Update perldelta.

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=head1 NAME

perldelta - what's new for perl v5.6 (as of v5.005_62)

=head1 DESCRIPTION

This is an unsupported alpha release, meant for intrepid Perl developers
only.  The included sources may not even build correctly on some platforms.
Subscribing to perl5-porters is the best way to monitor and contribute
to the progress of development releases (see www.perl.org for info).

This document describes differences between the 5.005 release and this one.

=head1 Incompatible Changes

=head2 Perl Source Incompatibilities

Beware that any new warnings that have been added are B<not> considered
incompatible changes.

Since all new warnings must be explicitly requested via the C<-w>
switch or the C<warnings> pragma, it is ultimately the programmer's
responsibility to ensure that warnings are enabled judiciously.

=over 4

=item Possibly changed pseudo-random number generator

In 5.005_0x and earlier, perl's rand() function used the C library
rand(3) function.  As of 5.005_52, Configure tests for drand48(),
random(), and rand() (in that order) and picks the first one it finds.
Perl programs that depend on reproducing a specific set of pseudo-random
numbers will now likely produce different output.

=item Hashing function for hash keys has changed

Perl hashes are not order preserving.  The apparently random order
encountered when iterating on the contents of a hash is determined
by the hashing algorithm used.  To improve the distribution of lower
bits in the hashed value, the algorithm has changed slightly as of
5.005_52.  When iterating over hashes, this may yield a random order
that is B<different> from that of previous versions.

=item C<undef> fails on read only values

Using the C<undef> operator on a readonly value (such as $1) has
the same effect as assigning C<undef> to the readonly value--it
throws an exception.

=item Close-on-exec bit may be set on pipe() handles

On systems that support a close-on-exec flag on filehandles, the
flag will be set for any handles created by pipe(), if that is
warranted by the value of $^F that may be in effect.  Earlier
versions neglected to set the flag for handles created with
pipe().  See L<perlfunc/pipe> and L<perlvar/$^F>.

=item Writing C<"$$1"> to mean C<"${$}1"> is unsupported

Perl 5.004 deprecated the interpretation of C<$$1> and
similar within interpolated strings to mean C<$$ . "1">,
but still allowed it.

In Perl 5.6 and later, C<"$$1"> always means C<"${$1}">.

=item values(%h) and C<\(%h)> operate on aliases to values, not copies

each(), values() and hashes in a list context return the actual
values in the hash, instead of copies (as they used to in earlier
versions).  Typical idioms for using these constructs copy the
returned values, but this is can make a significant difference when
creating references to the returned values.

Keys in the hash are still returned as copies when iterating on
on a hash.

=item vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS

vec() generates a run-time error if the BITS arguments is not
a valid power-of-two integer.

=item Text of some diagnostic output has changed

Most references to internal Perl operations in diagnostics
have been changed to be more descriptive.  This may be an
issue for programs that may incorrectly rely on the exact
text of diagnostics for proper functioning.

=item C<%@> has been removed

The undocumented special variable C<%@> that used to accumulate
"background" errors (such as those that happen in DESTROY())
has been removed, because it could potentially result in memory
leaks.

=back

=head2 C Source Incompatibilities

=over 4

=item C<PERL_POLLUTE>

Release 5.005 grandfathered old global symbol names by providing preprocessor
macros for extension source compatibility.  As of release 5.6, these
preprocessor definitions are not available by default.  You need to explicitly
compile perl with C<-DPERL_POLLUTE> to get these definitions.  For
extensions still using the old symbols, this option can be
specified via MakeMaker:

    perl Makefile.PL POLLUTE=1

=item C<PERL_IMPLICIT_CONTEXT>

This new build option provides a set of macros for all API functions
such that an implicit interpreter/thread context argument is passed to
every API function.  As a result of this, something like C<sv_setsv(foo,bar)>
amounts to a macro invocation that actually translates to something like
C<Perl_sv_setsv(my_perl,foo,bar)>.  While this is generally expected
to not have any significant source compatibility issues, the difference
between a macro and a real function call will need to be considered.

This means that there B<is> a source compatibility issue as a result of
this if your extensions attempt to use pointers to any of the Perl API
functions.

Note that the above issue is not relevant to the default build of
Perl, whose interfaces continue to match those of prior versions
(but subject to the other options described here).

PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
with one of -Dusethreads, -Dusemultiplicity, or both.

See L<perlguts/"The Perl API"> for detailed information on the
ramifications of building Perl using this option.

=item C<PERL_POLLUTE_MALLOC>

Enabling Perl's malloc in release 5.005 and earlier caused
the namespace of system versions of the malloc family of functions to
be usurped by the Perl versions, since by default they used the
same names.

Besides causing problems on platforms that do not allow these functions to
be cleanly replaced, this also meant that the system versions could not
be called in programs that used Perl's malloc.  Previous versions of Perl
have allowed this behaviour to be suppressed with the HIDEMYMALLOC and
EMBEDMYMALLOC preprocessor definitions.

