=head1 NAME perldelta - what's new for perl5.004 =head1 DESCRIPTION This document describes differences between the 5.003 release (as documented in I, second edition--the Camel Book) and this one. =head1 Supported Environments Perl5.004 builds out of the box on Unix, Plan9, LynxOS, VMS, OS/2, QNX, and AmigaOS. =head1 Core Changes Most importantly, many bugs were fixed. See the F file in the distribution for details. =head2 Compilation Option: Binary Compatibility With 5.003 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. =head2 New Opcode Module and Revised Safe Module 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. =head2 Internal Change: FileHandle Deprecated Filehandles are now stored internally as type IO::Handle. Although C and C<*STDOUT{FILEHANDLE}> are still supported for backwards compatibility, C (or C or C) and C<*STDOUT{IO}> are the way of the future. =head2 Internal Change: PerlIO internal IO abstraction interface It is now possible to build Perl with AT&T's sfio IO package instead of stdio. See L for more details, and the F file for how to use it. =head2 New and Changed Built-in Variables =over =item $^E Extended error message under some platforms ($EXTENDED_OS_ERROR if you C). =item $^H The current set of syntax checks enabled by C. See the documentation of C for more details. Not actually new, but newly documented. Because it is intended for internal use by Perl core components, there is no C long name for this variable. =item $^M By default, running out of memory it is not trappable. However, if compiled for this, Perl may use the contents of C<$^M> as an emergency pool after die()ing with this message. Suppose that your Perl were compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then $^M = 'a' x (1<<16); would allocate a 64K buffer for use when in emergency. See the F file for information on how to enable this option. As a disincentive to casual use of this advanced feature, there is no C long name for this variable. =back =head2 New and Changed Built-in Functions =over =item delete on slices This now works. (e.g. C) =item flock is now supported on more platforms, and prefers fcntl to lockf when emulating. =item keys as an lvalue As an lvalue, C allows you to increase the number of hash buckets allocated for the given associative array. 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 C<%hash> will have at least 200 buckets allocated for it. These buckets will be retained even if you do C<%hash = ()>; use C if you want to free the storage while C<%hash> is still in scope. You can't shrink the number of buckets allocated for the hash using C in this way (but you needn't worry about doing this by accident, as trying has no effect). =item my() in Control Structures You can now use my() (with or without the parentheses) in the control expressions of control structures such as: while (my $line = <>) { $line = lc $line; } continue { print $line; } if ((my $answer = ) =~ /^y(es)?$/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. =item unpack() and pack() A new format 'w' represents a BER compressed integer (as defined in ASN.1). Its format is a sequence of one or more bytes, each of which provides seven bits of the total value, with the most significant first. Bit eight of each byte is set, except for the last byte, in which bit eight is clear. =item use VERSION If the first argument to C 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 C occurs at compile time, this check happens immediately during the compilation process, unlike C, which waits until run-time for the check. This is often useful if you need to check the current Perl version before Cing library modules which have changed in incompatible ways from older versions of Perl. (We try not to do this more than we have to.) =item use Module VERSION LIST If the VERSION argument is present between Module and LIST, then the C 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. =item prototype(FUNCTION) Returns the prototype of a function as a string (or C 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.) =item $_ as Default Functions documented in the Camel to default to $_ now in fact do, and all those that do are so documented in L. =item C does not trigger a pos() reset on failure The C match iteration construct used to reset the iteration when it failed to match (so that the next C match would start at the beginning of the string). You now have to explicitly do a C to reset the "last match" position, or modify the string in some way. This change makes it practical to chain C matches together in conjunction with ordinary matches using the C<\G> zero-width assertion. See L and L. =item nested C closures work now Prior to the 5.004 release, nested anonymous functions didn't work right. They do now. =item formats work right on changing lexicals Just like anonymous functions that contain lexical variables that change (like a lexical index variable for a C loop), formats now work properly. For example, this silently failed before, and is fine now: my $i; foreach $i ( 1 .. 