perl5131delta


DESCRIPTION
       This document describes differences between the 5.13.0 release and the
       5.13.1 release.

       If you are upgrading from an earlier release such as 5.10, first read
       perl5120delta, which describes differences between 5.10 and 5.12.

Incompatible Changes
   ""\cX""
       The backslash-c construct was designed as a way of specifying non-
       printable characters, but there were no restrictions (on ASCII
       platforms) on what the character following the "c" could be.  Now, that
       character must be one of the ASCII characters.

   localised tied hashes, arrays and scalars are no longed tied
       In the following:

           tie @a, ...;
           {
               local @a;
               # here, @a is a now a new, untied array
           }
           # here, @a refers again to the old, tied array

       The new local array used to be made tied too, which was fairly
       pointless, and has now been fixed. This fix could however potentially
       cause a change in behaviour of some code.

   "given" return values
       Starting from this release, "given" blocks returns the last evaluated
       expression, or an empty list if the block was exited by "break". Thus
       you can now write:

           my $type = do {
            given ($num) {
             break     when undef;
             'integer' when /^[+-]?[0-9]+$/;
             'float'   when /^[+-]?[0-9]+(?:\.[0-9]+)?$/;
             'unknown';
            }
           };

       See "Return value" in perlsyn for details.

Core Enhancements
   Exception Handling Reliability
       Several changes have been made to the way "die", "warn", and $@ behave,
       in order to make them more reliable and consistent.

       When an exception is thrown inside an "eval", the exception is no
       longer at risk of being clobbered by code running during unwinding
       (e.g., destructors).  Previously, the exception was written into $@
       early in the throwing process, and would be overwritten if "eval" was
       Exceptions thrown from object destructors no longer modify the $@ of
       the surrounding context.  (If the surrounding context was exception
       unwinding, this used to be another way to clobber the exception being
       thrown.  Due to the above change it no longer has that significance,
       but there are other situations where $@ is significant.)  Previously
       such an exception was sometimes emitted as a warning, and then either
       string-appended to the surrounding $@ or completely replaced the
       surrounding $@, depending on whether that exception and the surrounding
       $@ were strings or objects.  Now, an exception in this situation is
       always emitted as a warning, leaving the surrounding $@ untouched.  In
       addition to object destructors, this also affects any function call
       performed by XS code using the "G_KEEPERR" flag.

       $@ is also no longer used as an internal temporary variable when
       preparing to "die".  Previously it was internally necessary to put any
       exception object (any non-string exception) into $@ first, before it
       could be used as an exception.  (The C API still offers the old option,
       so an XS module might still clobber $@ in the old way.)  This change
       together with the foregoing means that, in various places, $@ may be
       observed to contain its previously-assigned value, rather than having
       been overwritten by recent exception-related activity.

       Warnings for "warn" can now be objects, in the same way as exceptions
       for "die".  If an object-based warning gets the default handling, of
       writing to standard error, it will of course still be stringified along
       the way.  But a $SIG{__WARN__} handler will now receive an object-based
       warning as an object, where previously it was passed the result of
       stringifying the object.

Modules and Pragmata
   Updated Modules
       "Errno"
           The implementation of "Errno" has been refactored to use about 55%
           less memory.  There should be no user-visible changes.

       Perl 4 ".pl" libraries
           These historical libraries have been minimally modified to avoid
           using $[.  This is to prepare them for the deprecation of $[.

       "B::Deparse"
           A bug has been fixed when deparsing a nextstate op that has both a
           change of package (relative to the previous nextstate), or a change
           of "%^H" or other state, and a label.  Previously the label was
           emitted first, leading to syntactically invalid output because a
           label is not permitted immediately before a package declaration,
           BEGIN block, or some other things.  Now the label is emitted last.

   Removed Modules and Pragmata
       The following modules have been removed from the core distribution, and
       if needed should be installed from CPAN instead.

       "Class::ISA"
       "Pod::Plainer"
       "Switch"

       o   FETCH is no longer called needlessly on some tied variables.

       o   The trie runtime code should no longer allocate massive amounts of
           memory, fixing #74484.

Changed Internals
       o   The protocol for unwinding the C stack at the last stage of a "die"
           has changed how it identifies the target stack frame.  This now
           uses a separate variable "PL_restartjmpenv", where previously it
           relied on the "blk_eval.cur_top_env" pointer in the "eval" context
           frame that has nominally just been discarded.  This change means
           that code running during various stages of Perl-level unwinding no
           longer needs to take care to avoid destroying the ghost frame.

       o   The format of entries on the scope stack has been changed,
           resulting in a reduction of memory usage of about 10%. In
           particular, the memory used by the scope stack to record each
           active lexical variable has been halved.

       o   Memory allocation for pointer tables has been changed. Previously
           "Perl_ptr_table_store" allocated memory from the same arena system
           as "SV" bodies and "HE"s, with freed memory remaining bound to
           those arenas until interpreter exit. Now it allocates memory from
           arenas private to the specific pointer table, and that memory is
           returned to the system when "Perl_ptr_table_free" is called.
           Additionally, allocation and release are both less CPU intensive.

       o   A new function, Perl_magic_methcall has been added that wraps the
           setup needed to call a magic method like FETCH (the existing
           S_magic_methcall function has been renamed S_magic_methcall1).

Deprecations
       The following items are now deprecated.

       "Perl_ptr_table_clear"
           "Perl_ptr_table_clear" is no longer part of Perl's public API.
           Calling it now generates a deprecation warning, and it will be
           removed in a future release.

Acknowledgements
       Perl 5.13.1 represents thirty days of development since Perl 5.13.0 and
       contains 15390 lines of changes across 289 files from 34 authors and
       committers.

       Thank you to the following for contributing to this release:

       var Arnfjoer` Bjarmason, Arkturuz, Chris 'BinGOs' Williams, Craig A.
       Berry, Curtis Jewell, Dan Dascalescu, David Golden, David Mitchell,
       Father Chrysostomos, Gene Sullivan, gfx, Gisle Aas, H.Merijn Brand,
       James E Keenan, James Mastros, Jan Dubois, Jesse Vincent, Karl
       Williamson, Leon Brocard, Lubomir Rintel (GoodData), Nicholas Clark,
       Philippe Bruhat (BooK), Rafael Garcia-Suarez, Rainer Tammer, Ricardo
       Signes, Richard Soderberg, Robin Barker, Ruslan Zakirov, Steffen
       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.

SEE ALSO
       The Changes file for an explanation of how to view 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 v5.14.2                      2011-09-26                  PERL5131DELTA(1)
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