As of release 5.6, Perl's malloc family of functions have default names
distinct from the system versions.  You need to explicitly compile perl with
C<-DPERL_POLLUTE_MALLOC> to get the older behaviour.  HIDEMYMALLOC
and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now
the default.

Note that these functions do B<not> constitute Perl's memory allocation API.
See L<perlguts/"Memory Allocation"> for further information about that.

=item C<PL_na> and C<dTHR> Issues

The C<PL_na> global is now thread local, so a C<dTHR> declaration is needed
in the scope in which the global appears.  XSUBs should handle this automatically,
but if you have used C<PL_na> in support functions, you either need to
change the C<PL_na> to a local variable (which is recommended), or put in
a C<dTHR>.

=back

=head2 Compatible C Source API Changes

=over

=item C<PATCHLEVEL> is now C<PERL_VERSION>

The cpp macros C<PERL_REVISION>, C<PERL_VERSION>, and C<PERL_SUBVERSION>
are now available by default from perl.h, and reflect the base revision,
patchlevel, and subversion respectively.  C<PERL_REVISION> had no
prior equivalent, while C<PERL_VERSION> and C<PERL_SUBVERSION> were
previously available as C<PATCHLEVEL> and C<SUBVERSION>.

The new names cause less pollution of the B<cpp> namespace and reflect what
the numbers have come to stand for in common practice.  For compatibility,
the old names are still supported when F<patchlevel.h> is explicitly
included (as required before), so there is no source incompatibility
from the change.

=item Support for C++ exceptions

change#3386, also needs perlguts documentation
[TODO - Chip Salzenberg <chip@perlsupport.com>]

=back

=head2 Binary Incompatibilities

The default build of this release is binary compatible with the 5.005
release or its maintenance versions.

The usethreads or usemultiplicity builds are B<not> binary compatible
with the corresponding builds in 5.005.

=head1 Installation and Configuration Improvements

=head2 New Configure flags

The following new flags may be enabled on the Configure command line
by running Configure with C<-Dflag>.

    usemultiplicity

    uselongdouble
    usemorebits
    uselargefiles

=head2 -Dusethreads and -Duse64bits now more daring

The Configure options enabling the use of threads and the use of
64-bitness are now more daring in the sense that they no more have
an explicit list of operating systems of known threads/64-bit
capabilities.  In other words: if your operating system has the
necessary APIs, you should be able just to go ahead and use them.
See also L<"64-bit support">.

=head2 Long Doubles

Some platforms have "long doubles", floating point numbers of even
larger range than ordinary "doubles".  To enable using ng doubles for
Perl's scalars, use -Duselongdouble.

=head2 -Dusemorebits

You can enable both -Duse64bits and -Dlongdouble by -Dusemorebits.
See also L<"64-bit support">.

=head2 -Duselargefiles

Some platforms support large files, files larger than two gigabytes.
See L<"Large file support"> for more information. 

=head2 installusrbinperl

You can use "Configure -Uinstallusrbinperl" which causes installperl
to skip installing perl also as /usr/bin/perl.  This is useful if you
prefer not to modify /usr/bin for some reason or another but harmful
because many scripts assume to find Perl in /usr/bin/perl.

=head2 SOCKS support

You can use "Configure -Dusesocks" which causes Perl to probe
for the SOCKS proxy protocol library, http://www.socks.nec.com/

=head2 C<-A> flag

You can "post-edit" the Configure variables using the Configure C<-A>
flag.  The editing happens immediately after the platform specific
hints files have been processed but before the actual configuration
process starts.  Run C<Configure -h> to find out the full C<-A> syntax.

=head2 New Installation Scheme

vendorprefix et al
[TODO - Andy Dougherty <doughera@lafcol.lafayette.edu>]

=head1 Core Changes

=head2 Unicode and UTF-8 support

Perl can optionally use UTF-8 as its internal representation for character
strings.  The C<utf8> pragma enables this support in the current lexical
scope.  See L<utf8> for more information.

=head2 Lexically scoped warning categories

You can now control the granularity of warnings emitted by perl at a finer
level using the C<use warnings> pragma.  See L<warnings> and L<perllexwarn>
for details.

=head2 Lvalue subroutines

WARNING: This is an experimental feature.

change#4081
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>,
Tuomas Lukka <lukka@fas.harvard.edu>)]

=head2 "our" declarations

An "our" declaration introduces a value that can be best understood
as a lexically scoped symbolic alias to a global variable in the
current package.  This is mostly useful as an alternative to the
C<vars> pragma, but also provides the opportunity to introduce
typing and other attributes for such variables.  See L<perlfunc/our>.

