perl591delta - what is new for perl v5.9.1
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.
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.
:unique
attribute is only meaningful for globalsNow applying :unique
to lexical variables and to subroutines will
result in a compilation error.
$_
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 $_
.
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 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.
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 Benchmark
, cmpthese() and timestr() now use the time statistics of
children instead of parent when the selected style is 'nop'.
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
will now recognize grouping tags (such as :name
) anywhere
in the import list, not only at the beginning.
A function again
is provided to resolve problems where modules in different
directories wish to use FindBin.
You can now weaken references to read only values.
cond_wait
has a new two argument form. cond_timedwait
has been added.
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.)
The documentation has been revised in places to produce more standard manpages.
The long-existing feature of /(?{...})/
regexps setting $_
and pos()
is now documented.
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.)
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.
Hashes with the :unique
attribute weren't made read-only in new
threads. They are now.
$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 (/(?{...})/
).
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.)
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.
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.)
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.
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.)
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.
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.
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.)
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.
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.
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.
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.