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[perl5.git] / pod / perldelta.pod

=head1 NAME

perldelta - what's new for perl5.005

=head1 DESCRIPTION

This document describes differences between the 5.004 release and this one.

[XXX this needs more verbose summaries of the sub topics, instead of just
the "See foo."  Scheduled for a second iteration. GSAR]

=head1 About the new versioning system

=head1 Incompatible Changes

=head2 WARNING:  This version is not binary compatible with Perl 5.004.

Starting with Perl 5.004_50 there were many deep and far-reaching changes
to the language internals.  If you have dynamically loaded extensions
that you built under perl 5.003 or 5.004, you can continue to use them
with 5.004, but you will need to rebuild and reinstall those extensions
to use them 5.005.  See L<INSTALL> for detailed instructions on how to
upgrade.

=head2 Default installation structure has changed

The new Configure defaults are designed to allow a smooth upgrade from
5.004 to 5.005, but you should read L<INSTALL> for a detailed
discussion of the changes in order to adapt them to your system.

=head2 Perl Source Compatibility

When none of the experimental features are enabled, there should be
no user-visible Perl source compatibility issue.

If threads are enabled, then some caveats apply. C<@_> and C<$_> become
lexical variables.  The effect of this should be largely transparent to
the user, but there are some boundary conditions under which user will
need to be aware of the issues. [XXX Add e.g. here.]

Some new keywords have been introduced.  These are generally expected to
have very little impact on compatibility.  See L</New C<INIT> keyword>,
L</New C<lock> keyword>, and L</New C<qr//> operator>.

Certain barewords are now reserved.  Use of these will provoke a warning
if you have asked for them with the C<-w> switch.
See L</C<our> is now a reserved word>.

=head2 C Source Compatibility

=item Core sources now require ANSI C compiler

=item Enabling threads has source compatibility issues

=head2 Binary Compatibility

This version is NOT binary compatible with older versions.  All extensions
will need to be recompiled.

=head2 Security fixes may affect compatibility

A few taint leaks and taint omissions have been corrected.  This may lead
to "failure" of scripts that used to work with older versions.  Compiling
with -DINCOMPLETE_TAINTS provides a perl with minimal amounts of changes
to the tainting behavior.  But note that the resulting perl will have
known insecurities.

Oneliners with the C<-e> switch do not create temporary files anymore.

=head2 Relaxed new mandatory warnings introduced in 5.004

Many new warnings that were introduced in 5.004 have been made
optional.  Some of these warnings are still present, but perl's new
features make them less often a problem.  See L<New Diagnostics>.

=head2 Licensing

Perl has a new Social Contract for contributors.  See F<Porting/Contract>.

The license included in much of the Perl documentation has changed.
[XXX See where?]

=head1 Core Changes


=head2 Threads

WARNING: Threading is considered an experimental feature.  Details of the
implementation may change without notice.  There are known limitations
and and some bugs.

See L<README.threads>.

=head2 Compiler

WARNING: The Compiler and related tools are considered experimental.
Features may change without notice, and there are known limitations
and bugs.

The Compiler produces three different types of transformations of a
perl program.  The C backend generates C code that captures perl's state
just before execution begins.  It eliminates the compile-time overheads
of the regular perl interpreter, but the run-time performance remains
comparatively the same.  The CC backend generates optimized C code
equivivalent to the code path at run-time.  The CC backend has greater
potential for big optimizations, but only a few optimizations are
implemented currently.  The Bytecode backend generates a platform
independent bytecode representation of the interpreter's state
just before execution.  Thus, the Bytecode back end also eliminates
much of the compilation overhead of the interpreter.

The compiler comes with several valuable utilities.

C<B::Lint> is an experimental module to detect and warn about suspicious
code, especially the cases that the C<-w> switch does not detect.

C<B::Deparse> can be used to demystify perl code, and understand
how perl optimizes certain constructs.

C<B::Xref> generates cross reference reports of all definition and use
of variables, subroutines and formats in a program.

C<B::Showlex> show the lexical variables used by a subroutine or file
at a glance.

C<perlcc> is a simple frontend for compiling perl.

See C<ext/B/README>.

=head2 Regular Expressions

See L<perlre> and L<perlop>.

=head2   Improved malloc()

See banner at the beginning of C<malloc.c> for details.

=head2 Quicksort is internally implemented

See C<perlfunc/sort>.

=head2 Reliable signals

Two kinds.

Via C<Thread::Signal>.

Via switched runtime op loop.  [XXX Not yet available.]

=head2 Reliable stack pointers

The internals now reallocate the perl stack only at predictable times.
In particular, magic calls never trigger reallocations of the stack,
because all reentrancy of the runtime is handled using a "stack of stacks".
This should improve reliability of cached stack pointers in the internals
and in XSUBs.

