| perl5004delta - what's new for perl5.004 |
AUTOLOAD for non-methods$)wantarray may return undefeval EXPR determines value of EXPR in scalar context
perl5004delta - what's new for perl5.004
This document describes differences between the 5.003 release (as documented in Programming Perl, second edition--the Camel Book) and this one.
Perl5.004 builds out of the box on Unix, Plan 9, LynxOS, VMS, OS/2, QNX, AmigaOS, and Windows NT. Perl runs on Windows 95 as well, but it cannot be built there, for lack of a reasonable command interpreter.
Most importantly, many bugs were fixed, including several security problems. See the Changes file in the distribution for details.
%ENV = () and %ENV = @list now work as expected (except on VMS
where it generates a fatal error).
The error ``Can't locate Foo.pm in @INC'' now lists the contents of @INC for easier debugging.
There is a new Configure question that asks if you want to maintain binary compatibility with Perl 5.003. If you choose binary compatibility, you do not have to recompile your extensions, but you might have symbol conflicts if you embed Perl in another application, just as in the 5.003 release. By default, binary compatibility is preserved at the expense of symbol table pollution.
You may now put Perl options in the $PERL5OPT environment variable. Unless Perl is running with taint checks, it will interpret this variable as if its contents had appeared on a ``#!perl'' line at the beginning of your script, except that hyphens are optional. PERL5OPT may only be used to set the following switches: -[DIMUdmw].
The -M and -m options are no longer allowed on the #! line of
a script. If a script needs a module, it should invoke it with the
use pragma.
The -T option is also forbidden on the #! line of a script,
unless it was present on the Perl command line. Due to the way #!
works, this usually means that -T must be in the first argument.
Thus:
#!/usr/bin/perl -T -w
will probably work for an executable script invoked as scriptname,
while:
#!/usr/bin/perl -w -T
will probably fail under the same conditions. (Non-Unix systems will
probably not follow this rule.) But perl scriptname is guaranteed
to fail, since then there is no chance of -T being found on the
command line before it is found on the #! line.
If you removed the -w option from your Perl 5.003 scripts because it made Perl too verbose, we recommend that you try putting it back when you upgrade to Perl 5.004. Each new perl version tends to remove some undesirable warnings, while adding new warnings that may catch bugs in your scripts.
AUTOLOAD for non-methodsBefore Perl 5.004, AUTOLOAD functions were looked up as methods
(using the @ISA hierarchy), even when the function to be autoloaded
was called as a plain function (e.g. Foo::bar()), not a method
(e.g. Foo->bar() or $obj->bar()).
Perl 5.005 will use method lookup only for methods' AUTOLOADs.
However, there is a significant base of existing code that may be using
the old behavior. So, as an interim step, Perl 5.004 issues an optional
warning when a non-method uses an inherited AUTOLOAD.
The simple rule is: Inheritance will not work when autoloading
non-methods. The simple fix for old code is: In any module that used to
depend on inheriting AUTOLOAD for non-methods from a base class named
BaseClass, execute *AUTOLOAD = \&BaseClass::AUTOLOAD during startup.
Using %OVERLOAD to define overloading was deprecated in 5.003. Overloading is now defined using the overload pragma. %OVERLOAD is still used internally but should not be used by Perl scripts. See the overload manpage for more details.
In Perl 5.004, nonexistent array and hash elements used as subroutine
parameters are brought into existence only if they are actually
assigned to (via @_).
Earlier versions of Perl vary in their handling of such arguments. Perl versions 5.002 and 5.003 always brought them into existence. Perl versions 5.000 and 5.001 brought them into existence only if they were not the first argument (which was almost certainly a bug). Earlier versions of Perl never brought them into existence.
For example, given this code:
undef @a; undef %a;
sub show { print $_[0] };
sub change { $_[0]++ };
show($a[2]);
change($a{b});
After this code executes in Perl 5.004, $a{b} exists but $a[2] does not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed (but $a[2]'s value would have been undefined).
$)The $) special variable has always (well, in Perl 5, at least)
reflected not only the current effective group, but also the group list
as returned by the getgroups() C function (if there is one).
