


PERL594DELTA(1)  Perl Programmers Reference Guide PERL594DELTA(1)


NAME
       perl594delta - what is new for perl v5.9.4

DESCRIPTION
       This document describes differences between the 5.9.3 and
       the 5.9.4 development releases. See perl590delta,
       perl591delta, perl592delta and perl593delta for the
       differences between 5.8.0 and 5.9.3.

Incompatible Changes
   chdir FOO
       A bareword argument to chdir() is now recognized as a file
       handle.  Earlier releases interpreted the bareword as a
       directory name.  (Gisle Aas)

   Handling of pmc files
       An old feature of perl was that before "require" or "use"
       look for a file with a .pm extension, they will first look
       for a similar filename with a .pmc extension. If this file
       is found, it will be loaded in place of any potentially
       existing file ending in a .pm extension.

       Previously, .pmc files were loaded only if more recent
       than the matching .pm file. Starting with 5.9.4, they'll
       be always loaded if they exist. (This trick is used by
       Pugs.)

   @- and @+ in patterns
       The special arrays "@-" and "@+" are no longer
       interpolated in regular expressions. (Sadahiro Tomoyuki)

   $AUTOLOAD can now be tainted
       If you call a subroutine by a tainted name, and if it
       defers to an AUTOLOAD function, then $AUTOLOAD will be
       (correctly) tainted.  (Rick Delaney)

Core Enhancements
   state() variables
       A new class of variables has been introduced. State
       variables are similar to "my" variables, but are declared
       with the "state" keyword in place of "my". They're visible
       only in their lexical scope, but their value is
       persistent: unlike "my" variables, they're not undefined
       at scope entry, but retain their previous value. (Rafael
       Garcia-Suarez)

       To use state variables, one needs to enable them by using

           use feature "state";

       or by using the "-E" command-line switch in one-liners.

       See "Persistent variables via state()" in perlsub.




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   UNIVERSAL::DOES()
       The "UNIVERSAL" class has a new method, "DOES()". It has
       been added to solve semantic problems with the "isa()"
       method. "isa()" checks for inheritance, while "DOES()" has
       been designed to be overridden when module authors use
       other types of relations between classes (in addition to
       inheritance). (chromatic)

       See "$obj->DOES( ROLE )" in UNIVERSAL.

   Exceptions in constant folding
       The constant folding routine is now wrapped in an
       exception handler, and if folding throws an exception
       (such as attempting to evaluate 0/0), perl now retains the
       current optree, rather than aborting the whole program.
       (Nicholas Clark, Dave Mitchell)

   Source filters in @INC
       It's possible to enhance the mechanism of subroutine hooks
       in @INC by adding a source filter on top of the filehandle
       opened and returned by the hook. This feature was planned
       a long time ago, but wasn't quite working until now. See
       "require" in perlfunc for details. (Nicholas Clark)

   MAD
       MAD, which stands for Misc Attribute Decoration, is a
       still-in-development work leading to a Perl 5 to Perl 6
       converter. To enable it, it's necessary to pass the
       argument "-Dmad" to Configure. The obtained perl isn't
       binary compatible with a regular perl 5.9.4, and has space
       and speed penalties; moreover not all regression tests
       still pass with it. (Larry Wall, Nicholas Clark)

Modules and Pragmas
       o   "encoding::warnings" is now a lexical pragma.
           (Although on older perls, which don't have support for
           lexical pragmas, it keeps its global behaviour.)
           (Audrey Tang)

       o   "threads" is now a dual-life module, also available on
           CPAN. It has been expanded in many ways. A kill()
           method is available for thread signalling.  One can
           get thread status, or the list of running or joinable
           threads.

           A new "threads->exit()" method is used to exit from
           the application (this is the default for the main
           thread) or from the current thread only (this is the
           default for all other threads). On the other hand, the
           exit() built-in now always causes the whole
           application to terminate. (Jerry D. Hedden)

   New Core Modules
       o   "Hash::Util::FieldHash", by Anno Siegel, has been



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           added. This module provides support for field hashes:
           hashes that maintain an association of a reference
           with a value, in a thread-safe garbage-collected way.
           Such hashes are useful to implement inside-out
           objects.

       o   "Module::Build", by Ken Williams, has been added. It's
           an alternative to "ExtUtils::MakeMaker" to build and
           install perl modules.

       o   "Module::Load", by Jos Boumans, has been added. It
           provides a single interface to load Perl modules and
           .pl files.

       o   "Module::Loaded", by Jos Boumans, has been added. It's
           used to mark modules as loaded or unloaded.

       o   "Package::Constants", by Jos Boumans, has been added.
           It's a simple helper to list all constants declared in
           a given package.

       o   "Win32API::File", by Tye McQueen, has been added (for
           Windows builds).  This module provides low-level
           access to Win32 system API calls for files/dirs.

Utility Changes
   config_data
       "config_data" is a new utility that comes with
       "Module::Build". It provides a command-line interface to
       the configuration of Perl modules that use Module::Build's
       framework of configurability (that is, *::ConfigData
       modules that contain local configuration information for
       their parent modules.)

Documentation
   New manpage, perlpragma
       The perlpragma manpage documents how to write one's own
       lexical pragmas in pure Perl (something that is possible
       starting with 5.9.4).

   New manpage, perlreguts
       The perlreguts manpage, courtesy of Yves Orton, describes
       internals of the Perl regular expression engine.

