perl595delta - what is new for perl v5.9.5
This document describes differences between the 5.9.4 and the 5.9.5 development releases. See perl590delta, perl591delta, perl592delta, perl593delta and perl594delta for the differences between 5.8.0 and 5.9.4.
When perl is run under taint mode, printf() and sprintf() will now
reject any tainted format argument. (Rafael Garcia-Suarez)
Undefining or deleting a signal handler via undef $SIG{FOO}
is now
equivalent to setting it to 'DEFAULT'
. (Rafael)
defined @$foo
and defined %$bar
are now subject to strict 'refs'
(that is, $foo
and $bar
shall be proper references there.)
(Nicholas Clark)
(However, defined(@foo) and defined(%bar) are discouraged constructs
anyway.)
(?p{}) has been removedThe regular expression construct (?p{}), which was deprecated in perl
5.8, has been removed. Use (??{})
instead. (Rafael)
Support for pseudo-hashes has been removed from Perl 5.9. (The fields
pragma remains here, but uses an alternate implementation.)
perlcc
, the byteloader and the supporting modules (B::C, B::CC,
B::Bytecode, etc.) are no longer distributed with the perl sources. Those
experimental tools have never worked reliably, and, due to the lack of
volunteers to keep them in line with the perl interpreter developments, it
was decided to remove them instead of shipping a broken version of those.
The last version of those modules can be found with perl 5.9.4.
However the B compiler framework stays supported in the perl core, as with the more useful modules it has permitted (among others, B::Deparse and B::Concise).
The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
Perl will now immediately throw an exception if you modify any package's
@ISA
in such a way that it would cause recursive inheritance.
Previously, the exception would not occur until Perl attempted to make
use of the recursive inheritance while resolving a method or doing a
$foo->isa($bar)
lookup.
It is now possible to write recursive patterns without using the (??{})
construct. This new way is more efficient, and in many cases easier to
read.
Each capturing parenthesis can now be treated as an independent pattern
that can be entered by using the (?PARNO) syntax (PARNO
standing for
"parenthesis number"). For example, the following pattern will match
nested balanced angle brackets:
- /
- ^ # start of line
- ( # start capture buffer 1
- < # match an opening angle bracket
- (?: # match one of:
- (?> # don't backtrack over the inside of this group
- [^<>]+ # one or more non angle brackets
- ) # end non backtracking group
- | # ... or ...
- (?1) # recurse to bracket 1 and try it again
- )* # 0 or more times.
- > # match a closing angle bracket
- ) # end capture buffer one
- $ # end of line
- /x
Note, users experienced with PCRE will find that the Perl implementation of this feature differs from the PCRE one in that it is possible to backtrack into a recursed pattern, whereas in PCRE the recursion is atomic or "possessive" in nature. (Yves Orton)
It is now possible to name capturing parenthesis in a pattern and refer to
the captured contents by name. The naming syntax is (?<NAME>....).
It's possible to backreference to a named buffer with the \k<NAME>
syntax. In code, the new magical hashes %+
and %-
can be used to
access the contents of the capture buffers.
Thus, to replace all doubled chars, one could write
- s/(?<letter>.)\k<letter>/$+{letter}/g
Only buffers with defined contents will be "visible" in the %+
hash, so
it's possible to do something like
The %-
hash is a bit more complete, since it will contain array refs
holding values from all capture buffers similarly named, if there should
be many of them.
%+
and %-
are implemented as tied hashes through the new module
Tie::Hash::NamedCapture
.
Users exposed to the .NET regex engine will find that the perl implementation differs in that the numerical ordering of the buffers is sequential, and not "unnamed first, then named". Thus in the pattern
- /(A)(?<B>B)(C)(?<D>D)/
$1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer would expect. This is considered a feature. :-) (Yves Orton)
Perl now supports the "possessive quantifier" syntax of the "atomic match"
pattern. Basically a possessive quantifier matches as much as it can and never
gives any back. Thus it can be used to control backtracking. The syntax is
similar to non-greedy matching, except instead of using a '?' as the modifier
the '+' is used. Thus ?+, *+
, ++
, {min,max}+
are now legal
quantifiers. (Yves Orton)
The regex engine now supports a number of special-purpose backtrack control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL) and (*ACCEPT). See perlre for their descriptions. (Yves Orton)
A new syntax \g{N}
or \gN
where "N" is a decimal integer allows a
safer form of back-reference notation as well as allowing relative
backreferences. This should make it easier to generate and embed patterns
that contain backreferences. See Capture buffers in perlre. (Yves Orton)
\K
escape
The functionality of Jeff Pinyan's module Regexp::Keep has been added to
the core. You can now use in regular expressions the special escape \K
as a way to do something like floating length positive lookbehind. It is
also useful in substitutions like:
- s/(foo)bar/$1/g
that can now be converted to
- s/foo\Kbar//g
which is much more efficient. (Yves Orton)
Regular expressions now recognize the \v
and \h
escapes, that match
vertical and horizontal whitespace, respectively. \V
and \H
logically match their complements.
