recursive-descent expression parsing

[perl5.git] / pod / perldelta.pod

=encoding utf8

=for comment
This has been completed up to a1fba7e, except for:
d9a4b459f94297889956ac3adc42707365f274c2
bf5522a13a381257966e7ed6b731195a873b153e
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=head1 NAME

[ this is a template for a new perldelta file. Any text flagged as
XXX needs to be processed before release. ]

perldelta - what is new for perl v5.13.8

=head1 DESCRIPTION

This document describes differences between the 5.13.8 release and
the 5.13.7 release.

If you are upgrading from an earlier release such as 5.13.6, first read
L<perl5137delta>, which describes differences between 5.13.6 and
5.13.7.

=head1 Notice

XXX Any important notices here

=head1 Core Enhancements

XXX New core language features go here. Summarise user-visible core language
enhancements. Particularly prominent performance optimisations could go
here, but most should go in the L</Performance Enhancements> section.

[ List each enhancement as a =head2 entry ]

=head2 C<-d:-foo> calls C<Devel::foo::unimport>

The syntax C<-dI<B<:>foo>> was extended in 5.6.1 to make C<-dI<:fooB<=bar>>>
equivalent to C<-MDevel::foo=bar>, which expands
internally to C<use Devel::foo 'bar';>.
F<perl> now allows prefixing the module name with C<->, with the same
semantics as C<-M>, I<i.e.>

=over 4

=item C<-d:-foo>

Equivalent to C<-M-Devel::foo>, expands to
C<no Devel::foo;>, calls C<< Devel::foo->unimport() >>
if the method exists.

=item C<-d:-foo=bar>

Equivalent to C<-M-Devel::foo=bar>, expands to C<no Devel::foo 'bar';>,
calls C<< Devel::foo->unimport('bar') >> if the method exists.

=back

This is particularly useful to suppresses the default actions of a
C<Devel::*> module's C<import> method whilst still loading it for debugging.

=head2 Filehandle method calls load IO::File on demand

When a method call on a filehandle would die because the method can not
be resolved and L<IO::File> has not been loaded, Perl now loads IO::File
via C<require> and attempts method resolution again:

  open my $fh, ">", $file;
  $fh->binmode(":raw");     # loads IO::File and succeeds

This also works for globs like STDOUT, STDERR and STDIN:

  STDOUT->autoflush(1);

Because this on-demand load only happens if method resolution fails, the
legacy approach of manually loading an IO::File parent class for partial
method support still works as expected:

  use IO::Handle;
  open my $fh, ">", $file;
  $fh->autoflush(1);        # IO::File not loaded

=head2 Full functionality for C<use feature 'unicode_strings'>

This release provides full functionality for C<use feature
'unicode_strings'>.  Under its scope, all string operations executed and
regular expressions compiled (even if executed outside its scope) have
Unicode semantics.   See L<feature>.

This feature avoids the "Unicode Bug" (See
L<perlunicode/The "Unicode Bug"> for details.)  If their is a
possibility that your code will process Unicode strings, you are
B<strongly> encouraged to use this subpragma to avoid nasty surprises.

This availability of this should strongly affect the whole tone of
various documents, such as L<perlunicode> and L<perluniintro>, but this
work has not been done yet.

=head2 Exception Handling Backcompat Hack

When an exception is thrown in an C<eval BLOCK>, C<$@> is now set before
unwinding, as well as being set after unwinding as the eval block exits.  This
early setting supports code that has historically treated C<$@> during unwinding
as an indicator of whether the unwinding was due to an exception.  These modules
had been broken by 5.13.1's change from setting C<$@> early to setting it late.
This double setting arrangement is a stopgap until the reason for unwinding can
be made properly introspectable.  C<$@> has never been a reliable indicator of
this.

=head1 Security

XXX Any security-related notices go here.  In particular, any security
vulnerabilities closed should be noted here rather than in the
L</Selected Bug Fixes> section.

[ List each security issue as a =head2 entry ]

=head1 Incompatible Changes

=head2 Attempting to use C<:=> as an empty attribute list is now a syntax error

Previously C<my $pi := 4;> was exactly equivalent to C<my $pi : = 4;>,
with the C<:> being treated as the start of an attribute list, ending before
the C<=>. The use of C<:=> to mean C<: => was deprecated in 5.12.0, and is now
a syntax error. This will allow the future use of C<:=> as a new token.

