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=head1 NAME

perldelta - what's new for perl v5.6 (as of v5.005_61)

=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

TODO

=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.

=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 Core Changes

=head2 Unicode and UTF-8 support

Perl can optionally use UTF-8 as its internal representation for character
strings.  The C<use 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 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 syswrite() ease-of-use

The length argument of C<syswrite()> is now optional.

=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 (&, |, ^, ~, <<, >>) are not 64-bit clean,
they are explictly forced to be 32-bit.

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.

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

Adjusting your file system/system limits is outside the scope of Perl.
For process limits, you may try to increase the limits using your
shell's limit/ulimit command before running Perl.  The BSD::Resource
extension (not included with the standard Perl distribution) may also
be of use.
 
(Large file support is also related to 64-bit support, for obvious reasons)

=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 $^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>.

=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 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 Buffered data discarded from input filehandle when dup'ed.

C<open(NEW, "E<lt>&OLD")> now discards any data that was previously
read and buffered in C<OLD>.  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.

=head1 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

=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 ByteLoader

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

=item B

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

=item Devel::DProf

Devel::DProf, a Perl source code profiler has been added.

=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)".

=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 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::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 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 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.

=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--
but on the other hand they now accept "out-of-limits" day-of-month
to make "Julian date" conversions easier.

=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.

C<use filetest> to control the behaviour of filetests (C<-r> C<-w> ...).
Currently only one subpragma implemented, "use filetest 'access';",
that enables the use of 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

Todo.

=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.

=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.

=head1 Obsolete Diagnostics

Todo.

=head1 Configuration Changes

=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/

=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@umich.edu>>, with many contributions
from The Perl Porters.

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

=cut