However, until this release, there has not been a way to call the
setgroups() C function from Perl.
In Perl 5.004, assigning to $) is exactly symmetrical with examining
it: The first number in its string value is used as the effective gid;
if there are any numbers after the first one, they are passed to the
setgroups() C function (if there is one).
Perl versions before 5.004 misinterpreted any type marker followed by ``$'' and a digit. For example, ``$$0'' was incorrectly taken to mean ``${$}0'' instead of ``${$0}''. This bug is (mostly) fixed in Perl 5.004.
However, the developers of Perl 5.004 could not fix this bug completely, because at least two widely-used modules depend on the old meaning of ``$$0'' in a string. So Perl 5.004 still interprets ``$$<digit>'' in the old (broken) way inside strings; but it generates this message as a warning. And in Perl 5.005, this special treatment will cease.
Perl versions before 5.004 did not always properly localize the regex-related special variables. Perl 5.004 does localize them, as the documentation has always said it should. This may result in $1, $2, etc. no longer being set where existing programs use them.
The documentation for Perl 5.0 has always stated that $. is not
reset when an already-open file handle is reopened with no intervening
call to close. Due to a bug, perl versions 5.000 through 5.003
did reset $. under that circumstance; Perl 5.004 does not.
wantarray may return undefThe wantarray operator returns true if a subroutine is expected to
return a list, and false otherwise. In Perl 5.004, wantarray can
also return the undefined value if a subroutine's return value will
not be used at all, which allows subroutines to avoid a time-consuming
calculation of a return value if it isn't going to be used.
eval EXPR determines value of EXPR in scalar contextPerl (version 5) used to determine the value of EXPR inconsistently, sometimes incorrectly using the surrounding context for the determination. Now, the value of EXPR (before being parsed by eval) is always determined in a scalar context. Once parsed, it is executed as before, by providing the context that the scope surrounding the eval provided. This change makes the behavior Perl4 compatible, besides fixing bugs resulting from the inconsistent behavior. This program:
@a = qw(time now is time);
print eval @a;
print '|', scalar eval @a;
used to print something like ``timenowis881399109|4'', but now (and in perl4) prints ``4|4''.
A bug in previous versions may have failed to detect some insecure
conditions when taint checks are turned on. (Taint checks are used
in setuid or setgid scripts, or when explicitly turned on with the
-T invocation option.) Although it's unlikely, this may cause a
previously-working script to now fail, which should be construed
as a blessing since that indicates a potentially-serious security
hole was just plugged.
The new restrictions when tainting include:
glob() or <*>
A new Opcode module supports the creation, manipulation and application of opcode masks. The revised Safe module has a new API and is implemented using the new Opcode module. Please read the new Opcode and Safe documentation.
In older versions of Perl it was not possible to create more than one Perl interpreter instance inside a single process without leaking like a sieve and/or crashing. The bugs that caused this behavior have all been fixed. However, you still must take care when embedding Perl in a C program. See the updated perlembed manpage for tips on how to manage your interpreters.
File handles are now stored internally as type IO::Handle. The FileHandle module is still supported for backwards compatibility, but it is now merely a front end to the IO::* modules, specifically IO::Handle, IO::Seekable, and IO::File. We suggest, but do not require, that you use the IO::* modules in new code.
In harmony with this change, *GLOB{FILEHANDLE} is now just a
backward-compatible synonym for *GLOB{IO}.
It is now possible to build Perl with AT&T's sfio IO package instead of stdio. See the perlapio manpage for more details, and the INSTALL file for how to use it.
This new syntax follows the pattern of $hashref->{FOO} and
$aryref->[$foo]: You may now write &$subref($foo) as
$subref->($foo). All these arrow terms may be chained;
thus, &{$table->{FOO}}($bar) may now be written
$table->{FOO}->($bar).
package; directive). Like
__FILE__ and __LINE__, __PACKAGE__ does not interpolate
into strings.
use English).
use strict. See the
documentation of strict for more details. Not actually new, but
newly documented.
Because it is intended for internal use by Perl core components,
there is no use English long name for this variable.
