


PERL593DELTA(1)  Perl Programmers Reference Guide PERL593DELTA(1)


NAME
       perl593delta - what is new for perl v5.9.3

DESCRIPTION
       This document describes differences between the 5.9.2 and
       the 5.9.3 development releases. See perl590delta,
       perl591delta and perl592delta for the differences between
       5.8.0 and 5.9.2.

Incompatible Changes
   Parsing of "-f _"
       The identifier "_" is now forced to be a bareword after a
       filetest operator. This solves a number of misparsing
       issues when a global "_" subroutine is defined.

   "mkdir()"
       "mkdir()" without arguments now defaults to $_.

   Magic goto and eval
       The construct "eval { goto &foo }" is now disallowed.
       (Note that the similar construct, but with "eval("")"
       instead, was already forbidden.)

   $# has been removed
       The deprecated $# variable (output format for numbers) has
       been removed. A new warning, "$# is no longer supported",
       has been added.

   ":unique"
       The ":unique" attribute has been made a no-op, since its
       current implementation was fundamentally flawed and not
       threadsafe.

   Scoping of the "sort" pragma
       The "sort" pragma is now lexically scoped. Its effect used
       to be global.

Core Enhancements
   The "feature" pragma
       The "feature" pragma is used to enable new syntax that
       would break Perl's backwards-compatibility with older
       releases of the language. It's a lexical pragma, like
       "strict" or "warnings".

       Currently the following new features are available:
       "switch" (adds a switch statement), "~~" (adds a Perl
       6-like smart match operator), "say" (adds a "say" built-in
       function), and "err" (adds an "err" keyword).  Those
       features are described below.

       Note that "err" low-precedence defined-or operator used to
       be enabled by default (although as a weak keyword, meaning
       that any function would override it). It's now only
       recognized when explicitly turned on (and is then a



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       regular keyword).

       Those features, and the "feature" pragma itself, have been
       contributed by Robin Houston.

   Switch and Smart Match operator
       Perl 5 now has a switch statement. It's available when
       "use feature 'switch'" is in effect. This feature
       introduces three new keywords, "given", "when", and
       "default":

           given ($foo) {
               when (/^abc/) { $abc = 1; }
               when (/^def/) { $def = 1; }
               when (/^xyz/) { $xyz = 1; }
               default { $nothing = 1; }
           }

       A more complete description of how Perl matches the switch
       variable against the "when" conditions is given in "Switch
       statements" in perlsyn.

       This kind of match is called smart match, and it's also
       possible to use it outside of switch statements, via the
       new "~~" operator (enabled via the "use feature '~~'"
       directive). See "Smart matching in detail" in perlsyn.

   "say()"
       say() is a new built-in, only available when "use feature
       'say'" is in effect, that is similar to print(), but that
       implicitly appends a newline to the printed string. See
       "say" in perlfunc.

   "CLONE_SKIP()"
       Perl has now support for the "CLONE_SKIP" special
       subroutine. Like "CLONE", "CLONE_SKIP" is called once per
       package; however, it is called just before cloning starts,
       and in the context of the parent thread. If it returns a
       true value, then no objects of that class will be cloned.
       See perlmod for details. (Contributed by Dave Mitchell.)

   "${^CHILD_ERROR_NATIVE}"
       A new internal variable, "${^CHILD_ERROR_NATIVE}", gives
       the native status returned by the last pipe close,
       backtick command, successful call to wait() or waitpid(),
       or from the system() operator. See perlrun for details.
       (Contributed by Gisle Aas.)

   Assertions
       The support for assertions, introduced in perl 5.9.0, has
       been improved.  The syntax for the "-A" command-line
       switch has changed; it now accepts an optional module
       name, defaulting to "assertions::activate". See assertions
       and perlrun. (Contributed by Salvador Fandin~o Garcia.)



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   Unicode Character Database 4.1.0
       The copy of the Unicode Character Database included in
       Perl 5.9 has been updated to 4.1.0.

   "no VERSION"
       You can now use "no" followed by a version number to
       specify that you want to use a version of perl older than
       the specified one.

   Recursive sort subs
       You can now use recursive subroutines with sort(), thanks
       to Robin Houston.

   Effect of pragmas in eval
       The compile-time value of the "%^H" hint variable can now
       propagate into eval("")uated code. This makes it more
       useful to implement lexical pragmas.

       As a side-effect of this, the overloaded-ness of constants
       now propagates into eval("").

   New -E command-line switch
       -E is equivalent to -e, but it implicitly enables all
       optional features (like "use feature ":5.10"").

   "chdir", "chmod" and "chown" on filehandles
       "chdir", "chmod" and "chown" can now work on filehandles
       as well as filenames, if the system supports respectively
       "fchdir", "fchmod" and "fchown", thanks to a patch
       provided by Gisle Aas.

   OS groups
       $( and $) now return groups in the order where the OS
       returns them, thanks to Gisle Aas. This wasn't previously
       the case.