=head2 Weak references

WARNING: This is an experimental feature.

change#3385, also need perlguts documentation

[TODO - Tuomas Lukka <lukka@fas.harvard.edu>]

=head2 Binary numbers supported

Binary numbers are now supported as literals, in s?printf formats, and
C<oct()>:

    $answer = 0b101010;
    printf "The answer is: %b\n", oct("0b101010");

=head2 Some arrows may be omitted in calls through references

Perl now allows the arrow to be omitted in many constructs
involving subroutine calls through references.  For example,
C<$foo[10]->('foo')> may now be written C<$foo[10]('foo')>.
This is rather similar to how the arrow may be omitted from
C<$foo[10]->{'foo'}>.  Note however, that the arrow is still
required for C<foo(10)->('bar')>.

=head2 syswrite() ease-of-use

The length argument of C<syswrite()> has become optional.

=head2 Filehandles can be autovivified

The construct C<open(my $fh, ...)> can be used to create filehandles
more easily.  The filehandle will be automatically closed at the end
of the scope of $fh, provided there are no other references to it.  This
largely eliminates the need for typeglobs when opening filehandles
that must be passed around, as in the following example:

    sub myopen {
        open my $fh, "@_"
             or die "Can't open '@_': $!";
        return $fh;
    }

    {
        my $f = myopen("</etc/motd");
        print <$f>;
        # $f implicitly closed here
    }

[TODO - this idiom needs more pod penetration]

=head2 64-bit support

All platforms that have 64-bit integers either (a) natively as longs
or ints (b) via special compiler flags (c) using long long are able to
use "quads" (64-integers) as follows:

=over 4

=item *

constants (decimal, hexadecimal, octal, binary) in the code 

=item *

arguments to oct() and hex()

=item *

arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)

=item *

printed as such

=item *

pack() and unpack() "q" and "Q" formats

=item *

in basic arithmetics: + - * / %

=item *

vec() (but see the below note about bit arithmetics)

=back

Note that unless you have the case (a) you will have to configure
and compile Perl using the -Duse64bits Configure flag.

Unfortunately bit arithmetics (&, |, ^, ~, <<, >>) for numbers are not
64-bit clean, they are explictly forced to be 32-bit.  Bit arithmetics
for bit vectors (created by vec()) are not limited in their width.

Last but not least: note that due to Perl's habit of always using
floating point numbers the quads are still not true integers.
When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
-9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
are silently promoted to floating point numbers, after which they will
start losing precision (their lower digits).

=head2 Large file support

If you have filesystems that support "large files" (files larger than
2 gigabytes), you may now also be able to create and access them from
Perl.  You have to use Configure -Duselargefiles.  Turning on the
large file support turns on also the 64-bit support, for obvious reasons.

Note that in addition to requiring a proper file system to do large
files you may also need to adjust your per-process (or your
per-system, or per-process-group, or per-user-group) maximum filesize
limits before running Perl scripts that try to handle large files,
especially if you intend to write such files.

Finally, in addition to your process/process group maximum filesize
limits, you may have quota limits on your filesystems that stop you
(your user id or your user group id) from using large files.

Adjusting your process/user/group/file system/operating system limits
is outside the scope of Perl core language.  For process limits, you
may try increasing the limits using your shell's limits/limit/ulimit
command before running Perl.  The BSD::Resource extension (not
included with the standard Perl distribution) may also be of use, it
offers the getrlimit/setrlimit interface that can be used to adjust
process resource usage limits, including the maximum filesize limit.
 
=head2 Long doubles

In some systems you may be able to use long doubles to enhance the
range of precision of your double precision floating point numbers
(that is, Perl's numbers).  Use Configure -Duselongdouble to enable
this support (if it is available).

=head2 "more bits"

You can Configure -Dusemorebits to turn on both the 64-bit support
and the long double support.

=head2 Better syntax checks on parenthesized unary operators

Expressions such as:

    print defined(&foo,&bar,&baz);
    print uc("foo","bar","baz");
    undef($foo,&bar);

used to be accidentally allowed in earlier versions, and produced
unpredictable behaviour.  Some produced ancillary warnings
when used in this way; others silently did the wrong thing.

The parenthesized forms of most unary operators that expect a single
argument now ensure that they are not called with more than one
argument, making the cases shown above syntax errors.  The usual
behaviour of:

    print defined &foo, &bar, &baz;
    print uc "foo", "bar", "baz";
    undef $foo, &bar;

remains unchanged.  See L<perlop>.

=head2 POSIX character class syntax [: :] supported

For example to match alphabetic characters use /[[:alpha:]]/.
See L<perlre> for details.

=head2 Improved C<qw//> operator

The C<qw//> operator is now evaluated at compile time into a true list
instead of being replaced with a run time call to C<split()>.  This
removes the confusing misbehaviour of C<qw//> in scalar context, which
had inherited that behaviour from split().

Thus:

    $foo = ($bar) = qw(a b c); print "$foo|$bar\n";

now correctly prints "3|a", instead of "2|a".

=head2 pack() format 'Z' supported

The new format type 'Z' is useful for packing and unpacking null-terminated
strings.  See L<perlfunc/"pack">.

