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 Installation structure has changed
27 Extensions that have with architecture-dependent files are now always
28 installed in the architecture-dependent locations. Previously, they
29 were shared will multiple versions of perl, an were therefore liable to
30 be overwritten with newer versions that may have subtle incompatibilities.
32 =head2 Perl Source Compatibility
34 When none of the experimental features are enabled, there should be
35 no user-visible Perl source compatibility issue.
37 If threads are enabled, then some caveats apply. C<@_> and C<$_> become
38 lexical variables. The effect of this should be largely transparent to
39 the user, but there are some boundary conditions under which user will
40 need to be aware of the issues. [XXX Add e.g. here.]
42 =head2 C Source Compatibility
44 =item Core sources now require ANSI C compiler
46 =item Enabling threads has source compatibility issues
48 =head2 Binary Compatibility
50 This version is NOT binary compatible with older versions. All extensions
51 will need to be recompiled.
53 =head2 Security fixes may affect compatibility
55 A few taint leaks and taint omissions have been corrected. This may lead
56 to "failure" of scripts that used to work with older versions. Compiling
57 with -DINCOMPLETE_TAINTS provides a perl with minimal amounts of changes
58 to the tainting behavior. But note that the resulting perl will have
61 Oneliners with the C<-e> switch do not create temporary files anymore.
63 =head2 Relaxed new mandatory warnings introduced in 5.004
65 Many new warnings that were introduced in 5.004 have either been made
66 optional. Some of these warnings are still present, but perl's new
67 features make them less often a problem. See L<New Diagnostics>.
71 Perl has a new Social Contract for contributors.
73 Perl's documentation license has changed.
80 WARNING: Threading is considered an experimental feature. Details of the
81 implementation may change without notice. There are known limitations
84 See L<README.threads>.
88 WARNING: The Compiler and related tools are considered experimental.
89 Features may change without notice, and there are known limitations
92 B::Lint is an experimental module to detect and warn about suspicious
93 code, especially the cases that the -w switch does not detect.
95 B::Deparse can be used to demystify perl code.
99 =head2 Regular Expressions
101 See L<perlre> and L<perlop>.
103 =head2 Improved malloc()
105 See banner at the beginning of C<malloc.c> for details.
107 =head2 Quicksort is internally implemented
109 See C<perlfunc/sort>.
111 =head2 Reliable signals
115 Via switched runtime op loop.
117 =head2 Reliable stack pointers
119 The internals now reallocate the perl stack only at predicatable times.
120 In particular, magic calls never trigger reallocations of the stack,
121 because all reentrancy of the runtime is handled using a "stack of stacks".
122 This should improve reliability of cached stack pointers in XSUBs.
124 =head2 Behavior of local() on composites is well-defined
126 See L<perlfunc/local>.
128 =head2 C<%!> is transparently tied to the L<Errno> module
132 =head2 Pseudo-hashes are supported
136 =head2 C<EXPR foreach EXPR> is supported
140 =head2 Slice notation on glob elements is supported
144 =head2 Keywords can be globally overridden
148 =head2 C<$^E> is meaningful on Win32
152 =head2 C<foreach (1..1000000)> optimized
154 C<foreach (1..1000000)> is now optimized into a counting loop. It does
155 not try to allocate a 1000000-size list anymore.
157 =head2 C<Foo::> can be used as implicitly quoted package name
161 =head2 C<exists $Foo::{Bar::}> tests existence of a package
165 =head2 Better locale support
169 =head2 Better support for 64-bit platforms
173 =head2 prototype() returns useful results on builtins
175 See L<perlfunc/prototype>.
177 =head2 Re-blessing in DESTROY() supported for chaining DESTROY() methods
179 See L<perlobj/Destructors>.
181 =head2 All C<printf> format conversions are handled internally
183 See L<perlfunc/printf>.
185 =head2 New C<INIT> keyword
187 C<INIT> subs are like C<BEGIN> and C<END>, but they get called just before
188 the perl runtime begins execution.
