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PERL595DELTA(1)                       Perl Programmers Reference Guide                       PERL595DELTA(1)



NAME
       perl595delta - what is new for perl v5.9.5

DESCRIPTION
       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.

Incompatible Changes
   Tainting and printf
       When perl is run under taint mode, "printf()" and "sprintf()" will now reject any tainted format
       argument. (Rafael Garcia-Suarez)

   undef and signal handlers
       Undefining or deleting a signal handler via "undef $SIG{FOO}" is now equivalent to setting it to
       'DEFAULT'. (Rafael)

   strictures and array/hash dereferencing in defined()
       "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 removed
       The regular expression construct "(?p{})", which was deprecated in perl 5.8, has been removed. Use
       "(??{})" instead. (Rafael)

   Pseudo-hashes have been removed
       Support for pseudo-hashes has been removed from Perl 5.9. (The "fields" pragma remains here, but uses
       an alternate implementation.)

   Removal of the bytecode compiler and of perlcc
       "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).

   Removal of the JPL
       The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.

   Recursive inheritance detected earlier
       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.

Core Enhancements
   Regular expressions
       Recursive Patterns
           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)

       Named Capture Buffers
           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

               foreach my $name (keys %+) {
                   print "content of buffer '$name' is $+{$name}\n";
               }

           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)

       Possessive Quantifiers
           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)

       Backtracking control verbs
           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)

       Relative backreferences
           A new syntax "\g{N}" or "\gN" where "N" is a decimal integer allows a safer form of back-reference backreference
           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)

       Vertical and horizontal whitespace, and linebreak
           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".

   The "_" prototype
       A 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 blocks
       "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)

   readpipe() is now overridable
       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)

   default argument for readline()
       readline() now defaults to *ARGV if no argument is provided. (Rafael)

   UCD 5.0.0
       The copy of the Unicode Character Database included in Perl 5.9 has been updated to version 5.0.0.

   Smart match
       The smart match operator ("~~") is now available by default (you don't need to enable it with "use
       feature" any longer). (Michael G Schwern)

   Implicit loading of "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.

Modules and Pragmas
   New Pragma, "mro"
       A new pragma, "mro" (for Method Resolution Order) has been added. It permits to switch, on a per-class perclass
       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.

   bignum, bigint, bigrat
       The three numeric pragmas "bignum", "bigint" and "bigrat" are now lexically scoped. (Tels)

   Math::BigInt/Math::BigFloat
       Many bugs have been fixed; noteworthy are comparisons with NaN, which no longer warn about undef
       values.

       The following things are new:

       config()
           The config() method now also supports the calling-style "config('lib')" in addition to
           "config()->{'lib'}".

       import()
           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.

       roundmode common
           A rounding mode of "common" is now supported.

       Also, support for the following methods has been added:

       bpi(), bcos(), bsin(), batan(), batan2()
       bmuladd()
       bexp(), bnok()
       from_hex(), from_oct(), and from_bin()
       as_oct()

       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.

   New Core Modules
       •   "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.

   Module changes
       "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:

               use warnings;
               require Carp;
               Carp::confess "argh";

       "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.

Utility Changes
   "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)

Documentation
   New manpage, perlunifaq
       A new manual page, perlunifaq (the Perl Unicode FAQ), has been added (Juerd Waalboer).

Installation and Configuration Improvements
   C++ compatibility
       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.)

   Visual C++
       Perl now can be compiled with Microsoft Visual C++ 2005.

   Static build on Win32
       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)

   win32 builds
       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.

   Help
       "Configure -h" has been extended with the most used option.

       Much less 'Whoa there' messages.

   64bit systems
       Better detection of 64bit(only) systems, and setting all the (library) paths accordingly.

   Ports
       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.

Selected Bug Fixes
       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)

New or Changed Diagnostics
   Deprecations
       Two deprecation warnings have been added: (Rafael)

           Opening dirhandle %s also as a file
           Opening filehandle %s also as a directory

Changed Internals
       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).

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 v5.12.5                                     2012-11-03                                  PERL595DELTA(1)