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More delta info from Perl 5.9.5
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1=head1 NAME
2
3perldelta - what is new for perl 5.10.0
4
5=head1 DESCRIPTION
6
7This document describes the differences between the 5.8.8 release and
8the 5.10.0 release.
9
10Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance
11releases; they are not duplicated here and are documented in the set of
12man pages named perl58[1-8]?delta.
13
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14=head1 Core Enhancements
15
16=head2 The C<feature> pragma
17
18The C<feature> pragma is used to enable new syntax that would break Perl's
19backwards-compatibility with older releases of the language. It's a lexical
20pragma, like C<strict> or C<warnings>.
21
22Currently the following new features are available: C<switch> (adds a
23switch statement), C<say> (adds a C<say> built-in function), and C<state>
24(adds an C<state> keyword for declaring "static" variables). Those
25features are described in their own sections of this document.
26
27The C<feature> pragma is also implicitly loaded when you require a minimal
28perl version (with the C<use VERSION> construct) greater than, or equal
29to, 5.9.5. See L<feature> for details.
30
31=head2 New B<-E> command-line switch
32
33B<-E> is equivalent to B<-e>, but it implicitly enables all
34optional features (like C<use feature ":5.10">).
35
36=head2 Defined-or operator
37
38A new operator C<//> (defined-or) has been implemented.
39The following statement:
40
41 $a // $b
42
43is merely equivalent to
44
45 defined $a ? $a : $b
46
47and
48
49 $c //= $d;
50
51can now be used instead of
52
53 $c = $d unless defined $c;
54
55The C<//> operator has the same precedence and associativity as C<||>.
56Special care has been taken to ensure that this operator Do What You Mean
57while not breaking old code, but some edge cases involving the empty
58regular expression may now parse differently. See L<perlop> for
59details.
60
61=head2 Switch and Smart Match operator
62
63Perl 5 now has a switch statement. It's available when C<use feature
64'switch'> is in effect. This feature introduces three new keywords,
65C<given>, C<when>, and C<default>:
66
67 given ($foo) {
68 when (/^abc/) { $abc = 1; }
69 when (/^def/) { $def = 1; }
70 when (/^xyz/) { $xyz = 1; }
71 default { $nothing = 1; }
72 }
73
74A more complete description of how Perl matches the switch variable
75against the C<when> conditions is given in L<perlsyn/"Switch statements">.
76
77This kind of match is called I<smart match>, and it's also possible to use
78it outside of switch statements, via the new C<~~> operator. See
79L<perlsyn/"Smart matching in detail">.
80
81This feature was contributed by Robin Houston.
82
83=head2 Regular expressions
84
85=over 4
86
87=item Recursive Patterns
88
89It is now possible to write recursive patterns without using the C<(??{})>
90construct. This new way is more efficient, and in many cases easier to
91read.
92
93Each capturing parenthesis can now be treated as an independent pattern
94that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
95"parenthesis number"). For example, the following pattern will match
96nested balanced angle brackets:
97
98 /
99 ^ # start of line
100 ( # start capture buffer 1
101 < # match an opening angle bracket
102 (?: # match one of:
103 (?> # don't backtrack over the inside of this group
104 [^<>]+ # one or more non angle brackets
105 ) # end non backtracking group
106 | # ... or ...
107 (?1) # recurse to bracket 1 and try it again
108 )* # 0 or more times.
109 > # match a closing angle bracket
110 ) # end capture buffer one
111 $ # end of line
112 /x
113
114Note, users experienced with PCRE will find that the Perl implementation
115of this feature differs from the PCRE one in that it is possible to
116backtrack into a recursed pattern, whereas in PCRE the recursion is
117atomic or "possessive" in nature. (Yves Orton)
118
119=item Named Capture Buffers
120
121It is now possible to name capturing parenthesis in a pattern and refer to
122the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
123It's possible to backreference to a named buffer with the C<< \k<NAME> >>
124syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
125access the contents of the capture buffers.
126
127Thus, to replace all doubled chars, one could write
128
129 s/(?<letter>.)\k<letter>/$+{letter}/g
130
131Only buffers with defined contents will be "visible" in the C<%+> hash, so
132it's possible to do something like
133
134 foreach my $name (keys %+) {
135 print "content of buffer '$name' is $+{$name}\n";
136 }
137
138The C<%-> hash is a bit more complete, since it will contain array refs
139holding values from all capture buffers similarly named, if there should
140be many of them.
141
142C<%+> and C<%-> are implemented as tied hashes through the new module
143C<Tie::Hash::NamedCapture>.
144
145Users exposed to the .NET regex engine will find that the perl
146implementation differs in that the numerical ordering of the buffers
147is sequential, and not "unnamed first, then named". Thus in the pattern
148
149 /(A)(?<B>B)(C)(?<D>D)/
150
151$1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
152$1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
153would expect. This is considered a feature. :-) (Yves Orton)
154
155=item Possessive Quantifiers
156
157Perl now supports the "possessive quantifier" syntax of the "atomic match"
158pattern. Basically a possessive quantifier matches as much as it can and never
159gives any back. Thus it can be used to control backtracking. The syntax is
160similar to non-greedy matching, except instead of using a '?' as the modifier
161the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
162quantifiers. (Yves Orton)
163
164=item Backtracking control verbs
165
166The regex engine now supports a number of special-purpose backtrack
167control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
168and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
169
170=item Relative backreferences
171
172A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
173safer form of back-reference notation as well as allowing relative
174backreferences. This should make it easier to generate and embed patterns
175that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
176
177=item C<\K> escape
178
179The functionality of Jeff Pinyan's module Regexp::Keep has been added to
180the core. You can now use in regular expressions the special escape C<\K>
181as a way to do something like floating length positive lookbehind. It is
182also useful in substitutions like:
183
184 s/(foo)bar/$1/g
185
186that can now be converted to
187
188 s/foo\Kbar//g
189
190which is much more efficient. (Yves Orton)
191
192=item Vertical and horizontal whitespace, and linebreak
193
194Regular expressions now recognize the C<\v> and C<\h> escapes, that match
195vertical and horizontal whitespace, respectively. C<\V> and C<\H>
196logically match their complements.