=head2 Behavior of local() on composites is now well-defined

See L<perlfunc/local>.

=head2 C<%!> is transparently tied to the L<Errno> module

See L<perlvar>, and L<Errno>.

=head2 Pseudo-hashes are supported

See L<perlref>.

=head2 C<EXPR foreach EXPR> is supported

See L<perlsyn>.

=head2 Slice notation on glob elements is supported

[XXX See what?]

=head2 Keywords can be globally overridden

See L<perlsub>.

=head2 C<$^E> is meaningful on Win32

See L<perlvar>.

=head2 C<foreach (1..1000000)> optimized

C<foreach (1..1000000)> is now optimized into a counting loop.  It does
not try to allocate a 1000000-size list anymore.

=head2 C<Foo::> can be used as implicitly quoted package name

[XXX See what?]

=head2 C<exists $Foo::{Bar::}> tests existence of a package

[XXX See what?]

=head2 Better locale support

See L<perllocale>.

=head2 Experimental support for 64-bit platforms

Perl5 has always had 64-bit support on systems with 64-bit longs.
Starting with 5.005, the beginnings of experimental support for systems
with 32-bit long and 64-bit 'long long' integers has been added.
If you add -DUSE_LONG_LONG to your ccflags in config.sh (or manually
define it in perl.h) then perl will be built with 'long long' support.
There will be many compiler warnings, and the resultant perl may not
work on all systems.  There are many other issues related to
third-party extensions and libraries.  This option exists to allow
people to work on those issues.

=head2 prototype() returns useful results on builtins

See L<perlfunc/prototype>.

=head2 Extended support for exception handling

C<die()> now accepts a reference value, and C<$@> gets set to that
value in exception traps.  This makes it possible to propagate
exception objects.  See L<perlfunc/eval>.  [XXX there's nothing
about this in perlfunc/eval yet.]

=head2 Re-blessing in DESTROY() supported for chaining DESTROY() methods

See L<perlobj/Destructors>.

=head2 All C<printf> format conversions are handled internally

See L<perlfunc/printf>.

=head2 New C<INIT> keyword

C<INIT> subs are like C<BEGIN> and C<END>, but they get run just before
the perl runtime begins execution.  e.g., the Perl Compiler makes use of
C<INIT> blocks to initialize and resolve pointers to XSUBs.

[XXX Needs to be documented in perlsub or perlmod.]

=head2 New C<lock> keyword

The C<lock> keyword is the fundamental synchronization primitive
in threaded perl.  When threads are not enabled, it is currently a noop.

To minimize impact on source compatibility this keyword is "weak", i.e., any
user-defined subroutine of the same name overrides it, unless a C<use Thread>
has been seen.

=head2 New C<qr//> operator

The C<qr//> operator, which is syntactically similar to the other quote-like
operators, is used to create compiled regular expressions.  This compiled
form can now be explicitly passed around in variables, and interpolated in
other regular expressions.  See L<perlop> and L<perlre>.

=head2 C<our> is now a reserved word

=head2 Tied arrays are now fully supported

See L<Tie::Array>.

=head2 Tied handles support is better

Several missing hooks have been added.  There is also a new base class for
TIEARRAY implementations.  See L<Tie::Array>.


=head1 Supported Platforms

Configure has many incremental improvements.  Site-wide policy for building
perl can now be made persistent, via Policy.sh.  Configure also records
the command-line arguments used in F<config.sh>.

=head2 New Platforms

BeOS is now supported.  See L<README.beos>.

DOS is now supported under the DJGPP tools.  See L<README.dos>.

MPE/iX is now supported.  See L<README.mpeix>.

=head2 Changes in existing support

Win32 support has been vastly enhanced.  Support for Perl Object, a C++
encapsulation of Perl.  GCC and EGCS are now supported on Win32.
[XXX Perl Object needs a big explanation elsewhere, and a pointer to
that location here.]

VMS configuration system has been rewritten.  See L<README.vms>.

OpenBSD better supported.  [XXX what others?]

=head1 Modules and Pragmata

=head2 New Modules

=over

=item B

Perl compiler and tools.  See [XXX what?].

=item Data::Dumper

A module to pretty print Perl data.  See L<Data::Dumper>.

=item Errno

A module to look up errors more conveniently.  See L<Errno>.

=item File::Spec

A portable API for file operations.

=item ExtUtils::Installed

Query and manage installed modules.

=item ExtUtils::Packlist

Manipulate .packlist files.

=item Fatal

Make functions/builtins succeed or die.

=item IPC::SysV

Constants and other support infrastructure for System V IPC operations
in perl.

=item Test

A framework for writing testsuites.

=item Tie::Array

Base class for tied arrays.

=item Tie::Handle

Base class for tied handles.