190 [XXX Needs to be documented in perlsub or perlmod.]
192 =head2 New C<lock> keyword
194 To minimize impact on source compatibility this keyword is "weak", i.e., any
195 user-defined subroutine of the same name overrides it, unless a C<use Thread>
198 =head2 Tied arrays are now fully supported
202 =head2 Tied handles support is better
204 Several missing hooks have been added. There is also a new base class for
205 TIEARRAY implementations. See L<Tie::Array>.
208 =head1 Supported Platforms
210 Configure has many incremental improvements. Site-wide policy for building
211 perl can now be made perlsistent, via Policy.sh. Configure can also remember
212 the arguments used in previous invocations.
216 BeOS is now supported. See L<README.beos>.
218 DOS is now supported under the DJGPP tools. See L<README.dos>.
220 =head2 Changes in existing support
222 Win32 support has been vastly enhanced. Support for Perl Object, a C++
223 encapsulation of Perl. GCC and EGCS are now supported on Win32.
224 [XXX Perl Object needs a big explanation elsewhere, and a pointer to
227 VMS configuration system has been rewritten. See L<README.vms>.
229 OpenBSD better supported. [XXX what others?]
231 =head1 Modules and Pragmata
239 Perl compiler and tools. See [XXX what?].
243 A module to pretty print Perl data. See L<Data::Dumper>.
247 A module to look up errors more conveniently. See L<Errno>.
251 A portable API for file operations.
253 =item ExtUtils::Installed
255 Query and manage installed modules.
257 =item ExtUtils::Packlist
259 Manipulate .packlist files.
263 Make functions/builtins succeed or die.
267 Constants and other support infrastructure for System V IPC operations
272 A framework for writing testsuites.
276 Base class for tied arrays.
280 Base class for tied handles.
284 Perl thread creation, manipulation, and support.
288 Set subroutine attributes.
292 Compile-time class fields.
296 Various pragmata to control behavior of regular expressions.
300 =head2 Changes in existing modules
306 CGI has been updated to version 2.42.
310 POSIX now has its own platform-specific hints files.
314 DB_File supports version 2.x of Berkeley DB. See C<ext/DB_File/Changes>.
318 MakeMaker now supports writing empty makefiles, provides a way to
319 specify that site umask() policy should be honored. There is also
320 better support for manipulation of .packlist files, and getting
321 information about installed modules.
329 Cwd::cwd is faster on most platforms.
337 =head1 Utility Changes
339 The crude GNU configure emulator is now called configure.gnu.
341 h2ph and related utilities have been vastly overhauled.
343 perlcc, a new experimental front end for the compiler is available.
347 =head2 Incompatible Changes
349 =head2 Deprecations, Extensions
353 =head1 Documentation Changes
355 Config.pm now has a glossary of variables.
357 Porting/patching.pod has detailed instructions on how to create and
358 submit patches for perl.
360 =head1 New Diagnostics
364 =item Ambiguous call resolved as CORE::%s(), qualify as such or use &
366 (W) A subroutine you have declared has the same name as a Perl keyword,
367 and you have used the name without qualification for calling one or the
368 other. Perl decided to call the builtin because the subroutine is
371 To force interpretation as a subroutine call, either put an ampersand
372 before the subroutine name, or qualify the name with its package.
373 Alternatively, you can import the subroutine (or pretend that it's
374 imported with the C<use subs> pragma).
376 To silently interpret it as the Perl operator, use the C<CORE::> prefix
377 on the operator (e.g. C<CORE::log($x)>) or by declaring the subroutine
378 to be an object method (see L<attrs>).
380 =item Bad index while coercing array into hash
382 (F) The index looked up in the hash found as the 0'th element of a
383 pseudo-hash is not legal. Index values must be at 1 or greater.
386 =item Bareword "%s" refers to nonexistent package
388 (W) You used a qualified bareword of the form C<Foo::>, but
389 the compiler saw no other uses of that namespace before that point.
