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 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 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 "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" 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.
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.
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.