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perl591delta (1)


perl591delta - what is new for perl v5.9.1


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Perl Programmers Reference Guide                  PERL591DELTA(1)

     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.

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

             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 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

Modules and Pragmata
         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

         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.

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.)

     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

     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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     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

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

     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 "/(?{...})/"

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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
     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 =

     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",

     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
     .  There may also be information at ,
     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 to be analysed by the Perl porting team.

     See attributes(5) for descriptions of the following

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     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
     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.

     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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