   New manpage, perlunitut
       The perlunitut manpage is an tutorial for programming with
       Unicode and string encodings in Perl, courtesy of Juerd
       Waalboer.

Performance Enhancements
   Memory optimisations
       Several internal data structures (typeglobs, GVs, CVs,
       formats) have been restructured to use less memory.
       (Nicholas Clark)



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   UTF-8 cache optimisation
       The UTF-8 caching code is now more efficient, and used
       more often.  (Nicholas Clark)

   Regular expressions
       Engine de-recursivised
           The regular expression engine is no longer recursive,
           meaning that patterns that used to overflow the stack
           will either die with useful explanations, or run to
           completion, which, since they were able to blow the
           stack before, will likely take a very long time to
           happen. If you were experiencing the occasional stack
           overflow (or segfault) and upgrade to discover that
           now perl apparently hangs instead, look for a
           degenerate regex. (Dave Mitchell)

       Single char char-classes treated as literals
           Classes of a single character are now treated the same
           as if the character had been used as a literal,
           meaning that code that uses char-classes as an
           escaping mechanism will see a speedup. (Yves Orton)

       Trie optimisation of literal string alternations
           Alternations, where possible, are optimised into more
           efficient matching structures. String literal
           alternations are merged into a trie and are matched
           simultaneously.  This means that instead of O(N) time
           for matching N alternations at a given point the new
           code performs in O(1) time. (Yves Orton)

           Note: Much code exists that works around perl's
           historic poor performance on alternations. Often the
           tricks used to do so will disable the new
           optimisations. Hopefully the utility modules used for
           this purpose will be educated about these new
           optimisations by the time 5.10 is released.

       Aho-Corasick start-point optimisation
           When a pattern starts with a trie-able alternation and
           there aren't better optimisations available the regex
           engine will use Aho-Corasick matching to find the
           start point. (Yves Orton)

   Sloppy stat on Windows
       On Windows, perl's stat() function normally opens the file
       to determine the link count and update attributes that may
       have been changed through hard links. Setting
       ${^WIN32_SLOPPY_STAT} to a true value speeds up stat() by
       not performing this operation. (Jan Dubois)

Installation and Configuration Improvements
   Relocatable installations
       There is now Configure support for creating a relocatable
       perl tree. If you Configure with "-Duserelocatableinc",



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       then the paths in @INC (and everything else in %Config)
       can be optionally located via the path of the perl
       executable.

       That means that, if the string ".../" is found at the
       start of any path, it's substituted with the directory of
       $^X. So, the relocation can be configured on a per-
       directory basis, although the default with
       "-Duserelocatableinc" is that everything is relocated. The
       initial install is done to the original configured prefix.

   Ports
       Many improvements have been made towards making Perl work
       correctly on z/OS.

       Perl has been reported to work on DragonFlyBSD.

   Compilation improvements
       All ppport.h files in the XS modules bundled with perl are
       now autogenerated at build time. (Marcus Holland-Moritz)

   New probes
       The configuration process now detects whether strlcat()
       and strlcpy() are available.  When they are not available,
       perl's own version is used (from Russ Allbery's public
       domain implementation).  Various places in the perl
       interpreter now use them. (Steve Peters)

   Windows build improvements
       Building XS extensions
           Support for building XS extension modules with the
           free MinGW compiler has been improved in the case
           where perl itself was built with the Microsoft VC++
           compiler. (ActiveState)

       Support for 64-bit compiler
           Support for building perl with Microsoft's 64-bit
           compiler has been improved. (ActiveState)

Selected Bug Fixes
   PERL5SHELL and tainting
       On Windows, the PERL5SHELL environment variable is now
       checked for taintedness. (Rafael Garcia-Suarez)

   Using *FILE{IO}
       "stat()" and "-X" filetests now treat *FILE{IO}
       filehandles like *FILE filehandles. (Steve Peters)

   Overloading and reblessing
       Overloading now works when references are reblessed into
       another class.  Internally, this has been implemented by
       moving the flag for "overloading" from the reference to
       the referent, which logically is where it should always
       have been. (Nicholas Clark)



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   Overloading and UTF-8
       A few bugs related to UTF-8 handling with objects that
       have stringification overloaded have been fixed. (Nicholas
       Clark)

   eval memory leaks fixed
       Traditionally, "eval 'syntax error'" has leaked badly.
       Many (but not all) of these leaks have now been eliminated
       or reduced. (Dave Mitchell)

   Random device on Windows
       In previous versions, perl would read the file
       /dev/urandom if it existed when seeding its random number
       generator.  That file is unlikely to exist on Windows, and
       if it did would probably not contain appropriate data, so
       perl no longer tries to read it on Windows. (Alex Davies)

New or Changed Diagnostics
       State variable %s will be reinitialized
           One can assign initial values to state variables, but
           not when they're declared as a sub-part of a list
           assignment. See perldiag.

Changed Internals
       A new file, mathoms.c, contains functions that aren't used
       anymore in the perl core, but remain around because
       modules out there might still use them. They come from a
       factorization effort: for example, many PP functions are
       now shared for several ops.

       The implementation of the special variables $^H and %^H
       has changed, to allow implementing lexical pragmas in pure
       perl.

Known Problems
       One warning test (number 263 in lib/warnings.t) fails
       under UTF-8 locales.

       Bytecode tests fail under several platforms. We are
       considering removing support for byteloader and compiler
       before the 5.10.0 release.

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://rt.perl.org/rt3/ .  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



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       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.















































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