$^M as an emergency
pool after die()ing with this message. Suppose that your Perl were
compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. Then
$^M = 'a' x (1<<16);
would allocate a 64K buffer for use when in emergency.
See the INSTALL file for information on how to enable this option.
As a disincentive to casual use of this advanced feature,
there is no use English long name for this variable.
delete @ENV{'PATH', 'MANPATH'})
sprintf() any more, except for floating-point
numbers, and even then only known flags are allowed. As a result, it
is now possible to know which conversions and flags will work, and
what they will do.
The new conversions in Perl's sprintf() are:
%i a synonym for %d
%p a pointer (the address of the Perl value, in hexadecimal)
%n special: *stores* the number of characters output so far
into the next variable in the parameter list
The new flags that go between the % and the conversion are:
# prefix octal with "0", hex with "0x" h interpret integer as C type "short" or "unsigned short" V interpret integer as Perl's standard integer type
Also, where a number would appear in the flags, an asterisk (``*'') may be used instead, in which case Perl uses the next item in the parameter list as the given number (that is, as the field width or precision). If a field width obtained through ``*'' is negative, it has the same effect as the '-' flag: left-justification.
See sprintf in the perlfunc manpage for a complete list of conversion and flags.
keys allows you to increase the number of hash buckets
allocated for the given hash. This can gain you a measure of efficiency if
you know the hash is going to get big. (This is similar to pre-extending
an array by assigning a larger number to $#array.) If you say
keys %hash = 200;
then %hash will have at least 200 buckets allocated for it. These
buckets will be retained even if you do %hash = (); use undef
%hash if you want to free the storage while %hash is still in scope.
You can't shrink the number of buckets allocated for the hash using
keys in this way (but you needn't worry about doing this by accident,
as trying has no effect).
my() in Control Structuresmy() (with or without the parentheses) in the control
expressions of control structures such as:
while (defined(my $line = <>)) {
$line = lc $line;
} continue {
print $line;
}
if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
user_agrees();
} elsif ($answer =~ /^n(o)?$/i) {
user_disagrees();
} else {
chomp $answer;
die "`$answer' is neither `yes' nor `no'";
}
Also, you can declare a foreach loop control variable as lexical by preceding it with the word ``my''. For example, in:
foreach my $i (1, 2, 3) {
some_function();
}
$i is a lexical variable, and the scope of $i extends to the end of the loop, but not beyond it.
Note that you still cannot use my() on global punctuation variables
such as $_ and the like.
pack() and unpack()If 'p' or 'P' are given undef as values, they now generate a NULL pointer.
Both pack() and unpack() now fail when their templates contain invalid
types. (Invalid types used to be ignored.)
sysseek()sysseek() operator is a variant of seek() that sets and gets the
file's system read/write position, using the lseek(2) system call. It is
the only reliable way to seek before using sysread() or syswrite(). Its
return value is the new position, or the undefined value on failure.
use is a number, it is treated as a version
number instead of a module name. If the version of the Perl interpreter
is less than VERSION, then an error message is printed and Perl exits
immediately. Because use occurs at compile time, this check happens
immediately during the compilation process, unlike require VERSION,
which waits until runtime for the check. This is often useful if you
need to check the current Perl version before useing library modules
which have changed in incompatible ways from older versions of Perl.
(We try not to do this more than we have to.)
use will call the VERSION method in class Module with the given
version as an argument. The default VERSION method, inherited from
the UNIVERSAL class, croaks if the given version is larger than the
value of the variable $Module::VERSION. (Note that there is not a
comma after VERSION!)
This version-checking mechanism is similar to the one currently used in the Exporter module, but it is faster and can be used with modules that don't use the Exporter. It is the recommended method for new code.
prototype(FUNCTION)undef if the
function has no prototype). FUNCTION is a reference to or the name of the
function whose prototype you want to retrieve.
(Not actually new; just never documented before.)
srand, which used to be time, has been changed.
Now it's a heady mix of difficult-to-predict system-dependent values,
which should be sufficient for most everyday purposes.
Previous to version 5.004, calling rand without first calling srand
would yield the same sequence of random numbers on most or all machines.
