3 perldelta - what's new for perl5.005
7 This document describes differences between the 5.004 release and this one.
9 [XXX this needs more verbose summaries of the sub topics, instead of just
10 the "See L<foo>." Scheduled for a second iteration. GSAR]
12 =head1 About the new versioning system
14 =head1 Incompatible Changes
16 =head2 WARNING: This version is not binary compatible with Perl 5.004.
18 Starting with Perl 5.004_50 there were many deep and far-reaching changes
19 to the language internals. If you have dynamically loaded extensions
20 that you built under perl 5.003 or 5.004, you can continue to use them
21 with 5.004, but you will need to rebuild and reinstall those extensions
22 to use them 5.005. See L<INSTALL> for detailed instructions on how to
25 =head2 Default installation structure has changed
27 The new Configure defaults are designed to allow a smooth upgrade from
28 5.004 to 5.005, but you should read L<INSTALL> for a detailed
29 discussion of the changes in order to adapt them to your system.
31 =head2 Perl Source Compatibility
33 When none of the experimental features are enabled, there should be
34 no user-visible Perl source compatibility issue.
36 If threads are enabled, then some caveats apply. C<@_> and C<$_> become
37 lexical variables. The effect of this should be largely transparent to
38 the user, but there are some boundary conditions under which user will
39 need to be aware of the issues. [XXX Add e.g. here.]
41 =head2 C Source Compatibility
43 =item Core sources now require ANSI C compiler
45 =item Enabling threads has source compatibility issues
47 =head2 Binary Compatibility
49 This version is NOT binary compatible with older versions. All extensions
50 will need to be recompiled.
52 =head2 Security fixes may affect compatibility
54 A few taint leaks and taint omissions have been corrected. This may lead
55 to "failure" of scripts that used to work with older versions. Compiling
56 with -DINCOMPLETE_TAINTS provides a perl with minimal amounts of changes
57 to the tainting behavior. But note that the resulting perl will have
60 Oneliners with the C<-e> switch do not create temporary files anymore.
62 =head2 Relaxed new mandatory warnings introduced in 5.004
64 Many new warnings that were introduced in 5.004 have either been made
65 optional. Some of these warnings are still present, but perl's new
66 features make them less often a problem. See L<New Diagnostics>.
70 Perl has a new Social Contract for contributors.
72 Perl's documentation license has changed.
79 WARNING: Threading is considered an experimental feature. Details of the
80 implementation may change without notice. There are known limitations
83 See L<README.threads>.
87 WARNING: The Compiler and related tools are considered experimental.
88 Features may change without notice, and there are known limitations
91 B::Lint is an experimental module to detect and warn about suspicious
92 code, especially the cases that the -w switch does not detect.
94 B::Deparse can be used to demystify perl code.
98 =head2 Regular Expressions
100 See L<perlre> and L<perlop>.
102 =head2 Improved malloc()
104 See banner at the beginning of C<malloc.c> for details.
106 =head2 Quicksort is internally implemented
108 See C<perlfunc/sort>.
110 =head2 Reliable signals
114 Via switched runtime op loop.
116 =head2 Reliable stack pointers
118 The internals now reallocate the perl stack only at predicatable times.
119 In particular, magic calls never trigger reallocations of the stack,
120 because all reentrancy of the runtime is handled using a "stack of stacks".
121 This should improve reliability of cached stack pointers in XSUBs.
123 =head2 Behavior of local() on composites is well-defined
125 See L<perlfunc/local>.
127 =head2 C<%!> is transparently tied to the L<Errno> module
131 =head2 Pseudo-hashes are supported
135 =head2 C<EXPR foreach EXPR> is supported
139 =head2 Slice notation on glob elements is supported
143 =head2 Keywords can be globally overridden
147 =head2 C<$^E> is meaningful on Win32
151 =head2 C<foreach (1..1000000)> optimized
153 C<foreach (1..1000000)> is now optimized into a counting loop. It does
154 not try to allocate a 1000000-size list anymore.
156 =head2 C<Foo::> can be used as implicitly quoted package name
160 =head2 C<exists $Foo::{Bar::}> tests existence of a package
164 =head2 Better locale support
168 =head2 Experimental support for 64-bit platforms
170 Perl5 has always had 64-bit support on systems with 64-bit longs.
171 Starting with 5.005, the beginnings of experimental support for systems
172 with 32-bit long and 64-bit 'long long' integers has been added.