\R
matches a generic linebreak, that is, vertical whitespace, plus
the multi-character sequence "\x0D\x0A"
.
_
prototypeA new prototype character has been added. _
is equivalent to $
(it
denotes a scalar), but defaults to $_
if the corresponding argument
isn't supplied. Due to the optional nature of the argument, you can only
use it at the end of a prototype, or before a semicolon.
This has a small incompatible consequence: the prototype() function has
been adjusted to return _
for some built-ins in appropriate cases (for
example, prototype('CORE::rmdir')). (Rafael)
UNITCHECK
, a new special code block has been introduced, in addition to
BEGIN
, CHECK
, INIT
and END
.
CHECK
and INIT
blocks, while useful for some specialized purposes,
are always executed at the transition between the compilation and the
execution of the main program, and thus are useless whenever code is
loaded at runtime. On the other hand, UNITCHECK
blocks are executed
just after the unit which defined them has been compiled. See perlmod
for more information. (Alex Gough)
The built-in function readpipe() is now overridable. Overriding it permits
also to override its operator counterpart, qx// (a.k.a. ``
).
Moreover, it now defaults to $_
if no argument is provided. (Rafael)
readline() now defaults to *ARGV
if no argument is provided. (Rafael)
The copy of the Unicode Character Database included in Perl 5.9 has been updated to version 5.0.0.
The smart match operator (~~
) is now available by default (you don't
need to enable it with use feature
any longer). (Michael G Schwern)
feature
The feature
pragma is now implicitly loaded when you require a minimal
perl version (with the use VERSION
construct) greater than, or equal
to, 5.9.5.
mro
A new pragma, mro
(for Method Resolution Order) has been added. It
permits to switch, on a per-class basis, the algorithm that perl uses to
find inherited methods in case of a multiple inheritance hierarchy. The
default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
available: the C3 algorithm. See mro for more information.
(Brandon Black)
Note that, due to changes in the implementation of class hierarchy search,
code that used to undef the *ISA
glob will most probably break. Anyway,
undef'ing *ISA
had the side-effect of removing the magic on the @ISA
array and should not have been done in the first place.
The three numeric pragmas bignum
, bigint
and bigrat
are now
lexically scoped. (Tels)
Many bugs have been fixed; noteworthy are comparisons with NaN, which no longer warn about undef values.
The following things are new:
The config() method now also supports the calling-style
config('lib')
in addition to config()->{'lib'}
.
Upon import, using lib => 'Foo'
now warns if the low-level library
cannot be found. To suppress the warning, you can use try => 'Foo'
instead. To convert the warning into a die, use only => 'Foo'
instead.
A rounding mode of common
is now supported.
Also, support for the following methods has been added:
In addition, the default math-backend (Calc (Perl) and FastCalc (XS)) now support storing numbers in parts with 9 digits instead of 7 on Perls with either 64bit integer or long double support. This means math operations scale better and are thus faster for really big numbers.
Locale::Maketext::Simple
, needed by CPANPLUS, is a simple wrapper around
Locale::Maketext::Lexicon
. Note that Locale::Maketext::Lexicon
isn't
included in the perl core; the behaviour of Locale::Maketext::Simple
gracefully degrades when the later isn't present.
Params::Check
implements a generic input parsing/checking mechanism. It
is used by CPANPLUS.
Term::UI
simplifies the task to ask questions at a terminal prompt.
Object::Accessor
provides an interface to create per-object accessors.
Module::Pluggable
is a simple framework to create modules that accept
pluggable sub-modules.
Module::Load::Conditional
provides simple ways to query and possibly
load installed modules.
Time::Piece
provides an object oriented interface to time functions,
overriding the built-ins localtime() and gmtime().
IPC::Cmd
helps to find and run external commands, possibly
interactively.
File::Fetch
provide a simple generic file fetching mechanism.
Log::Message
and Log::Message::Simple
are used by the log facility
of CPANPLUS
.
Archive::Extract
is a generic archive extraction mechanism
for .tar (plain, gziped or bzipped) or .zip files.