390 Perhaps you need to predeclare a package?
392 =item Can't call method "%s" on an undefined value
394 (F) You used the syntax of a method call, but the slot filled by the
395 object reference or package name contains an undefined value.
396 Something like this will reproduce the error:
399 process $BADREF 1,2,3;
400 $BADREF->process(1,2,3);
402 =item Can't coerce array into hash
404 (F) You used an array where a hash was expected, but the array has no
405 information on how to map from keys to array indices. You can do that
406 only with arrays that have a hash reference at index 0.
408 =item Can't goto subroutine from an eval-string
410 (F) The "goto subroutine" call can't be used to jump out of an eval "string".
411 (You can use it to jump out of an eval {BLOCK}, but you probably don't want to.)
413 =item Can't use %%! because Errno.pm is not available
415 (F) The first time the %! hash is used, perl automatically loads the
416 Errno.pm module. The Errno module is expected to tie the %! hash to
417 provide symbolic names for C<$!> errno values.
419 =item Can't use %%! because Errno.pm is not available
421 (F) The first time the %! hash is used, perl automatically loads the
422 Errno.pm module. The Errno module is expected to tie the %! hash to
423 provide symbolic names for C<$!> errno values.
425 =item Cannot find an opnumber for "%s"
427 (F) A string of a form C<CORE::word> was given to prototype(), but
428 there is no builtin with the name C<word>.
430 =item Character class syntax [. .] is reserved for future extensions
432 (W) Within regular expression character classes ([]) the syntax beginning
433 with "[." and ending with ".]" is reserved for future extensions.
434 If you need to represent those character sequences inside a regular
435 expression character class, just quote the square brackets with the
436 backslash: "\[." and ".\]".
438 =item Character class syntax [: :] is reserved for future extensions
440 (W) Within regular expression character classes ([]) the syntax beginning
441 with "[:" and ending with ":]" is reserved for future extensions.
442 If you need to represent those character sequences inside a regular
443 expression character class, just quote the square brackets with the
444 backslash: "\[:" and ":\]".
446 =item Character class syntax [= =] is reserved for future extensions
448 (W) Within regular expression character classes ([]) the syntax
449 beginning with "[=" and ending with "=]" is reserved for future extensions.
450 If you need to represent those character sequences inside a regular
451 expression character class, just quote the square brackets with the
452 backslash: "\[=" and "=\]".
454 =item %s: Eval-group in insecure regular expression
456 (F) Perl detected tainted data when trying to compile a regular expression
457 that contains the C<(?{ ... })> zero-width assertion, which is unsafe.
458 See L<perlre/(?{ code })>, and L<perlsec>.
460 =item %s: Eval-group not allowed, use re 'eval'
462 (F) A regular expression contained the C<(?{ ... })> zero-width assertion,
463 but that construct is only allowed when the C<use re 'eval'> pragma is
464 in effect. See L<perlre/(?{ code })>.
466 =item %s: Eval-group not allowed at run time
468 (F) Perl tried to compile a regular expression containing the C<(?{ ... })>
469 zero-width assertion at run time, as it would when the pattern contains
470 interpolated values. Since that is a security risk, it is not allowed.
471 If you insist, you may still do this by explicitly building the pattern
472 from an interpolated string at run time and using that in an eval().
473 See L<perlre/(?{ code })>.
475 =item Explicit blessing to '' (assuming package main)
477 (W) You are blessing a reference to a zero length string. This has
478 the effect of blessing the reference into the package main. This is
479 usually not what you want. Consider providing a default target
480 package, e.g. bless($ref, $p or 'MyPackage');
482 =item Illegal hex digit ignored
484 (W) You may have tried to use a character other than 0 - 9 or A - F in a
485 hexadecimal number. Interpretation of the hexadecimal number stopped
486 before the illegal character.
488 =item No such array field
490 (F) You tried to access an array as a hash, but the field name used is
491 not defined. The hash at index 0 should map all valid field names to
492 array indices for that to work.