197
198C<\R> matches a generic linebreak, that is, vertical whitespace, plus
199the multi-character sequence C<"\x0D\x0A">.
200
201=back
202
203=head2 C<say()>
204
205say() is a new built-in, only available when C<use feature 'say'> is in
206effect, that is similar to print(), but that implicitly appends a newline
207to the printed string. See L<perlfunc/say>. (Robin Houston)
208
209=head2 Lexical C<$_>
210
211The default variable C<$_> can now be lexicalized, by declaring it like
212any other lexical variable, with a simple
213
214 my $_;
215
216The operations that default on C<$_> will use the lexically-scoped
217version of C<$_> when it exists, instead of the global C<$_>.
218
219In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
220C<$_> inside the block is lexical as well (and scoped to the block).
221
222In a scope where C<$_> has been lexicalized, you can still have access to
223the global version of C<$_> by using C<$::_>, or, more simply, by
597bb945 224overriding the lexical declaration with C<our $_>. (Rafael Garcia-Suarez)
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225
226=head2 The C<_> prototype
227
228A new prototype character has been added. C<_> is equivalent to C<$> (it
229denotes a scalar), but defaults to C<$_> if the corresponding argument
230isn't supplied. Due to the optional nature of the argument, you can only
231use it at the end of a prototype, or before a semicolon.
232
233This has a small incompatible consequence: the prototype() function has
234been adjusted to return C<_> for some built-ins in appropriate cases (for
235example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
236
237=head2 UNITCHECK blocks
238
239C<UNITCHECK>, a new special code block has been introduced, in addition to
240C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
241
242C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
243are always executed at the transition between the compilation and the
244execution of the main program, and thus are useless whenever code is
245loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
246just after the unit which defined them has been compiled. See L<perlmod>
247for more information. (Alex Gough)
248
249=head2 New Pragma, C<mro>
250
251A new pragma, C<mro> (for Method Resolution Order) has been added. It
252permits to switch, on a per-class basis, the algorithm that perl uses to
253find inherited methods in case of a mutiple inheritance hierachy. The
254default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
255available: the C3 algorithm. See L<mro> for more information.
256(Brandon Black)
257
258Note that, due to changes in the implentation of class hierarchy search,
259code that used to undef the C<*ISA> glob will most probably break. Anyway,
260undef'ing C<*ISA> had the side-effect of removing the magic on the @ISA
261array and should not have been done in the first place.
262
263=head2 readpipe() is now overridable
264
265The built-in function readpipe() is now overridable. Overriding it permits
266also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
267Moreover, it now defaults to C<$_> if no argument is provided. (Rafael
268Garcia-Suarez)
269
597bb945 270=head2 Default argument for readline()
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271
272readline() now defaults to C<*ARGV> if no argument is provided. (Rafael
273Garcia-Suarez)
274
275=head2 state() variables
276
277A new class of variables has been introduced. State variables are similar
278to C<my> variables, but are declared with the C<state> keyword in place of
279C<my>. They're visible only in their lexical scope, but their value is
280persistent: unlike C<my> variables, they're not undefined at scope entry,
281but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)
282
283To use state variables, one needs to enable them by using
284
285 use feature "state";
286
287or by using the C<-E> command-line switch in one-liners.
288See L<perlsub/"Persistent variables via state()">.
289
290=head2 Stacked filetest operators
291
292As a new form of syntactic sugar, it's now possible to stack up filetest
293operators. You can now write C<-f -w -x $file> in a row to mean
294C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
295
296=head2 UNIVERSAL::DOES()
297
298The C<UNIVERSAL> class has a new method, C<DOES()>. It has been added to
299solve semantic problems with the C<isa()> method. C<isa()> checks for
300inheritance, while C<DOES()> has been designed to be overridden when
301module authors use other types of relations between classes (in addition
302to inheritance). (chromatic)
303
304See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
305
306=head2 C<CLONE_SKIP()>
307
308Perl has now support for the C<CLONE_SKIP> special subroutine. Like
309C<CLONE>, C<CLONE_SKIP> is called once per package; however, it is called
310just before cloning starts, and in the context of the parent thread. If it
311returns a true value, then no objects of that class will be cloned. See
312L<perlmod> for details. (Contributed by Dave Mitchell.)
313
314=head2 Formats
315
316Formats were improved in several ways. A new field, C<^*>, can be used for
317variable-width, one-line-at-a-time text. Null characters are now handled
318correctly in picture lines. Using C<@#> and C<~~> together will now
319produce a compile-time error, as those format fields are incompatible.
320L<perlform> has been improved, and miscellaneous bugs fixed.
321
322=head2 Byte-order modifiers for pack() and unpack()
323
324There are two new byte-order modifiers, C<E<gt>> (big-endian) and C<E<lt>>
325(little-endian), that can be appended to most pack() and unpack() template
326characters and groups to force a certain byte-order for that type or group.
327See L<perlfunc/pack> and L<perlpacktut> for details.
328
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329=head2 C<no VERSION>
330
331You can now use C<no> followed by a version number to specify that you
332want to use a version of perl older than the specified one.
333
334=head2 C<chdir>, C<chmod> and C<chown> on filehandles
335
336C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
337filenames, if the system supports respectively C<fchdir>, C<fchmod> and
338C<fchown>, thanks to a patch provided by Gisle Aas.
339
340=head2 OS groups
341
342C<$(> and C<$)> now return groups in the order where the OS returns them,
343thanks to Gisle Aas. This wasn't previously the case.
344
345=head2 Recursive sort subs
346
347You can now use recursive subroutines with sort(), thanks to Robin Houston.
348
349=head2 Exceptions in constant folding
350
351The constant folding routine is now wrapped in an exception handler, and
352if folding throws an exception (such as attempting to evaluate 0/0), perl
353now retains the current optree, rather than aborting the whole program.
