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PERL591DELTA(1)                       Perl Programmers Reference Guide                       PERL591DELTA(1)



NAME
       perl591delta - what is new for perl v5.9.1

DESCRIPTION
       This document describes differences between the 5.9.0 and the 5.9.1 development releases. See
       perl590delta for the differences between 5.8.0 and 5.9.0.

Incompatible Changes
   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.

   The ":unique" attribute is only meaningful for globals
       Now applying ":unique" to lexical variables and to subroutines will result in a compilation error.

Core Enhancements
   Lexical $_
       The default variable $_ can now be lexicalized, by declaring it like any other lexical variable, with
       a simple

           my $_;

       The operations that default on $_ will use the lexically-scoped version of $_ when it exists, instead
       of the global $_.

       In a "map" or a "grep" block, if $_ was previously my'ed, then the $_ inside the block is lexical as
       well (and scoped to the block).

       In a scope where $_ has been lexicalized, you can still have access to the global version of $_ by
       using $::_, or, more simply, by overriding the lexical declaration with "our $_".

   Tied hashes in scalar context
       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 old nonsensical behaviour was always to return false, regardless of whether the hash is empty or
       has elements.

       There is now an interface for the implementors of tied hashes to implement the behaviour of a hash in
       scalar context, via the SCALAR method (see perltie).  Without a SCALAR method, perl will try to guess
       whether the hash is empty, by testing if it's inside an iteration (in this case it can't be empty) or
       by calling FIRSTKEY.

   Formats
       Formats were improved in several ways. A new field, "^*", can be used for variable-width, one-line-at-a-time one-lineat-a-time
       at-a-time text. Null characters are now handled correctly in picture lines. Using "@#" and "~~"
       together will now produce a compile-time error, as those format fields are incompatible.  perlform
       has been improved, and miscellaneous bugs fixed.

   Stacked filetest operators
       As a new form of syntactic sugar, it's now possible to stack up filetest operators. You can now write
       "-f -w -x $file" in a row to mean "-x $file && -w _ && -f _". See "-X" in perlfunc.

Modules and Pragmata
       Benchmark
           In "Benchmark", cmpthese() and timestr() now use the time statistics of children instead of
           parent when the selected style is 'nop'.

       Carp
           The error messages produced by "Carp" now include spaces between the arguments in function
           argument lists: this makes long error messages appear more nicely in browsers and other tools.

       Exporter
           "Exporter" will now recognize grouping tags (such as ":name") anywhere in the import list, not
           only at the beginning.

       FindBin
           A function "again" is provided to resolve problems where modules in different directories wish to
           use FindBin.

       List::Util
           You can now weaken references to read only values.

       threads::shared
           "cond_wait" has a new two argument form. "cond_timedwait" has been added.

Utility Changes
       "find2perl" now assumes "-print" as a default action. Previously, it needed to be specified
       explicitly.

       A new utility, "prove", makes it easy to run an individual regression test at the command line.
       "prove" is part of Test::Harness, which users of earlier Perl versions can install from CPAN.

       The perl debugger now supports a "save" command, to save the current history to a file, and an "i"
       command, which prints the inheritance tree of its argument (if the "Class::ISA" module is installed.)

Documentation
       The documentation has been revised in places to produce more standard manpages.

       The long-existing feature of "/(?{...})/" regexps setting $_ and pos() is now documented.

Performance Enhancements
       Sorting arrays in place ("@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(), "//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.)

Selected Bug Fixes
   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.

   Threading bugs
       Hashes with the ":unique" attribute weren't made read-only in new threads. They are now.

   More bugs
       "$a .. $b" will now work as expected when either $a or $b is "undef".

       Reading $^E now preserves $!. Previously, the C code implementing $^E did not preserve "errno", so
       reading $^E could cause "errno" and therefore $! to change unexpectedly.

       "strict" wasn't in effect in regexp-eval blocks ("/(?{...})/").

New or Changed Diagnostics
       A new deprecation warning, 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 perldiag.

       The fatal error DESTROY created new reference to dead object is now documented in perldiag.

       A new error, %ENV is aliased to %s, is produced when taint checks are enabled and when *ENV has been
       aliased (and thus doesn't reflect the program's environment anymore.)

Changed Internals
       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 "B::" modules counts), or like to run Perl with the "-D"
       option.

   Reordering of SVt_* constants
       The relative ordering of constants that define the various types of "SV" have changed; in particular,
       "SVt_PVGV" has been moved before "SVt_PVLV", "SVt_PVAV", "SVt_PVHV" and "SVt_PVCV".  This is unlikely
       to make any difference unless you have code that explicitly makes assumptions about that ordering.
       (The inheritance hierarchy of "B::*" objects has been changed to reflect this.)

   Removal of CPP symbols
       The C preprocessor symbols "PERL_PM_APIVERSION" and "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.

   Less space is used by ops
       The "BASEOP" structure now uses less space. The "op_seq" field has been removed and replaced by two
       one-bit fields, "op_opt" and "op_static".  "opt_type" is now 9 bits long. (Consequently, the "B::OP"
       class doesn't provide an "seq" method anymore.)

   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.

Configuration and Building
       "Configure" now invokes callbacks regardless of the value of the variable they are called for.
       Previously callbacks were only invoked in the "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.

Known Problems
       There are still a couple of problems in the implementation of the lexical $_: it doesn't work inside
       "/(?{...})/" blocks and with regard to the reverse() built-in used without arguments. (See the TODO
       tests in t/op/mydef.t.)

   Platform Specific Problems
       The test 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 lib/Time/Local.t fails.  When configured with long
       doubles, perl may fail tests 224-236 in t/op/pow.t on the same platform.

       For threaded builds, ext/threads/shared/t/wait.t has been reported to fail some tests on HP-UX 10.20.

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 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) ("sort", "re", "encoding" for
       example). MJD has a preliminary patch that implements this.

       Fix (or rewrite) the implementation of the "/(?{...})/" 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, "_", meaning "this argument defaults to
       $_".

       Make the peephole optimizer optional.

       Allow lexical aliases (maybe via the syntax "my \$alias = \$foo".

       Fix the bugs revealed by running the test suite with the "-t" switch (via "make test.taintwarn").

       Make threads more robust.

       Make "no 6" and "no v6" work (opposite of "use 5.005", etc.).

       A test suite for the B module would be nice.

       A ponie.

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.org/ , the Perl Home Page.

       If you believe you have an unreported bug, please run the perlbug program included with your release.
       Be sure to trim your bug down to a tiny but sufficient test case.  Your bug report, along with the
       output of "perl -V", will be sent off to perlbug@perl.org to be analysed by the Perl porting team.

SEE ALSO
       The Changes file for exhaustive details on what changed.

       The INSTALL file for how to build Perl.

       The README file for general stuff.

       The Artistic and Copying files for copyright information.



perl v5.12.5                                     2012-11-03                                  PERL591DELTA(1)