=item Thread

Perl thread creation, manipulation, and support.

=item attrs

Set subroutine attributes.

=item fields

Compile-time class fields.

=item re

Various pragmata to control behavior of regular expressions.

=back

=head2 Changes in existing modules

=over

=item CGI

CGI has been updated to version 2.42.

=item POSIX

POSIX now has its own platform-specific hints files.

=item DB_File

DB_File supports version 2.x of Berkeley DB.  See C<ext/DB_File/Changes>.

=item MakeMaker

MakeMaker now supports writing empty makefiles, provides a way to
specify that site umask() policy should be honored.  There is also
better support for manipulation of .packlist files, and getting
information about installed modules.

Extensions that have both architecture-dependent and
architecture-independent files are now always installed completely in
the architecture-dependent locations.  Previously, the shareable parts
were shared both across architectures and across perl versions and were
therefore liable to be overwritten with newer versions that might have
subtle incompatibilities.

=item CPAN

[XXX What?]

=item Cwd

Cwd::cwd is faster on most platforms.

=item Benchmark

Keeps better time.

=back

=head1 Utility Changes

h2ph and related utilities have been vastly overhauled.

perlcc, a new experimental front end for the compiler is available.

The crude GNU configure emulator is now called configure.gnu.

=head1 API Changes

=head2 Incompatible Changes

=head2 Deprecations, Extensions

=head2 C++ Support

=head1 Documentation Changes

Config.pm now has a glossary of variables.

Porting/patching.pod has detailed instructions on how to create and
submit patches for perl.

=head1 New Diagnostics

=over

=item Ambiguous call resolved as CORE::%s(), qualify as such or use &

(W) A subroutine you have declared has the same name as a Perl keyword,
and you have used the name without qualification for calling one or the
other.  Perl decided to call the builtin because the subroutine is
not imported.

To force interpretation as a subroutine call, either put an ampersand
before the subroutine name, or qualify the name with its package.
Alternatively, you can import the subroutine (or pretend that it's
imported with the C<use subs> pragma).

To silently interpret it as the Perl operator, use the C<CORE::> prefix
on the operator (e.g. C<CORE::log($x)>) or by declaring the subroutine
to be an object method (see L<attrs>).

=item Bad index while coercing array into hash

(F) The index looked up in the hash found as the 0'th element of a
pseudo-hash is not legal.  Index values must be at 1 or greater.
See L<perlref>.

=item Bareword "%s" refers to nonexistent package

(W) You used a qualified bareword of the form C<Foo::>, but
the compiler saw no other uses of that namespace before that point.
Perhaps you need to predeclare a package?

=item Can't call method "%s" on an undefined value

(F) You used the syntax of a method call, but the slot filled by the
object reference or package name contains an undefined value.
Something like this will reproduce the error:

    $BADREF = 42;
    process $BADREF 1,2,3;
    $BADREF->process(1,2,3);

=item Can't coerce array into hash

(F) You used an array where a hash was expected, but the array has no
information on how to map from keys to array indices.  You can do that
only with arrays that have a hash reference at index 0.

=item Can't goto subroutine from an eval-string

(F) The "goto subroutine" call can't be used to jump out of an eval "string".
(You can use it to jump out of an eval {BLOCK}, but you probably don't want to.)

=item Can't use %%! because Errno.pm is not available

(F) The first time the %! hash is used, perl automatically loads the
Errno.pm module. The Errno module is expected to tie the %! hash to
provide symbolic names for C<$!> errno values.

=item Cannot find an opnumber for "%s"

(F) A string of a form C<CORE::word> was given to prototype(), but
there is no builtin with the name C<word>.

=item Character class syntax [. .] is reserved for future extensions

(W) Within regular expression character classes ([]) the syntax beginning
with "[." and ending with ".]" is reserved for future extensions.
If you need to represent those character sequences inside a regular
expression character class, just quote the square brackets with the
backslash: "\[." and ".\]".

=item Character class syntax [: :] is reserved for future extensions

(W) Within regular expression character classes ([]) the syntax beginning
with "[:" and ending with ":]" is reserved for future extensions.
If you need to represent those character sequences inside a regular
expression character class, just quote the square brackets with the
backslash: "\[:" and ":\]".

=item Character class syntax [= =] is reserved for future extensions

(W) Within regular expression character classes ([]) the syntax
beginning with "[=" and ending with "=]" is reserved for future extensions.
If you need to represent those character sequences inside a regular
expression character class, just quote the square brackets with the
backslash: "\[=" and "=\]".

=item %s: Eval-group in insecure regular expression

(F) Perl detected tainted data when trying to compile a regular expression
that contains the C<(?{ ... })> zero-width assertion, which is unsafe.
See L<perlre/(?{ code })>, and L<perlsec>.