354(Nicholas Clark, Dave Mitchell)
355
356=head2 Source filters in @INC
357
358It's possible to enhance the mechanism of subroutine hooks in @INC by
359adding a source filter on top of the filehandle opened and returned by the
360hook. This feature was planned a long time ago, but wasn't quite working
361until now. See L<perlfunc/require> for details. (Nicholas Clark)
362
363=head2 New internal variables
364
365=over 4
366
367=item C<${^RE_DEBUG_FLAGS}>
368
369This variable controls what debug flags are in effect for the regular
370expression engine when running under C<use re "debug">. See L<re> for
371details.
372
373=item C<${^CHILD_ERROR_NATIVE}>
374
375This variable gives the native status returned by the last pipe close,
376backtick command, successful call to wait() or waitpid(), or from the
377system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)
378
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379=item C<${^RE_TRIE_MAXBUF}>
380
381See L</"Trie optimisation of literal string alternations">.
382
383=item C<${^WIN32_SLOPPY_STAT}>
384
385See L</"Sloppy stat on Windows">.
386
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387=back
388
389=head2 Miscellaneous
390
391C<unpack()> now defaults to unpacking the C<$_> variable.
392
393C<mkdir()> without arguments now defaults to C<$_>.
394
395The internal dump output has been improved, so that non-printable characters
396such as newline and backspace are output in C<\x> notation, rather than
397octal.
398
399The B<-C> option can no longer be used on the C<#!> line. It wasn't
400working there anyway.
401
402=head2 UCD 5.0.0
403
404The copy of the Unicode Character Database included in Perl 5 has
405been updated to version 5.0.0.
406
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407=head2 MAD
408
409MAD, which stands for I<Misc Attribute Decoration>, is a
410still-in-development work leading to a Perl 5 to Perl 6 converter. To
411enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
412obtained perl isn't binary compatible with a regular perl 5.9.4, and has
413space and speed penalties; moreover not all regression tests still pass
414with it. (Larry Wall, Nicholas Clark)
415
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416=head1 Incompatible Changes
417
418=head2 Packing and UTF-8 strings
419
420=for XXX update this
421
422The semantics of pack() and unpack() regarding UTF-8-encoded data has been
423changed. Processing is now by default character per character instead of
424byte per byte on the underlying encoding. Notably, code that used things
425like C<pack("a*", $string)> to see through the encoding of string will now
426simply get back the original $string. Packed strings can also get upgraded
427during processing when you store upgraded characters. You can get the old
428behaviour by using C<use bytes>.
429
430To be consistent with pack(), the C<C0> in unpack() templates indicates
431that the data is to be processed in character mode, i.e. character by
432character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
433the packed string is processed in its UTF-8-encoded Unicode form on a byte
434by byte basis. This is reversed with regard to perl 5.8.X.
435
436Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
437respectively character and byte modes.
438
439C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
440specified encoding mode, honoring parens grouping. Previously, parens were
441ignored.
442
443Also, there is a new pack() character format, C<W>, which is intended to
444replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
445the strings internal representation. C<W> represents unsigned (logical)
446character values, which can be greater than 255. It is therefore more
447robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
448values outside the range 0..255, and not respect the string encoding).
449
450In practice, that means that pack formats are now encoding-neutral, except
451C<C>.
452
453For consistency, C<A> in unpack() format now trims all Unicode whitespace
454from the end of the string. Before perl 5.9.2, it used to strip only the
455classical ASCII space characters.
456
457=head2 Byte/character count feature in unpack()
458
459A new unpack() template character, C<".">, returns the number of bytes or
460characters (depending on the selected encoding mode, see above) read so far.
461
462=head2 The C<$*> and C<$#> variables have been removed
463
464C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
465modifiers, has been removed.
466
467The deprecated C<$#> variable (output format for numbers) has been
468removed.
469
470Two new warnings, C<$#/$* is no longer supported>, have been added.
471
472=head2 substr() lvalues are no longer fixed-length
473
474The lvalues returned by the three argument form of substr() used to be a
475"fixed length window" on the original string. In some cases this could
476cause surprising action at distance or other undefined behaviour. Now the
477length of the window adjusts itself to the length of the string assigned to
478it.
479
480=head2 Parsing of C<-f _>
481
482The identifier C<_> is now forced to be a bareword after a filetest
483operator. This solves a number of misparsing issues when a global C<_>
484subroutine is defined.
485
486=head2 C<:unique>
487
488The C<:unique> attribute has been made a no-op, since its current
489implementation was fundamentally flawed and not threadsafe.
490
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491=head2 Effect of pragmas in eval
492
493The compile-time value of the C<%^H> hint variable can now propagate into
494eval("")uated code. This makes it more useful to implement lexical
495pragmas.
496
497As a side-effect of this, the overloaded-ness of constants now propagates
498into eval("").
499
500=head2 chdir FOO
501
502A bareword argument to chdir() is now recognized as a file handle.
503Earlier releases interpreted the bareword as a directory name.
504(Gisle Aas)
505
506=head2 Handling of .pmc files
507
508An old feature of perl was that before C<require> or C<use> look for a
509file with a F<.pm> extension, they will first look for a similar filename
510with a F<.pmc> extension. If this file is found, it will be loaded in
511place of any potentially existing file ending in a F<.pm> extension.
512
513Previously, F<.pmc> files were loaded only if more recent than the
514matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
515they exist.
516
517=head2 @- and @+ in patterns
518
519The special arrays C<@-> and C<@+> are no longer interpolated in regular
520expressions. (Sadahiro Tomoyuki)
521
522=head2 $AUTOLOAD can now be tainted
523
524If you call a subroutine by a tainted name, and if it defers to an
525AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
526(Rick Delaney)
527
528=head2 Tainting and printf
529
530When perl is run under taint mode, C<printf()> and C<sprintf()> will now
531reject any tainted format argument. (Rafael Garcia-Suarez)
532
533=head2 undef and signal handlers
534
535Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
536equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
537
538=head2 strictures and dereferencing in defined()
539
540C<use strict "refs"> was ignoring taking a hard reference in an argument
541to defined(), as in :
542
543 use strict "refs";
544 my $x = "foo";
545 if (defined $$x) {...}
546
547This now correctly produces the run-time error C<Can't use string as a
548SCALAR ref while "strict refs" in use>.
