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.
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.
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's 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.