10 ) { format = my i is @# $i . write; } =back =head2 New Built-in Methods The C package automatically contains the following methods that are inherited by all other classes: =over =item isa(CLASS) C returns I if its object is blessed into a sub-class of C C is also exportable and can be called as a sub with two arguments. This allows the ability to check what a reference points to. Example: use UNIVERSAL qw(isa); if(isa($ref, 'ARRAY')) { ... } =item can(METHOD) C checks to see if its object has a method called C, if it does then a reference to the sub is returned; if it does not then I is returned. =item VERSION( [NEED] ) C 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 C form of C. use A 1.2 qw(some imported subs); # implies: A->VERSION(1.2); =item class() C returns the class name of its object. =item is_instance() C returns true if its object is an instance of some class, false if its object is the class (package) itself. Example A->is_instance(); # False $var = 'A'; $var->is_instance(); # False $ref = bless [], 'A'; $ref->is_instance(); # True This can be useful for methods that wish to easily distinguish whether they were invoked as class or as instance methods. sub some_meth { my $classname = shift; if ($classname->is_instance()) { die "unexpectedly called as instance not class method"; } ..... } =back B C directly uses Perl's internal code for method lookup, and C 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 C in order to make these methods available to your program. This is necessary only if you wish to have C available as a plain subroutine in the current package. =head2 TIEHANDLE Now Supported See L for other kinds of tie()s. =over =item TIEHANDLE classname, LIST This is the constructor for the class. That means it is expected to return an object of some sort. The reference can be used to hold some internal information. sub TIEHANDLE { print "\n"; my $i; return bless \$i, shift; } =item PRINT this, LIST This method will be triggered every time the tied handle is printed to. Beyond its self reference it also expects the list that was passed to the print function. sub PRINT { $r = shift; $$r++; return print join( $, => map {uc} @_), $\; } =item READLINE this This method will be called when the handle is read from. The method should return undef when there is no more data. sub READLINE { $r = shift; return "PRINT called $$r times\n"; } =item DESTROY this As with the other types of ties, this method will be called when the tied handle is about to be destroyed. This is useful for debugging and possibly for cleaning up. sub DESTROY { print "\n"; } =back =item Efficiency Enhancements All hash keys with the same string are only allocated once, so even if you have 100 copies of the same hash, the immutable keys never have to be re-allocated. Functions that have an empty prototype and that do nothing but return a fixed value are now inlined (e.g. C). =head1 Pragmata Three new pragmatic modules exist: =over =item use blib =item use blib 'dir' Looks for MakeMaker-like I<'blib'> directory structure starting in I (or current directory) and working back up to five levels of parent directories. Intended for use on command line with B<-M> option as a way of testing arbitrary scripts against an uninstalled version of a package. =item use locale Tells the compiler to enable (or disable) the use of POSIX locales for built-in operations. When C 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 formating in printf and sprintf (but B in print). LC_NUMERIC is always used in write, since lexical scoping of formats is problematic at best. Each C or C 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 L for more information. =item use ops Disable unsafe opcodes, or any named opcodes, when compiling Perl code. =back =head1 Modules =head2 Fcntl 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. C). =head2 Module Information Summary Brand new modules, arranged by topic rather than strictly alphabetically: CPAN interface to Comprehensive Perl Archive Network CPAN::FirstTime create a CPAN configuration file CPAN::Nox run 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 Fatal.pm Make do-or-die equivalents of functions FindBin.pm Find path of currently executing program Class/Template.pm Structure/member template builder File/stat.pm Object-oriented wrapper around CORE::stat Net/hostent.pm Object-oriented wrapper around CORE::gethost* Net/netent.pm Object-oriented wrapper around CORE::getnet* Net/protoent.pm Object-oriented wrapper around CORE::getproto* Net/servent.pm Object-oriented wrapper around CORE::getserv* Time/gmtime.pm Object-oriented wrapper around CORE::gmtime Time/localtime.pm Object-oriented wrapper around CORE::localtime Time/tm.pm Perl implementation of "struct tm" for {gm,local}time User/grent.pm Object-oriented wrapper around CORE::getgr* User/pwent.pm Object-oriented wrapper around CORE::getpw* Tie/RefHash.pm Base class for tied hashes with references as keys UNIVERSAL.pm Base class for *ALL* classes =head2 IO The IO module provides a simple mechanism to load all of 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. =head2 Math::Complex 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 cbrt root tan cotan asin acos atan acotan sinh cosh tanh cotanh asinh acosh atanh acotanh cplx cplxe =head2 DB_File There have been quite a few changes made to DB_File. Here are a few of the highlights: =over =item * Fixed a handful of bugs. =item * By public demand, added support for the standard hash function exists(). =item * Made it compatible with Berkeley DB 1.86. =item * Made negative