=item %s: Eval-group not allowed, use re 'eval'

(F) A regular expression contained the C<(?{ ... })> zero-width assertion,
but that construct is only allowed when the C<use re 'eval'> pragma is
in effect.  See L<perlre/(?{ code })>.

=item %s: Eval-group not allowed at run time

(F) Perl tried to compile a regular expression containing the C<(?{ ... })>
zero-width assertion at run time, as it would when the pattern contains
interpolated values.  Since that is a security risk, it is not allowed.
If you insist, you may still do this by explicitly building the pattern
from an interpolated string at run time and using that in an eval().
See L<perlre/(?{ code })>.

=item Explicit blessing to '' (assuming package main)

(W) You are blessing a reference to a zero length string.  This has
the effect of blessing the reference into the package main.  This is
usually not what you want.  Consider providing a default target
package, e.g. bless($ref, $p or 'MyPackage');

=item Illegal hex digit ignored

(W) You may have tried to use a character other than 0 - 9 or A - F in a
hexadecimal number.  Interpretation of the hexadecimal number stopped
before the illegal character.

=item No such array field

(F) You tried to access an array as a hash, but the field name used is
not defined.  The hash at index 0 should map all valid field names to
array indices for that to work.

=item No such field "%s" in variable %s of type %s

(F) You tried to access a field of a typed variable where the type
does not know about the field name.  The field names are looked up in
the %FIELDS hash in the type package at compile time.  The %FIELDS hash
is usually set up with the 'fields' pragma.

=item Out of memory during ridiculously large request

(F) You can't allocate more than 2^31+"small amount" bytes.  This error
is most likely to be caused by a typo in the Perl program. e.g., C<$arr[time]>
instead of C<$arr[$time]>.

=item Range iterator outside integer range

(F) One (or both) of the numeric arguments to the range operator ".."
are outside the range which can be represented by integers internally.
One possible workaround is to force Perl to use magical string
increment by prepending "0" to your numbers.

=item Recursive inheritance detected while looking for method '%s' in package '%s'

(F) More than 100 levels of inheritance were encountered while invoking a
method.  Probably indicates an unintended loop in your inheritance hierarchy.

=item Reference found where even-sized list expected

(W) You gave a single reference where Perl was expecting a list with
an even number of elements (for assignment to a hash). This
usually means that you used the anon hash constructor when you meant 
to use parens. In any case, a hash requires key/value B<pairs>.

    %hash = { one => 1, two => 2, };   # WRONG
    %hash = [ qw/ an anon array / ];   # WRONG
    %hash = ( one => 1, two => 2, );   # right
    %hash = qw( one 1 two 2 );                 # also fine

=item Undefined value assigned to typeglob

(W) An undefined value was assigned to a typeglob, a la C<*foo = undef>.
This does nothing.  It's possible that you really mean C<undef *foo>.

=item Use of reserved word "%s" is deprecated

(D) The indicated bareword is a reserved word.  Future versions of perl
may use it as a keyword, so you're better off either explicitly quoting
the word in a manner appropriate for its context of use, or using a
different name altogether.  The warning can be suppressed for subroutine
names by either adding a C<&> prefix, or using a package qualifier,
e.g. C<&our()>, or C<Foo::our()>.

=item perl: warning: Setting locale failed.

(S) The whole warning message will look something like:

       perl: warning: Setting locale failed.
       perl: warning: Please check that your locale settings:
               LC_ALL = "En_US",
               LANG = (unset)
           are supported and installed on your system.
       perl: warning: Falling back to the standard locale ("C").

Exactly what were the failed locale settings varies.  In the above the
settings were that the LC_ALL was "En_US" and the LANG had no value.
This error means that Perl detected that you and/or your system
administrator have set up the so-called variable system but Perl could
not use those settings.  This was not dead serious, fortunately: there
is a "default locale" called "C" that Perl can and will use, the
script will be run.  Before you really fix the problem, however, you
will get the same error message each time you run Perl.  How to really
fix the problem can be found in L<perllocale> section B<LOCALE PROBLEMS>.

=back


=head1 Obsolete Diagnostics

=over

=item Can't mktemp()

(F) The mktemp() routine failed for some reason while trying to process
a B<-e> switch.  Maybe your /tmp partition is full, or clobbered.

=item Can't write to temp file for B<-e>: %s

(F) The write routine failed for some reason while trying to process
a B<-e> switch.  Maybe your /tmp partition is full, or clobbered.

=item Cannot open temporary file

(F) The create routine failed for some reason while trying to process
a B<-e> switch.  Maybe your /tmp partition is full, or clobbered.


=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<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 C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
analysed by the Perl porting team.

=head1 SEE ALSO

The F<Changes> file for exhaustive details on what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=head1 HISTORY

=cut