173 If you add -DUSE_LONG_LONG to your ccflags in config.sh (or manually
174 define it in perl.h) then perl will be built with 'long long' support.
175 There will be many compiler warnings, and the resultant perl may not
176 work on all systems. There are many other issues related to
177 third-party extensions and libraries. This option exists to allow
178 people to work on those issues.
180 =head2 prototype() returns useful results on builtins
182 See L<perlfunc/prototype>.
184 =head2 Re-blessing in DESTROY() supported for chaining DESTROY() methods
186 See L<perlobj/Destructors>.
188 =head2 All C<printf> format conversions are handled internally
190 See L<perlfunc/printf>.
192 =head2 New C<INIT> keyword
194 C<INIT> subs are like C<BEGIN> and C<END>, but they get called just before
195 the perl runtime begins execution.
197 [XXX Needs to be documented in perlsub or perlmod.]
199 =head2 New C<lock> keyword
201 To minimize impact on source compatibility this keyword is "weak", i.e., any
202 user-defined subroutine of the same name overrides it, unless a C<use Thread>
205 =head2 Tied arrays are now fully supported
209 =head2 Tied handles support is better
211 Several missing hooks have been added. There is also a new base class for
212 TIEARRAY implementations. See L<Tie::Array>.
215 =head1 Supported Platforms
217 Configure has many incremental improvements. Site-wide policy for building
218 perl can now be made perlsistent, via Policy.sh. Configure also records
219 the command-line arguments used in F<config.sh>.
223 BeOS is now supported. See L<README.beos>.
225 DOS is now supported under the DJGPP tools. See L<README.dos>.
227 =head2 Changes in existing support
229 Win32 support has been vastly enhanced. Support for Perl Object, a C++
230 encapsulation of Perl. GCC and EGCS are now supported on Win32.
231 [XXX Perl Object needs a big explanation elsewhere, and a pointer to
234 VMS configuration system has been rewritten. See L<README.vms>.
236 OpenBSD better supported. [XXX what others?]
238 =head1 Modules and Pragmata
246 Perl compiler and tools. See [XXX what?].
250 A module to pretty print Perl data. See L<Data::Dumper>.
254 A module to look up errors more conveniently. See L<Errno>.
258 A portable API for file operations.
260 =item ExtUtils::Installed
262 Query and manage installed modules.
264 =item ExtUtils::Packlist
266 Manipulate .packlist files.
270 Make functions/builtins succeed or die.
274 Constants and other support infrastructure for System V IPC operations
279 A framework for writing testsuites.
283 Base class for tied arrays.
287 Base class for tied handles.
291 Perl thread creation, manipulation, and support.
295 Set subroutine attributes.
299 Compile-time class fields.
303 Various pragmata to control behavior of regular expressions.
307 =head2 Changes in existing modules
313 CGI has been updated to version 2.42.
317 POSIX now has its own platform-specific hints files.
321 DB_File supports version 2.x of Berkeley DB. See C<ext/DB_File/Changes>.
325 MakeMaker now supports writing empty makefiles, provides a way to
326 specify that site umask() policy should be honored. There is also
327 better support for manipulation of .packlist files, and getting
328 information about installed modules.
330 Extensions that have both architecture-dependent and
331 architecture-independent files are now always installed completely in
332 the architecture-dependent locations. Previously, the shareable parts
333 were shared both across architectures and across perl versions and were
334 therefore liable to be overwritten with newer versions that might have
335 subtle incompatibilities.
343 Cwd::cwd is faster on most platforms.
351 =head1 Utility Changes
353 h2ph and related utilities have been vastly overhauled.
355 perlcc, a new experimental front end for the compiler is available.
357 The crude GNU configure emulator is now called configure.gnu.
361 =head2 Incompatible Changes
363 =head2 Deprecations, Extensions
367 =head1 Documentation Changes
369 Config.pm now has a glossary of variables.
371 Porting/patching.pod has detailed instructions on how to create and
372 submit patches for perl.
374 =head1 New Diagnostics
378 =item Ambiguous call resolved as CORE::%s(), qualify as such or use &
380 (W) A subroutine you have declared has the same name as a Perl keyword,
381 and you have used the name without qualification for calling one or the
382 other. Perl decided to call the builtin because the subroutine is
385 To force interpretation as a subroutine call, either put an ampersand
386 before the subroutine name, or qualify the name with its package.
