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   1  =head1 NAME
   2  
   3  perl593delta - what is new for perl v5.9.3
   4  
   5  =head1 DESCRIPTION
   6  
   7  This document describes differences between the 5.9.2 and the 5.9.3
   8  development releases. See L<perl590delta>, L<perl591delta> and
   9  L<perl592delta> for the differences between 5.8.0 and 5.9.2.
  10  
  11  =head1 Incompatible Changes
  12  
  13  =head2 Parsing of C<-f _>
  14  
  15  The identifier C<_> is now forced to be a bareword after a filetest
  16  operator. This solves a number of misparsing issues when a global C<_>
  17  subroutine is defined.
  18  
  19  =head2 C<mkdir()>
  20  
  21  C<mkdir()> without arguments now defaults to C<$_>.
  22  
  23  =head2 Magic goto and eval
  24  
  25  The construct C<eval { goto &foo }> is now disallowed. (Note that the
  26  similar construct, but with C<eval("")> instead, was already forbidden.)
  27  
  28  =head2 C<$#> has been removed
  29  
  30  The deprecated C<$#> variable (output format for numbers) has been
  31  removed. A new warning, C<$# is no longer supported>, has been added.
  32  
  33  =head2 C<:unique>
  34  
  35  The C<:unique> attribute has been made a no-op, since its current
  36  implementation was fundamentally flawed and not threadsafe.
  37  
  38  =head2 Scoping of the C<sort> pragma
  39  
  40  The C<sort> pragma is now lexically scoped. Its effect used to be global.
  41  
  42  =head1 Core Enhancements
  43  
  44  =head2 The C<feature> pragma
  45  
  46  The C<feature> pragma is used to enable new syntax that would break Perl's
  47  backwards-compatibility with older releases of the language. It's a lexical
  48  pragma, like C<strict> or C<warnings>.
  49  
  50  Currently the following new features are available: C<switch> (adds a
  51  switch statement), C<~~> (adds a Perl 6-like smart match operator), C<say>
  52  (adds a C<say> built-in function), and C<err> (adds an C<err> keyword).
  53  Those features are described below.
  54  
  55  Note that C<err> low-precedence defined-or operator used to be enabled by
  56  default (although as a weak keyword, meaning that any function would
  57  override it). It's now only recognized when explicitly turned on (and is
  58  then a regular keyword).
  59  
  60  Those features, and the C<feature> pragma itself, have been contributed by
  61  Robin Houston.
  62  
  63  =head2 Switch and Smart Match operator
  64  
  65  Perl 5 now has a switch statement. It's available when C<use feature
  66  'switch'> is in effect. This feature introduces three new keywords,
  67  C<given>, C<when>, and C<default>:
  68  
  69      given ($foo) {
  70      when (/^abc/) { $abc = 1; }
  71      when (/^def/) { $def = 1; }
  72      when (/^xyz/) { $xyz = 1; }
  73      default { $nothing = 1; }
  74      }
  75  
  76  A more complete description of how Perl matches the switch variable
  77  against the C<when> conditions is given in L<perlsyn/"Switch statements">.
  78  
  79  This kind of match is called I<smart match>, and it's also possible to use
  80  it outside of switch statements, via the new C<~~> operator (enabled via
  81  the C<use feature '~~'> directive). See L<perlsyn/"Smart matching in
  82  detail">.
  83  
  84  =head2 C<say()>
  85  
  86  say() is a new built-in, only available when C<use feature 'say'> is in
  87  effect, that is similar to print(), but that implicitly appends a newline
  88  to the printed string. See L<perlfunc/say>.
  89  
  90  =head2 C<CLONE_SKIP()>
  91  
  92  Perl has now support for the C<CLONE_SKIP> special subroutine. Like
  93  C<CLONE>, C<CLONE_SKIP> is called once per package; however, it is called
  94  just before cloning starts, and in the context of the parent thread. If it
  95  returns a true value, then no objects of that class will be cloned. See
  96  L<perlmod> for details. (Contributed by Dave Mitchell.)
  97  
  98  =head2 C<${^CHILD_ERROR_NATIVE}>
  99  
 100  A new internal variable, C<${^CHILD_ERROR_NATIVE}>, gives the native
 101  status returned by the last pipe close, backtick command, successful call
 102  to wait() or waitpid(), or from the system() operator. See L<perlrun> for
 103  details. (Contributed by Gisle Aas.)