549
550C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
551'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
552(C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
553(Nicholas Clark)
554
555=head2 C<(?p{})> has been removed
556
557The regular expression construct C<(?p{})>, which was deprecated in perl
5585.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
559
560=head2 Pseudo-hashes have been removed
561
562Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
563pragma remains here, but uses an alternate implementation.)
564
565=head2 Removal of the bytecode compiler and of perlcc
566
567C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
568B::Bytecode, etc.) are no longer distributed with the perl sources. Those
569experimental tools have never worked reliably, and, due to the lack of
570volunteers to keep them in line with the perl interpreter developments, it
571was decided to remove them instead of shipping a broken version of those.
572The last version of those modules can be found with perl 5.9.4.
573
574However the B compiler framework stays supported in the perl core, as with
575the more useful modules it has permitted (among others, B::Deparse and
576B::Concise).
577
578=head2 Removal of the JPL
579
580The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
581
582=head2 Recursive inheritance detected earlier
583
584Perl will now immediately throw an exception if you modify any package's
585C<@ISA> in such a way that it would cause recursive inheritance.
586
587Previously, the exception would not occur until Perl attempted to make
588use of the recursive inheritance while resolving a method or doing a
589C<$foo-E<gt>isa($bar)> lookup.
590
cf6c151c 591=head1 Modules and Pragmata
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593=head2 Pragmata Changes
594
595=over 4
596
597=item C<feature>
598
599The new pragma C<feature> is used to enable new features that might break
600old code. See L</"The C<feature> pragma"> above.
601
602=item C<mro>
603
604This new pragma enables to change the algorithm used to resolve inherited
605methods. See L</"New Pragma, C<mro>"> above.
606
607=item Scoping of the C<sort> pragma
608
609The C<sort> pragma is now lexically scoped. Its effect used to be global.
610
611=item Scoping of C<bignum>, C<bigint>, C<bigrat>
612
613The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
614lexically scoped. (Tels)
615
616=item C<base>
617
618The C<base> pragma now warns if a class tries to inherit from itself.
619(Curtis "Ovid" Poe)
620
621=item C<strict> and C<warnings>
622
623C<strict> and C<warnings> will now complain loudly if they are loaded via
624incorrect casing (as in C<use Strict;>). (Johan Vromans)
625
626=item C<warnings>
627
628The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
629that used C<Carp> routines without having loaded it at compile time might
630need to be adjusted; typically, the following (faulty) code won't work
631anymore, and will require parentheses to be added after the function name:
632
633 use warnings;
634 require Carp;
635 Carp::confess "argh";
636
637=item C<less>
638
639C<less> now does something useful (or at least it tries to). In fact, it
640has been turned into a lexical pragma. So, in your modules, you can now
641test whether your users have requested to use less CPU, or less memory,
642less magic, or maybe even less fat. See L<less> for more. (Joshua ben
643Jore)
644
645=back
646
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RGS
647=head2 New modules
648
649=over 4
650
651=item *
652
653C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
654whenever an ASCII character string containing high-bit bytes is implicitly
597bb945
RGS
655converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
656perls, its effect is global.
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RGS
657
658=item *
659
660C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
661you what versions of core modules ship with any versions of Perl 5. It
662comes with a command-line frontend, C<corelist>.
663
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RGS
664=item *
665
666C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
667C<Math::BigInt::Calc>.
668
669=item *
670
671C<Compress::Zlib> is an interface to the zlib compression library. It
672comes with a bundled version of zlib, so having a working zlib is not a
673prerequisite to install it. It's used by C<Archive::Tar> (see below).
674
675=item *
676
677C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
678
679=item *
680
681C<Archive::Tar> is a module to manipulate C<tar> archives.
682
683=item *
684
685C<Digest::SHA> is a module used to calculate many types of SHA digests,
686has been included for SHA support in the CPAN module.
687
688=item *
689
690C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
691
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RGS
692=item *
693
694C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
695provides support for I<field hashes>: hashes that maintain an association
696of a reference with a value, in a thread-safe garbage-collected way.
697Such hashes are useful to implement inside-out objects.
698
699=item *
700
701C<Module::Build>, by Ken Williams, has been added. It's an alternative to
702C<ExtUtils::MakeMaker> to build and install perl modules.
703
704=item *
705
706C<Module::Load>, by Jos Boumans, has been added. It provides a single
707interface to load Perl modules and F<.pl> files.
708
709=item *
710
711C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
712modules as loaded or unloaded.
713
714=item *
715
716C<Package::Constants>, by Jos Boumans, has been added. It's a simple
717helper to list all constants declared in a given package.
718
719=item *
720
721C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
722This module provides low-level access to Win32 system API calls for
723files/dirs.
724
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RGS
725=item *
726
727C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
728C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
729included in the perl core; the behaviour of C<Locale::Maketext::Simple>
730gracefully degrades when the later isn't present.
731
732=item *
733
734C<Params::Check> implements a generic input parsing/checking mechanism. It
735is used by CPANPLUS.
736
737=item *
738
739C<Term::UI> simplifies the task to ask questions at a terminal prompt.
740
741=item *
742
743C<Object::Accessor> provides an interface to create per-object accessors.
744
745=item *
746
747C<Module::Pluggable> is a simple framework to create modules that accept
748pluggable sub-modules.
749
750=item *
751
752C<Module::Load::Conditional> provides simple ways to query and possibly
753load installed modules.
754
755=item *
756
757C<Time::Piece> provides an object oriented interface to time functions,
758overriding the built-ins localtime() and gmtime().
759
760=item *
761
762C<IPC::Cmd> helps to find and run external commands, possibly
763interactively.
764
765=item *
766
767C<File::Fetch> provide a simple generic file fetching mechanism.
768
769=item *
770
771C<Log::Message> and C<Log::Message::Simple> are used by the log facility
772of C<CPANPLUS>.