387 Alternatively, you can import the subroutine (or pretend that it's
388 imported with the C<use subs> pragma).
390 To silently interpret it as the Perl operator, use the C<CORE::> prefix
391 on the operator (e.g. C<CORE::log($x)>) or by declaring the subroutine
392 to be an object method (see L<attrs>).
394 =item Bad index while coercing array into hash
396 (F) The index looked up in the hash found as the 0'th element of a
397 pseudo-hash is not legal. Index values must be at 1 or greater.
400 =item Bareword "%s" refers to nonexistent package
402 (W) You used a qualified bareword of the form C<Foo::>, but
403 the compiler saw no other uses of that namespace before that point.
404 Perhaps you need to predeclare a package?
406 =item Can't call method "%s" on an undefined value
408 (F) You used the syntax of a method call, but the slot filled by the
409 object reference or package name contains an undefined value.
410 Something like this will reproduce the error:
413 process $BADREF 1,2,3;
414 $BADREF->process(1,2,3);
416 =item Can't coerce array into hash
418 (F) You used an array where a hash was expected, but the array has no
419 information on how to map from keys to array indices. You can do that
420 only with arrays that have a hash reference at index 0.
422 =item Can't goto subroutine from an eval-string
424 (F) The "goto subroutine" call can't be used to jump out of an eval "string".
425 (You can use it to jump out of an eval {BLOCK}, but you probably don't want to.)
427 =item Can't use %%! because Errno.pm is not available
429 (F) The first time the %! hash is used, perl automatically loads the
430 Errno.pm module. The Errno module is expected to tie the %! hash to
431 provide symbolic names for C<$!> errno values.
433 =item Can't use %%! because Errno.pm is not available
435 (F) The first time the %! hash is used, perl automatically loads the
436 Errno.pm module. The Errno module is expected to tie the %! hash to
437 provide symbolic names for C<$!> errno values.
439 =item Cannot find an opnumber for "%s"
441 (F) A string of a form C<CORE::word> was given to prototype(), but
442 there is no builtin with the name C<word>.
444 =item Character class syntax [. .] is reserved for future extensions
446 (W) Within regular expression character classes ([]) the syntax beginning
447 with "[." and ending with ".]" is reserved for future extensions.
448 If you need to represent those character sequences inside a regular
449 expression character class, just quote the square brackets with the
450 backslash: "\[." and ".\]".
452 =item Character class syntax [: :] is reserved for future extensions
454 (W) Within regular expression character classes ([]) the syntax beginning
455 with "[:" and ending with ":]" is reserved for future extensions.
456 If you need to represent those character sequences inside a regular
457 expression character class, just quote the square brackets with the
458 backslash: "\[:" and ":\]".
460 =item Character class syntax [= =] is reserved for future extensions
462 (W) Within regular expression character classes ([]) the syntax
463 beginning with "[=" and ending with "=]" is reserved for future extensions.
464 If you need to represent those character sequences inside a regular
465 expression character class, just quote the square brackets with the
466 backslash: "\[=" and "=\]".
468 =item %s: Eval-group in insecure regular expression
470 (F) Perl detected tainted data when trying to compile a regular expression
471 that contains the C<(?{ ... })> zero-width assertion, which is unsafe.
472 See L<perlre/(?{ code })>, and L<perlsec>.
474 =item %s: Eval-group not allowed, use re 'eval'
476 (F) A regular expression contained the C<(?{ ... })> zero-width assertion,
477 but that construct is only allowed when the C<use re 'eval'> pragma is
478 in effect. See L<perlre/(?{ code })>.
480 =item %s: Eval-group not allowed at run time
482 (F) Perl tried to compile a regular expression containing the C<(?{ ... })>
483 zero-width assertion at run time, as it would when the pattern contains
484 interpolated values. Since that is a security risk, it is not allowed.
485 If you insist, you may still do this by explicitly building the pattern
486 from an interpolated string at run time and using that in an eval().
487 See L<perlre/(?{ code })>.
489 =item Explicit blessing to '' (assuming package main)
491 (W) You are blessing a reference to a zero length string. This has
492 the effect of blessing the reference into the package main. This is
493 usually not what you want. Consider providing a default target
494 package, e.g. bless($ref, $p or 'MyPackage');
496 =item Illegal hex digit ignored
498 (W) You may have tried to use a character other than 0 - 9 or A - F in a
499 hexadecimal number. Interpretation of the hexadecimal number stopped
500 before the illegal character.