 104  
 105  =head2 Assertions
 106  
 107  The support for assertions, introduced in perl 5.9.0, has been improved.
 108  The syntax for the C<-A> command-line switch has changed; it now accepts
 109  an optional module name, defaulting to C<assertions::activate>. See
 110  L<assertions> and L<perlrun>. (Contributed by Salvador Fandiño García.)
 111  
 112  =head2 Unicode Character Database 4.1.0
 113  
 114  The copy of the Unicode Character Database included in Perl 5.9 has
 115  been updated to 4.1.0.
 116  
 117  =head2 C<no VERSION>
 118  
 119  You can now use C<no> followed by a version number to specify that you
 120  want to use a version of perl older than the specified one.
 121  
 122  =head2 Recursive sort subs
 123  
 124  You can now use recursive subroutines with sort(), thanks to Robin Houston.
 125  
 126  =head2 Effect of pragmas in eval
 127  
 128  The compile-time value of the C<%^H> hint variable can now propagate into
 129  eval("")uated code. This makes it more useful to implement lexical
 130  pragmas.
 131  
 132  As a side-effect of this, the overloaded-ness of constants now propagates
 133  into eval("").
 134  
 135  =head2 New B<-E> command-line switch
 136  
 137  B<-E> is equivalent to B<-e>, but it implicitly enables all
 138  optional features (like C<use feature ":5.10">).
 139  
 140  =head2 C<chdir>, C<chmod> and C<chown> on filehandles
 141  
 142  C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
 143  filenames, if the system supports respectively C<fchdir>, C<fchmod> and
 144  C<fchown>, thanks to a patch provided by Gisle Aas.
 145  
 146  =head2 OS groups
 147  
 148  C<$(> and C<$)> now return groups in the order where the OS returns them,
 149  thanks to Gisle Aas. This wasn't previously the case.
 150  
 151  =head1 Modules and Pragmata
 152  
 153  =head2 New Core Modules
 154  
 155  =over 4
 156  
 157  =item *
 158  
 159  A new pragma, C<feature>, has been added; see above in L</"Core
 160  Enhancements">.
 161  
 162  =item *
 163  
 164  C<assertions::compat>, also available on CPAN, allows the use of assertions on
 165  perl versions prior to 5.9.0 (that is the first one to natively support
 166  them).
 167  
 168  =item *
 169  
 170  C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
 171  C<Math::BigInt::Calc>.
 172  
 173  =item *
 174  
 175  C<Compress::Zlib> is an interface to the zlib compression library. It
 176  comes with a bundled version of zlib, so having a working zlib is not a
 177  prerequisite to install it. It's used by C<Archive::Tar> (see below).
 178  
 179  =item *
 180  
 181  C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
 182  
 183  =item *
 184  
 185  C<Archive::Tar> is a module to manipulate C<tar> archives.
 186  
 187  =item *
 188  
 189  C<Digest::SHA> is a module used to calculate many types of SHA digests,
 190  has been included for SHA support in the CPAN module.
 191  
 192  =item *
 193  
 194  C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
 195  
 196  =back
 197  
 198  =head1 Utility Changes
 199  
 200  =head2 C<ptar>
 201  
 202  C<ptar> is a pure perl implementation of C<tar>, that comes with
 203  C<Archive::Tar>.
 204  
 205  =head2 C<ptardiff>
 206  
 207  C<ptardiff> is a small script used to generate a diff between the contents
 208  of a tar archive and a directory tree. Like C<ptar>, it comes with
 209  C<Archive::Tar>.
 210  
 211  =head2 C<shasum>
 212  
 213  This command-line utility, used to print or to check SHA digests, comes
 214  with the new C<Digest::SHA> module.
