perl591delta
(1)
Name
perl591delta - what is new for perl v5.9.1
Synopsis
Please see following description for synopsis
Description
Perl Programmers Reference Guide PERL591DELTA(1)
NAME
perl591delta - what is new for perl v5.9.1
DESCRIPTION
This document describes differences between the 5.9.0 and
the 5.9.1 development releases. See perl590delta for the
differences between 5.8.0 and 5.9.0.
Incompatible Changes
substr() lvalues are no longer fixed-length
The lvalues returned by the three argument form of substr()
used to be a "fixed length window" on the original string.
In some cases this could cause surprising action at distance
or other undefined behaviour. Now the length of the window
adjusts itself to the length of the string assigned to it.
The ":unique" attribute is only meaningful for globals
Now applying ":unique" to lexical variables and to
subroutines will result in a compilation error.
Core Enhancements
Lexical $_
The default variable $_ can now be lexicalized, by declaring
it like any other lexical variable, with a simple
my $_;
The operations that default on $_ will use the lexically-
scoped version of $_ when it exists, instead of the global
$_.
In a "map" or a "grep" block, if $_ was previously my'ed,
then the $_ inside the block is lexical as well (and scoped
to the block).
In a scope where $_ has been lexicalized, you can still have
access to the global version of $_ by using $::_, or, more
simply, by overriding the lexical declaration with "our $_".
Tied hashes in scalar context
As of perl 5.8.2/5.9.0, tied hashes did not return anything
useful in scalar context, for example when used as boolean
tests:
if (%tied_hash) { ... }
The old nonsensical behaviour was always to return false,
regardless of whether the hash is empty or has elements.
There is now an interface for the implementors of tied
hashes to implement the behaviour of a hash in scalar
context, via the SCALAR method (see perltie). Without a
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SCALAR method, perl will try to guess whether the hash is
empty, by testing if it's inside an iteration (in this case
it can't be empty) or by calling FIRSTKEY.
Formats
Formats were improved in several ways. A new field, "^*",
can be used for variable-width, one-line-at-a-time text.
Null characters are now handled correctly in picture lines.
Using "@#" and "~~" together will now produce a compile-time
error, as those format fields are incompatible. perlform
has been improved, and miscellaneous bugs fixed.
Stacked filetest operators
As a new form of syntactic sugar, it's now possible to stack
up filetest operators. You can now write "-f -w -x $file" in
a row to mean "-x $file && -w _ && -f _". See "-X" in
perlfunc.
Modules and Pragmata
Benchmark
In "Benchmark", cmpthese() and timestr() now use the
time statistics of children instead of parent when the
selected style is 'nop'.
Carp
The error messages produced by "Carp" now include spaces
between the arguments in function argument lists: this
makes long error messages appear more nicely in browsers
and other tools.
Exporter
"Exporter" will now recognize grouping tags (such as
":name") anywhere in the import list, not only at the
beginning.
FindBin
A function "again" is provided to resolve problems where
modules in different directories wish to use FindBin.
List::Util
You can now weaken references to read only values.
threads::shared
"cond_wait" has a new two argument form.
"cond_timedwait" has been added.
Utility Changes
"find2perl" now assumes "-print" as a default action.
Previously, it needed to be specified explicitly.
A new utility, "prove", makes it easy to run an individual
regression test at the command line. "prove" is part of
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Test::Harness, which users of earlier Perl versions can
install from CPAN.
The perl debugger now supports a "save" command, to save the
current history to a file, and an "i" command, which prints
the inheritance tree of its argument (if the "Class::ISA"
module is installed.)
Documentation
The documentation has been revised in places to produce more
standard manpages.
The long-existing feature of "/(?{...})/" regexps setting $_
and pos() is now documented.
Performance Enhancements
Sorting arrays in place ("@a = sort @a") is now optimized to
avoid making a temporary copy of the array.
The operations involving case mapping on UTF-8 strings
(uc(), lc(), "//i", etc.) have been greatly speeded up.
Access to elements of lexical arrays via a numeric constant
between 0 and 255 is now faster. (This used to be only the
case for global arrays.)
Selected Bug Fixes
UTF-8 bugs
Using substr() on a UTF-8 string could cause subsequent
accesses on that string to return garbage. This was due to
incorrect UTF-8 offsets being cached, and is now fixed.
join() could return garbage when the same join() statement
was used to process 8 bit data having earlier processed
UTF-8 data, due to the flags on that statement's temporary
workspace not being reset correctly. This is now fixed.
Using Unicode keys with tied hashes should now work
correctly.
chop() and chomp() used to mangle UTF-8 strings. This has
been fixed.
sprintf() used to misbehave when the format string was in
UTF-8. This is now fixed.
Threading bugs
Hashes with the ":unique" attribute weren't made read-only
in new threads. They are now.
