path of the
1164 That means that, if the string C<".../"> is found at the start of any
1165 path, it's substituted with the directory of $^X. So, the relocation can
1166 be configured on a per-directory basis, although the default with
1167 C<-Duserelocatableinc> is that everything is relocated. The initial
1168 install is done to the original configured prefix.
1170 =item strlcat() and strlcpy()
1172 The configuration process now detects whether strlcat() and strlcpy() are
1173 available. When they are not available, perl's own version is used (from
1174 Russ Allbery's public domain implementation). Various places in the perl
1175 interpreter now use them. (Steve Peters)
1177 =item C<d_pseudofork> and C<d_printf_format_null>
1179 A new configuration variable, available as C<$Config{d_pseudofork}> in
1180 the L<Config> module, has been added, to distinguish real fork() support
1181 from fake pseudofork used on Windows platforms.
1183 A new configuration variable, C<d_printf_format_null>, has been added,
1184 to see if printf-like formats are allowed to be NULL.
1186 =item Configure help
1188 C<Configure -h> has been extended with the most commonly used options.
1192 =head2 Compilation improvements
1196 =item Parallel build
1198 Parallel makes should work properly now, although there may still be problems
1199 if C<make test> is instructed to run in parallel.
1201 =item Borland's compilers support
1203 Building with Borland's compilers on Win32 should work more smoothly. In
1204 particular Steve Hay has worked to side step many warnings emitted by their
1205 compilers and at least one C compiler internal error.
1207 =item Static build on Windows
1209 Perl extensions on Windows now can be statically built into the Perl DLL.
1211 Also, it's now possible to build a C<perl-static.exe> that doesn't depend
1212 on the Perl DLL on Win32. See the Win32 makefiles for details.
1215 =item ppport.h files
1217 All F<ppport.h> files in the XS modules bundled with perl are now
1218 autogenerated at build time. (Marcus Holland-Moritz)
1220 =item C++ compatibility
1222 Efforts have been made to make perl and the core XS modules compilable
1223 with various C++ compilers (although the situation is not perfect with
1224 some of the compilers on some of the platforms tested.)
1226 =item Support for Microsoft 64-bit compiler
1228 Support for building perl with Microsoft's 64-bit compiler has been
1229 improved. (ActiveState)
1233 Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).
1237 All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
1241 =head2 Installation improvements
1245 =item Module auxiliary files
1247 README files and changelogs for CPAN modules bundled with perl are no
1252 =head2 New Or Improved Platforms
1254 Perl has been reported to work on Symbian OS. See L<perlsymbian> for more
1257 Many improvements have been made towards making Perl work correctly on
1260 Perl has been reported to work on DragonFlyBSD and MidnightBSD.
1262 Perl has also been reported to work on NexentaOS
1263 ( http://www.gnusolaris.org/ ).
1265 The VMS port has been improved. See L<perlvms>.
1267 Support for Cray XT4 Catamount/Qk has been added. See
1268 F<hints/catamount.sh> in the source code distribution for more
1271 Vendor patches have been merged for RedHat and Gentoo.
1273 DynaLoader::dl_unload_file() now works on Windows.
1275 =head1 Selected Bug Fixes
1279 =item strictures in regexp-eval blocks
1281 C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
1283 =item Calling CORE::require()
1285 CORE::require() and CORE::do() were always parsed as require() and do()
1286 when they were overridden. This is now fixed.
1288 =item Subscripts of slices
1290 You can now use a non-arrowed form for chained subscripts after a list
1293 ({foo => "bar"})[0]{foo}
1295 This used to be a syntax error; a C<< -> >> was required.
1297 =item C<no warnings 'category'> works correctly with -w
1299 Previously when running with warnings enabled globally via C<-w>, selective
1300 disabling of specific warning categories would actually turn off all warnings.
1301 This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
1302 C<io> class. Previously it would erroneously turn off all warnings.
1304 =item threads improvements
1306 Several memory leaks in ithreads were closed. Also, ithreads were made
1307 less memory-intensive.
1309 C<threads> is now a dual-life module, also available on CPAN. It has been
1310 expanded in many ways. A kill() method is available for thread signalling.
1311 One can get thread status, or the list of running or joinable threads.
1313 A new C<< threads->exit() >> method is used to exit from the application
1314 (this is the default for the main thread) or from the current thread only
1315 (this is the default for all other threads). On the other hand, the exit()
1316 built-in now always causes the whole application to terminate. (Jerry
1319 =item chr() and negative values
1321 chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
1322 character, unless when the C<bytes> pragma is in effect, where the low
1323 eight bits of the value are used.