=head2 pack() format modifier '!' supported

The new format type modifier '!' is useful for packing and unpacking
native shorts, ints, and longs.  See L<perlfunc/"pack">.

=head2 pack() and unpack() support counted strings

The template character '/' can be used to specify a counted string
type to be packed or unpacked.  See L<perlfunc/"pack">.

=head2 Comments in pack() templates

The '#' character in a template introduces a comment up to
end of the line.  This facilitates documentation of pack()
templates.

=head2 $^X variables may now have names longer than one character

Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
error.  Now variable names that begin with a control character may be
arbitrarily long.  However, for compatibility reasons, these variables
I<must> be written with explicit braces, as C<${^XY}> for example.
C<${^XYZ}> is synonymous with ${"\cXYZ"}.  Variable names with more
than one control character, such as C<${^XY^Z}>, are illegal.

The old syntax has not changed.  As before, `^X' may be either a
literal control-X character or the two-character sequence `caret' plus
`X'.  When braces are omitted, the variable name stops after the
control character.  Thus C<"$^XYZ"> continues to be synonymous with
C<$^X . "YZ"> as before.

As before, lexical variables may not have names beginning with control
characters.  As before, variables whose names begin with a control
character are always forced to be in package `main'.  All such variables
are reserved for future extensions, except those that begin with
C<^_>, which may be used by user programs and are guaranteed not to
acquire special meaning in any future version of Perl.

=head2 C<use attrs> implicit in subroutine attributes

Formerly, if you wanted to mark a subroutine as being a method call or
as requiring an automatic lock() when it is entered, you had to declare
that with a C<use attrs> pragma in the body of the subroutine.
That can now be accomplished with a declaration syntax, like this:

    sub mymethod : locked, method ;
    ...
    sub mymethod : locked, method {
        ...
    }

F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes
with the stubs they provide.  See L<attributes>.

=head2 Regular expression improvements

change#2827,2373,2372,2365,1813,1800,4112,4158,4215,4301
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head2 Overloading improvements

change#2150
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head2 open() with more than two arguments

[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head2 Support for interpolating named characters

change#4052
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head2 Experimental support form user-hooks in @INC

[TODO - Ken Fox <kfox@ford.com>]

=head2 C<require> and C<do> may be overridden

C<require> and C<do 'file'> operations may be overridden locally
by importing subroutines of the same name into the current package 
(or globally by importing them into the CORE::GLOBAL:: namespace).
Overriding C<require> will also affect C<use>, provided the override
is visible at compile-time.
See L<perlsub/"Overriding Built-in Functions">.

=head2 New variable $^C reflects C<-c> switch

C<$^C> contains a boolean that reflects whether perl is being run
in compile-only mode (i.e. via the C<-c> switch).  Since
BEGIN blocks are executed under such conditions, this variable
enables perl code to determine whether actions that make sense
only during normal running are warranted.  See L<perlvar>.

=head2 Optional Y2K warnings

If Perl is built with the cpp macro C<PERL_Y2KWARN> defined,
it emits optional warnings when concatenating the number 19
with another number.

This behavior must be specifically enabled when running Configure.
See L<INSTALL> and L<README.Y2K>.

=head1 Significant bug fixes

=head2 E<lt>HANDLEE<gt> on empty files

With C<$/> set to C<undef>, slurping an empty file returns a string of
zero length (instead of C<undef>, as it used to) the first time the
HANDLE is read.  Further reads yield C<undef>.

This means that the following will append "foo" to an empty file (it used
to do nothing):

    perl -0777 -pi -e 's/^/foo/' empty_file

The behaviour of:

    perl -pi -e 's/^/foo/' empty_file

is unchanged (it continues to leave the file empty).

=head2 C<eval '...'> improvements

Line numbers (as reflected by caller() and most diagnostics) within
C<eval '...'> were often incorrect when here documents were involved.
This has been corrected.

Lexical lookups for variables appearing in C<eval '...'> within
functions that were themselves called within an C<eval '...'> were
searching the wrong place for lexicals.  The lexical search now
correctly ends at the subroutine's block boundary.

Parsing of here documents used to be flawed when they appeared as
the replacement expression in C<eval 's/.../.../e'>.  This has
been fixed.

=head2 All compilation errors are true errors

Some "errors" encountered at compile time were by neccessity 
generated as warnings followed by eventual termination of the
program.  This enabled more such errors to be reported in a
single run, rather than causing a hard stop at the first error
that was encountered.

The mechanism for reporting such errors has been reimplemented
to queue compile-time errors and report them at the end of the
compilation as true errors rather than as warnings.  This fixes
error messages that used to leak through as warnings when code
was compiled at run time using C<eval STRING>, and allows such
errors to be reliably trapped using __DIE__ hooks.

=head2 Automatic flushing of output buffers

fork(), exec(), system(), qx//, and pipe open()s now flush buffers
of all files opened for output when the operation
was attempted.  This mostly eliminates confusing 
buffering mishaps suffered by users unaware of how Perl internally
handles I/O.