We find no Perl 5 code on CPAN using this construction, outside the core's
tests for it, so we believe that this change will have very little impact on
real-world codebases.

If it is absolutely necessary to have empty attribute lists (for example,
because of a code generator) then avoid the error by adding a space before
the C<=>.

=head2 Run-time code block in regular expressions

Code blocks in regular expressions (C<(?{...})> and C<(??{...})>) used not
to inherit any pragmata (strict, warnings, etc.) if the regular expression
was compiled at run time as happens in cases like these two:

  use re 'eval';
  $foo =~ $bar; # when $bar contains (?{...})
  $foo =~ /$bar(?{ $finished = 1 })/;

This was a bug, which has now been fixed. But it has the potential to break
any code that was relying on this bug.

=head1 Deprecations

XXX Any deprecated features, syntax, modules etc. should be listed here.
In particular, deprecated modules should be listed here even if they are
listed as an updated module in the L</Modules and Pragmata> section.

[ List each deprecation as a =head2 entry ]

=head2 C<?PATTERN?> is deprecated

C<?PATTERN?> (without the initial m) has been deprecated and now produces
a warning.

=head2 C<sv_compile_2op> is now deprecated

The C<sv_compile_2op> is now deprecated, and will be removed. Searches suggest
that nothing on CPAN is using it, so this should have zero impact.

It attempted to provide an API to compile code down to an optree, but failed
to bind correctly to lexicals in the enclosing scope. It's not possible to
fix this problem within the constraints of its parameters and return value.

=head2 Tie functions on scalars holding typeglobs

Calling a tie function (C<tie>, C<tied>, C<untie>) with a scalar argument
acts on a file handle if the scalar happens to hold a typeglob.

This is a long-standing bug that will be removed in Perl 5.16, as
there is currently no way to tie the scalar itself when it holds
a typeglob, and no way to untie a scalar that has had a typeglob
assigned to it.

This bug was fixed in 5.13.7 but, because of the breakage it caused, the
fix has been reverted. Now there is a deprecation warning whenever a tie
function is used on a handle without an explicit C<*>.

=head1 Performance Enhancements

XXX Changes which enhance performance without changing behaviour go here. There
may well be none in a stable release.

[ List each enhancement as a =item entry ]

=over 4

=item *

XXX

=back

=head1 Modules and Pragmata

XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
go here.  If Module::CoreList is updated, generate an initial draft of the
following sections using F<Porting/corelist-perldelta.pl>, which prints stub
entries to STDOUT.  Results can be pasted in place of the '=head2' entries
below.  A paragraph summary for important changes should then be added by hand.
In an ideal world, dual-life modules would have a F<Changes> file that could be
cribbed.

[ Within each section, list entries as a =item entry ]

=head2 New Modules and Pragmata

=over 4

=item *

XXX

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

C<ExtUtils::CBuilder> has been upgraded from 0.2703 to 0.2801

=item *

C<if> has been upgraded from 0.06 to 0.0601.

=item *

C<Devel::SelfStubber> has been upgraded from version 1.03 to 1.04.

=item *

C<IPC::Cmd> has been upgraded from 0.64 to 0.66

Resolves an issue with splitting Win32 command lines
and documentation enhancements.

=item *

C<Locale::Codes> has been upgraded from version 3.14 to 3.15

=item *

C<Memoize> has been upgraded from version 1.01_03 to 1.02.

=item *

C<MIME::Base64> has been upgraded from 3.10 to 3.13

Now provides encode_base64url and decode_base64url functions to process
the base64 scheme for "URL applications".

=item *

C<mro> has been upgraded from version 1.05 to 1.06.

C<next::method> I<et al.> now take into account that every class inherits
from UNIVERSAL
L<[perl #68654]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=68654>.

=item *

C<overload> has been upgraded from 1.11 to 1.12.

=item *

C<PerlIO::scalar> has been upgraded from 0.10 to 0.11.

A C<read> after a C<seek> beyond the end of the string no longer thinks it
has data to read
L<[perl #78716]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=78716>.

=item *

C<re> has been upgraded from 0.14 to 0.15.