1325 =item PERL5SHELL and tainting
1327 On Windows, the PERL5SHELL environment variable is now checked for
1328 taintedness. (Rafael Garcia-Suarez)
1330 =item Using *FILE{IO}
1332 C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
1333 filehandles. (Steve Peters)
1335 =item Overloading and reblessing
1337 Overloading now works when references are reblessed into another class.
1338 Internally, this has been implemented by moving the flag for "overloading"
1339 from the reference to the referent, which logically is where it should
1340 always have been. (Nicholas Clark)
1342 =item Overloading and UTF-8
1344 A few bugs related to UTF-8 handling with objects that have
1345 stringification overloaded have been fixed. (Nicholas Clark)
1347 =item eval memory leaks fixed
1349 Traditionally, C<eval 'syntax error'> has leaked badly. Many (but not all)
1350 of these leaks have now been eliminated or reduced. (Dave Mitchell)
1352 =item Random device on Windows
1354 In previous versions, perl would read the file F</dev/urandom> if it
1355 existed when seeding its random number generator. That file is unlikely
1356 to exist on Windows, and if it did would probably not contain appropriate
1357 data, so perl no longer tries to read it on Windows. (Alex Davies)
1361 The C<PERLIO_DEBUG> environment variable no longer has any effect for
1362 setuid scripts and for scripts run with B<-T>.
1364 Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
1365 an internal buffer overflow. This has been fixed.
1367 =item PerlIO::scalar and read-only scalars
1369 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
1370 seek() is now supported with PerlIO::scalar-based filehandles, the
1371 underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
1373 =item study() and UTF-8
1375 study() never worked for UTF-8 strings, but could lead to false results.
1376 It's now a no-op on UTF-8 data. (Yves Orton)
1378 =item Critical signals
1380 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
1381 "unsafe" manner (contrary to other signals, that are deferred until the
1382 perl interpreter reaches a reasonably stable state; see
1383 L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
1387 When a module or a file is loaded through an @INC-hook, and when this hook
1388 has set a filename entry in %INC, __FILE__ is now set for this module
1389 accordingly to the contents of that %INC entry. (Rafael)
1391 =item C<-t> switch fix
1393 The C<-w> and C<-t> switches can now be used together without messing
1394 up which categories of warnings are activated. (Rafael)
1396 =item Duping UTF-8 filehandles
1398 Duping a filehandle which has the C<:utf8> PerlIO layer set will now
1399 properly carry that layer on the duped filehandle. (Rafael)
1401 =item Localisation of hash elements
1403 Localizing a hash element whose key was given as a variable didn't work
1404 correctly if the variable was changed while the local() was in effect (as
1405 in C<local $h{$x}; ++$x>). (Bo Lindbergh)
1409 =head1 New or Changed Diagnostics
1413 =item Use of uninitialized value
1415 Perl will now try to tell you the name of the variable (if any) that was
1418 =item Deprecated use of my() in false conditional
1420 A new deprecation warning, I<Deprecated use of my() in false conditional>,
1421 has been added, to warn against the use of the dubious and deprecated
1426 See L<perldiag>. Use C<state> variables instead.
1428 =item !=~ should be !~
1430 A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
1431 of the non-matching operator.
1433 =item Newline in left-justified string
1435 The warning I<Newline in left-justified string> has been removed.
1437 =item Too late for "-T" option
1439 The error I<Too late for "-T" option> has been reformulated to be more
1442 =item "%s" variable %s masks earlier declaration
1444 This warning is now emitted in more consistent cases; in short, when one
1445 of the declarations involved is a C<my> variable:
1447 my $x; my $x; # warns
1448 my $x; our $x; # warns
1449 our $x; my $x; # warns
1451 On the other hand, the following:
1455 now gives a C<"our" variable %s redeclared> warning.
1457 =item readdir()/closedir()/etc. attempted on invalid dirhandle
1459 These new warnings are now emitted when a dirhandle is used but is
1460 either closed or not really a dirhandle.
1462 =item Opening dirhandle/filehandle %s also as a file/directory
1464 Two deprecation warnings have been added: (Rafael)
1466 Opening dirhandle %s also as a file
1467 Opening filehandle %s also as a directory
1469 =item Use of -P is deprecated
1471 Perl's command-line switch C<-P> is now deprecated.
1473 =item v-string in use/require is non-portable
1475 Perl will warn you against potential backwards compatibility problems with
1476 the C<use VERSION> syntax.
1480 C<perl -V> has several improvements, making it more useable from shell
1481 scripts to get the value of configuration variables. See L<perlrun> for
1486 =head1 Changed Internals
1488 In general, the source code of perl has been refactored, tidied up,
1489 and optimized in many places. Also, memory management and allocation
1490 has been improved in several points.