=head2 Better diagnostics on meaningless filehandle operations

Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
are compile time errors.  Attempting to read from filehandles that
were opened only for writing will now produce warnings (just as
writing to read-only filehandles does).

=head2 Where possible, buffered data discarded from duped input filehandle

C<open(NEW, "E<lt>&OLD")> now attempts to discard any data that
was previously read and buffered in C<OLD> before duping the handle.
On platforms where doing this is allowed, the next read operation
on C<NEW> will return the same data as the corresponding operation
on C<OLD>.  Formerly, it would have returned the data from the start
of the following disk block instead.

=head2 system(), backticks and pipe open now reflect exec() failure

On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
etc., are implemented via fork() and exec().  When the underlying
exec() fails, earlier versions did not report the error properly,
since the exec() happened to be in a different process.

The child process now communicates with the parent about the
error in launching the external command, which allow these
constructs to return with their usual error value and set $!.

=head2 Implicitly closed filehandles are safer

Sometimes implicitly closed filehandles (as when they are localized,
and Perl automatically closes them on exiting the scope) could
inadvertently set $? or $!.  This has been corrected.

=head2 C<(\$)> prototype and C<$foo{a}>

An scalar reference prototype now correctly allows a hash or
array element in that slot.

=head2 Pseudo-hashes work better

Dereferencing some types of reference values in a pseudo-hash,
such as C<$ph->{foo}[1]>, was accidentally disallowed.  This has
been corrected.

When applied to a pseudo-hash element, exists() now reports whether
the specified value exists, not merely if the key is valid.

=head2 C<goto &sub> and AUTOLOAD

C<goto &sub> construct works correctly when C<&sub> happens
to be autoloaded.

=head2 C<-bareword> allowed under C<use integer>

The autoquoting of barewords preceded by C<-> did not work
in prior versions when the C<integer> pragma was enabled.
This has been fixed.

=head2 Boolean assignment operators are legal lvalues

Constructs such as C<($a ||= 2) += 1> are now allowed.

=head2 C<sort $coderef @foo> allowed

sort() did not accept a subroutine reference as the comparison
function in earlier versions.  This has been fixed.

=head2 Failures in DESTROY()

When code in a destructor threw an exception, it went unnoticed
in earlier versions of Perl, unless someone happened to be
looking in $@ just after the point the destructor happened to
run.  Such failures are now visible as warnings when warnings are
enabled.

=head2 Locale bugs fixed

printf() and sprintf() previously did reset the numeric locale
back to the default "C" locale.  This has been fixed.

Numbers formatted according to the local numeric locale
(such as using a decimal comma instead of a decimal dot) caused
"isn't numeric" warnings, even while the operations accessing
those numbers produced correct results.  The warnings are gone.

=head2 Memory leaks

The C<eval 'return sub {...}'> construct could sometimes leak
memory.  This has been fixed.

Operations that aren't filehandle constructors used to leak memory
when used on invalid filehandles.  This has been fixed.

Constructs that modified C<@_> could fail to deallocate values
in C<@_> and thus leak memory.  This has been corrected.

=head2 Spurious subroutine stubs after failed subroutine calls

Perl could sometimes create empty subroutine stubs when a
subroutine was not found in the package.  Such cases stopped
later method lookups from progressing into base packages.
This has been corrected.

=head2 Consistent numeric conversions

change#3378,3318
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head2 Taint failures under C<-U>

When running in unsafe mode, taint violations could sometimes
cause silent failures.  This has been fixed.

=head2 END blocks and the C<-c> switch

Prior versions used to run BEGIN B<and> END blocks when Perl was
run in compile-only mode.  Since this is typically not the expected
behavior, END blocks are not executed when the C<-c> switch
is used.

Note that something resembling the previous behavior can still be
obtained by putting C<BEGIN { $^C = 0; exit; } at the very end of
the top level source file.

=head2 Potential to leak DATA filehandles

Using the C<__DATA__> token creates an implicit filehandle to
the file that contains the token.  It is the program's
responsibility to close it when it is done reading from it.

This caveat is now better explained in the documentation.
See L<perldata>.

=head2 Diagnostics follow STDERR

Diagnostic output now goes to whichever file the C<STDERR> handle
is pointing at, instead of always going to the underlying C runtime
library's C<stderr>.

=head2 Other fixes for better diagnostics

Line numbers are suppressed no more (under most likely circumstances)
during the global destruction phase.

Diagnostics emitted from code running in threads other than the main
thread are now accompanied by the thread ID.

Embedded null characters in diagnostics now actually show up.  They
used to truncate the message in prior versions.

$foo::a and $foo::b are now exempt from "possible typo" warnings only
if sort() is encountered in package foo.

Unrecognized alphabetic escapes encountered when parsing quoting
constructs now generate a warning, since they may take on new
semantics in later versions of Perl.