Now, when perl sees that you're calling rand and haven't yet called
srand, it calls srand with the default seed. You should still call
srand manually if your code might ever be run on a pre-5.004 system,
of course, or if you want a seed other than the default.
m//gc does not reset search position on failurem//g match iteration construct has always reset its target
string's search position (which is visible through the pos operator)
when a match fails; as a result, the next m//g match after a failure
starts again at the beginning of the string. With Perl 5.004, this
reset may be disabled by adding the ``c'' (for ``continue'') modifier,
i.e. m//gc. This feature, in conjunction with the \G zero-width
assertion, makes it possible to chain matches together. See the perlop manpage
and the perlre manpage.
m//x ignores whitespace before ?*+{}m//x construct has always been intended to ignore all unescaped
whitespace. However, before Perl 5.004, whitespace had the effect of
escaping repeat modifiers like ``*'' or ``?''; for example, /a *b/x was
(mis)interpreted as /a\*b/x. This bug has been fixed in 5.004.
sub{} closures work nowforeach loop),
formats now work properly. For example, this silently failed
before (printed only zeros), but is fine now:
my $i;
foreach $i ( 1 .. 10 ) {
write;
}
format =
my i is @#
$i
.
However, it still fails (without a warning) if the foreach is within a subroutine:
my $i;
sub foo {
foreach $i ( 1 .. 10 ) {
write;
}
}
foo;
format =
my i is @#
$i
.
The UNIVERSAL package automatically contains the following methods that
are inherited by all other classes:
isa(CLASS)isa returns true if its object is blessed into a subclass of CLASS
isa is also exportable and can be called as a sub with two arguments. This
allows the ability to check what a reference points to. Example:
use UNIVERSAL qw(isa);
if(isa($ref, 'ARRAY')) {
...
}
can(METHOD)can checks to see if its object has a method called METHOD,
if it does then a reference to the sub is returned; if it does not then
undef is returned.
VERSION returns the version number of the class (package). If the
NEED argument is given then it will check that the current version (as
defined by the $VERSION variable in the given package) not less than
NEED; it will die if this is not the case. This method is normally
called as a class method. This method is called automatically by the
VERSION form of use.
use A 1.2 qw(some imported subs);
# implies:
A->VERSION(1.2);
NOTE: can directly uses Perl's internal code for method lookup, and
isa uses a very similar method and caching strategy. This may cause
strange effects if the Perl code dynamically changes @ISA in any package.
You may add other methods to the UNIVERSAL class via Perl or XS code.
You do not need to use UNIVERSAL in order to make these methods
available to your program. This is necessary only if you wish to
have isa available as a plain subroutine in the current package.
See the perltie manpage for other kinds of tie()s.
sub TIEHANDLE {
print "<shout>\n";
my $i;
return bless \$i, shift;
}
sub PRINT {
$r = shift;
$$r++;
return print join( $, => map {uc} @_), $\;
}
printf() function.
Beyond its self reference it also expects the format and list that was
passed to the printf function.
sub PRINTF {
shift;
my $fmt = shift;
print sprintf($fmt, @_)."\n";
}
read
or sysread functions.
sub READ {
$r = shift;
my($buf,$len,$offset) = @_;
print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
}
sub READLINE {
$r = shift;
return "PRINT called $$r times\n"
}
getc function is called.
sub GETC { print "Don't GETC, Get Perl"; return "a"; }
sub DESTROY {
print "</shout>\n";
}
If perl is compiled with the malloc included with the perl distribution
(that is, if perl -V:d_mymalloc is 'define') then you can print
memory statistics at runtime by running Perl thusly:
env PERL_DEBUG_MSTATS=2 perl your_script_here
The value of 2 means to print statistics after compilation and on exit; with a value of 1, the statistics are printed only on exit. (If you want the statistics at an arbitrary time, you'll need to install the optional module Devel::Peek.)
Three new compilation flags are recognized by malloc.c. (They have no
effect if perl is compiled with system malloc().)
$^M. See $^M.