502 =item No such array field
504 (F) You tried to access an array as a hash, but the field name used is
505 not defined. The hash at index 0 should map all valid field names to
506 array indices for that to work.
508 =item No such field "%s" in variable %s of type %s
510 (F) You tried to access a field of a typed variable where the type
511 does not know about the field name. The field names are looked up in
512 the %FIELDS hash in the type package at compile time. The %FIELDS hash
513 is usually set up with the 'fields' pragma.
515 =item Out of memory during ridiculously large request
517 (F) You can't allocate more than 2^31+"small amount" bytes. This error
518 is most likely to be caused by a typo in the Perl program. e.g., C<$arr[time]>
519 instead of C<$arr[$time]>.
521 =item Range iterator outside integer range
523 (F) One (or both) of the numeric arguments to the range operator ".."
524 are outside the range which can be represented by integers internally.
525 One possible workaround is to force Perl to use magical string
526 increment by prepending "0" to your numbers.
528 =item Recursive inheritance detected while looking for method '%s' in package '%s'
530 (F) More than 100 levels of inheritance were encountered while invoking a
531 method. Probably indicates an unintended loop in your inheritance hierarchy.
533 =item Reference found where even-sized list expected
535 (W) You gave a single reference where Perl was expecting a list with
536 an even number of elements (for assignment to a hash). This
537 usually means that you used the anon hash constructor when you meant
538 to use parens. In any case, a hash requires key/value B<pairs>.
540 %hash = { one => 1, two => 2, }; # WRONG
541 %hash = [ qw/ an anon array / ]; # WRONG
542 %hash = ( one => 1, two => 2, ); # right
543 %hash = qw( one 1 two 2 ); # also fine
545 =item Undefined value assigned to typeglob
547 (W) An undefined value was assigned to a typeglob, a la C<*foo = undef>.
548 This does nothing. It's possible that you really mean C<undef *foo>.
550 =item Use of reserved word "%s" is deprecated
552 (D) The indicated bareword is a reserved word. Future versions of perl
553 may use it as a keyword, so you're better off either explicitly quoting
554 the word in a manner appropriate for its context of use, or using a
555 different name altogether. The warning can be suppressed for subroutine
556 names by either adding a C<&> prefix, or using a package qualifier,
557 e.g. C<&our()>, or C<Foo::our()>.
559 =item perl: warning: Setting locale failed.
561 (S) The whole warning message will look something like:
563 perl: warning: Setting locale failed.
564 perl: warning: Please check that your locale settings:
567 are supported and installed on your system.
568 perl: warning: Falling back to the standard locale ("C").
570 Exactly what were the failed locale settings varies. In the above the
571 settings were that the LC_ALL was "En_US" and the LANG had no value.
572 This error means that Perl detected that you and/or your system
573 administrator have set up the so-called variable system but Perl could
574 not use those settings. This was not dead serious, fortunately: there
575 is a "default locale" called "C" that Perl can and will use, the
576 script will be run. Before you really fix the problem, however, you
577 will get the same error message each time you run Perl. How to really
578 fix the problem can be found in L<perllocale> section B<LOCALE PROBLEMS>.
583 =head1 Obsolete Diagnostics
589 (F) The mktemp() routine failed for some reason while trying to process
590 a B<-e> switch. Maybe your /tmp partition is full, or clobbered.
592 =item Can't write to temp file for B<-e>: %s
594 (F) The write routine failed for some reason while trying to process
595 a B<-e> switch. Maybe your /tmp partition is full, or clobbered.
597 =item Cannot open temporary file
599 (F) The create routine failed for some reason while trying to process
600 a B<-e> switch. Maybe your /tmp partition is full, or clobbered.
607 If you find what you think is a bug, you might check the headers of
608 recently posted articles in the comp.lang.perl.misc newsgroup.
609 There may also be information at http://www.perl.com/perl/, the Perl
612 If you believe you have an unreported bug, please run the B<perlbug>
613 program included with your release. Make sure you trim your bug down
614 to a tiny but sufficient test case. Your bug report, along with the
615 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
616 analysed by the Perl porting team.
620 The F<Changes> file for exhaustive details on what changed.
622 The F<INSTALL> file for how to build Perl.
624 The F<README> file for general stuff.
626 The F<Artistic> and F<Copying> files for copyright information.