=head1 DESCRIPTION
-This document describes differences between the 5.9.0 release and
-the 5.9.1 release.
+This document describes differences between the 5.9.0 and the 5.9.1
+development releases. See L<perl590delta> for the differences between
+5.8.0 and 5.9.0.
=head1 Incompatible Changes
+=head2 substr() lvalues are no longer fixed-length
+
+The lvalues returned by the three argument form of substr() used to be a
+"fixed length window" on the original string. In some cases this could
+cause surprising action at distance or other undefined behaviour. Now the
+length of the window adjusts itself to the length of the string assigned to
+it.
+
+=head2 The C<:unique> attribute is only meaningful for globals
+
+Now applying C<:unique> to lexical variables and to subroutines will
+result in a compilation error.
+
=head1 Core Enhancements
+=head2 Lexical C<$_>
+
+The default variable C<$_> can now be lexicalized, by declaring it like
+any other lexical variable, with a simple
+
+ my $_;
+
+The operations that default on C<$_> will use the lexically-scoped
+version of C<$_> when it exists, instead of the global C<$_>.
+
+In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
+C<$_> inside the block is lexical as well (and scoped to the block).
+
+In a scope where C<$_> has been lexicalized, you can still have access to
+the global version of C<$_> by using C<$::_>, or, more simply, by
+overriding the lexical declaration with C<our $_>.
+
=head2 Tied hashes in scalar context
-As of perl 5.8.2, tied hashes did not return anything useful in scalar
-context, for example when used as boolean tests:
+As of perl 5.8.2/5.9.0, tied hashes did not return anything useful in
+scalar context, for example when used as boolean tests:
if (%tied_hash) { ... }
the hash is empty, by testing if it's inside an iteration (in this case
it can't be empty) or by calling FIRSTKEY.
+=head2 Formats
+
+Formats were improved in several ways. A new field, C<^*>, can be used for
+variable-width, one-line-at-a-time text. Null characters are now handled
+correctly in picture lines. Using C<@#> and C<~~> together will now
+produce a compile-time error, as those format fields are incompatible.
+L<perlform> has been improved, and miscellaneous bugs fixed.
+
+=head2 Stacked filetest operators
+
+As a new form of syntactic sugar, it's now possible to stack up filetest
+operators. You can now write C<-f -w -x $file> in a row to mean
+C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
+
=head1 Modules and Pragmata
+=over 4
+
+=item Benchmark
+
+In C<Benchmark>, cmpthese() and timestr() now use the time statistics of
+children instead of parent when the selected style is 'nop'.
+
+=item Carp
+
+The error messages produced by C<Carp> now include spaces between the
+arguments in function argument lists: this makes long error messages
+appear more nicely in browsers and other tools.
+
+=item Exporter
+
+C<Exporter> will now recognize grouping tags (such as C<:name>) anywhere
+in the import list, not only at the beginning.
+
+=item FindBin
+
+A function C<again> is provided to resolve problems where modules in different
+directories wish to use FindBin.
+
+=item List::Util
+
+You can now weaken references to read only values.
+
+=item threads::shared
+
+C<cond_wait> has a new two argument form. C<cond_timedwait> has been added.
+
+=back
+
=head1 Utility Changes
C<find2perl> now assumes C<-print> as a default action. Previously, it
needed to be specified explicitly.
-=head1 New Documentation
+A new utility, C<prove>, makes it easy to run an individual regression test
+at the command line. C<prove> is part of Test::Harness, which users of earlier
+Perl versions can install from CPAN.
+
+The perl debugger now supports a C<save> command, to save the current
+history to a file, and an C<i> command, which prints the inheritance tree
+of its argument (if the C<Class::ISA> module is installed.)
+
+=head1 Documentation
+
+The documentation has been revised in places to produce more standard manpages.
+
+The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
+is now documented.
=head1 Performance Enhancements
-=head1 Installation and Configuration Improvements
+Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
+making a temporary copy of the array.
+
+The operations involving case mapping on UTF-8 strings (uc(), lc(),
+C<//i>, etc.) have been greatly speeded up.
+
+Access to elements of lexical arrays via a numeric constant between 0 and
+255 is now faster. (This used to be only the case for global arrays.)
=head1 Selected Bug Fixes
+=head2 UTF-8 bugs
+
+Using substr() on a UTF-8 string could cause subsequent accesses on that
+string to return garbage. This was due to incorrect UTF-8 offsets being
+cached, and is now fixed.
+
+join() could return garbage when the same join() statement was used to
+process 8 bit data having earlier processed UTF-8 data, due to the flags
+on that statement's temporary workspace not being reset correctly. This
+is now fixed.
+
+Using Unicode keys with tied hashes should now work correctly.
+
+chop() and chomp() used to mangle UTF-8 strings. This has been fixed.
+
+sprintf() used to misbehave when the format string was in UTF-8. This is
+now fixed.
+
+=head2 Threading bugs
+
+Hashes with the C<:unique> attribute weren't made read-only in new
+threads. They are now.
+
+=head2 More bugs
+
+C<$a .. $b> will now work as expected when either $a or $b is C<undef>.
+
+Reading $^E now preserves $!. Previously, the C code implementing $^E
+did not preserve C<errno>, so reading $^E could cause C<errno> and therefore
+C<$!> to change unexpectedly.
