=head1 NAME

perldelta - what is new for perl v5.11.2

=head1 DESCRIPTION

This document describes differences between the 5.11.1 release and the
5.11.2 release.

=head1 Core Enhancements

=head2 qr overloading

It is now possible to overload the C<qr//> operator, that is,
conversion to regexp, like it was already possible to overload
conversion to boolean, string or number of objects. It is invoked when
an object appears on the right hand side of the C<=~> operator, or when
it is interpolated into a regexp. See L<overload>.

=head2 Pluggable keywords

Extension modules can now cleanly hook into the Perl parser to define
new kinds of keyword-headed expression and compound statement. The
syntax following the keyword is defined entirely by the extension. This
allow a completely non-Perl sublanguage to be parsed inline, with the
right ops cleanly generated. This feature is currently considered
experimental.

See L<perlapi/PL_keyword_plugin> for the mechanism. The Perl core
source distribution also includes a new module
L<XS::APItest::KeywordRPN>, which implements reverse Polish notation
arithmetic via pluggable keywords. This module is mainly used for test
purposes, and is not normally installed, but also serves as an example
of how to use the new mechanism.

=head2 APIs for more internals

The lowest layers of the lexer and parts of the pad system now have C
APIs available to XS extensions. These are necessary to support proper
use of pluggable keywords, but have other uses too. The new APIs are
experimental, and only cover a small proportion of what would be
necessary to take full advantage of the core's facilities in these
areas. It is intended that the Perl 5.13 development cycle will see the
addition of a full range of clean, supported interfaces.

=head2 Overridable function lookup

Where an extension module hooks the creation of rv2cv ops to modify the
subroutine lookup process, this now works correctly for bareword
subroutine calls. This means that prototypes on subroutines referenced
this way will be processed correctly. (Previously bareword subroutine
names were initially looked up, for parsing purposes, by an unhookable
mechanism, so extensions could only properly influence subroutine names
that appeared with an C<&> sigil.)

=head1 Modules and Pragmata

=head2 New Modules and Pragmata

=over 4

=item C<legacy>

Preserves legacy behaviors or enable new non-default behaviors.
Currently the only behaviour concerns semantics for the 128 characters
on ASCII systems that have the 8th bit set.

=back

=head2 Pragmata Changes

=over 4

=item C<diagnostics>

Supports %.0f formatting internally.

=item C<overload>

Allow overloading of 'qr'.

=back

=head2 Updated Modules

=over 4

=item C<B::Concise>

Optimize reversing an array in-place, avoid using defined %hash in core
code and tests.

=item C<B::Deparse>

Teach B::Deparse about in-place reverse.

=item C<Carp>

Refine Carp caller() fix and add tests.

=item C<Compress::Zlib>

Updated to 2.022.

=item C<CPANPLUS>

Updated to 0.89_09.

=item C<Encode>

Updated to 2.38.

=item C<ExtUtils::CBuilder>

Updated to 0.27.

=item C<Env>

Add EXISTS and DELETE methods to Env.pm.

=item C<File::Fetch>

Updated to 0.22.

=item C<I8N::Langinfo>

Correctly document export of I18N::Langinfo.

=item C<I8N::LangTags>

In I18N::LangTags::Detect, avoid using defined @array and defined
%hash.

=item C<IO::Compress>

Updated to 2.022.

=item C<IPC::Cmd>

Updated to 0.54.

=item C<List::Util>

Updated to 1.22.

=item C<Locale::Maketext>

In Locale::Maketext, avoid using defined @array and defined %hash.
Convert the odd Locale::Maketext test out from Test to Test::More.

=item C<Module::Build>

Updated to 0.35_08.

=item C<Module::CoreList>

Implemented is_deprecated().

=item C<Pod::Simple>

Updated to 3.10.

=item C<Scalar::Util>

Updated to 1.22.

=item C<Switch>

Updated to 2.16.

=back

=head1 Utility Changes

=over 4

=item F<a2p>

Fixed bugs with the match() operator in list context, remove mention of
$[.