CPANPLUS
provides an API and a command-line tool to access the CPAN
mirrors.
assertions
The assertions
pragma, its submodules assertions::activate
and
assertions::compat
and the -A command-line switch have been removed.
The interface was not judged mature enough for inclusion in a stable
release.
base
The base
pragma now warns if a class tries to inherit from itself.
(Curtis "Ovid" Poe)
strict
and warnings
strict
and warnings
will now complain loudly if they are loaded via
incorrect casing (as in use Strict;
). (Johan Vromans)
warnings
The warnings
pragma doesn't load Carp
anymore. That means that code
that used Carp
routines without having loaded it at compile time might
need to be adjusted; typically, the following (faulty) code won't work
anymore, and will require parentheses to be added after the function name:
less
less
now does something useful (or at least it tries to). In fact, it
has been turned into a lexical pragma. So, in your modules, you can now
test whether your users have requested to use less CPU, or less memory,
less magic, or maybe even less fat. See less for more. (Joshua ben
Jore)
Attribute::Handlers
Attribute::Handlers
can now report the caller's file and line number.
(David Feldman)
B::Lint
B::Lint
is now based on Module::Pluggable
, and so can be extended
with plugins. (Joshua ben Jore)
B
It's now possible to access the lexical pragma hints (%^H
) by using the
method B::COP::hints_hash(). It returns a B::RHE
object, which in turn
can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
ben Jore)
Thread
As the old 5005thread threading model has been removed, in favor of the
ithreads scheme, the Thread
module is now a compatibility wrapper, to
be used in old code only. It has been removed from the default list of
dynamic extensions.
cpanp
cpanp
, the CPANPLUS shell, has been added. (cpanp-run-perl
, an
helper for CPANPLUS operation, has been added too, but isn't intended for
direct use).
cpan2dist
cpan2dist
is a new utility, that comes with CPANPLUS. It's a tool to
create distributions (or packages) from CPAN modules.
pod2html
The output of pod2html
has been enhanced to be more customizable via
CSS. Some formatting problems were also corrected. (Jari Aalto)
A new manual page, perlunifaq (the Perl Unicode FAQ), has been added (Juerd Waalboer).
Efforts have been made to make perl and the core XS modules compilable with various C++ compilers (although the situation is not perfect with some of the compilers on some of the platforms tested.)
Perl now can be compiled with Microsoft Visual C++ 2005.
It's now possible to build a perl-static.exe
that doesn't depend
on perl59.dll
on Win32. See the Win32 makefiles for details.
(Vadim Konovalov)
All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
d_pseudofork
and d_printf_format_null
A new configuration variable, available as $Config{d_pseudofork}
in
the Config module, has been added, to distinguish real fork() support
from fake pseudofork used on Windows platforms.
A new configuration variable, d_printf_format_null
, has been added,
to see if printf-like formats are allowed to be NULL.
Configure -h
has been extended with the most used option.
Much less 'Whoa there' messages.
Better detection of 64bit(only) systems, and setting all the (library) paths accordingly.
Perl has been reported to work on MidnightBSD.
Support for Cray XT4 Catamount/Qk has been added.
Vendor patches have been merged for RedHat and GenToo.
PerlIO::scalar will now prevent writing to read-only scalars. Moreover, seek() is now supported with PerlIO::scalar-based filehandles, the underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
study() never worked for UTF-8 strings, but could lead to false results. It's now a no-op on UTF-8 data. (Yves Orton)
The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an "unsafe" manner (contrary to other signals, that are deferred until the perl interpreter reaches a reasonably stable state; see Deferred Signals (Safe Signals) in perlipc). (Rafael)
When a module or a file is loaded through an @INC-hook, and when this hook has set a filename entry in %INC, __FILE__ is now set for this module accordingly to the contents of that %INC entry. (Rafael)
The -w
and -t
switches can now be used together without messing
up what categories of warnings are activated or not. (Rafael)
Duping a filehandle which has the :utf8
PerlIO layer set will now
properly carry that layer on the duped filehandle. (Rafael)
Localizing an hash element whose key was given as a variable didn't work
correctly if the variable was changed while the local() was in effect (as
in local $h{$x}; ++$x
). (Bo Lindbergh)
Two deprecation warnings have been added: (Rafael)
- Opening dirhandle %s also as a file
- Opening filehandle %s also as a directory
The anonymous hash and array constructors now take 1 op in the optree instead of 3, now that pp_anonhash and pp_anonlist return a reference to an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
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.
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.