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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.

   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
       ·   "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)

       ·   "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
       ·   "Hash::Util::FieldHash", by Anno Siegel, has been 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.

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

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

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

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

       ·   "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)

   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", 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)

   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 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 v5.10.1			  2009-02-12		       PERL594DELTA(1)
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