=back

=head1 Performance Enhancements

=over 4

=item *

Reversing an array to itself (as in C<@a = reverse @a>) in void context
now happens in-place and is several orders of magnitude faster than it
used to be. It will also preserve non-existent elements whenever
possible, i.e. for non magical arrays or tied arrays with C<EXISTS> and
C<DELETE> methods.

=back

=head1 New or Changed Diagnostics

Several new diagnostics, see L<perldiag> for details.

=over 4

=item C<Bad plugin affecting keyword '%s'>

=item C<gmtime(%.0f) too large>

=item C<Lexing code attempted to stuff non-Latin-1 character into Latin-1 input>

=item C<Lexing code internal error (%s)>

=item C<localtime(%.0f) too large>

=item C<Overloaded dereference did not return a reference>

=item C<Overloaded qr did not return a REGEXP>

=item C<Perl_pmflag() is deprecated, and will be removed from the XS API>

=back

One diagnostic has been removed:

=over 4

=item C<Runaway format>

=back

=head1 Changed Internals

=over 4

=item *

C<Perl_pmflag> has been removed from the public API. Calling it now
generates a deprecation warning, and it will be removed in a future
release. Although listed as part of the API, it was never documented,
and only ever used in F<toke.c>, and prior to 5.10, F<regcomp.c>. In
core, it has been replaced by a static function.

=back

=head1 New Tests

=over 4

=item F<t/op/while_readdir.t>

Test that a bare readdir in while loop sets $_.

=back

=head1 Known Problems

=over 4

=item Known test failures on VMS

Perl 5.11.2 fails a small set of core and CPAN tests as of this
release. With luck, that'll be sorted out for 5.11.3.

=back

=head1 Deprecations

The following items are now deprecated.

=head2 Use of C<:=> to mean an empty attribute list is now deprecated.

An accident of Perl's parser meant that these constructions were all
equivalent:

    my $pi := 4;
    my $pi : = 4;
    my $pi :  = 4;

with the C<:> being treated as the start of an attribute list, which
ends before the C<=>. As whitespace is not significant here, all are
parsed as an empty attribute list, hence all the above are equivalent
to, and better written as

    my $pi = 4;

because no attribute processing is done for an empty list.

As is, this meant that C<:=> cannot be used as a new token, without
silently changing the meaning of existing code. Hence that particular
form is now deprecated, and will become a syntax error. If it is
absolutely necessary to have empty attribute lists (for example,
because of a code generator) then avoid the warning by adding a space
before the C<=>.

=head1 Acknowledgements

Perl 5.11.2 represents approximately 3 weeks development since Perl
5.11.1 contains 29,992 lines of changes across 458 files from 38
authors and committers:

Abhijit Menon-Sen, Abigail, Ben Morrow, Bo Borgerson, Brad Gilbert,
Bram, Chris Williams, Craig A. Berry, Daniel Frederick Crisman, Dave
Rolsky, David E. Wheeler, David Golden, Eric Brine, Father
Chrysostomos, Frank Wiegand, Gerard Goossen, Gisle Aas, Graham Barr,
Harmen, H.Merijn Brand, Jan Dubois, Jerry D. Hedden, Jesse Vincent,
Karl Williamson, Kevin Ryde, Leon Brocard, Nicholas Clark, Paul
Marquess, Philippe Bruhat, Rafael Garcia-Suarez, Sisyphus, Steffen
Mueller, Steve Hay, Steve Peters, Vincent Pit, Yuval Kogman, Yves
Orton, and Zefram.

Many of the changes included in this version originated in the CPAN
modules included in Perl's core. We're grateful to the entire CPAN
community for helping Perl to flourish.

=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/perlbug/ . 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.

If the bug you are reporting has security implications, which make it
inappropriate to send to a publicly archived mailing list, then please
send it to perl5-security-report@perl.org. This points to a closed
subscription unarchived mailing list, which includes all the core
committers, who be able to help assess the impact of issues, figure out
a resolution, and help co-ordinate the release of patches to mitigate
or fix the problem across all platforms on which Perl is supported.
Please only use this address for security issues in the Perl core, not
for modules independently distributed on CPAN.

=head1 SEE ALSO

The F<Changes> file for an explanation of how to view 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