494 =item No such field "%s" in variable %s of type %s
496 (F) You tried to access a field of a typed variable where the type
497 does not know about the field name. The field names are looked up in
498 the %FIELDS hash in the type package at compile time. The %FIELDS hash
499 is usually set up with the 'fields' pragma.
501 =item Out of memory during ridiculously large request
503 (F) You can't allocate more than 2^31+"small amount" bytes. This error
504 is most likely to be caused by a typo in the Perl program. e.g., C<$arr[time]>
505 instead of C<$arr[$time]>.
507 =item Range iterator outside integer range
509 (F) One (or both) of the numeric arguments to the range operator ".."
510 are outside the range which can be represented by integers internally.
511 One possible workaround is to force Perl to use magical string
512 increment by prepending "0" to your numbers.
514 =item Recursive inheritance detected while looking for method '%s' in package '%s'
516 (F) More than 100 levels of inheritance were encountered while invoking a
517 method. Probably indicates an unintended loop in your inheritance hierarchy.
519 =item Reference found where even-sized list expected
521 (W) You gave a single reference where Perl was expecting a list with
522 an even number of elements (for assignment to a hash). This
523 usually means that you used the anon hash constructor when you meant
524 to use parens. In any case, a hash requires key/value B<pairs>.
526 %hash = { one => 1, two => 2, }; # WRONG
527 %hash = [ qw/ an anon array / ]; # WRONG
528 %hash = ( one => 1, two => 2, ); # right
529 %hash = qw( one 1 two 2 ); # also fine
531 =item Undefined value assigned to typeglob
533 (W) An undefined value was assigned to a typeglob, a la C<*foo = undef>.
534 This does nothing. It's possible that you really mean C<undef *foo>.
536 =item Use of reserved word "%s" is deprecated
538 (D) The indicated bareword is a reserved word. Future versions of perl
539 may use it as a keyword, so you're better off either explicitly quoting
540 the word in a manner appropriate for its context of use, or using a
541 different name altogether. The warning can be suppressed for subroutine
542 names by either adding a C<&> prefix, or using a package qualifier,
543 e.g. C<&our()>, or C<Foo::our()>.
545 =item perl: warning: Setting locale failed.
547 (S) The whole warning message will look something like:
549 perl: warning: Setting locale failed.
550 perl: warning: Please check that your locale settings:
553 are supported and installed on your system.
554 perl: warning: Falling back to the standard locale ("C").
556 Exactly what were the failed locale settings varies. In the above the
557 settings were that the LC_ALL was "En_US" and the LANG had no value.
558 This error means that Perl detected that you and/or your system
559 administrator have set up the so-called variable system but Perl could
560 not use those settings. This was not dead serious, fortunately: there
561 is a "default locale" called "C" that Perl can and will use, the
562 script will be run. Before you really fix the problem, however, you
563 will get the same error message each time you run Perl. How to really
564 fix the problem can be found in L<perllocale> section B<LOCALE PROBLEMS>.
569 =head1 Obsolete Diagnostics
575 (F) The mktemp() routine failed for some reason while trying to process
576 a B<-e> switch. Maybe your /tmp partition is full, or clobbered.
578 =item Can't write to temp file for B<-e>: %s
580 (F) The write routine failed for some reason while trying to process
581 a B<-e> switch. Maybe your /tmp partition is full, or clobbered.
583 =item Cannot open temporary file
585 (F) The create routine failed for some reason while trying to process
586 a B<-e> switch. Maybe your /tmp partition is full, or clobbered.
593 If you find what you think is a bug, you might check the headers of
594 recently posted articles in the comp.lang.perl.misc newsgroup.
595 There may also be information at http://www.perl.com/perl/, the Perl
598 If you believe you have an unreported bug, please run the B<perlbug>
599 program included with your release. Make sure you trim your bug down
600 to a tiny but sufficient test case. Your bug report, along with the
601 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
602 analysed by the Perl porting team.
606 The F<Changes> file for exhaustive details on what changed.
608 The F<INSTALL> file for how to build Perl.
610 The F<README> file for general stuff.
612 The F<Artistic> and F<Copying> files for copyright information.