Modules and Pragmata
   New Core Modules
       o   A new pragma, "feature", has been added; see above in
           "Core Enhancements".

       o   "assertions::compat", also available on CPAN, allows
           the use of assertions on perl versions prior to 5.9.0
           (that is the first one to natively support them).

       o   "Math::BigInt::FastCalc" is an XS-enabled, and thus
           faster, version of "Math::BigInt::Calc".

       o   "Compress::Zlib" is an interface to the zlib
           compression library. It comes with a bundled version
           of zlib, so having a working zlib is not a
           prerequisite to install it. It's used by
           "Archive::Tar" (see below).




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       o   "IO::Zlib" is an "IO::"-style interface to
           "Compress::Zlib".

       o   "Archive::Tar" is a module to manipulate "tar"
           archives.

       o   "Digest::SHA" is a module used to calculate many types
           of SHA digests, has been included for SHA support in
           the CPAN module.

       o   "ExtUtils::CBuilder" and "ExtUtils::ParseXS" have been
           added.

Utility Changes
   "ptar"
       "ptar" is a pure perl implementation of "tar", that comes
       with "Archive::Tar".

   "ptardiff"
       "ptardiff" is a small script used to generate a diff
       between the contents of a tar archive and a directory
       tree. Like "ptar", it comes with "Archive::Tar".

   "shasum"
       This command-line utility, used to print or to check SHA
       digests, comes with the new "Digest::SHA" module.

   "h2xs" enhancements
       "h2xs" implements a new option "--use-xsloader" to force
       use of "XSLoader" even in backwards compatible modules.

       The handling of authors' names that had apostrophes has
       been fixed.

       Any enums with negative values are now skipped.

   "perlivp" enhancements
       "perlivp" no longer checks for *.ph files by default.  Use
       the new "-a" option to run all tests.

Documentation
   Perl Glossary
       The perlglossary manpage is a glossary of terms used in
       the Perl documentation, technical and otherwise, kindly
       provided by O'Reilly Media, Inc.

       perltodo now lists a rough roadmap to Perl 5.10.

Performance Enhancements
   XS-assisted SWASHGET
       Some pure-perl code that perl was using to retrieve
       Unicode properties and transliteration mappings has been
       reimplemented in XS.




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   Constant subroutines
       The interpreter internals now support a far more memory
       efficient form of inlineable constants. Storing a
       reference to a constant value in a symbol table is
       equivalent to a full typeglob referencing a constant
       subroutine, but using about 400 bytes less memory. This
       proxy constant subroutine is automatically upgraded to a
       real typeglob with subroutine if necessary.  The approach
       taken is analogous to the existing space optimisation for
       subroutine stub declarations, which are stored as plain
       scalars in place of the full typeglob.

       Several of the core modules have been converted to use
       this feature for their system dependent constants - as a
       result "use POSIX;" now takes about 200K less memory.

   "PERL_DONT_CREATE_GVSV"
       The new compilation flag "PERL_DONT_CREATE_GVSV",
       introduced as an option in perl 5.8.8, is turned on by
       default in perl 5.9.3. It prevents perl from creating an
       empty scalar with every new typeglob. See perl589delta for
       details.

   Weak references are cheaper
       Weak reference creation is now O(1) rather than O(n),
       courtesy of Nicholas Clark. Weak reference deletion
       remains O(n), but if deletion only happens at program
       exit, it may be skipped completely.

   sort() enhancements
       Salvador Fandin~o provided improvements to reduce the
       memory usage of "sort" and to speed up some cases.

Installation and Configuration Improvements
   Compilation improvements
       Parallel makes should work properly now, although there
       may still be problems if "make test" is instructed to run
       in parallel.

       Building with Borland's compilers on Win32 should work
       more smoothly. In particular Steve Hay has worked to side
       step many warnings emitted by their compilers and at least
       one C compiler internal error.

       Perl extensions on Windows now can be statically built
       into the Perl DLL, thanks to a work by Vadim Konovalov.

   New Or Improved Platforms
       Perl is being ported to Symbian OS. See perlsymbian for
       more information.

       The VMS port has been improved. See perlvms.

       DynaLoader::dl_unload_file() now works on Windows.



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       Portability of Perl on various recent compilers on Windows
       has been improved (Borland C++, Visual C++ 7.0).

   New probes
       "Configure" will now detect "clearenv" and "unsetenv",
       thanks to a patch from Alan Burlison. It will also probe
       for "futimes" (and use it internally if available), and
       whether "sprintf" correctly returns the length of the
       formatted string.

   Module auxiliary files
       README files and changelogs for CPAN modules bundled with
       perl are no longer installed.

Selected Bug Fixes
   "defined $$x"
       "use strict "refs"" was ignoring taking a hard reference
       in an argument to defined(), as in :

           use strict "refs";
           my $x = "foo";
           if (defined $$x) {...}

       This now correctly produces the run-time error "Can't use
       string as a SCALAR ref while "strict refs" in use".
       (However, "defined @$foo" and "defined %$foo" are still
       allowed. Those constructs are discouraged anyway.)

   Calling CORE::require()
       CORE::require() and CORE::do() were always parsed as
       require() and do() when they were overridden. This is now
       fixed.

   Subscripts of slices
       You can now use a non-arrowed form for chained subscripts
       after a list slice, like in:

           ({foo => "bar"})[0]{foo}

       This used to be a syntax error; a "->" was required.

