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 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 $_ and
pos() is now documented.
Sorting arrays in place ("@a = sort @a") is now optimized to avoid
making a temporary copy of the array.
The operations involving case mapping on UTF-8 strings (
uc(),
lc(), "//i", etc.) have been greatly speeded up.
Access to elements of lexical arrays via a numeric constant between 0 and 255 is
now faster. (This used to be only the case for global arrays.)
Selected Bug Fixes¶
UTF-8 bugs¶
Using
substr() on a UTF-8 string could cause subsequent accesses on that
string to return garbage. This was due to incorrect UTF-8 offsets being
cached, and is now fixed.
join() could return garbage when the same
join() statement was
used to process 8 bit data having earlier processed UTF-8 data, due to the
flags on that statement's temporary workspace not being reset correctly. This
is now fixed.
Using Unicode keys with tied hashes should now work correctly.
chop() and
chomp() used to mangle UTF-8 strings. This has been
fixed.
sprintf() used to misbehave when the format string was in UTF-8. This is
now fixed.
Threading bugs¶
Hashes with the ":unique" attribute weren't made read-only in new
threads. They are now.
More bugs¶
"$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.)
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.