=head1 Performance enhancements

=head2 Simple sort() using { $a <=> $b } and the like are optimized

Many common sort() opertions using a simple inlined block are now
optimized for faster performance.

=head2 Optimized assignments to lexical variables

Certain operations in the RHS of assignment statements have been
optimized to directly set the lexical variable on the LHS,
eliminating redundant copying overheads.

=head2 Method lookups optimized

[TODO - Chip Salzenberg <chip@perlsupport.com>]

=head2 Faster mechanism to invoke XSUBs

change#4044,4125
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head2 Perl_malloc() improvements

change#4237
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head2 Faster subroutine calls

Minor changes in how subroutine calls are handled internally
provide marginal improvements in performance.

=head1 Platform specific changes

=head2 Additional supported platforms

=over 4

=item *

VM/ESA is now supported.

=item *

Siemens BS2000 is now supported under the POSIX Shell.

=item *

The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
extension.

=item *

GNU/Hurd is now supported.

=item *

Rhapsody is now supported.

=item *

EPOC is is now supported (on Psion 5).

=back

=head2 DOS

[TODO - Laszlo Molnar <laszlo.molnar@eth.ericsson.se>]

=head2 OS/2

[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head2 VMS

[TODO - Charles Bailey <bailey@newman.upenn.edu>]

=head2 Win32

Site library searches failed to look for ".../site/5.XXX/lib"
if ".../site/5.XXXYY/lib" wasn't found.  This has been corrected.

When given a pathname that consists only of a drivename, such
as C<A:>, opendir() and stat() now use the current working
directory for the drive rather than the drive root.

The builtin XSUB functions in the Win32:: namespace are
documented.  See L<Win32>.

$^X now contains the full path name of the running executable.

A Win32::GetLongPathName() function is provided to complement
Win32::GetFullPathName() and Win32::GetShortPathName().  See L<Win32>.

POSIX::uname() is supported.

system(1,...) now returns true process IDs rather than process
handles.  kill() accepts any real process id, rather than strictly
return values from system(1,...).

The C<Shell> module is supported.

[TODO - GSAR]

=head1 New tests

=over 4

=item   lib/attrs

Compatibility tests for C<sub : attrs> vs the older C<use attrs>.

=item   lib/io_const

IO constants (SEEK_*, _IO*).

=item   lib/io_dir

Directory-related IO methods (new, read, close, rewind, tied delete).

=item   lib/io_multihomed

INET sockets with multi-homed hosts.

=item   lib/io_poll

IO poll().

=item   lib/io_unix

UNIX sockets.

=item   op/attrs

Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>.

=item   op/filetest

File test operators.

=item   op/lex_assign

Verify operations that access pad objects (lexicals and temporaries).

=back

=head1 Modules and Pragmata

=head2 Modules

=over 4

=item attributes

While used internally by Perl as a pragma, this module also
provides a way to fetch subroutine and variable attributes.
See L<attributes>.

=item B

[TODO - Vishal Bhatia <vishal@gol.com>,
Nick Ing-Simmons <nick@ni-s.u-net.com>]

=item ByteLoader

The ByteLoader is a dedicated extension to generate and run
Perl bytecode.  See L<ByteLoader>.

=item B

The Perl Compiler suite has been extensively reworked for this
release.

=item constant

References can now be used.  See L<constant>.

=item charnames

change#4052
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=item Data::Dumper

A C<Maxdepth> setting can be specified to avoid venturing
too deeply into data structures that may be very deep.
See L<Data::Dumper>.

Dumping C<qr//> objects works correctly.

=item DB

C<DB> is an experimental module that exposes a clean abstraction
to Perl's debugging API.

=item DB_File

[TODO - Paul Marquess <paul.marquess@bt.com>]

=item Devel::DProf

Devel::DProf, a Perl source code profiler has been added.  See L<DProf>.

=item Dumpvalue

Added Dumpvalue module provides screen dumps of Perl data.

=item Benchmark

You can now run tests for I<n> seconds instead of guessing the right
number of tests to run: e.g. timethese(-5, ...) will run each 
code for at least 5 CPU seconds.  Zero as the "number of repetitions"
means "for at least 3 CPU seconds".  The output format has also
changed.  For example:

use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})

will now output something like this:

Benchmark: running a, b, each for at least 5 CPU seconds...
         a:  5 wallclock secs ( 5.77 usr +  0.00 sys =  5.77 CPU) @ 200551.91/s (n=1156516)
         b:  4 wallclock secs ( 5.00 usr +  0.02 sys =  5.02 CPU) @ 159605.18/s (n=800686)

New features: "each for at least N CPU seconds...", "wallclock secs",
and the "@ operations/CPU second (n=operations)".

change#4265,4266,4292
[TODO - Barrie Slaymaker <barries@slaysys.com>]

=item Devel::Peek

The Devel::Peek module provides access to the internal representation
of Perl variables and data.  It is a data debugging tool for the XS programmer.

