Re-apply #31429, which was accidentally undone by #31632

[perl5.git] / pod / perl595delta.pod

=head1 NAME

perldelta - what is new for perl v5.9.5

=head1 DESCRIPTION

This document describes differences between the 5.9.4 and the 5.9.5
development releases. See L<perl590delta>, L<perl591delta>,
L<perl592delta>, L<perl593delta> and L<perl594delta> for the differences
between 5.8.0 and 5.9.4.

=head1 Incompatible Changes

=head2 Tainting and printf

When perl is run under taint mode, C<printf()> and C<sprintf()> will now
reject any tainted format argument. (Rafael Garcia-Suarez)

=head2 undef and signal handlers

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

=head2 strictures and array/hash dereferencing in defined()

C<defined @$foo> and C<defined %$bar> are now subject to C<strict 'refs'>
(that is, C<$foo> and C<$bar> shall be proper references there.)
(Nicholas Clark)

(However, C<defined(@foo)> and C<defined(%bar)> are discouraged constructs
anyway.)

=head2 C<(?p{})> has been removed

The regular expression construct C<(?p{})>, which was deprecated in perl
5.8, has been removed. Use C<(??{})> instead. (Rafael)

=head2 Pseudo-hashes have been removed

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

=head2 Removal of the bytecode compiler and of perlcc

C<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).

=head2 Removal of the JPL

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

=head2 Recursive inheritance detected earlier

Perl will now immediately throw an exception if you modify any package's
C<@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
C<$foo-E<gt>isa($bar)> lookup.

=head1 Core Enhancements

=head2 Regular expressions

=over 4

=item Recursive Patterns

It is now possible to write recursive patterns without using the C<(??{})>
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 C<(?PARNO)> syntax (C<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)

=item 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 C<< (?<NAME>....) >>.
It's possible to backreference to a named buffer with the C<< \k<NAME> >>
syntax. In code, the new magical hashes C<%+> and C<%-> 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 C<%+> hash, so
it's possible to do something like

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

The C<%-> 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.

C<%+> and C<%-> are implemented as tied hashes through the new module
C<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)

=item 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 C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
quantifiers. (Yves Orton)

=item 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 L<perlre> for their descriptions. (Yves Orton)

=item Relative backreferences

A new syntax C<\g{N}> or C<\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 L<perlre/"Capture buffers">. (Yves Orton)

=item C<\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 C<\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)

=item Vertical and horizontal whitespace, and linebreak

Regular expressions now recognize the C<\v> and C<\h> escapes, that match
vertical and horizontal whitespace, respectively. C<\V> and C<\H>
logically match their complements.

C<\R> matches a generic linebreak, that is, vertical whitespace, plus
the multi-character sequence C<"\x0D\x0A">.

=back

=head2 The C<_> prototype

A new prototype character has been added. C<_> is equivalent to C<$> (it
denotes a scalar), but defaults to C<$_> 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 C<_> for some built-ins in appropriate cases (for
example, C<prototype('CORE::rmdir')>). (Rafael)

=head2 UNITCHECK blocks

C<UNITCHECK>, a new special code block has been introduced, in addition to
C<BEGIN>, C<CHECK>, C<INIT> and C<END>.

C<CHECK> and C<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, C<UNITCHECK> blocks are executed
just after the unit which defined them has been compiled. See L<perlmod>
for more information. (Alex Gough)

=head2 readpipe() is now overridable

The built-in function readpipe() is now overridable. Overriding it permits
also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
Moreover, it now defaults to C<$_> if no argument is provided. (Rafael)

=head2 default argument for readline()

readline() now defaults to C<*ARGV> if no argument is provided. (Rafael)

=head2 UCD 5.0.0

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

=head2 Smart match

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

=head2 Implicit loading of C<feature>

The C<feature> pragma is now implicitly loaded when you require a minimal
perl version (with the C<use VERSION> construct) greater than, or equal
to, 5.9.5.

=head1 Modules and Pragmas

=head2 New Pragma, C<mro>

A new pragma, C<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 mutiple inheritance hierachy. The
default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
available: the C3 algorithm. See L<mro> for more information.
(Brandon Black)

Note that, due to changes in the implentation of class hierarchy search,
code that used to undef the C<*ISA> glob will most probably break. Anyway,
undef'ing C<*ISA> had the side-effect of removing the magic on the @ISA
array and should not have been done in the first place.

