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.