=item ExtUtils::MakeMaker

change#4135, also needs docs in module pod
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=item Fcntl

More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
large (more than 4G) file access (64-bit support is not yet
working, though, so no need to get overly excited), Free/Net/OpenBSD
locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.

=item File::Compare

A compare_text() function has been added, which allows custom
comparison functions.  See L<File::Compare>.

=item File::Find

File::Find now works correctly when the wanted() function is either
autoloaded or is a symbolic reference.

A bug that cause File::Find to lose track of the working directory
when pruning top-level directories has been fixed.

=item File::Spec

New methods have been added to the File::Spec module: devnull() returns
the name of the null device (/dev/null on Unix) and tmpdir() the name of
the temp directory (normally /tmp on Unix).  There are now also methods
to convert between absolute and relative filenames: abs2rel() and
rel2abs().  For compatibility with operating systems that specify volume
names in file paths, the splitpath(), splitdir(), and catdir() methods
have been added.

=item File::Spec::Functions

The new File::Spec::Functions modules provides a function interface
to the File::Spec module.  Allows shorthand

    $fullname = catfile($dir1, $dir2, $file);

instead of

    $fullname = File::Spec->catfile($dir1, $dir2, $file);

=item Getopt::Long

[TODO - Johan Vromans <jvromans@squirrel.nl>]

=item IO

write() and syswrite() will now accept a single-argument
form of the call, for consistency with Perl's syswrite().

You can now create a TCP-based IO::Socket::INET without forcing
a connect attempt.  This allows you to configure its options
(like making it non-blocking) and then call connect() manually.

A bug that prevented the IO::Socket::protocol() accessor
from ever returning the correct value has been corrected.

=item JPL

Java Perl Lingo is now distributed with Perl.  See jpl/README
for more information.

=item Math::BigInt

The logical operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
and C<~> are now supported on bigints.

=item Math::Complex

The accessor methods Re, Im, arg, abs, rho, and theta can now also
act as mutators (accessor $z->Re(), mutator $z->Re(3)).

=item Math::Trig

A little bit of radial trigonometry (cylindrical and spherical),
radial coordinate conversions, and the great circle distance were added.

=item Pod::Parser

[TODO - Brad Appleton <bradapp@enteract.com>]

=item Pod::Text and Pod::Man

[TODO - Russ Allbery <rra@stanford.edu>]

=item SDBM_File

An EXISTS method has been added to this module (and sdbm_exists() has
been added to the underlying sdbm library), so one can now call exists
on an SDBM_File tied hash and get the correct result, rather than a
runtime error.

A bug that may have caused data loss when more than one disk block
happens to be read from the database in a single FETCH() has been
fixed.

=item Time::Local

The timelocal() and timegm() functions used to silently return bogus
results when the date exceeded the machine's integer range.  They
now consistently croak() if the date falls in an unsupported range.

=item Win32

The error return value in list context has been changed for all functions
that return a list of values.  Previously these functions returned a list
with a single element C<undef> if an error occurred.  Now these functions
return the empty list in these situations.  This applies to the following
functions:

    Win32::FsType
    Win32::GetOSVersion

The remaining functions are unchanged and continue to return C<undef> on
error even in list context.

The Win32::SetLastError(ERROR) function has been added as a complement
to the Win32::GetLastError() function.

The new Win32::GetFullPathName(FILENAME) returns the full absolute
pathname for FILENAME in scalar context.  In list context it returns
a two-element list containing the fully qualified directory name and
the filename.

=item DBM Filters

A new feature called "DBM Filters" has been added to all the
DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
DBM Filters add four new methods to each DBM module:

    filter_store_key
    filter_store_value
    filter_fetch_key
    filter_fetch_value

These can be used to filter key-value pairs before the pairs are
written to the database or just after they are read from the database.
See L<perldbmfilter> for further information.

=back

=head2 Pragmata

C<use attrs> is now obsolescent, and is only provided for
backward-compatibility.  It's been replaced by the C<sub : attributes>
syntax.  See L<perlsub/"Subroutine Attributes"> and L<attributes>.

C<use utf8> to enable UTF-8 and Unicode support.

C<use caller 'encoding'> allows modules to inherit pragmatic attributes
from the caller's context.  C<encoding> is currently the only supported
attribute.

Lexical warnings pragma, C<use warnings;>, to control optional warnings.
See L<perllexwarn>.

C<use filetest> to control the behaviour of filetests (C<-r> C<-w>
...).  Currently only one subpragma implemented, "use filetest
'access';", that uses access(2) or equivalent to check permissions
instead of using stat(2) as usual.  This matters in filesystems
where there are ACLs (access control lists): the stat(2) might lie,
but access(2) knows better.

=head1 Utility Changes

=head2 h2ph

[TODO - Kurt Starsinic <kstar@chapin.edu>]

=head2 perlcc

C<perlcc> now supports the C and Bytecode backends.  By default,
it generates output from the simple C backend rather than the
optimized C backend.

Support for non-Unix platforms has been improved.