 215  
 216  =head2 C<h2xs> enhancements
 217  
 218  C<h2xs> implements a new option C<--use-xsloader> to force use of
 219  C<XSLoader> even in backwards compatible modules.
 220  
 221  The handling of authors' names that had apostrophes has been fixed.
 222  
 223  Any enums with negative values are now skipped.
 224  
 225  =head2 C<perlivp> enhancements
 226  
 227  C<perlivp> no longer checks for F<*.ph> files by default.  Use the new C<-a>
 228  option to run I<all> tests.
 229  
 230  =head1 Documentation
 231  
 232  =head2 Perl Glossary
 233  
 234  The L<perlglossary> manpage is a glossary of terms used in the Perl
 235  documentation, technical and otherwise, kindly provided by O'Reilly Media,
 236  Inc.
 237  
 238  L<perltodo> now lists a rough roadmap to Perl 5.10.
 239  
 240  =head1 Performance Enhancements
 241  
 242  =head2 XS-assisted SWASHGET
 243  
 244  Some pure-perl code that perl was using to retrieve Unicode properties and
 245  transliteration mappings has been reimplemented in XS.
 246  
 247  =head2 Constant subroutines
 248  
 249  The interpreter internals now support a far more memory efficient form of
 250  inlineable constants. Storing a reference to a constant value in a symbol
 251  table is equivalent to a full typeglob referencing a constant subroutine,
 252  but using about 400 bytes less memory. This proxy constant subroutine is
 253  automatically upgraded to a real typeglob with subroutine if necessary.
 254  The approach taken is analogous to the existing space optimisation for
 255  subroutine stub declarations, which are stored as plain scalars in place
 256  of the full typeglob.
 257  
 258  Several of the core modules have been converted to use this feature for
 259  their system dependent constants - as a result C<use POSIX;> now takes about
 260  200K less memory.
 261  
 262  =head2 C<PERL_DONT_CREATE_GVSV>
 263  
 264  The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
 265  in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
 266  from creating an empty scalar with every new typeglob. See L<perl588delta>
 267  for details.
 268  
 269  =head2 Weak references are cheaper
 270  
 271  Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
 272  Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
 273  happens at program exit, it may be skipped completely.
 274  
 275  =head2 sort() enhancements
 276  
 277  Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
 278  and to speed up some cases.
 279  
 280  =head1 Installation and Configuration Improvements
 281  
 282  =head2 Compilation improvements
 283  
 284  Parallel makes should work properly now, although there may still be problems
 285  if C<make test> is instructed to run in parallel.
 286  
 287  Building with Borland's compilers on Win32 should work more smoothly. In
 288  particular Steve Hay has worked to side step many warnings emitted by their
 289  compilers and at least one C compiler internal error.
 290  
 291  Perl extensions on Windows now can be statically built into the Perl DLL,
 292  thanks to a work by Vadim Konovalov.
 293  
 294  =head2 New Or Improved Platforms
 295  
 296  Perl is being ported to Symbian OS. See L<perlsymbian> for more
 297  information.
 298  
 299  The VMS port has been improved. See L<perlvms>.
 300  
 301  DynaLoader::dl_unload_file() now works on Windows.
 302  
 303  Portability of Perl on various recent compilers on Windows has been
 304  improved (Borland C++, Visual C++ 7.0).
 305  
 306  =head2 New probes
 307  
 308  C<Configure> will now detect C<clearenv> and C<unsetenv>, thanks to a
 309  patch from Alan Burlison. It will also probe for C<futimes> (and use it
 310  internally if available), and whether C<sprintf> correctly returns the
 311  length of the formatted string.
 312  
 313  =head2 Module auxiliary files
 314  
 315  README files and changelogs for CPAN modules bundled with perl are no
 316  longer installed.