+
+C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
+
=head1 New or Changed Diagnostics
+A new deprecation warning, I<Deprecated use of my() in false conditional>,
+has been added, to warn against the use of the dubious and deprecated
+construct
+
+ my $x if 0;
+
+See L<perldiag>.
+
+The fatal error I<DESTROY created new reference to dead object> is now
+documented in L<perldiag>.
+
+A new error, I<%ENV is aliased to %s>, is produced when taint checks are
+enabled and when C<*ENV> has been aliased (and thus doesn't reflect the
+program's environment anymore.)
+
=head1 Changed Internals
-=head1 New Tests
+These news matter to you only if you either write XS code or like to
+know about or hack Perl internals (using Devel::Peek or any of the
+C<B::> modules counts), or like to run Perl with the C<-D> option.
+
+=head2 Reordering of SVt_* constants
+
+The relative ordering of constants that define the various types of C<SV>
+have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
+C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
+difference unless you have code that explicitly makes assumptions about that
+ordering. (The inheritance hierarchy of C<B::*> objects has been changed
+to reflect this.)
+
+=head2 Removal of CPP symbols
+
+The C preprocessor symbols C<PERL_PM_APIVERSION> and
+C<PERL_XS_APIVERSION>, which were supposed to give the version number of
+the oldest perl binary-compatible (resp. source-compatible) with the
+present one, were not used, and sometimes had misleading values. They have
+been removed.
+
+=head2 Less space is used by ops
+
+The C<BASEOP> structure now uses less space. The C<op_seq> field has been
+removed and replaced by two one-bit fields, C<op_opt> and C<op_static>.
+C<opt_type> is now 9 bits long. (Consequently, the C<B::OP> class doesn't
+provide an C<seq> method anymore.)
+
+=head2 New parser
+
+perl's parser is now generated by bison (it used to be generated by
+byacc.) As a result, it seems to be a bit more robust.
+
+=head1 Configuration and Building
+
+C<Configure> now invokes callbacks regardless of the value of the variable
+they are called for. Previously callbacks were only invoked in the
+C<case $variable $define)> branch. This change should only affect platform
+maintainers writing configuration hints files.
+
+The portability and cleanliness of the Win32 makefiles has been improved.
=head1 Known Problems
-=head1 Platform Specific Problems
+There are still a couple of problems in the implementation of the lexical
+C<$_>: it doesn't work inside C</(?{...})/> blocks and with regard to the
+reverse() built-in used without arguments. (See the TODO tests in
+F<t/op/mydef.t>.)
+
+=head2 Platform Specific Problems
+
+The test F<ext/IPC/SysV/t/ipcsysv.t> may fail on OpenBSD. This hasn't been
+diagnosed yet.
+
+On some configurations on AIX 5, one test in F<lib/Time/Local.t> fails.
+When configured with long doubles, perl may fail tests 224-236 in
+F<t/op/pow.t> on the same platform.
+
+For threaded builds, F<ext/threads/shared/t/wait.t> has been reported to
+fail some tests on HP-UX 10.20.
+
+=head1 To-do for perl 5.10.0
+
+This is a non-exhaustive, non-ordered, non-contractual and non-definitive
+list of things to do (or nice to have) for perl 5.10.0 :
+
+Clean up and finish support for assertions. See L<assertions>.
+
+Reimplement the mechanism of lexical pragmas to be more extensible. Fix
+current pragmas that don't work well (or at all) with lexical scopes or in
+run-time eval(STRING) (C<sort>, C<re>, C<encoding> for example). MJD has a
+preliminary patch that implements this.
+
+Fix (or rewrite) the implementation of the C</(?{...})/> closures.
+
+Conversions from byte strings to UTF-8 currently map high bit characters
+to Unicode without translation (or, depending on how you look at it, by
+implicitly assuming that the byte strings are in Latin-1). As perl assumes
+the C locale by default, upgrading a string to UTF-8 may change the
+meaning of its contents regarding character classes, case mapping, etc.
+This should probably emit a warning (at least).
+
+Introduce a new special block, UNITCHECK, which is run at the end of a
+compilation unit (module, file, eval(STRING) block). This will correspond to
+the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
+O.pm/B.pm backend framework depends on it.
+
+Study the possibility of adding a new prototype character, C<_>, meaning
+"this argument defaults to $_".
+
+Make the peephole optimizer optional.
+
+Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
+
+Fix the bugs revealed by running the test suite with the C<-t> switch (via
+C<make test.taintwarn>).
+
+Make threads more robust.
+
+Make C<no 6> and C<no v6> work (opposite of C<use 5.005>, etc.).
+
+A test suite for the B module would be nice.
+
+A ponie.
=head1 Reporting Bugs
If you find what you think is a bug, you might check the articles
recently posted to the comp.lang.perl.misc newsgroup and the perl
bug database at http://bugs.perl.org/ . There may also be
-information at http://www.perl.com/ , the Perl Home Page.
+information at http://www.perl.org/ , the Perl Home Page.
If you believe you have an unreported bug, please run the B<perlbug>
program included with your release. Be sure to trim your bug down
https://perl5.git.perl.org / perl5.git / blobdiff