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.
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.