 317  
 318  =head1 Selected Bug Fixes
 319  
 320  =head2 C<defined $$x>
 321  
 322  C<use strict "refs"> was ignoring taking a hard reference in an argument
 323  to defined(), as in :
 324  
 325      use strict "refs";
 326      my $x = "foo";
 327      if (defined $$x) {...}
 328  
 329  This now correctly produces the run-time error C<Can't use string as a
 330  SCALAR ref while "strict refs" in use>. (However, C<defined @$foo> and
 331  C<defined %$foo> are still allowed. Those constructs are discouraged
 332  anyway.)
 333  
 334  =head2 Calling CORE::require()
 335  
 336  CORE::require() and CORE::do() were always parsed as require() and do()
 337  when they were overridden. This is now fixed.
 338  
 339  =head2 Subscripts of slices
 340  
 341  You can now use a non-arrowed form for chained subscripts after a list
 342  slice, like in:
 343  
 344      ({foo => "bar"})[0]{foo}
 345  
 346  This used to be a syntax error; a C<< -> >> was required.
 347  
 348  =head2 Remove over-optimisation
 349  
 350  Perl 5.9.2 introduced a change so that assignments of C<undef> to a
 351  scalar, or of an empty list to an array or a hash, were optimised out. As
 352  this could cause problems when C<goto> jumps were involved, this change
 353  was backed out.
 354  
 355  =head2 sprintf() fixes
 356  
 357  Using the sprintf() function with some formats could lead to a buffer
 358  overflow in some specific cases. This has been fixed, along with several
 359  other bugs, notably in bounds checking.
 360  
 361  In related fixes, it was possible for badly written code that did not follow
 362  the documentation of C<Sys::Syslog> to have formatting vulnerabilities.
 363  C<Sys::Syslog> has been changed to protect people from poor quality third
 364  party code.
 365  
 366  =head2 no warnings 'category' works correctly with -w
 367  
 368  Previously when running with warnings enabled globally via C<-w>, selective
 369  disabling of specific warning categories would actually turn off all warnings.
 370  This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
 371  C<io> class. Previously it would erroneously turn off all warnings.
 372  
 373  =head2 Smaller fixes
 374  
 375  =over 4
 376  
 377  =item *
 378  
 379  C<FindBin> now works better with directories where access rights are more
 380  restrictive than usual.
 381  
 382  =item *
 383  
 384  Several memory leaks in ithreads were closed. Also, ithreads were made
 385  less memory-intensive.
 386  
 387  =item *
 388  
 389  Trailing spaces are now trimmed from C<$!> and C<$^E>.
 390  
 391  =item *
 392  
 393  Operations that require perl to read a process' list of groups, such as reads
 394  of C<$(> and C<$)>, now dynamically allocate memory rather than using a
 395  fixed sized array. The fixed size array could cause C stack exhaustion on
 396  systems configured to use large numbers of groups.
 397  
 398  =item *
 399  
 400  C<PerlIO::scalar> now works better with non-default C<$/> settings.
 401  
 402  =item *
 403  
 404  The C<x> repetition operator is now able to operate on C<qw//> lists. This
 405  used to raise a syntax error.
 406  
 407  =item *
 408  
 409  The debugger now traces correctly execution in eval("")uated code that
 410  contains #line directives.
 411  
 412  =item *
 413  
 414  The value of the C<open> pragma is no longer ignored for three-argument
 415  opens.
 416  
 417  =item *
 418  
 419  Perl will now use the C library calls C<unsetenv> and C<clearenv> if present
 420  to delete keys from C<%ENV> and delete C<%ENV> entirely, thanks to a patch
 421  from Alan Burlison.
 422  
 423  =back
 424  
 425  =head2 More Unicode Fixes
 426  
 427  =over 4
 428  
 429  =item *
 430  
 431  chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
 432  character, unless when the C<bytes> pragma is in effect, where the low
 433  eight bytes of the value are used.
 434  
 435  =item *
 436  
 437  Some case insensitive matches between UTF-8 encoded data and 8 bit regexps,
 438  and vice versa, could give malformed character warnings. These have been
 439  fixed by Dave Mitchell and Yves Orton.
 440  
 441  =item *
 442  
 443  C<lcfirst> and C<ucfirst> could corrupt the string for certain cases where
 444  the length UTF-8 encoding of the string in lower case, upper case or title
 445  case differed. This was fixed by Nicholas Clark.