subscripts work with RECNO interface. =item * Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default mode from 0640 to 0666. =item * Made DB_File automatically import the open() constants (O_RDWR, O_CREAT etc.) from Fcntl, if available. =item * Updated documentation. =back 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. =head2 Net::Ping Major rewrite - support added for both udp echo and real icmp pings. =head2 Overridden Built-ins Many of the Perl built-ins 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); =head1 Utility Changes =head2 xsubpp =over =item C XSUBs now default to returning nothing Due to a documentation/implementation bug in previous versions of Perl, XSUBs with a return type of C 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 C, 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 C. For backward compatibility, I tries to guess whether a C XSUB is really C or if it wants to return an C. It does so by examining the text of the XSUB: if I finds what looks like an assignment to C, it assumes that the XSUB's return type is really C. =back =head1 C Language API Changes =over =item C and C The C 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 C. Instead, you should use the C macro on the GV to extract its CV, and pass the CV to C. The most likely symptom of passing the result of C to C is Perl's producing an "Undefined subroutine called" error on the I call to a given method (since there is no cache on the first call). =back =head1 Documentation Changes Many of the base and library pods were updated. These new pods are included in section 1: =over =item L This document. =item L Locale support (internationalization and localization). =item L Tutorial on Perl OO programming. =item L Perl internal IO abstraction interface. =item L Although not new, this has been massively updated. =item L Although not new, this has been massively updated. =back =head1 New Diagnostics 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 (non-trappable). (A) An alien error message (not generated by Perl). =over =item "my" variable %s masks earlier declaration in same scope (S) A lexical variable has been redeclared in the same scope, effectively eliminating all access to the previous instance. This is almost always a typographical error. Note that the earlier variable will still exist until the end of the scope or until all closure referents to it are destroyed. =item %s argument is not a HASH element or slice (F) The argument to 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"} =item Allocation too large: %lx (X) You can't allocate more than 64K on an MSDOS machine. =item Allocation too large (F) You can't allocate more than 2^31+"small amount" bytes. =item Attempt to free non-existent shared string (P) Perl maintains a reference counted internal table of strings to optimize the storage and access of hash keys and other strings. This indicates someone tried to decrement the reference count of a string that can no longer be found in the table. =item Attempt to use reference as lvalue in substr (W) You supplied a reference as the first argument to substr() used as an lvalue, which is pretty strange. Perhaps you forgot to dereference it first. See L. =item Unsupported function fork (F) Your version of executable does not support forking. 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 C, C, and so on. =item Ill-formed logical name |%s| in prime_env_iter (W) A warning peculiar to VMS. A logical name was encountered when preparing to iterate over %ENV which violates the syntactic rules governing logical names. Since it cannot be translated normally, it is skipped, and will not appear in %ENV. This may be a benign occurrence, as some software packages might directly modify logical name tables and introduce non-standard names, or it may indicate that a logical name table has been corrupted. =item Can't use bareword ("%s") as %s ref while "strict refs" in use (F) Only hard references are allowed by "strict refs". Symbolic references are disallowed. See L. =item Constant subroutine %s redefined (S) You redefined a subroutine which had previously been eligible for inlining. See L for commentary and workarounds. =item Died (F) You passed die() an empty string (the equivalent of C) or you called it with no args and both C<$@> and C<$_> were empty. =item Integer overflow in hex number (S) The literal hex number you have specified is too big for your architecture. On a 32-bit architecture the largest hex literal is 0xFFFFFFFF. =item Integer overflow in octal number (S) The literal octal number you have specified is too big for your architecture. On a 32-bit architecture the largest octal literal is 037777777777. =item Name "%s::%s" used only once: possible typo (W) Typographical errors often show up as unique variable names. If you had a good reason for having a unique name, then just mention it again somehow to suppress the message (the C pragma is provided for just this purpose). =item Null picture in formline (F) The first argument to formline must be a valid format picture specification. It was found to be empty, which probably means you supplied it an uninitialized value. See L. =item Offset outside string (F) You tried to do a read/write/send/recv operation with an offset pointing outside the buffer. This is difficult to