=head1 DESCRIPTION
This document describes differences between the 5.9.2 and the 5.9.3
-develop
ement releases. See L<perl590delta>, L<perl591delta> and
+development releases. See L<perl590delta>, L<perl591delta> and
L<perl592delta> for the differences between 5.8.0 and 5.9.2.
=head1 Incompatible Changes
-The 4-argument form of select() now returns C<undef> on error (instead of
--1).
+=head2 Parsing of C<-f _>
+
+The identifier C<_> is now forced to be a bareword after a filetest
+operator. This solves a number of misparsing issues when a global C<_>
+subroutine is defined.
+
+=head2 C<mkdir()>
+
+C<mkdir()> without arguments now defaults to C<$_>.
+
+=head2 Magic goto and eval
+
+The construct C<eval { goto &foo }> is now disallowed. (Note that the
+similar construct, but with C<eval("")> instead, was already forbidden.)
+
+=head2 C<$#> has been removed
+
+The deprecated C<$#> variable (output format for numbers) has been
+removed. A new warning, C<$# is no longer supported>, has been added.
+
+=head2 C<:unique>
+
+The C<:unique> attribute has been made a no-op, since its current
+implementation was fundamentally flawed and not threadsafe.
+
+=head2 Scoping of the C<sort> pragma
+
+The C<sort> pragma is now lexically scoped. Its effect used to be global.
=head1 Core Enhancements
+=head2 The C<feature> pragma
+
+The C<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 C<strict> or C<warnings>.
+
+Currently the following new features are available: C<switch> (adds a
+switch statement), C<~~> (adds a Perl 6-like smart match operator), C<say>
+(adds a C<say> built-in function), and C<err> (adds an C<err> keyword).
+Those features are described below.
+
+Note that C<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 regular keyword).
+
+Those features, and the C<feature> pragma itself, have been contributed by
+Robin Houston.
+
+=head2 Switch and Smart Match operator
+
+Perl 5 now has a switch statement. It's available when C<use feature
+'switch'> is in effect. This feature introduces three new keywords,
+C<given>, C<when>, and C<default>:
+
+ given ($foo) {
+ when (/^abc/) { $abc = 1; }
+ when (/^def/) { $def = 1; }
+ when (/^xyz/) { $xyz = 1; }
+ default { $nothing = 1; }
+ }
+
+A more complete description of how Perl matches the switch variable
+against the C<when> conditions is given in L<perlsyn/"Switch statements">.
+
+This kind of match is called I<smart match>, and it's also possible to use
+it outside of switch statements, via the new C<~~> operator (enabled via
+the C<use feature '~~'> directive). See L<perlsyn/"Smart matching in
+detail">.
+
+=head2 C<say()>
+
+say() is a new built-in, only available when C<use feature 'say'> is in
+effect, that is similar to print(), but that implicitly appends a newline
+to the printed string. See L<perlfunc/say>.
+
+=head2 C<CLONE_SKIP()>
+
+Perl has now support for the C<CLONE_SKIP> special subroutine. Like
+C<CLONE>, C<CLONE_SKIP> is called once per package; however, it is called
+just before cloning starts, and in the context of the parent thread. If it
+returns a true value, then no objects of that class will be cloned. See
+L<perlmod> for details. (Contributed by Dave Mitchell.)
+
+=head2 C<${^CHILD_ERROR_NATIVE}>
+
+A new internal variable, C<${^CHILD_ERROR_NATIVE}>, gives the native
+status returned by the last pipe close, backtick command, successful call
+to wait() or waitpid(), or from the system() operator. See L<perlrun> for
+details. (Contributed by Gisle Aas.)
+
+=head2 Assertions
+
+The support for assertions, introduced in perl 5.9.0, has been improved.
+The syntax for the C<-A> command-line switch has changed; it now accepts
+an optional module name, defaulting to C<assertions::activate>. See
+L<assertions> and L<perlrun>. (Contributed by Salvador Fandiño García.)
+
+=head2 Unicode Character Database 4.1.0
+
+The copy of the Unicode Character Database included in Perl 5.9 has
+been updated to 4.1.0.
+
+=head2 C<no VERSION>
+
+You can now use C<no> followed by a version number to specify that you
+want to use a version of perl inferior to the specified one.