773
774=item *
775
776C<Archive::Extract> is a generic archive extraction mechanism
777for F<.tar> (plain, gziped or bzipped) or F<.zip> files.
778
779=item *
780
781C<CPANPLUS> provides an API and a command-line tool to access the CPAN
782mirrors.
783
784=back
785
786=head2 Selected Changes to Core Modules
787
788=over 4
789
790=item C<Attribute::Handlers>
791
792C<Attribute::Handlers> can now report the caller's file and line number.
793(David Feldman)
794
795=item C<B::Lint>
796
797C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
798with plugins. (Joshua ben Jore)
799
800=item C<B>
801
802It's now possible to access the lexical pragma hints (C<%^H>) by using the
803method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
804can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
805ben Jore)
806
807=item C<Thread>
808
809As the old 5005thread threading model has been removed, in favor of the
810ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
811be used in old code only. It has been removed from the default list of
812dynamic extensions.
813
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RGS
814=back
815
cf6c151c 816=head1 Utility Changes
c0c97549
RGS
817
818=over 4
819
bd3831ee 820=item perl -d
c0c97549
RGS
821
822The Perl debugger can now save all debugger commands for sourcing later;
823notably, it can now emulate stepping backwards, by restarting and
824rerunning all bar the last command from a saved command history.
825
826It can also display the parent inheritance tree of a given class, with the
827C<i> command.
828
829Perl has a new -dt command-line flag, which enables threads support in the
830debugger.
831
bd3831ee
RGS
832=item ptar
833
834C<ptar> is a pure perl implementation of C<tar>, that comes with
835C<Archive::Tar>.
836
837=item ptardiff
838
839C<ptardiff> is a small script used to generate a diff between the contents
840of a tar archive and a directory tree. Like C<ptar>, it comes with
841C<Archive::Tar>.
842
843=item shasum
844
845C<shasum> is a command-line utility, used to print or to check SHA
846digests. It comes with the new C<Digest::SHA> module.
847
848=item corelist
0eece9c0
RGS
849
850The C<corelist> utility is now installed with perl (see L</"New modules">
851above).
852
bd3831ee 853=item h2ph and h2xs
0eece9c0
RGS
854
855C<h2ph> and C<h2xs> have been made a bit more robust with regard to
856"modern" C code.
857
bd3831ee
RGS
858C<h2xs> implements a new option C<--use-xsloader> to force use of
859C<XSLoader> even in backwards compatible modules.
860
861The handling of authors' names that had apostrophes has been fixed.
862
863Any enums with negative values are now skipped.
864
865=item perlivp
866
867C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
868option to run I<all> tests.
869
870=item find2perl
0eece9c0
RGS
871
872C<find2perl> now assumes C<-print> as a default action. Previously, it
873needed to be specified explicitly.
874
875Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
876C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
877added.
878
597bb945
RGS
879=item config_data
880
881C<config_data> is a new utility that comes with C<Module::Build>. It
882provides a command-line interface to the configuration of Perl modules
883that use Module::Build's framework of configurability (that is,
884C<*::ConfigData> modules that contain local configuration information for
885their parent modules.)
886
f0e260b8
RGS
887=head2 C<cpanp>
888
889C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, an
890helper for CPANPLUS operation, has been added too, but isn't intended for
891direct use).
892
893=head2 C<cpan2dist>
894
895C<cpan2dist> is a new utility, that comes with CPANPLUS. It's a tool to
896create distributions (or packages) from CPAN modules.
897
898=head2 C<pod2html>
899
900The output of C<pod2html> has been enhanced to be more customizable via
901CSS. Some formatting problems were also corrected. (Jari Aalto)
902
c0c97549
RGS
903=back
904
cf6c151c 905=head1 New Documentation
c0c97549 906
597bb945
RGS
907The L<perlpragma> manpage documents how to write one's own lexical
908pragmas in pure Perl (something that is possible starting with 5.9.4).
909
bd3831ee
RGS
910The new L<perlglossary> manpage is a glossary of terms used in the Perl
911documentation, technical and otherwise, kindly provided by O'Reilly Media,
912Inc.
913
597bb945
RGS
914The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
915Perl regular expression engine.
916
917The L<perlunitut> manpage is an tutorial for programming with Unicode and
918string encodings in Perl, courtesy of Juerd Waalboer.
919
f0e260b8
RGS
920A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
921(Juerd Waalboer).
922
c0c97549
RGS
923The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
924is now documented.
925
cf6c151c 926=head1 Performance Enhancements
c0c97549 927
597bb945 928=head2 In-place sorting
0eece9c0 929
c0c97549
RGS
930Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
931making a temporary copy of the array.
932
0eece9c0
RGS
933Likewise, C<reverse sort ...> is now optimized to sort in reverse,
934avoiding the generation of a temporary intermediate list.
935
597bb945 936=head2 Lexical array access
0eece9c0 937
c0c97549
RGS
938Access to elements of lexical arrays via a numeric constant between 0 and
939255 is now faster. (This used to be only the case for global arrays.)
940
597bb945 941=head2 XS-assisted SWASHGET
bd3831ee
RGS
942
943Some pure-perl code that perl was using to retrieve Unicode properties and
944transliteration mappings has been reimplemented in XS.
945
597bb945 946=head2 Constant subroutines
bd3831ee
RGS
947
948The interpreter internals now support a far more memory efficient form of
949inlineable constants. Storing a reference to a constant value in a symbol
950table is equivalent to a full typeglob referencing a constant subroutine,
951but using about 400 bytes less memory. This proxy constant subroutine is
952automatically upgraded to a real typeglob with subroutine if necessary.
953The approach taken is analogous to the existing space optimisation for
954subroutine stub declarations, which are stored as plain scalars in place
955of the full typeglob.
956
957Several of the core modules have been converted to use this feature for
958their system dependent constants - as a result C<use POSIX;> now takes about
959200K less memory.
960
597bb945 961=head2 C<PERL_DONT_CREATE_GVSV>
bd3831ee
RGS
962
963The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
964in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
965from creating an empty scalar with every new typeglob. See L<perl588delta>
966for details.