=item *

C<Socket> has been upgraded from 1.91 to 1.92.

It has several new functions for handling IPv6 addresses.

=item *

C<Storable> has been upgraded from 2.24 to 2.25.

This adds support for serialising code references that contain UTF-8 strings
correctly. The Storable minor version number changed as a result -- this means
Storable users that set C<$Storable::accept_future_minor> to a C<FALSE> value
will see errors (see L<Storable/FORWARD COMPATIBILITY> for more details).

=item *

C<Time::HiRes> has been upgraded from 1.9721 to 1.9721_01.

=item *

C<Unicode::Collate> has been upgraded from 0.67 to 0.68

=item *

C<Unicode::UCD> has been upgraded from 0.29 to 0.30.

=item *

C<version> has been upgraded from 0.82 to 0.86.

=item *

C<Win32> has been upgraded from 0.039 to 0.040.

=back

=head2 Removed Modules and Pragmata

=over 4

=item *

XXX

=back

=head1 Documentation

XXX Changes to files in F<pod/> go here.  Consider grouping entries by
file and be sure to link to the appropriate page, e.g. L<perlfunc>.

=head2 New Documentation

XXX Changes which create B<new> files in F<pod/> go here.

=head3 L<XXX>

XXX Description of the purpose of the new file here

=head2 Changes to Existing Documentation

XXX Changes which significantly change existing files in F<pod/> go here.
However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
section.

=head3 L<XXX>

=over 4

=item *

XXX Description of the change here

=back

=head1 Diagnostics

The following additions or changes have been made to diagnostic output,
including warnings and fatal error messages.  For the complete list of
diagnostic messages, see L<perldiag>.

XXX New or changed warnings emitted by the core's C<C> code go here. Also
include any changes in L<perldiag> that reconcile it to the C<C> code.

[ Within each section, list entries as a =item entry ]

=head2 New Diagnostics

XXX Newly added diagnostic messages go here

=over 4

=item *

There is a new "Closure prototype called" error.

=back

=head2 Changes to Existing Diagnostics

XXX Changes (i.e. rewording) of diagnostic messages go here

=over 4

=item *

The "Found = in conditional" warning that is emitted when a constant is
assigned to a variable in a condition is now withheld if the constant is
actually a subroutine or one generated by C<use constant>, since the value
of the constant may not be known at the time the program is written
L<[perl #77762]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=77762>.

=back

=head1 Utility Changes

XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go
here. Most of these are built within the directories F<utils> and F<x2p>.

[ List utility changes as a =head3 entry for each utility and =item
entries for each change
Use L<XXX> with program names to get proper documentation linking. ]

=head3 L<XXX>

=over 4

=item *

XXX

=back

=head1 Configuration and Compilation

XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
go here.  Any other changes to the Perl build process should be listed here.
However, any platform-specific changes should be listed in the
L</Platform Support> section, instead.

[ List changes as a =item entry ].

=over 4

=item *

XXX

=back

=head1 Testing

XXX Any significant changes to the testing of a freshly built perl should be
listed here.  Changes which create B<new> files in F<t/> go here as do any
large changes to the testing harness (e.g. when parallel testing was added).
Changes to existing files in F<t/> aren't worth summarising, although the bugs
that they represent may be covered elsewhere.

[ List each test improvement as a =item entry ]

=over 4

=item *

XXX

=back

=head1 Platform Support

XXX Any changes to platform support should be listed in the sections below.

[ Within the sections, list each platform as a =item entry with specific
changes as paragraphs below it. ]

=head2 New Platforms

XXX List any platforms that this version of perl compiles on, that previous
versions did not. These will either be enabled by new files in the F<hints/>
directories, or new subdirectories and F<README> files at the top level of the
source tree.

=over 4

=item XXX-some-platform

XXX

=back

=head2 Discontinued Platforms

XXX List any platforms that this version of perl no longer compiles on.

=over 4

=item XXX-some-platform

XXX

=back

=head2 Platform-Specific Notes

XXX List any changes for specific platforms. This could include configuration
and compilation changes or changes in portability/compatibility.  However,
changes within modules for platforms should generally be listed in the
L</Modules and Pragmata> section.