+
+=head2 Recursive sort subs
+
+You can now use recursive subroutines with sort(), thanks to Robin Houston.
+
+=head2 Effect of pragmas in eval
+
+The compile-time value of the C<%^H> hint variable can now propagate into
+eval("")uated code. This makes it more useful to implement lexical
+pragmas.
+
+As a side-effect of this, the overloaded-ness of constants now propagates
+into eval("").
+
+=head2 New B<-E> command-line switch
+
+B<-E> is equivalent to B<-e>, but it implicitly enables all
+optional features (like C<use feature ":5.10">).
+
+=head2 C<chdir>, C<chmod> and C<chown> on filehandles
+
+C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
+filenames, if the system supports respectively C<fchdir>, C<fchmod> and
+C<fchown>, thanks to a patch provided by Gisle Aas.
+
+=head2 OS groups
+
+C<$(> and C<$)> now return groups in the order where the OS returns them,
+thanks to Gisle Aas. This wasn't previously the case.
+
=head1 Modules and Pragmata
+=head2 New Core Modules
+
+=over 4
+
+=item *
+
+A new pragma, C<feature>, has been added; see above in L</"Core
+Enhancements">.
+
+=item *
+
+C<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).
+
+=item *
+
+C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
+C<Math::BigInt::Calc>.
+
+=item *
+
+C<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 C<Archive::Tar> (see below).
+
+=item *
+
+C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
+
+=item *
+
+C<Archive::Tar> is a module to manipulate C<tar> archives.
+
+=item *
+
+C<Digest::SHA> is a module used to calculate many types of SHA digests,
+has been included for SHA support in the CPAN module.
+
+=item *
+
+C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
+
+=back
+
=head1 Utility Changes
+=head2 C<ptar>
+
+C<ptar> is a pure perl implementation of C<tar>, that comes with
+C<Archive::Tar>.
+
+=head2 C<ptardiff>
+
+C<ptardiff> is a small script used to generate a diff between the contents
+of a tar archive and a directory tree. Like C<ptar>, it comes with
+C<Archive::Tar>.
+
+=head2 C<shasum>
+
+This command-line utility, used to print or to check SHA digests, comes
+with the new C<Digest::SHA> module.
+
+=head2 C<h2xs> enhancements
+
+C<h2xs> implements a new option C<--use-xsloader> to force use of
+C<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.
+
+=head2 C<perlivp> enhancements
+
+C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
+option to run I<all> tests.
+
=head1 Documentation
+=head2 Perl Glossary
+
+The L<perlglossary> manpage is a glossary of terms used in the Perl
+documentation, technical and otherwise, kindly provided by O'Reilly Media,
+Inc.
+
+L<perltodo> now lists a rough roadmap to Perl 5.10.
+
=head1 Performance Enhancements
+=head2 XS-assisted SWASHGET
+
+Some pure-perl code that perl was using to retrieve Unicode properties and
+transliteration mappings has been reimplemented in XS.
+
+=head2 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 C<use POSIX;> now takes about
+200K less memory.
+
+=head2 C<PERL_DONT_CREATE_GVSV>
+
+The new compilation flag C<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 L<perl588delta>
+for details.
+
+=head2 Weak references are cheaper
+
+Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
+Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
+happens at program exit, it may be skipped completely.
+
+=head2 sort() enhancements
+
+Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
+and to speed up some cases.
+
=head1 Installation and Configuration Improvements
+=head2 Compilation improvements
+
+Parallel makes should work properly now, although there may still be problems
+if C<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.
+
+=head2 New Or Improved Platforms
+
+Perl is being ported to Symbian OS. See L<perlsymbian> for more
+information.
+
+The VMS port has been improved. See L<perlvms>.
+
+DynaLoader::dl_unload_file() now works on Windows.
+
+Portability of Perl on various recent compilers on Windows has been
+improved (Borland C++, Visual C++ 7.0).
+
+=head2 New probes
+
+C<Configure> will now detect C<clearenv> and C<unsetenv>, thanks to a
+patch from Alan Burlison. It will also probe for C<futimes> (and use it
+internally if available), and whether C<sprintf> correctly returns the
+length of the formatted string.