=head2 h2xs

change#4232
[TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]

=head1 Documentation Changes

=over 4

=item perlopentut.pod

A tutorial on using open() effectively.

=item perlreftut.pod

A tutorial that introduces the essentials of references.

=item perltootc.pod

A tutorial on managing class data for object modules.

=item perlcompile.pod

An introduction to using the Perl Compiler suite.

=back

=head1 New Diagnostics

=item "my sub" not yet implemented

(F) Lexically scoped subroutines are not yet implemented.  Don't try that
yet.

=item %s package attribute may clash with future reserved word: %s

(W) A lowercase attribute name was used that had a package-specific handler.
That name might have a meaning to Perl itself some day, even though it
doesn't yet.  Perhaps you should use a mixed-case attribute name, instead.
See L<attributes>.

=item /%s/: Unrecognized escape \\%c passed through

(W) You used a backslash-character combination which is not recognized
by Perl.  This combination appears in an interpolated variable or a
C<'>-delimited regular expression.

=item Filehandle %s opened only for output

(W) You tried to read from a filehandle opened only for writing.  If you
intended it to be a read-write filehandle, you needed to open it with
"+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing.  If
you intended only to read from the file, use "E<lt>".  See
L<perlfunc/open>.

=item Invalid %s attribute: %s

The indicated attribute for a subroutine or variable was not recognized
by Perl or by a user-supplied handler.  See L<attributes>.

=item Invalid %s attributes: %s

The indicated attributes for a subroutine or variable were not recognized
by Perl or by a user-supplied handler.  See L<attributes>.

=item Invalid separator character %s in attribute list

(F) Something other than a comma or whitespace was seen between the
elements of an attribute list.  If the previous attribute
had a parenthesised parameter list, perhaps that list was terminated
too soon.  See L<attributes>.

=item Missing command in piped open

(W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
construction, but the command was missing or blank.

=item Missing name in "my sub"

(F) The reserved syntax for lexically scoped subroutines requires that they
have a name with which they can be found.

=item Unrecognized escape \\%c passed through

(W) You used a backslash-character combination which is not recognized
by Perl.

=item Unterminated attribute parameter in attribute list

(F) The lexer saw an opening (left) parenthesis character while parsing an
attribute list, but the matching closing (right) parenthesis
character was not found.  You may need to add (or remove) a backslash
character to get your parentheses to balance.  See L<attributes>.

=item Unterminated attribute list

(F) The lexer found something other than a simple identifier at the start
of an attribute, and it wasn't a semicolon or the start of a
block.  Perhaps you terminated the parameter list of the previous attribute
too soon.  See L<attributes>.

=item defined(@array) is deprecated

(D) defined() is not usually useful on arrays because it checks for an
undefined I<scalar> value.  If you want to see if the array is empty,
just use C<if (@array) { # not empty }> for example.  

=item defined(%hash) is deprecated

(D) defined() is not usually useful on hashes because it checks for an
undefined I<scalar> value.  If you want to see if the hash is empty,
just use C<if (%hash) { # not empty }> for example.  

=item Invalid separator character %s in subroutine attribute list

(F) Something other than a comma or whitespace was seen between the
elements of a subroutine attribute list.  If the previous attribute
had a parenthesised parameter list, perhaps that list was terminated
too soon.

=item Possible Y2K bug: %s

(W) You are concatenating the number 19 with another number, which
could be a potential Year 2000 problem.

=item Unterminated attribute parameter in subroutine attribute list

(F) The lexer saw an opening (left) parenthesis character while parsing a
subroutine attribute list, but the matching closing (right) parenthesis
character was not found.  You may need to add (or remove) a backslash
character to get your parentheses to balance.

=item Unterminated subroutine attribute list

(F) The lexer found something other than a simple identifier at the start
of a subroutine attribute, and it wasn't a semicolon or the start of a
block.  Perhaps you terminated the parameter list of the previous attribute
too soon.

=item /%s/ should probably be written as "%s"

(W) You have used a pattern where Perl expected to find a string,
like in the first argument to C<join>.  Perl will treat the true
or false result of matching the pattern against $_ as the string,
which is probably not what you had in mind.

=item %s() called too early to check prototype

(W) You've called a function that has a prototype before the parser saw a
definition or declaration for it, and Perl could not check that the call
conforms to the prototype.  You need to either add an early prototype
declaration for the subroutine in question, or move the subroutine
definition ahead of the call to get proper prototype checking.  Alternatively,
if you are certain that you're calling the function correctly, you may put
an ampersand before the name to avoid the warning.  See L<perlsub>.

=head1 Obsolete Diagnostics

Todo.

=head1 BUGS

If you find what you think is a bug, you might check the headers of
articles recently posted to 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 to 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 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

Written by Gurusamy Sarathy <F<gsar@activestate.com>>, with many
contributions from The Perl Porters.

Send omissions or corrections to <F<perlbug@perl.com>>.

=cut