1492 When compiling the perl core with gcc, as many gcc warning flags are
1493 turned on as is possible on the platform. (This quest for cleanliness
1494 doesn't extend to XS code because we cannot guarantee the tidiness of
1495 code we didn't write.) Similar strictness flags have been added or
1496 tightened for various other C compilers.
1498 =head2 Reordering of SVt_* constants
1500 The relative ordering of constants that define the various types of C<SV>
1501 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
1502 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
1503 difference unless you have code that explicitly makes assumptions about that
1504 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
1507 =head2 Elimination of SVt_PVBM
1509 Related to this, the internal type C<SVt_PVBM> has been removed. This
1510 dedicated type of C<SV> was used by the C<index> operator and parts of the
1511 regexp engine to facilitate fast Boyer-Moore matches. Its use internally has
1512 been replaced by C<SV>s of type C<SVt_PVGV>.
1514 =head2 New type SVt_BIND
1516 A new type C<SVt_BIND> has been added, in readiness for the project to
1517 implement Perl 6 on 5. There deliberately is no implementation yet, and
1518 they cannot yet be created or destroyed.
1520 =head2 Removal of CPP symbols
1522 The C preprocessor symbols C<PERL_PM_APIVERSION> and
1523 C<PERL_XS_APIVERSION>, which were supposed to give the version number of
1524 the oldest perl binary-compatible (resp. source-compatible) with the
1525 present one, were not used, and sometimes had misleading values. They have
1528 =head2 Less space is used by ops
1530 The C<BASEOP> structure now uses less space. The C<op_seq> field has been
1531 removed and replaced by a single bit bit-field C<op_opt>. C<op_type> is now 9
1532 bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
1537 perl's parser is now generated by bison (it used to be generated by
1538 byacc.) As a result, it seems to be a bit more robust.
1540 Also, Dave Mitchell improved the lexer debugging output under C<-DT>.
1542 =head2 Use of C<const>
1544 Andy Lester supplied many improvements to determine which function
1545 parameters and local variables could actually be declared C<const> to the C
1546 compiler. Steve Peters provided new C<*_set> macros and reworked the core to
1547 use these rather than assigning to macros in LVALUE context.
1551 A new file, F<mathoms.c>, has been added. It contains functions that are
1552 no longer used in the perl core, but that remain available for binary or
1553 source compatibility reasons. However, those functions will not be
1554 compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
1556 =head2 C<AvFLAGS> has been removed
1558 The C<AvFLAGS> macro has been removed.
1560 =head2 C<av_*> changes
1562 The C<av_*()> functions, used to manipulate arrays, no longer accept null
1567 The implementation of the special variables $^H and %^H has changed, to
1568 allow implementing lexical pragmas in pure Perl.
1570 =head2 B:: modules inheritance changed
1572 The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
1573 inherits from C<B::SV> (it used to inherit from C<B::IV>).
1575 =head2 Anonymous hash and array constructors
1577 The anonymous hash and array constructors now take 1 op in the optree
1578 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
1579 a hash/array when the op is flagged with OPf_SPECIAL. (Nicholas Clark)
1581 =head1 Known Problems
1583 There's still a remaining problem in the implementation of the lexical
1584 C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
1587 Stacked filetest operators won't work when the C<filetest> pragma is in
1588 effect, because they rely on the stat() buffer C<_> being populated, and
1589 filetest bypasses stat().
1591 =head2 UTF-8 problems
1593 The handling of Unicode still is unclean in several places, where it's
1594 dependent on whether a string is internally flagged as UTF-8. This will
1595 be made more consistent in perl 5.12, but that won't be possible without
1596 a certain amount of backwards incompatibility.
1598 =head1 Platform Specific Problems
1600 When compiled with g++ and thread support on Linux, it's reported that the
1601 C<$!> stops working correctly. This is related to the fact that the glibc
1602 provides two strerror_r(3) implementation, and perl selects the wrong
1605 =head1 Reporting Bugs
1607 If you find what you think is a bug, you might check the articles
1608 recently posted to the comp.lang.perl.misc newsgroup and the perl
1609 bug database at http://rt.perl.org/rt3/ . There may also be
1610 information at http://www.perl.org/ , the Perl Home Page.
1612 If you believe you have an unreported bug, please run the B<perlbug>
1613 program included with your release. Be sure to trim your bug down
1614 to a tiny but sufficient test case. Your bug report, along with the
1615 output of C<perl -V>, will be sent off to perlbug@perl.org to be
1616 analysed by the Perl porting team.
1620 The F<Changes> file and the perl590delta to perl595delta man pages for
1621 exhaustive details on what changed.
1623 The F<INSTALL> file for how to build Perl.
1625 The F<README> file for general stuff.
1627 The F<Artistic> and F<Copying> files for copyright information.