+
+=head2 Module auxiliary files
+
+README files and changelogs for CPAN modules bundled with perl are no
+longer installed.
+
=head1 Selected Bug Fixes
+=head2 C<defined $$x>
+
+C<use strict "refs"> was ignoring taking a hard reference in an argument
+to defined(), as in :
+
+ use strict "refs";
+ my $x = "foo";
+ if (defined $$x) {...}
+
+This now correctly produces the run-time error C<Can't use string as a
+SCALAR ref while "strict refs" in use>. (However, C<defined @$foo> and
+C<defined %$foo> are still allowed. Those constructs are discouraged
+anyway.)
+
+=head2 Calling CORE::require()
+
+CORE::require() and CORE::do() were always parsed as require() and do()
+when they were overridden. This is now fixed.
+
+=head2 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 C<< -> >> was required.
+
+=head2 Remove over-optimisation
+
+Perl 5.9.2 introduced a change so that assignments of C<undef> to a
+scalar, or of an empty list to an array or a hash, were optimised out. As
+this could cause problems when C<goto> jumps were involved, this change
+was backed out.
+
+=head2 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.
+
+In related fixes, it was possible for badly written code that did not follow
+the documentation of C<Sys::Syslog> to have formatting vulnerabilities.
+C<Sys::Syslog> has been changed to protect people from poor quality third
+party code.
+
+=head2 no warnings 'category' works correctly with -w
+
+Previously when running with warnings enabled globally via C<-w>, selective
+disabling of specific warning categories would actually turn off all warnings.
+This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
+C<io> class. Previously it would erroneously turn off all warnings.
+
+=head2 Smaller fixes
+
+=over 4
+
+=item *
+
+C<FindBin> now works better with directories where access rights are more
+restrictive than usual.
+
+=item *
+
+Several memory leaks in ithreads were closed. Also, ithreads were made
+less memory-intensive.
+
+=item *
+
+Trailing spaces are now trimmed from C<$!> and C<$^E>.
+
+=item *
+
+Operations that require perl to read a process' list of groups, such as reads
+of C<$(> and C<$)>, 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.
+
+=item *
+
+C<PerlIO::scalar> now works better with non-default C<$/> settings.
+
+=item *
+
+The C<x> repetition operator is now able to operate on C<qw//> lists. This
+used to raise a syntax error.
+
+=item *
+
+The debugger now traces correctly execution in eval("")uated code that
+contains #line directives.
+
+=item *
+
+The value of the C<open> pragma is no longer ignored for three-argument
+opens.
+
+=item *
+
+Perl will now use the C library calls C<unsetenv> and C<clearenv> if present
+to delete keys from C<%ENV> and delete C<%ENV> entirely, thanks to a patch
+from Alan Burlison.
+
+=back
+
+=head2 More Unicode Fixes
+
+=over 4
+
+=item *
+
+chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
+character, unless when the C<bytes> pragma is in effect, where the low
+eight bytes of the value are used.
+
+=item *
+
+Some case insensitive matches between UTF-8 encoded data and 8 bit regexps,
+and vice versa, could give malformed character warnings. These have been
+fixed by Dave Mitchell and Yves Orton.
+
+=item *
+
+C<lcfirst> and C<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.
+
+=back
+
=head1 New or Changed Diagnostics
+=head2 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;
+
+=head2 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);
+
+=head2 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 C<?PATTERN?> construct. Mentioning the ternary operator in
+this error message makes syntax diagnostic easier.
+
+=head2 "%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 C<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 C<"our" variable %s redeclared> warning.
+
+=head2 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.
+
=head1 Changed Internals
-=head1 Known Problems
+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 C<const> to the C
+compiler. Steve Peters provided new C<*_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 C<-DT>.
+
+A new file, F<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 C<-DNO_MATHOMS> in the compiler flags.
+
+The C<AvFLAGS> macro has been removed.
+
+The C<av_*()> functions, used to manipulate arrays, no longer accept null
+C<AV*> parameters.
+
+=head2 B:: modules inheritance changed
-=head2 Platform Specific Problems
+The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
+inherits from C<B::SV> (it used to inherit from C<B::IV>).
=head1 Reporting Bugs
https://perl5.git.perl.org / perl5.git / blobdiff