PACK_MALLOC is defined, perl uses
a slightly different algorithm for small allocations (up to 64 bytes
long), which makes it possible to have overhead down to 1 byte for
allocations which are powers of two (and appear quite often).
Expected memory savings (with 8-byte alignment in alignbytes) is
about 20% for typical Perl usage. Expected slowdown due to additional
malloc overhead is in fractions of a percent (hard to measure, because
of the effect of saved memory on speed).
PACK_MALLOC, this macro improves allocations of data
with size close to a power of two; but this works for big allocations
(starting with 16K by default). Such allocations are typical for big
hashes and special-purpose scripts, especially image processing.
On recent systems, the fact that perl requires 2M from system for 1M allocation will not affect speed of execution, since the tail of such a chunk is not going to be touched (and thus will not require real memory). However, it may result in a premature out-of-memory error. So if you will be manipulating very large blocks with sizes close to powers of two, it would be wise to define this macro.
Expected saving of memory is 0-100% (100% in applications which require most memory in such 2**n chunks); expected slowdown is negligible.
Functions that have an empty prototype and that do nothing but return
a fixed value are now inlined (e.g. sub PI () { 3.14159 }).
Each unique hash key is only allocated once, no matter how many hashes have an entry with that key. So even if you have 100 copies of the same hash, the hash keys never have to be reallocated.
Support for the following operating systems is new in Perl 5.004.
Perl 5.004 now includes support for building a ``native'' perl under Windows NT, using the Microsoft Visual C++ compiler (versions 2.0 and above) or the Borland C++ compiler (versions 5.02 and above). The resulting perl can be used under Windows 95 (if it is installed in the same directory locations as it got installed in Windows NT). This port includes support for perl extension building tools like the ExtUtils::MakeMaker manpage and h2xs, so that many extensions available on the Comprehensive Perl Archive Network (CPAN) can now be readily built under Windows NT. See http://www.perl.com/ for more information on CPAN and README.win32 in the perl distribution for more details on how to get started with building this port.
There is also support for building perl under the Cygwin32 environment. Cygwin32 is a set of GNU tools that make it possible to compile and run many Unix programs under Windows NT by providing a mostly Unix-like interface for compilation and execution. See README.cygwin32 in the perl distribution for more details on this port and how to obtain the Cygwin32 toolkit.
See README.plan9 in the perl distribution.
See README.qnx in the perl distribution.
See README.amigaos in the perl distribution.
Six new pragmatic modules exist:
require MODULE until someone calls one of the specified
subroutines (which must be exported by MODULE). This pragma should be
used with caution, and only when necessary.
Intended for use on command line with -M option as a way of testing arbitrary scripts against an uninstalled version of a package.
When use locale is in effect, the current LC_CTYPE locale is used
for regular expressions and case mapping; LC_COLLATE for string
ordering; and LC_NUMERIC for numeric formatting in printf and sprintf
(but not in print). LC_NUMERIC is always used in write, since
lexical scoping of formats is problematic at best.
Each use locale or no locale affects statements to the end of
the enclosing BLOCK or, if not inside a BLOCK, to the end of the
current file. Locales can be switched and queried with
POSIX::setlocale().
See the perllocale manpage for more information.
$? and
system return genuine VMS status values instead of emulating POSIX;
'exit', which makes exit take a genuine VMS status value instead of
assuming that exit 1 is an error; and 'time', which makes all times
relative to the local time zone, in the VMS tradition.
Though Perl 5.004 is compatible with almost all modules that work with Perl 5.003, there are a few exceptions:
Module Required Version for Perl 5.004
------ -------------------------------
Filter Filter-1.12
LWP libwww-perl-5.08
Tk Tk400.202 (-w makes noise)
Also, the majordomo mailing list program, version 1.94.1, doesn't work with Perl 5.004 (nor with perl 4), because it executes an invalid regular expression. This bug is fixed in majordomo version 1.94.2.
The installperl script now places the Perl source files for extensions in the architecture-specific library directory, which is where the shared libraries for extensions have always been. This change is intended to allow administrators to keep the Perl 5.004 library directory unchanged from a previous version, without running the risk of binary incompatibility between extensions' Perl source and shared libraries.
