PERL5131DELTA(1) Perl Programmers Reference Guide PERL5131DELTA(1)NAMEperl5131delta - what is new for perl v5.13.1
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
used internally in the destructor for an object that had to be freed
while exiting from the outer "eval". Now the exception is written into
$@ last thing before exiting the outer "eval", so the code running
immediately thereafter can rely on the value in $@ correctly
corresponding to that "eval".
Likewise, a "local $@" inside an "eval" will no longer clobber any
exception thrown in its scope. Previously, the restoration of $@ upon
unwinding would overwrite any exception being thrown. Now the
exception gets to the "eval" anyway. So "local $@" is safe inside an
"eval", albeit of rather limited use.
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"
The removal of "Shell" has been deferred until after 5.14, as the
implementation of "Shell" shipped with 5.12.0 did not correctly issue
the warning that it was to be removed from core.
New Documentation
perlgpl
perlgpl has been updated to contain GPL version 1, as is included
in the README distributed with perl.
Selected Bug Fixes
· Naming a deprecated character in \N{...} will not leak memory.
· FETCH is no longer called needlessly on some tied variables.
· The trie runtime code should no longer allocate massive amounts of
memory, fixing #74484.
Changed Internals
· 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.
· 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.
· 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.
· 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
Mueller, Todd Rinaldo, Tony Cook, Vincent Pit, Zefram
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 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.
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)
