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-indevelopment 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 garbagecollected 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 AhoCorasick 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.

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