=over 4

=item NetBSD

The NetBSD hints file has been changed to make the system's malloc the
default.

=back

=head1 Internal Changes

XXX Changes which affect the interface available to C<XS> code go here.
Other significant internal changes for future core maintainers should
be noted as well.

[ List each test improvement as a =item entry ]

=over 4

=item *

C<mg_findext> and C<sv_unmagicext> have been added.

These new functions allow extension authors to find and remove magic attached to
scalars based on both the magic type and the magic virtual table, similar to how
C<sv_magicext> attaches magic of a certain type and with a given virtual table
to a scalar. This eliminates the need for extensions to walk the list of
C<MAGIC> pointers of an C<SV> to find the magic that belongs to them.

=back

=head1 Selected Bug Fixes

XXX Important bug fixes in the core language are summarised here.
Bug fixes in files in F<ext/> and F<lib/> are best summarised in
L</Modules and Pragmata>.

[ List each fix as a =item entry ]

=over 4

=item *

C<BEGIN {require 5.12.0}> now behaves as documented, rather than behaving
identically to C<use 5.12.0;>. Previously, C<require> in a C<BEGIN> block
was erroneously executing the C<use feature ':5.12.0'> and
C<use strict; use warnings;> behaviour, which only C<use> was documented to
provide
L<[perl #69050]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=69050>.

=item *

C<use 5.42>
L<[perl #69050]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=69050>,
C<use 6> and C<no 5> no longer leak memory.

=item *

C<eval "BEGIN{die}"> no longer leaks memory on non-threaded builds.

=item *

PerlIO no longer crashes when called recursively, e.g., from a signal
handler. Now it just leaks memory
L<[perl #75556]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=75556>.

=item *

Defining a constant with the same name as one of perl's special blocks
(e.g., INIT) stopped working in 5.12.0, but has now been fixed
L<[perl #78634]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=78634>.

=item *

A reference to a literal value used as a hash key (C<$hash{\"foo"}>) used
to be stringified, even if the hash was tied
L<[perl #79178]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=79178>.

=item *

A closure containing an C<if> statement followed by a constant or variable
is no longer treated as a constant
L<[perl #63540]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=63540>.

=item *

Calling a closure prototype (what is passed to an attribute handler for a
closure) now results in a "Closure prototype called" error message
L<[perl #68560]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=68560>.

=item *

A regular expression optimisation would sometimes cause a match with a
C<{n,m}> quantifier to fail when it should match
L<[perl #79152]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=79152>.

=item *

What has become known as the "Unicode Bug" is resolved in this release.
Under C<use feature 'unicode_strings'>, the internal storage format of a
string no longer affects the external semantics.  There are two known
exceptions.  User-defined case changing functions, which are planned to
be deprecated in 5.14, require utf8-encoded strings to function; and the
character C<LATIN SMALL LETTER SHARP S> in regular expression
case-insensitive matching has a somewhat different set of bugs depending
on the internal storage format.  Case-insensitive matching of all
characters that have multi-character matches, as this one does, is
problematical in Perl.
L<[perl #58182]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=58182>.

=item *

Mentioning a read-only lexical variable from the enclosing scope in a
string C<eval> would cause the variable to become writable
L<[perl #19135]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=19135>.

=item *

C<state> can now be used with attributes. It used to mean the same thing as
C<my> if attributes were present
L<[perl #68658]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=68658>.

=item *

Expressions like C<< @$a > 3 >> no longer cause C<$a> to be mentioned in
the "Use of uninitialized value in numeric gt" warning when C<$a> is
undefined (since it is not part of the C<E<gt>> expression, but the operand
of the C<@>)
L<[perl #72090]|http://rt.perl.org/rt3/Public/Bug/Display.html?id=72090>.

=back

=head1 Known Problems

XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
tests that had to be C<TODO>ed for the release would be noted here, unless
they were specific to a particular platform (see below).

This is a list of some significant unfixed bugs, which are regressions
from either 5.XXX.XXX or 5.XXX.XXX.

[ List each fix as a =item entry ]

=over 4

=item *

XXX

=back

=head1 Obituary

XXX If any significant core contributor has died, we've added a short obituary
here.

=head1 Acknowledgements

XXX The list of people to thank goes here.

=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 L<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