967
597bb945 968=head2 Weak references are cheaper
bd3831ee
RGS
969
970Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
971Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
972happens at program exit, it may be skipped completely.
973
597bb945 974=head2 sort() enhancements
bd3831ee
RGS
975
976Salvador FandiƱo provided improvements to reduce the memory usage of C<sort>
977and to speed up some cases.
978
597bb945
RGS
979=head2 Memory optimisations
980
981Several internal data structures (typeglobs, GVs, CVs, formats) have been
982restructured to use less memory. (Nicholas Clark)
983
984=head2 UTF-8 cache optimisation
985
986The UTF-8 caching code is now more efficient, and used more often.
987(Nicholas Clark)
988
989=head2 Sloppy stat on Windows
990
991On Windows, perl's stat() function normally opens the file to determine
992the link count and update attributes that may have been changed through
993hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up
994stat() by not performing this operation. (Jan Dubois)
995
597bb945
RGS
996=head2 Regular expressions optimisations
997
998=over 4
999
1000=item Engine de-recursivised
1001
1002The regular expression engine is no longer recursive, meaning that
1003patterns that used to overflow the stack will either die with useful
1004explanations, or run to completion, which, since they were able to blow
1005the stack before, will likely take a very long time to happen. If you were
1006experiencing the occasional stack overflow (or segfault) and upgrade to
1007discover that now perl apparently hangs instead, look for a degenerate
1008regex. (Dave Mitchell)
1009
1010=item Single char char-classes treated as literals
1011
1012Classes of a single character are now treated the same as if the character
1013had been used as a literal, meaning that code that uses char-classes as an
1014escaping mechanism will see a speedup. (Yves Orton)
1015
1016=item Trie optimisation of literal string alternations
1017
1018Alternations, where possible, are optimised into more efficient matching
1019structures. String literal alternations are merged into a trie and are
1020matched simultaneously. This means that instead of O(N) time for matching
1021N alternations at a given point, the new code performs in O(1) time.
1022A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune
1023this optimization. (Yves Orton)
1024
1025B<Note:> Much code exists that works around perl's historic poor
1026performance on alternations. Often the tricks used to do so will disable
1027the new optimisations. Hopefully the utility modules used for this purpose
1028will be educated about these new optimisations by the time 5.10 is
1029released.
1030
1031=item Aho-Corasick start-point optimisation
1032
1033When a pattern starts with a trie-able alternation and there aren't
1034better optimisations available the regex engine will use Aho-Corasick
1035matching to find the start point. (Yves Orton)
1036
0eece9c0
RGS
1037=back
1038
cf6c151c 1039=head1 Installation and Configuration Improvements
c0c97549 1040
597bb945
RGS
1041=head2 Configuration improvements
1042
1043=over 4
1044
1045=item C<-Dusesitecustomize>
bd3831ee 1046
0eece9c0 1047Run-time customization of @INC can be enabled by passing the
597bb945 1048C<-Dusesitecustomize> flag to Configure. When enabled, this will make perl
0eece9c0
RGS
1049run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
1050then be set up to add additional entries to @INC.
1051
597bb945
RGS
1052=item Relocatable installations
1053
1054There is now Configure support for creating a relocatable perl tree. If
1055you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
1056everything else in %Config) can be optionally located via the path of the
1057perl executable.
1058
1059That means that, if the string C<".../"> is found at the start of any
1060path, it's substituted with the directory of $^X. So, the relocation can
1061be configured on a per-directory basis, although the default with
1062C<-Duserelocatableinc> is that everything is relocated. The initial
1063install is done to the original configured prefix.
1064
1065=item strlcat() and strlcpy()
1066
1067The configuration process now detects whether strlcat() and strlcpy() are
1068available. When they are not available, perl's own version is used (from
1069Russ Allbery's public domain implementation). Various places in the perl
1070interpreter now use them. (Steve Peters)
1071
f0e260b8
RGS
1072=item C<d_pseudofork> and C<d_printf_format_null>
1073
1074A new configuration variable, available as C<$Config{d_pseudofork}> in
1075the L<Config> module, has been added, to distinguish real fork() support
1076from fake pseudofork used on Windows platforms.
1077
1078A new configuration variable, C<d_printf_format_null>, has been added,
1079to see if printf-like formats are allowed to be NULL.
1080
1081=item Configure help
1082
1083C<Configure -h> has been extended with the most commonly used options.
1084
597bb945
RGS
1085=back
1086
1087=head2 Compilation improvements
1088
1089=over 4
1090
1091=item Parallel build
0eece9c0 1092
bd3831ee
RGS
1093Parallel makes should work properly now, although there may still be problems
1094if C<make test> is instructed to run in parallel.
1095
597bb945
RGS
1096=item Borland's compilers support
1097
bd3831ee
RGS
1098Building with Borland's compilers on Win32 should work more smoothly. In
1099particular Steve Hay has worked to side step many warnings emitted by their
1100compilers and at least one C compiler internal error.
1101
597bb945
RGS
1102=item Static build on Windows
1103
f0e260b8
RGS
1104Perl extensions on Windows now can be statically built into the Perl DLL.
1105
1106Also, it's now possible to build a C<perl-static.exe> that doesn't depend
1107on the Perl DLL on Win32. See the Win32 makefiles for details.
1108(Vadim Konovalov)
bd3831ee 1109
597bb945
RGS
1110=item pport.h files
1111
1112All F<ppport.h> files in the XS modules bundled with perl are now
1113autogenerated at build time. (Marcus Holland-Moritz)
1114
f0e260b8
RGS
1115=item C++ compatibility
1116
1117Efforts have been made to make perl and the core XS modules compilable
1118with various C++ compilers (although the situation is not perfect with
1119some of the compilers on some of the platforms tested.)
1120
597bb945
RGS
1121=item Building XS extensions on Windows
1122
1123Support for building XS extension modules with the free MinGW compiler has
1124been improved in the case where perl itself was built with the Microsoft
1125VC++ compiler. (ActiveState)
1126
1127=item Support for Microsoft 64-bit compiler
1128
1129Support for building perl with Microsoft's 64-bit compiler has been
1130improved. (ActiveState)
1131
f0e260b8
RGS
1132=item Visual C++
1133
1134Perl now can be compiled with Microsoft Visual C++ 2005.