   Remove over-optimisation
       Perl 5.9.2 introduced a change so that assignments of
       "undef" to a scalar, or of an empty list to an array or a
       hash, were optimised out. As this could cause problems
       when "goto" jumps were involved, this change was backed
       out.

   sprintf() fixes
       Using the sprintf() function with some formats could lead
       to a buffer overflow in some specific cases. This has been
       fixed, along with several other bugs, notably in bounds
       checking.




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       In related fixes, it was possible for badly written code
       that did not follow the documentation of "Sys::Syslog" to
       have formatting vulnerabilities.  "Sys::Syslog" has been
       changed to protect people from poor quality third party
       code.

   no warnings 'category' works correctly with -w
       Previously when running with warnings enabled globally via
       "-w", selective disabling of specific warning categories
       would actually turn off all warnings.  This is now fixed;
       now "no warnings 'io';" will only turn off warnings in the
       "io" class. Previously it would erroneously turn off all
       warnings.

   Smaller fixes
       o   "FindBin" now works better with directories where
           access rights are more restrictive than usual.

       o   Several memory leaks in ithreads were closed. Also,
           ithreads were made less memory-intensive.

       o   Trailing spaces are now trimmed from $! and $^E.

       o   Operations that require perl to read a process' list
           of groups, such as reads of $( and $), now dynamically
           allocate memory rather than using a fixed sized array.
           The fixed size array could cause C stack exhaustion on
           systems configured to use large numbers of groups.

       o   "PerlIO::scalar" now works better with non-default $/
           settings.

       o   The "x" repetition operator is now able to operate on
           "qw//" lists. This used to raise a syntax error.

       o   The debugger now traces correctly execution in
           eval("")uated code that contains #line directives.

       o   The value of the "open" pragma is no longer ignored
           for three-argument opens.

       o   Perl will now use the C library calls "unsetenv" and
           "clearenv" if present to delete keys from %ENV and
           delete %ENV entirely, thanks to a patch from Alan
           Burlison.

   More Unicode Fixes
       o   chr() on a negative value now gives "\x{FFFD}", the
           Unicode replacement character, unless when the "bytes"
           pragma is in effect, where the low eight bytes of the
           value are used.

       o   Some case insensitive matches between UTF-8 encoded
           data and 8 bit regexps, and vice versa, could give



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           malformed character warnings. These have been fixed by
           Dave Mitchell and Yves Orton.

       o   "lcfirst" and "ucfirst" could corrupt the string for
           certain cases where the length UTF-8 encoding of the
           string in lower case, upper case or title case
           differed. This was fixed by Nicholas Clark.

New or Changed Diagnostics
   Attempt to set length of freed array
       This is a new warning, produced in situations like the
       following one:

           $r = do {my @a; \$#a};
           $$r = 503;

   Non-string passed as bitmask
       This is a new warning, produced when number has been
       passed as a argument to select(), instead of a bitmask.

           # Wrong, will now warn
           $rin = fileno(STDIN);
           ($nfound,$timeleft) = select($rout=$rin, undef, undef, $timeout);

           # Should be
           $rin = '';
           vec($rin,fileno(STDIN),1) = 1;
           ($nfound,$timeleft) = select($rout=$rin, undef, undef, $timeout);

   Search pattern not terminated or ternary operator parsed as
       search pattern
       This syntax error indicates that the lexer couldn't find
       the final delimiter of a "?PATTERN?" construct. Mentioning
       the ternary operator in this error message makes syntax
       diagnostic easier.

   "%s" variable %s masks earlier declaration
       This warning is now emitted in more consistent cases; in
       short, when one of the declarations involved is a "my"
       variable:

           my $x;   my $x;     # warns
           my $x;  our $x;     # warns
           our $x;  my $x;     # warns

       On the other hand, the following:

           our $x; our $x;

       now gives a ""our" variable %s redeclared" warning.

   readdir()/closedir()/etc. attempted on invalid dirhandle
       These new warnings are now emitted when a dirhandle is
       used but is either closed or not really a dirhandle.



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Changed Internals
       In general, the source code of perl has been refactored,
       tied up, and optimized in many places. Also, memory
       management and allocation has been improved in a couple of
       points.

       Andy Lester supplied many improvements to determine which
       function parameters and local variables could actually be
       declared "const" to the C compiler. Steve Peters provided
       new *_set macros and reworked the core to use these rather
       than assigning to macros in LVALUE context.

       Dave Mitchell improved the lexer debugging output under
       "-DT".

       A new file, mathoms.c, has been added. It contains
       functions that are no longer used in the perl core, but
       that remain available for binary or source compatibility
       reasons. However, those functions will not be compiled in
       if you add "-DNO_MATHOMS" in the compiler flags.

       The "AvFLAGS" macro has been removed.

       The "av_*()" functions, used to manipulate arrays, no
       longer accept null "AV*" parameters.

   B:: modules inheritance changed
       The inheritance hierarchy of "B::" modules has changed;
       "B::NV" now inherits from "B::SV" (it used to inherit from
       "B::IV").

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.




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