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 $file && -w _ && -f _>. See L<perlfunc/-X>.
67 =head1 Modules and Pragmata
73 In C<Benchmark>, cmpthese() and timestr() now use the time statistics of
74 children instead of parent when the selected style is 'nop'.
78 The error messages produced by C<Carp> now include spaces between the
79 arguments in function argument lists: this makes long error messages
80 appear more nicely in browsers and other tools.
84 C<Exporter> will now recognize grouping tags (such as C<:name>) anywhere
85 in the import list, not only at the beginning.
89 A function C<again> is provided to resolve problems where modules in different
90 directories wish to use FindBin.
94 You can now weaken references to read only values.
98 C<cond_wait> has a new two argument form. C<cond_timedwait> has been added.
102 =head1 Utility Changes
104 C<find2perl> now assumes C<-print> as a default action. Previously, it
105 needed to be specified explicitly.
107 A new utility, C<prove>, makes it easy to run an individual regression test
108 at the command line. C<prove> is part of Test::Harness, which users of earlier
109 Perl versions can install from CPAN.
113 The documentation has been revised in places to produce more standard manpages.
115 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
118 The perl debugger now supports a C<save> command, to save the current
119 history to a file, and an C<i> command, which prints the inheritance tree
120 of its argument (if the C<Class::ISA> module is installed.)
122 =head1 Performance Enhancements
124 =head1 Installation and Configuration Improvements
126 =head1 Selected Bug Fixes
130 Using substr() on a UTF8 string could cause subsequent accesses on that
131 string to return garbage. This was due to incorrect UTF8 offsets being
132 cached, and is now fixed.
134 join() could return garbage when the same join() statement was used to
135 process 8 bit data having earlier processed UTF8 data, due to the flags
136 on that statement's temporary workspace not being reset correctly. This
139 Using Unicode keys with tied hashes should now work correctly.
141 chop() and chomp() used to mangle UTF8 strings. This has been fixed.
143 =head2 Threading bugs
145 Hashes with the C<:unique> attribute weren't made read-only in new
146 threads. They are now.
150 C<$a .. $b> will now work as expected when either $a or $b is C<undef>
152 Reading $^E now preserves $!. Previously, the C code implementing $^E
153 did not preserve C<errno>, so reading $^E could cause C<errno> and therefore
154 C<$!> to change unexpectedly.
156 Reentrant functions will (once more) work with C++. 5.8.2 introduced a bugfix
157 which accidentally broke the compilation of Perl extensions written in C++.
159 C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
161 =head1 New or Changed Diagnostics
163 The fatal error "DESTROY created new reference to dead object" is now
164 documented in L<perldiag>.
166 A new error, "%ENV is aliased to %s", is produced when taint checks are
167 enabled and when *ENV has been aliased (and thus doesn't reflect the
168 program's environment anymore.)
170 =head1 Changed Internals
172 These news matter to you only if you either write XS code or like to
173 know about or hack Perl internals (using Devel::Peek or any of the
174 C<B::> modules counts), or like to run Perl with the C<-D> option.
176 =head2 Reordering of SVt_* constants
178 The relative ordering of constants that define the various types of C<SV>
179 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
180 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
181 difference unless you have code that explicitly makes assumptions about that
182 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
185 =head2 Removal of CPP symbols
187 The C preprocessor symbols C<PERL_PM_APIVERSION> and
188 C<PERL_XS_APIVERSION>, which were supposed to give the version number of
189 the oldest perl binary-compatible (resp. source-compatible) with the
190 present one, were not used, and sometimes had misleading values. They have
193 =head2 Less space is used by ops
195 The C<BASEOP> structure now uses less space. The C<op_seq> field has been
196 removed and replaced by two one-bit fields, C<op_opt> and C<op_static>.
197 C<opt_type> is now 9 bits long. (Consequently, the C<B::OP> class doesn't
198 provide an C<seq> method anymore.)
200 =head1 Configuration and Building
202 C<Configure> now invokes callbacks regardless of the value of the variable
203 they are called for. Previously callbacks were only invoked in the
204 C<case $variable $define)> branch. This change should only affect platform
205 maintainers writing configuration hints files.
209 =head1 Known Problems
211 =head1 Platform Specific Problems
213 =head1 Reporting Bugs
215 If you find what you think is a bug, you might check the articles
216 recently posted to the comp.lang.perl.misc newsgroup and the perl
217 bug database at http://bugs.perl.org/ . There may also be
218 information at http://www.perl.com/ , the Perl Home Page.
220 If you believe you have an unreported bug, please run the B<perlbug>
221 program included with your release. Be sure to trim your bug down
222 to a tiny but sufficient test case. Your bug report, along with the
223 output of C<perl -V>, will be sent off to perlbug@perl.org to be
224 analysed by the Perl porting team.
228 The F<Changes> file for exhaustive details on what changed.
230 The F<INSTALL> file for how to build Perl.
232 The F<README> file for general stuff.
234 The F<Artistic> and F<Copying> files for copyright information.