1135
1136=item Win32 builds
1137
1138All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
1139
597bb945
RGS
1140=back
1141
1142=head2 Installation improvements
1143
1144=over 4
1145
1146=item Module auxiliary files
1147
1148README files and changelogs for CPAN modules bundled with perl are no
1149longer installed.
1150
1151=back
1152
bd3831ee
RGS
1153=head2 New Or Improved Platforms
1154
597bb945 1155Perl has been reported to work on Symbian OS. See L<perlsymbian> for more
bd3831ee
RGS
1156information.
1157
597bb945
RGS
1158Many improvements have been made towards making Perl work correctly on
1159z/OS.
1160
f0e260b8 1161Perl has been reported to work on DragonFlyBSD and MidnightBSD.
597bb945 1162
bd3831ee
RGS
1163The VMS port has been improved. See L<perlvms>.
1164
f0e260b8 1165Support for Cray XT4 Catamount/Qk has been added.
bd3831ee 1166
f0e260b8
RGS
1167Vendor patches have been merged for RedHat and Gentoo.
1168
1169DynaLoader::dl_unload_file() now works on Windows.
bd3831ee 1170
cf6c151c 1171=head1 Selected Bug Fixes
c0c97549 1172
bd3831ee
RGS
1173=over 4
1174
1175=item strictures in regexp-eval blocks
1176
c0c97549
RGS
1177C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
1178
bd3831ee
RGS
1179=item Calling CORE::require()
1180
1181CORE::require() and CORE::do() were always parsed as require() and do()
1182when they were overridden. This is now fixed.
1183
1184=item Subscripts of slices
1185
1186You can now use a non-arrowed form for chained subscripts after a list
1187slice, like in:
1188
1189 ({foo => "bar"})[0]{foo}
1190
1191This used to be a syntax error; a C<< -> >> was required.
1192
1193=item C<no warnings 'category'> works correctly with -w
1194
1195Previously when running with warnings enabled globally via C<-w>, selective
1196disabling of specific warning categories would actually turn off all warnings.
1197This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
1198C<io> class. Previously it would erroneously turn off all warnings.
1199
597bb945 1200=item threads improvements
bd3831ee
RGS
1201
1202Several memory leaks in ithreads were closed. Also, ithreads were made
1203less memory-intensive.
1204
597bb945
RGS
1205C<threads> is now a dual-life module, also available on CPAN. It has been
1206expanded in many ways. A kill() method is available for thread signalling.
1207One can get thread status, or the list of running or joinable threads.
1208
1209A new C<< threads->exit() >> method is used to exit from the application
1210(this is the default for the main thread) or from the current thread only
1211(this is the default for all other threads). On the other hand, the exit()
1212built-in now always causes the whole application to terminate. (Jerry
1213D. Hedden)
1214
bd3831ee
RGS
1215=item chr() and negative values
1216
1217chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
1218character, unless when the C<bytes> pragma is in effect, where the low
1219eight bytes of the value are used.
1220
597bb945
RGS
1221=item PERL5SHELL and tainting
1222
1223On Windows, the PERL5SHELL environment variable is now checked for
1224taintedness. (Rafael Garcia-Suarez)
1225
1226=item Using *FILE{IO}
1227
1228C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
1229filehandles. (Steve Peters)
1230
1231=item Overloading and reblessing
1232
1233Overloading now works when references are reblessed into another class.
1234Internally, this has been implemented by moving the flag for "overloading"
1235from the reference to the referent, which logically is where it should
1236always have been. (Nicholas Clark)
1237
1238=item Overloading and UTF-8
1239
1240A few bugs related to UTF-8 handling with objects that have
1241stringification overloaded have been fixed. (Nicholas Clark)
1242
1243=item eval memory leaks fixed
1244
1245Traditionally, C<eval 'syntax error'> has leaked badly. Many (but not all)
1246of these leaks have now been eliminated or reduced. (Dave Mitchell)
1247
1248=item Random device on Windows
1249
1250In previous versions, perl would read the file F</dev/urandom> if it
1251existed when seeding its random number generator. That file is unlikely
1252to exist on Windows, and if it did would probably not contain appropriate
1253data, so perl no longer tries to read it on Windows. (Alex Davies)
1254
1255=item PERLIO_DEBUG
1256
1257The C<PERLIO_DEBUG> environment variable has no longer any effect for
1258setuid scripts and for scripts run with B<-T>.
1259
1260Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
1261an internal buffer overflow. This has been fixed.
1262
f0e260b8
RGS
1263=item PerlIO::scalar and read-only scalars
1264
1265PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
1266seek() is now supported with PerlIO::scalar-based filehandles, the
1267underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
1268
1269=item study() and UTF-8
1270
1271study() never worked for UTF-8 strings, but could lead to false results.
1272It's now a no-op on UTF-8 data. (Yves Orton)
1273
1274=item Critical signals
1275
1276The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
1277"unsafe" manner (contrary to other signals, that are deferred until the
1278perl interpreter reaches a reasonably stable state; see
1279L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
1280
1281=item @INC-hook fix
1282
1283When a module or a file is loaded through an @INC-hook, and when this hook
1284has set a filename entry in %INC, __FILE__ is now set for this module
1285accordingly to the contents of that %INC entry. (Rafael)
1286
1287=item C<-t> switch fix
1288
1289The C<-w> and C<-t> switches can now be used together without messing
1290up what categories of warnings are activated or not. (Rafael)
1291
1292=item Duping UTF-8 filehandles
1293
1294Duping a filehandle which has the C<:utf8> PerlIO layer set will now
1295properly carry that layer on the duped filehandle. (Rafael)
1296
1297=item Localisation of hash elements
1298
1299Localizing an hash element whose key was given as a variable didn't work
1300correctly if the variable was changed while the local() was in effect (as
1301in C<local $h{$x}; ++$x>). (Bo Lindbergh)
1302
bd3831ee 1303=back
0eece9c0 1304
cf6c151c 1305=head1 New or Changed Diagnostics
c0c97549 1306
bd3831ee
RGS
1307=over 4
1308
1309=item Deprecated use of my() in false conditional
1310
c0c97549
RGS
1311A new deprecation warning, I<Deprecated use of my() in false conditional>,
1312has been added, to warn against the use of the dubious and deprecated
1313construct
1314
1315 my $x if 0;
1316
1317See L<perldiag>. Use C<state> variables instead.
