


PERL591DELTA(1)  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



perl v5.10.1                2008-09-29                          1





PERL591DELTA(1)  Perl Programmers Reference Guide PERL591DELTA(1)


       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



perl v5.10.1                2008-09-29                          2





PERL591DELTA(1)  Perl Programmers Reference Guide PERL591DELTA(1)


       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".



perl v5.10.1                2008-09-29                          3





PERL591DELTA(1)  Perl Programmers Reference Guide PERL591DELTA(1)


       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.)




perl v5.10.1                2008-09-29                          4





PERL591DELTA(1)  Perl Programmers Reference Guide PERL591DELTA(1)


   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



perl v5.10.1                2008-09-29                          5





PERL591DELTA(1)  Perl Programmers Reference Guide PERL591DELTA(1)


       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.




perl v5.10.1                2008-09-29                          6


