3 perldelta - what is new for perl v5.9.1
7 This document describes differences between the 5.9.0 release and
8 the 5.9.1 release. See L<perl590delta> for the differences between
11 =head1 Incompatible Changes
13 =head1 Core Enhancements
17 The default variable C<$_> can now be lexicalized, by declaring it like
18 any other lexical variable, with a simple
22 The operations that default on C<$_> will use the lexically-scoped
23 version of C<$_> when it exists, instead of the global C<$_>.
25 In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
26 C<$_> inside the block is lexical as well (and scoped to the block).
28 In a scope where C<$_> has been lexicalized, you can still have access to
29 the global version of C<$_> by using C<$::_>, or, more simply, by
30 overriding the lexical declaration with C<our $_>.
32 =head2 Tied hashes in scalar context
34 As of perl 5.8.2, tied hashes did not return anything useful in scalar
35 context, for example when used as boolean tests:
37 if (%tied_hash) { ... }
39 The old nonsensical behaviour was always to return false,
40 regardless of whether the hash is empty or has elements.
42 There is now an interface for the implementors of tied hashes to implement
43 the behaviour of a hash in scalar context, via the SCALAR method (see
44 L<perltie>). Without a SCALAR method, perl will try to guess whether
45 the hash is empty, by testing if it's inside an iteration (in this case
46 it can't be empty) or by calling FIRSTKEY.
50 Formats were improved in several ways. A new field, C<^*>, can be used for
51 variable-width, one-line-at-a-time text. Null characters are now handled
52 correctly in picture lines. Using C<@#> and C<~~> together will now
53 produce a compile-time error, as those format fields are incompatible.
54 L<perlform> has been improved, and miscellaneous bugs fixed.
56 =head2 The C<:unique> attribute is only meaningful for globals
58 Now applying C<:unique> to lexical variables and to subroutines will
59 result in a compilation error.
61 =head2 Stacked filetest operators
63 As a new form of syntactic sugar, it's now possible to stack up filetest
64 operators. You can now write C<-f -w -x $file> in a row to mean
65 C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
67 =head1 Modules and Pragmata
73 The error messages produced by C<Carp> now include spaces between the
74 arguments in function argument lists: this makes long error messages
75 appear more nicely in browsers and other tools.
79 C<Exporter> will now recognize grouping tags (such as C<:name>) anywhere
80 in the import list, not only at the beginning.
84 A function C<again> is provided to resolve problems where modules in different
85 directories wish to use FindBin.
89 You can now weaken references to read only values.
93 C<cond_wait> has a new two argument form. C<cond_timedwait> has been added.
97 =head1 Utility Changes
99 C<find2perl> now assumes C<-print> as a default action. Previously, it
100 needed to be specified explicitly.
102 A new utility, C<prove>, makes it easy to run an individual regression test
103 at the command line. C<prove> is part of Test::Harness, which users of earlier
104 Perl versions can install from CPAN.
108 The documentation has been revised in places to produce more standard manpages.
110 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
113 =head1 Performance Enhancements
115 =head1 Installation and Configuration Improvements
117 =head1 Selected Bug Fixes
121 Using substr() on a UTF8 string could cause subsequent accesses on that
122 string to return garbage. This was due to incorrect UTF8 offsets being
123 cached, and is now fixed.
125 join() could return garbage when the same join() statement was used to
126 process 8 bit data having earlier processed UTF8 data, due to the flags
127 on that statement's temporary workspace not being reset correctly. This
130 Using Unicode keys with tied hashes should now work correctly.
132 chop() and chomp() used to mangle UTF8 strings. This has been fixed.
134 =head2 Threading bugs
136 Hashes with the C<:unique> attribute weren't made read-only in new
137 threads. They are now.
141 C<$a .. $b> will now work as expected when either $a or $b is C<undef>
143 Reading $^E now preserves $!. Previously, the C code implementing $^E
144 did not preserve C<errno>, so reading $^E could cause C<errno> and therefore
145 C<$!> to change unexpectedly.
147 Reentrant functions will (once more) work with C++. 5.8.2 introduced a bugfix
148 which accidentally broke the compilation of Perl extensions written in C++
150 =head1 New or Changed Diagnostics
152 The fatal error "DESTROY created new reference to dead object" is now
153 documented in L<perldiag>.
155 A new error, "%ENV is aliased to %s", is produced when taint checks are
156 enabled and when *ENV has been aliased (and thus doesn't reflect the
157 program's environment anymore.)
159 =head1 Changed Internals
161 These news matter to you only if you either write XS code or like to
162 know about or hack Perl internals (using Devel::Peek or any of the
163 C<B::> modules counts), or like to run Perl with the C<-D> option.
165 =head2 Reordering of SVt_* constants
167 The relative ordering of constants that define the various types of C<SV>
168 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
169 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
170 difference unless you have code that explicitly makes assumptions about that
171 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
174 =head1 Configuration and Building
176 C<Configure> now invokes callbacks regardless of the value of the variable
177 they are called for. Previously callbacks were only invoked in the
178 C<case $variable $define)> branch. This change should only affect platform
179 maintainers writing configuration hints files.
183 =head1 Known Problems
185 =head1 Platform Specific Problems
187 =head1 Reporting Bugs
189 If you find what you think is a bug, you might check the articles
190 recently posted to the comp.lang.perl.misc newsgroup and the perl
191 bug database at http://bugs.perl.org/ . There may also be
192 information at http://www.perl.com/ , the Perl Home Page.
194 If you believe you have an unreported bug, please run the B<perlbug>
195 program included with your release. Be sure to trim your bug down
196 to a tiny but sufficient test case. Your bug report, along with the
197 output of C<perl -V>, will be sent off to perlbug@perl.org to be
198 analysed by the Perl porting team.
202 The F<Changes> file for exhaustive details on what changed.
204 The F<INSTALL> file for how to build Perl.
206 The F<README> file for general stuff.
208 The F<Artistic> and F<Copying> files for copyright information.