1318
bd3831ee
RGS
1319=item !=~ should be !~
1320
0eece9c0
RGS
1321A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
1322of the non-matching operator.
1323
bd3831ee
RGS
1324=item Newline in left-justified string
1325
0eece9c0
RGS
1326The warning I<Newline in left-justified string> has been removed.
1327
bd3831ee
RGS
1328=item Too late for "-T" option
1329
0eece9c0
RGS
1330The error I<Too late for "-T" option> has been reformulated to be more
1331descriptive.
1332
bd3831ee
RGS
1333=item "%s" variable %s masks earlier declaration
1334
1335This warning is now emitted in more consistent cases; in short, when one
1336of the declarations involved is a C<my> variable:
1337
1338 my $x; my $x; # warns
1339 my $x; our $x; # warns
1340 our $x; my $x; # warns
1341
1342On the other hand, the following:
1343
1344 our $x; our $x;
1345
1346now gives a C<"our" variable %s redeclared> warning.
1347
1348=item readdir()/closedir()/etc. attempted on invalid dirhandle
1349
1350These new warnings are now emitted when a dirhandle is used but is
1351either closed or not really a dirhandle.
1352
f0e260b8
RGS
1353=item Opening dirhandle/filehandle %s also as a file/directory
1354
1355Two deprecation warnings have been added: (Rafael)
1356
1357 Opening dirhandle %s also as a file
1358 Opening filehandle %s also as a directory
1359
bd3831ee
RGS
1360=item perl -V
1361
0eece9c0
RGS
1362C<perl -V> has several improvements, making it more useable from shell
1363scripts to get the value of configuration variables. See L<perlrun> for
1364details.
1365
bd3831ee
RGS
1366=back
1367
cf6c151c 1368=head1 Changed Internals
c0c97549 1369
bd3831ee
RGS
1370In general, the source code of perl has been refactored, tied up, and
1371optimized in many places. Also, memory management and allocation has been
1372improved in a couple of points.
1373
c0c97549
RGS
1374=head2 Reordering of SVt_* constants
1375
1376The relative ordering of constants that define the various types of C<SV>
1377have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
1378C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
1379difference unless you have code that explicitly makes assumptions about that
1380ordering. (The inheritance hierarchy of C<B::*> objects has been changed
1381to reflect this.)
1382
1383=head2 Removal of CPP symbols
1384
1385The C preprocessor symbols C<PERL_PM_APIVERSION> and
1386C<PERL_XS_APIVERSION>, which were supposed to give the version number of
1387the oldest perl binary-compatible (resp. source-compatible) with the
1388present one, were not used, and sometimes had misleading values. They have
1389been removed.
1390
1391=head2 Less space is used by ops
1392
1393The C<BASEOP> structure now uses less space. The C<op_seq> field has been
1394removed and replaced by the one-bit fields C<op_opt>. C<op_type> is now 9
1395bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
1396method anymore.)
1397
1398=head2 New parser
1399
1400perl's parser is now generated by bison (it used to be generated by
1401byacc.) As a result, it seems to be a bit more robust.
1402
bd3831ee
RGS
1403Also, Dave Mitchell improved the lexer debugging output under C<-DT>.
1404
1405=head2 Use of C<const>
1406
1407Andy Lester supplied many improvements to determine which function
1408parameters and local variables could actually be declared C<const> to the C
1409compiler. Steve Peters provided new C<*_set> macros and reworked the core to
1410use these rather than assigning to macros in LVALUE context.
1411
1412=head2 Mathoms
1413
1414A new file, F<mathoms.c>, has been added. It contains functions that are
1415no longer used in the perl core, but that remain available for binary or
1416source compatibility reasons. However, those functions will not be
1417compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
1418
1419=head2 C<AvFLAGS> has been removed
1420
1421The C<AvFLAGS> macro has been removed.
1422
1423=head2 C<av_*> changes
1424
1425The C<av_*()> functions, used to manipulate arrays, no longer accept null
1426C<AV*> parameters.
1427
597bb945
RGS
1428=head2 $^H and %^H
1429
1430The implementation of the special variables $^H and %^H has changed, to
1431allow implementing lexical pragmas in pure perl.
1432
bd3831ee
RGS
1433=head2 B:: modules inheritance changed
1434
1435The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
1436inherits from C<B::SV> (it used to inherit from C<B::IV>).
1437
f0e260b8
RGS
1438=head2 Anonymous hash and array constructors
1439
1440The anonymous hash and array constructors now take 1 op in the optree
1441instead of 3, now that pp_anonhash and pp_anonlist return a reference to
1442an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
1443
1444=for p5p XXX have we some docs on how to create regexp engine plugins, since that's now possible ? (perlreguts)
1445
1446=for p5p XXX new BIND SV type, #29544, #29642
1447
cf6c151c 1448=head1 New Tests
c0c97549 1449
cf6c151c 1450=head1 Known Problems
c0c97549
RGS
1451
1452There's still a remaining problem in the implementation of the lexical
1453C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
1454F<t/op/mydef.t>.)
1455
cf6c151c 1456=head1 Platform Specific Problems
c0c97549 1457
cf6c151c
RGS
1458=head1 Reporting Bugs
1459
1460=head1 SEE ALSO
1461
1462The F<Changes> file and the perl590delta to perl595delta man pages for
1463exhaustive details on what changed.
1464
1465The F<INSTALL> file for how to build Perl.
1466
1467The F<README> file for general stuff.
1468
1469The F<Artistic> and F<Copying> files for copyright information.
1470
1471=cut