imagine. The sole exception to this is that Cing past the buffer will extend the buffer and zero pad the new area. =item Stub found while resolving method `%s' overloading `%s' in package `%s' (P) Overloading resolution over @ISA tree may be broken by importing stubs. Stubs should never be implicitely created, but explicit calls to C may break this. =item Cannot resolve method `%s' overloading `%s' in package `s' (P) Internal error trying to resolve overloading specified by a method name (as opposed to a subroutine reference). =item Out of memory! (X|F) The 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 C<$^M> as an emergency pool after die()ing with this message. In this case the error is trappable I. =item Out of memory during request for %s (F) The 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. =item Possible attempt to put comments in qw() list (W) qw() 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 exclamation marks 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 ); =item Possible attempt to separate words with commas (W) 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 !; =item Scalar value @%s{%s} better written as $%s{%s} (W) You've used a hash slice (indicated by @) to select a single element of a hash. Generally it's better to ask for a scalar value (indicated by $). The difference is that C<$foo{&bar}> always behaves like a scalar, both when assigning to it and when evaluating its argument, while C<@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. =item untie attempted while %d inner references still exist (W) A copy of the object returned from C (or C) was still valid when C was called. =item Value of %s construct can be "0"; test with defined() (W) In a conditional expression, you used , <*> (glob), or C 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 C operator. =item Variable "%s" may be unavailable (W) An inner (nested) I subroutine is inside a I subroutine, and outside that is another subroutine; and the anonymous (innermost) subroutine is referencing a lexical variable defined in the outermost subroutine. For example: sub outermost { my $a; sub middle { sub { $a } } } If the anonymous subroutine is called or referenced (directly or indirectly) from the outermost subroutine, it will share the variable as you would expect. But if the anonymous subroutine is called or referenced when the outermost subroutine is not active, it will see the value of the shared variable as it was before and during the *first* call to the outermost subroutine, which is probably not what you want. In these circumstances, it is usually best to make the middle subroutine anonymous, using the C syntax. Perl has specific support for shared variables in nested anonymous subroutines; a named subroutine in between interferes with this feature. =item Variable "%s" will not stay shared (W) An inner (nested) I subroutine is referencing a lexical variable defined in an outer subroutine. When the inner subroutine is called, it will probably see the value of the outer subroutine's variable as it was before and during the *first* call to the outer subroutine; in this case, after the first call to the outer subroutine is complete, the inner and outer subroutines will no longer share a common value for the variable. In other words, the variable will no longer be shared. Furthermore, if the outer subroutine is anonymous and references a lexical variable outside itself, then the outer and inner subroutines will I share the given variable. This problem can usually be solved by making the inner subroutine anonymous, using the C syntax. When inner anonymous subs that reference variables in outer subroutines are called or referenced, they are automatically re-bound to the current values of such variables. =item Warning: something's wrong (W) You passed warn() an empty string (the equivalent of C) or you called it with no args and C<$_> was empty. =item Got an error from DosAllocMem (P) An error peculiar to OS/2. Most probably you're using an obsolete version of Perl, and this should not happen anyway. =item Malformed PERLLIB_PREFIX (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form prefix1;prefix2 or prefix1 prefix2 with non-empty prefix1 and prefix2. If C 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 L. =item PERL_SH_DIR too long (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the C-shell in. See L. =item Process terminated by SIG%s (W) This is a standard message issued by OS/2 applications, while *nix applications die in silence. It is considered a feature of the OS/2 port. One can easily disable this by appropriate sighandlers, see L. See L. =back =head1 BUGS 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 B 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 C, will be sent off to perlbug@perl.com to be analysed by the Perl porting team. =head1 SEE ALSO The F file for exhaustive details on what changed. The F file for how to build Perl. This file has been significantly updated for 5.004, so even veteran users should look through it. The F file for general stuff. The F file for copyright information. =head1 HISTORY Constructed by Tom Christiansen, grabbing material with permission from innumerable contributors, with kibitzing by more than a few Perl porters. Last update: Tue Jan 14 14:03:02 EST 1997