Brand new modules, arranged by topic rather than strictly alphabetically:
CGI.pm Web server interface ("Common Gateway Interface")
CGI/Apache.pm Support for Apache's Perl module
CGI/Carp.pm Log server errors with helpful context
CGI/Fast.pm Support for FastCGI (persistent server process)
CGI/Push.pm Support for server push
CGI/Switch.pm Simple interface for multiple server types
CPAN Interface to Comprehensive Perl Archive Network
CPAN::FirstTime Utility for creating CPAN configuration file
CPAN::Nox Runs CPAN while avoiding compiled extensions
IO.pm Top-level interface to IO::* classes
IO/File.pm IO::File extension Perl module
IO/Handle.pm IO::Handle extension Perl module
IO/Pipe.pm IO::Pipe extension Perl module
IO/Seekable.pm IO::Seekable extension Perl module
IO/Select.pm IO::Select extension Perl module
IO/Socket.pm IO::Socket extension Perl module
Opcode.pm Disable named opcodes when compiling Perl code
ExtUtils/Embed.pm Utilities for embedding Perl in C programs
ExtUtils/testlib.pm Fixes up @INC to use just-built extension
FindBin.pm Find path of currently executing program
Class/Struct.pm Declare struct-like datatypes as Perl classes
File/stat.pm By-name interface to Perl's builtin stat
Net/hostent.pm By-name interface to Perl's builtin gethost*
Net/netent.pm By-name interface to Perl's builtin getnet*
Net/protoent.pm By-name interface to Perl's builtin getproto*
Net/servent.pm By-name interface to Perl's builtin getserv*
Time/gmtime.pm By-name interface to Perl's builtin gmtime
Time/localtime.pm By-name interface to Perl's builtin localtime
Time/tm.pm Internal object for Time::{gm,local}time
User/grent.pm By-name interface to Perl's builtin getgr*
User/pwent.pm By-name interface to Perl's builtin getpw*
Tie/RefHash.pm Base class for tied hashes with references as keys
UNIVERSAL.pm Base class for *ALL* classes
New constants in the existing Fcntl modules are now supported, provided that your operating system happens to support them:
F_GETOWN F_SETOWN
O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
O_EXLOCK O_SHLOCK
These constants are intended for use with the Perl operators sysopen()
and fcntl() and the basic database modules like SDBM_File. For the
exact meaning of these and other Fcntl constants please refer to your
operating system's documentation for fcntl() and open().
In addition, the Fcntl module now provides these constants for use with the Perl operator flock():
LOCK_SH LOCK_EX LOCK_NB LOCK_UN
These constants are defined in all environments (because where there is
no flock() system call, Perl emulates it). However, for historical
reasons, these constants are not exported unless they are explicitly
requested with the ``:flock'' tag (e.g. use Fcntl ':flock').
The IO module provides a simple mechanism to load all the IO modules at one go. Currently this includes:
IO::Handle
IO::Seekable
IO::File
IO::Pipe
IO::Socket
For more information on any of these modules, please see its respective documentation.
The Math::Complex module has been totally rewritten, and now supports more operations. These are overloaded:
+ - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
And these functions are now exported:
pi i Re Im arg
log10 logn ln cbrt root
tan
csc sec cot
asin acos atan
acsc asec acot
sinh cosh tanh
csch sech coth
asinh acosh atanh
acsch asech acoth
cplx cplxe
This new module provides a simpler interface to parts of Math::Complex for those who need trigonometric functions only for real numbers.
There have been quite a few changes made to DB_File. Here are a few of the highlights:
open() constants (O_RDWR,
O_CREAT etc.) from Fcntl, if available.
Updated documentation.
Refer to the HISTORY section in DB_File.pm for a complete list of changes. Everything after DB_File 1.01 has been added since 5.003.
Major rewrite - support added for both udp echo and real icmp pings.