More bugs
"$a .. $b" will now work as expected when either $a or $b is
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"undef".
Reading $^E now preserves $!. Previously, the C code
implementing $^E did not preserve "errno", so reading $^E
could cause "errno" and therefore $! to change unexpectedly.
"strict" wasn't in effect in regexp-eval blocks
("/(?{...})/").
New or Changed Diagnostics
A new deprecation warning, Deprecated use of my() in false
conditional, has been added, to warn against the use of the
dubious and deprecated construct
my $x if 0;
See perldiag.
The fatal error DESTROY created new reference to dead object
is now documented in perldiag.
A new error, %ENV is aliased to %s, is produced when taint
checks are enabled and when *ENV has been aliased (and thus
doesn't reflect the program's environment anymore.)
Changed Internals
These news matter to you only if you either write XS code or
like to know about or hack Perl internals (using Devel::Peek
or any of the "B::" modules counts), or like to run Perl
with the "-D" option.
Reordering of SVt_* constants
The relative ordering of constants that define the various
types of "SV" have changed; in particular, "SVt_PVGV" has
been moved before "SVt_PVLV", "SVt_PVAV", "SVt_PVHV" and
"SVt_PVCV". This is unlikely to make any difference unless
you have code that explicitly makes assumptions about that
ordering. (The inheritance hierarchy of "B::*" objects has
been changed to reflect this.)
Removal of CPP symbols
The C preprocessor symbols "PERL_PM_APIVERSION" and
"PERL_XS_APIVERSION", which were supposed to give the
version number of the oldest perl binary-compatible (resp.
source-compatible) with the present one, were not used, and
sometimes had misleading values. They have been removed.
Less space is used by ops
The "BASEOP" structure now uses less space. The "op_seq"
field has been removed and replaced by two one-bit fields,
"op_opt" and "op_static". "opt_type" is now 9 bits long.
(Consequently, the "B::OP" class doesn't provide an "seq"
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method anymore.)
New parser
perl's parser is now generated by bison (it used to be
generated by byacc.) As a result, it seems to be a bit more
robust.
Configuration and Building
"Configure" now invokes callbacks regardless of the value of
the variable they are called for. Previously callbacks were
only invoked in the "case $variable $define)" branch. This
change should only affect platform maintainers writing
configuration hints files.
The portability and cleanliness of the Win32 makefiles has
been improved.
Known Problems
There are still a couple of problems in the implementation
of the lexical $_: it doesn't work inside "/(?{...})/"
blocks and with regard to the reverse() built-in used
without arguments. (See the TODO tests in t/op/mydef.t.)
Platform Specific Problems
The test ext/IPC/SysV/t/ipcsysv.t may fail on OpenBSD. This
hasn't been diagnosed yet.
On some configurations on AIX 5, one test in
lib/Time/Local.t fails. When configured with long doubles,
perl may fail tests 224-236 in t/op/pow.t on the same
platform.
For threaded builds, ext/threads/shared/t/wait.t has been
reported to fail some tests on HP-UX 10.20.
To-do for perl 5.10.0
This is a non-exhaustive, non-ordered, non-contractual and
non-definitive list of things to do (or nice to have) for
perl 5.10.0 :
Clean up and finish support for assertions. See assertions.
Reimplement the mechanism of lexical pragmas to be more
extensible. Fix current pragmas that don't work well (or at
all) with lexical scopes or in run-time eval(STRING)
("sort", "re", "encoding" for example). MJD has a
preliminary patch that implements this.
Fix (or rewrite) the implementation of the "/(?{...})/"
closures.
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Conversions from byte strings to UTF-8 currently map high
bit characters to Unicode without translation (or, depending
on how you look at it, by implicitly assuming that the byte
strings are in Latin-1). As perl assumes the C locale by
default, upgrading a string to UTF-8 may change the meaning
of its contents regarding character classes, case mapping,
etc. This should probably emit a warning (at least).
Introduce a new special block, UNITCHECK, which is run at
the end of a compilation unit (module, file, eval(STRING)
block). This will correspond to the Perl 6 CHECK. Perl 5's
CHECK cannot be changed or removed because the O.pm/B.pm
backend framework depends on it.
Study the possibility of adding a new prototype character,
"_", meaning "this argument defaults to $_".
Make the peephole optimizer optional.
Allow lexical aliases (maybe via the syntax "my \$alias =
\$foo".
Fix the bugs revealed by running the test suite with the
"-t" switch (via "make test.taintwarn").
Make threads more robust.
Make "no 6" and "no v6" work (opposite of "use 5.005",
etc.).
A test suite for the B module would be nice.
A ponie.
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://bugs.perl.org/
. 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.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
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+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/perl-512 |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
The Changes file for 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.
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://www.cpan.org/src/5.0/perl-5.12.5.tar.bz2
Further information about this software can be found on the
open source community website at http://www.perl.org/.
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