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1=head1 NAME
2
3perldelta - what is new for perl v5.9.1
4
5=head1 DESCRIPTION
6
7This document describes differences between the 5.9.0 release and
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8the 5.9.1 release. See L<perl590delta> for the differences between
95.8.0 and 5.9.0.
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10
11=head1 Incompatible Changes
12
13=head1 Core Enhancements
14
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15=head2 Lexical C<$_>
16
17The default variable C<$_> can now be lexicalized, by declaring it like
18any other lexical variable, with a simple
19
20 my $_;
21
22The operations that default on C<$_> will use the lexically-scoped
23version of C<$_> when it exists, instead of the global C<$_>.
24
25In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
26C<$_> inside the block is lexical as well (and scoped to the block).
27
28In a scope where C<$_> has been lexicalized, you can still have access to
29the global version of C<$_> by using C<$::_>, or, more simply, by
30overriding the lexical declaration with C<our $_>.
31
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32=head2 Tied hashes in scalar context
33
34As of perl 5.8.2, tied hashes did not return anything useful in scalar
35context, for example when used as boolean tests:
36
37 if (%tied_hash) { ... }
38
39The old nonsensical behaviour was always to return false,
40regardless of whether the hash is empty or has elements.
41
42There is now an interface for the implementors of tied hashes to implement
43the behaviour of a hash in scalar context, via the SCALAR method (see
44L<perltie>). Without a SCALAR method, perl will try to guess whether
45the hash is empty, by testing if it's inside an iteration (in this case
46it can't be empty) or by calling FIRSTKEY.
47
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48=head2 Formats
49
50Formats were improved in several ways. A new field, C<^*>, can be used for
51variable-width, one-line-at-a-time text. Null characters are now handled
52correctly in picture lines. Using C<@#> and C<~~> together will now
53produce a compile-time error, as those format fields are incompatible.
54L<perlform> has been improved, and miscellaneous bugs fixed.
55
56=head2 The C<:unique> attribute is only meaningful for globals
57
58Now applying C<:unique> to lexical variables and to subroutines will
59result in a compilation error.
60
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61=head2 Stacked filetest operators
62
63As a new form of syntactic sugar, it's now possible to stack up filetest
64operators. You can now write C<-f -w -x $file> in a row to mean
65C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
66
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67=head1 Modules and Pragmata
68
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69=over 4
70
71=item Carp
72
73The error messages produced by C<Carp> now include spaces between the
74arguments in function argument lists: this makes long error messages
75appear more nicely in browsers and other tools.
76
77=item Exporter
78
79C<Exporter> will now recognize grouping tags (such as C<:name>) anywhere
80in the import list, not only at the beginning.
81
82=item FindBin
83
84A function C<again> is provided to resolve problems where modules in different
85directories wish to use FindBin.
86
87=item List::Util
88
89You can now weaken references to read only values.
90
91=item threads::shared
92
93C<cond_wait> has a new two argument form. C<cond_timedwait> has been added.
94
95=back
96
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97=head1 Utility Changes
98
99C<find2perl> now assumes C<-print> as a default action. Previously, it
100needed to be specified explicitly.
101
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102A new utility, C<prove>, makes it easy to run an individual regression test
103at the command line. C<prove> is part of Test::Harness, which users of earlier
104Perl versions can install from CPAN.
105
106=head1 Documentation
107
108The documentation has been revised in places to produce more standard manpages.
109
110The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
111is now documented.
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112
113=head1 Performance Enhancements
114
115=head1 Installation and Configuration Improvements
116
117=head1 Selected Bug Fixes
118
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119=head2 UTF8 bugs
120
121Using substr() on a UTF8 string could cause subsequent accesses on that
122string to return garbage. This was due to incorrect UTF8 offsets being
123cached, and is now fixed.
124
125join() could return garbage when the same join() statement was used to
126process 8 bit data having earlier processed UTF8 data, due to the flags
127on that statement's temporary workspace not being reset correctly. This
128is now fixed.
129
130Using Unicode keys with tied hashes should now work correctly.
131
132chop() and chomp() used to mangle UTF8 strings. This has been fixed.
133
134=head2 Threading bugs
135
136Hashes with the C<:unique> attribute weren't made read-only in new
137threads. They are now.
138
139=head2 More bugs
140
141C<$a .. $b> will now work as expected when either $a or $b is C<undef>
142
143Reading $^E now preserves $!. Previously, the C code implementing $^E
144did not preserve C<errno>, so reading $^E could cause C<errno> and therefore
145C<$!> to change unexpectedly.
146
147Reentrant functions will (once more) work with C++. 5.8.2 introduced a bugfix
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148which accidentally broke the compilation of Perl extensions written in C++.
149
150C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
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152=head1 New or Changed Diagnostics
153
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154The fatal error "DESTROY created new reference to dead object" is now
155documented in L<perldiag>.
156
157A new error, "%ENV is aliased to %s", is produced when taint checks are
158enabled and when *ENV has been aliased (and thus doesn't reflect the
159program's environment anymore.)
160
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161=head1 Changed Internals
162
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163These news matter to you only if you either write XS code or like to
164know about or hack Perl internals (using Devel::Peek or any of the
165C<B::> modules counts), or like to run Perl with the C<-D> option.
166
167=head2 Reordering of SVt_* constants
168
169The relative ordering of constants that define the various types of C<SV>
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171C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
172difference unless you have code that explicitly makes assumptions about that
173ordering. (The inheritance hierarchy of C<B::*> objects has been changed
174to reflect this.)
175
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176=head2 Removal of CPP symbols
177
178The C preprocessor symbols C<PERL_PM_APIVERSION> and
179C<PERL_XS_APIVERSION>, which were supposed to give the version number of
180the oldest perl binary-compatible (resp. source-compatible) with the
181present one, were not used, and sometimes had misleading values. They have
182been removed.
183
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184=head2 Less space is used by ops
185
186The C<BASEOP> structure now uses less space. The C<op_seq> field has been
187removed and replaced by two one-bit fields, C<op_opt> and C<op_static>.
188C<opt_type> is now 9 bits long. (Consequently, the C<B::OP> class doesn't
189provide an C<seq> method anymore.)
190
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191=head1 Configuration and Building
192
193C<Configure> now invokes callbacks regardless of the value of the variable
194they are called for. Previously callbacks were only invoked in the
195C<case $variable $define)> branch. This change should only affect platform
196maintainers writing configuration hints files.
197
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198=head1 New Tests
199
200=head1 Known Problems
201
202=head1 Platform Specific Problems
203
204=head1 Reporting Bugs
205
206If you find what you think is a bug, you might check the articles
207recently posted to the comp.lang.perl.misc newsgroup and the perl
208bug database at http://bugs.perl.org/ . There may also be
209information at http://www.perl.com/ , the Perl Home Page.
210
211If you believe you have an unreported bug, please run the B<perlbug>
212program included with your release. Be sure to trim your bug down
213to a tiny but sufficient test case. Your bug report, along with the
214output of C<perl -V>, will be sent off to perlbug@perl.org to be
215analysed by the Perl porting team.
216
217=head1 SEE ALSO
218
219The F<Changes> file for exhaustive details on what changed.
220
221The F<INSTALL> file for how to build Perl.
222
223The F<README> file for general stuff.
224
225The F<Artistic> and F<Copying> files for copyright information.
226
227=cut