Many of the Perl builtins returning lists now have object-oriented overrides. These are:
File::stat
Net::hostent
Net::netent
Net::protoent
Net::servent
Time::gmtime
Time::localtime
User::grent
User::pwent
For example, you can now say
use File::stat;
use User::pwent;
$his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
void XSUBs now default to returning nothingvoid have actually been
returning one value. Usually that value was the GV for the XSUB,
but sometimes it was some already freed or reused value, which would
sometimes lead to program failure.
In Perl 5.004, if an XSUB is declared as returning void, it
actually returns no value, i.e. an empty list (though there is a
backward-compatibility exception; see below). If your XSUB really
does return an SV, you should give it a return type of SV *.
For backward compatibility, xsubpp tries to guess whether a
void XSUB is really void or if it wants to return an SV *.
It does so by examining the text of the XSUB: if xsubpp finds
what looks like an assignment to ST(0), it assumes that the
XSUB's return type is really SV *.
gv_fetchmethod and perl_call_svgv_fetchmethod function finds a method for an object, just like
in Perl 5.003. The GV it returns may be a method cache entry.
However, in Perl 5.004, method cache entries are not visible to users;
therefore, they can no longer be passed directly to perl_call_sv.
Instead, you should use the GvCV macro on the GV to extract its CV,
and pass the CV to perl_call_sv.
The most likely symptom of passing the result of gv_fetchmethod to
perl_call_sv is Perl's producing an ``Undefined subroutine called''
error on the second call to a given method (since there is no cache
on the first call).
perl_eval_pvSV*s, so that tied hashes can be given
real scalars as keys rather than plain strings (nontied hashes still
can only use strings as keys). New extensions must use the new hash
access functions and macros if they wish to use SV* keys. These
additions also make it feasible to manipulate HE*s (hash entries),
which can be more efficient. See the perlguts manpage for details.
Many of the base and library pods were updated. These new pods are included in section 1:
Several new conditions will trigger warnings that were silent before. Some only affect certain platforms. The following new warnings and errors outline these. These messages are classified as follows (listed in increasing order of desperation):
(W) A warning (optional). (D) A deprecation (optional). (S) A severe warning (mandatory). (F) A fatal error (trappable). (P) An internal error you should never see (trappable). (X) A very fatal error (nontrappable). (A) An alien error message (not generated by Perl).
delete() must be either a hash element, such as
$foo{$bar}
$ref->[12]->{"susie"}
or a hash slice, such as
@foo{$bar, $baz, $xyzzy}
@{$ref->[12]}{"susie", "queue"}
scalar(%s)substr() used
as an lvalue, which is pretty strange. Perhaps you forgot to
dereference it first. See substr in the perlfunc manpage.
Foo::, but
the compiler saw no other uses of that namespace before that point.
Perhaps you need to predeclare a package?
sort { &func } @x instead of sort func @x.
die() an empty string (the equivalent of die "") or
you called it with no args and both $@ and $_ were empty.
$A::B). You've exceeded Perl's limits. Future versions of Perl are
likely to eliminate these arbitrary limitations.
print <<EOF;).
program(s) used for glob
and <*.c>. This may mean that your csh (C shell) is
broken. If so, you should change all of the csh-related variables in
config.sh: If you have tcsh, make the variables refer to it as if it
were csh (e.g. full_csh='/usr/bin/tcsh'); otherwise, make them all
empty (except that d_csh should be 'undef') so that Perl will
think csh is missing. In either case, after editing config.sh, run
./Configure -S and rebuild Perl.
use vars pragma is
provided for just this purpose).
sysread()ing past the buffer
will extend the buffer and zero pad the new area.
malloc() function returned 0, indicating there was insufficient
remaining memory (or virtual memory) to satisfy the request.
The request was judged to be small, so the possibility to trap it
depends on the way Perl was compiled. By default it is not trappable.
However, if compiled for this, Perl may use the contents of $^M as
an emergency pool after die()ing with this message. In this case the
error is trappable once.
malloc() function returned 0, indicating there was insufficient
remaining memory (or virtual memory) to satisfy the request. However,
the request was judged large enough (compile-time default is 64K), so
a possibility to shut down by trapping this error is granted.
frexp() failed, making printf(``%f'') impossible.
qw() listqw() lists contain items separated by whitespace; as with literal
strings, comment characters are not ignored, but are instead treated
as literal data. (You may have used different delimiters than the
parentheses shown here; braces are also frequently used.)
