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 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.)
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
· A new pragma, "feature", has been added; see above in "Core
Enhancements".
· "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).
· "Math::BigInt::FastCalc" is an XS-enabled, and thus faster, version
of "Math::BigInt::Calc".
· "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).
· "IO::Zlib" is an "IO::"-style interface to "Compress::Zlib".
· "Archive::Tar" is a module to manipulate "tar" archives.
· "Digest::SHA" is a module used to calculate many types of SHA
digests, has been included for SHA support in the CPAN module.
· "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.
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.
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.
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
· "FindBin" now works better with directories where access rights are
more restrictive than usual.
· Several memory leaks in ithreads were closed. Also, ithreads were
made less memory-intensive.
· Trailing spaces are now trimmed from $! and $^E.
· 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.
· "PerlIO::scalar" now works better with non-default $/ settings.
· The "x" repetition operator is now able to operate on "qw//" lists.
This used to raise a syntax error.
· The debugger now traces correctly execution in eval("")uated code
that contains #line directives.
· The value of the "open" pragma is no longer ignored for three-
argument opens.
· 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
· 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.
· 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.
· "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.
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.