 446  
 447  =back
 448  
 449  =head1 New or Changed Diagnostics
 450  
 451  =head2 Attempt to set length of freed array
 452  
 453  This is a new warning, produced in situations like the following one:
 454  
 455      $r = do {my @a; \$#a};
 456      $$r = 503;
 457  
 458  =head2 Non-string passed as bitmask
 459  
 460  This is a new warning, produced when number has been passed as a argument to
 461  select(), instead of a bitmask.
 462  
 463      # Wrong, will now warn
 464      $rin = fileno(STDIN);
 465      ($nfound,$timeleft) = select($rout=$rin, undef, undef, $timeout);
 466      
 467      # Should be
 468      $rin = '';
 469      vec($rin,fileno(STDIN),1) = 1;
 470      ($nfound,$timeleft) = select($rout=$rin, undef, undef, $timeout);
 471  
 472  =head2 Search pattern not terminated or ternary operator parsed as search pattern
 473  
 474  This syntax error indicates that the lexer couldn't find the final
 475  delimiter of a C<?PATTERN?> construct. Mentioning the ternary operator in
 476  this error message makes syntax diagnostic easier.
 477  
 478  =head2 "%s" variable %s masks earlier declaration
 479  
 480  This warning is now emitted in more consistent cases; in short, when one
 481  of the declarations involved is a C<my> variable:
 482  
 483      my $x;   my $x;    # warns
 484      my $x;  our $x;    # warns
 485      our $x;  my $x;    # warns
 486  
 487  On the other hand, the following:
 488  
 489      our $x; our $x;
 490  
 491  now gives a C<"our" variable %s redeclared> warning.
 492  
 493  =head2 readdir()/closedir()/etc. attempted on invalid dirhandle
 494  
 495  These new warnings are now emitted when a dirhandle is used but is
 496  either closed or not really a dirhandle.
 497  
 498  =head1 Changed Internals
 499  
 500  In general, the source code of perl has been refactored, tied up, and
 501  optimized in many places. Also, memory management and allocation has been
 502  improved in a couple of points.
 503  
 504  Andy Lester supplied many improvements to determine which function
 505  parameters and local variables could actually be declared C<const> to the C
 506  compiler. Steve Peters provided new C<*_set> macros and reworked the core to
 507  use these rather than assigning to macros in LVALUE context.
 508  
 509  Dave Mitchell improved the lexer debugging output under C<-DT>.
 510  
 511  A new file, F<mathoms.c>, has been added. It contains functions that are
 512  no longer used in the perl core, but that remain available for binary or
 513  source compatibility reasons. However, those functions will not be
 514  compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
 515  
 516  The C<AvFLAGS> macro has been removed.
 517  
 518  The C<av_*()> functions, used to manipulate arrays, no longer accept null
 519  C<AV*> parameters.
 520  
 521  =head2 B:: modules inheritance changed
 522  
 523  The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
 524  inherits from C<B::SV> (it used to inherit from C<B::IV>).
 525  
 526  =head1 Reporting Bugs
 527  
 528  If you find what you think is a bug, you might check the articles
 529  recently posted to the comp.lang.perl.misc newsgroup and the perl
 530  bug database at http://bugs.perl.org/ .  There may also be
 531  information at http://www.perl.org/ , the Perl Home Page.
 532  
 533  If you believe you have an unreported bug, please run the B<perlbug>
 534  program included with your release.  Be sure to trim your bug down
 535  to a tiny but sufficient test case.  Your bug report, along with the
 536  output of C<perl -V>, will be sent off to perlbug@perl.org to be
 537  analysed by the Perl porting team.
 538  
 539  =head1 SEE ALSO
 540  
 541  The F<Changes> file for exhaustive details on what changed.
 542  
 543  The F<INSTALL> file for how to build Perl.
 544  
 545  The F<README> file for general stuff.
 546  
 547  The F<Artistic> and F<Copying> files for copyright information.
 548  
 549  =cut