You probably wrote something like this:
@list = qw(
a # a comment
b # another comment
);
when you should have written this:
@list = qw(
a
b
);
If you really want comments, build your list the old-fashioned way, with quotes and commas:
@list = (
'a', # a comment
'b', # another comment
);
qw() lists contain items separated by whitespace; therefore commas
aren't needed to separate the items. (You may have used different
delimiters than the parentheses shown here; braces are also frequently
used.)
You probably wrote something like this:
qw! a, b, c !;
which puts literal commas into some of the list items. Write it without commas if you don't want them to appear in your data:
qw! a b c !;
$foo{&bar} always behaves like a scalar, both when
assigning to it and when evaluating its argument, while @foo{&bar} behaves
like a list when you assign to it, and provides a list context to its
subscript, which can do weird things if you're expecting only one subscript.
can
may break this.
tie (or tied) was still
valid when untie was called.
Note that under some systems, like OS/2, there may be different flavors of
Perl executables, some of which may support fork, some not. Try changing
the name you call Perl by to perl_, perl__, and so on.
However, the developers of Perl 5.004 could not fix this bug completely, because at least two widely-used modules depend on the old meaning of ``$$0'' in a string. So Perl 5.004 still interprets ``$$<digit>'' in the old (broken) way inside strings; but it generates this message as a warning. And in Perl 5.005, this special treatment will cease.
defined()each(),
or readdir() as a boolean value. Each of these constructs can return a
value of ``0''; that would make the conditional expression false, which is
probably not what you intended. When using these constructs in conditional
expressions, test their values with the defined operator.
sub outermost { my $a; sub middle { sub { $a } } }
If the anonymous subroutine is called or referenced (directly or indirectly) from the outermost subroutine, it will share the variable as you would expect. But if the anonymous subroutine is called or referenced when the outermost subroutine is not active, it will see the value of the shared variable as it was before and during the *first* call to the outermost subroutine, which is probably not what you want.
In these circumstances, it is usually best to make the middle
subroutine anonymous, using the sub {} syntax. Perl has specific
support for shared variables in nested anonymous subroutines; a named
subroutine in between interferes with this feature.
When the inner subroutine is called, it will probably see the value of the outer subroutine's variable as it was before and during the *first* call to the outer subroutine; in this case, after the first call to the outer subroutine is complete, the inner and outer subroutines will no longer share a common value for the variable. In other words, the variable will no longer be shared.
Furthermore, if the outer subroutine is anonymous and references a lexical variable outside itself, then the outer and inner subroutines will never share the given variable.
This problem can usually be solved by making the inner subroutine
anonymous, using the sub {} syntax. When inner anonymous subs that
reference variables in outer subroutines are called or referenced,
they are automatically rebound to the current values of such
variables.
warn() an empty string (the equivalent of warn "") or
you called it with no args and $_ was empty.
prefix1;prefix2
or
prefix1 prefix2
with nonempty prefix1 and prefix2. If prefix1 is indeed a prefix
of a builtin library search path, prefix2 is substituted. The error
may appear if components are not found, or are too long. See
``PERLLIB_PREFIX'' in README.os2.
sh-shell in. See ``PERL_SH_DIR'' in README.os2.
If you find what you think is a bug, you might check the headers of recently posted articles in the comp.lang.perl.misc newsgroup. There may also be information at http://www.perl.com/perl/ , the Perl Home Page.
If you believe you have an unreported bug, please run the perlbug
program included with your release. Make sure you 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.com> to be
analysed by the Perl porting team.
The Changes file for exhaustive details on what changed.
The INSTALL file for how to build Perl. This file has been significantly updated for 5.004, so even veteran users should look through it.
The README file for general stuff.
The Copying file for copyright information.
Constructed by Tom Christiansen, grabbing material with permission from innumerable contributors, with kibitzing by more than a few Perl porters.
Last update: Wed May 14 11:14:09 EDT 1997
| perl5004delta - what's new for perl5.004 |