=head2 bignum, bigint, bigrat

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

=head2 New Core Modules

=over 4

=item *

C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
included in the perl core; the behaviour of C<Locale::Maketext::Simple>
gracefully degrades when the later isn't present.

=item *

C<Params::Check> implements a generic input parsing/checking mechanism. It
is used by CPANPLUS.

=item *

C<Term::UI> simplifies the task to ask questions at a terminal prompt.

=item *

C<Object::Accessor> provides an interface to create per-object accessors.

=item *

C<Module::Pluggable> is a simple framework to create modules that accept
pluggable sub-modules.

=item *

C<Module::Load::Conditional> provides simple ways to query and possibly
load installed modules.

=item *

C<Time::Piece> provides an object oriented interface to time functions,
overriding the built-ins localtime() and gmtime().

=item *

C<IPC::Cmd> helps to find and run external commands, possibly
interactively.

=item *

C<File::Fetch> provide a simple generic file fetching mechanism.

=item *

C<Log::Message> and C<Log::Message::Simple> are used by the log facility
of C<CPANPLUS>.

=item *

C<Archive::Extract> is a generic archive extraction mechanism
for F<.tar> (plain, gziped or bzipped) or F<.zip> files.

=item *

C<CPANPLUS> provides an API and a command-line tool to access the CPAN
mirrors.

=back

=head2 Module changes

=over 4

=item C<assertions>

The C<assertions> pragma, its submodules C<assertions::activate> and
C<assertions::compat> and the B<-A> command-line switch have been removed.
The interface was not judged mature enough for inclusion in a stable
release.

=item C<base>

The C<base> pragma now warns if a class tries to inherit from itself.
(Curtis "Ovid" Poe)

=item C<strict> and C<warnings>

C<strict> and C<warnings> will now complain loudly if they are loaded via
incorrect casing (as in C<use Strict;>). (Johan Vromans)

=item C<warnings>

The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
that used C<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";

=item C<less>

C<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 L<less> for more. (Joshua ben
Jore)

=item C<Attribute::Handlers>

C<Attribute::Handlers> can now report the caller's file and line number.
(David Feldman)

=item C<B::Lint>

C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
with plugins. (Joshua ben Jore)

=item C<B>

It's now possible to access the lexical pragma hints (C<%^H>) by using the
method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
ben Jore)

=for p5p XXX document this in B.pm too

=item C<Thread>

As the old 5005thread threading model has been removed, in favor of the
ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
be used in old code only.

=back

=head1 Utility Changes

=head2 C<cpanp>

C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, an
helper for CPANPLUS operation, has been added too, but isn't intended for
direct use).

=head2 C<cpan2dist>

C<cpan2dist> is a new utility, that comes with CPANPLUS. It's a tool to
create distributions (or packages) from CPAN modules.

=head2 C<pod2html>

The output of C<pod2html> has been enhanced to be more customizable via
CSS. Some formatting problems were also corrected. (Jari Aalto)

=head1 Documentation

=head2 New manpage, perlunifaq

A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
(Juerd Waalboer).

=head1 Performance Enhancements

=head1 Installation and Configuration Improvements

=head2 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.)

=head2 Visual C++

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

=head2 Static build on Win32

It's now possible to build a C<perl-static.exe> that doesn't depend
on C<perl59.dll> on Win32. See the Win32 makefiles for details.
(Vadim Konovalov)

=head2 C<d_pseudofork>

A new configuration variable, available as C<$Config{d_pseudofork}> in
the L<Config> module, has been added, to distinguish real fork() support
from fake pseudofork used on Windows platforms.

=head2 Ports

Perl has been reported to work on MidnightBSD.

=head1 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
L<perlipc/"Deferred Signals (Safe Signals)">). (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 C<-w> and C<-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 C<: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 C<local $h{$x}; ++$x>). (Bo Lindbergh)

=head1 New or Changed Diagnostics

=head2 Deprecations

Two deprecation warnings have been added: (Rafael)

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

=head1 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).

=for p5p XXX have we some docs on how to create regexp engine plugins, since that's now possible ? (perlreguts)

=for p5p XXX new BIND SV type, #29544, #29642

=head1 Known Problems

=head2 Platform Specific Problems

=head1 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 B<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 C<perl -V>, will be sent off to perlbug@perl.org to be
analysed by the Perl porting team.

=head1 SEE ALSO

The F<Changes> file for exhaustive details on what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=cut