perl56delta.1

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.\" ========================================================================
.\"
.IX Title "PERL56DELTA 1"
.TH PERL56DELTA 1 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
perl56delta \- what's new for perl v5.6.0
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This document describes differences between the 5.005 release and the 5.6.0
release.
.SH "Core Enhancements"
.IX Header "Core Enhancements"
.Sh "Interpreter cloning, threads, and concurrency"
.IX Subsection "Interpreter cloning, threads, and concurrency"
Perl 5.6.0 introduces the beginnings of support for running multiple
interpreters concurrently in different threads.  In conjunction with
the \fIperl_clone()\fR \s-1API\s0 call, which can be used to selectively duplicate
the state of any given interpreter, it is possible to compile a
piece of code once in an interpreter, clone that interpreter
one or more times, and run all the resulting interpreters in distinct
threads.
.PP
On the Windows platform, this feature is used to emulate \fIfork()\fR at the
interpreter level.  See perlfork for details about that.
.PP
This feature is still in evolution.  It is eventually meant to be used
to selectively clone a subroutine and data reachable from that
subroutine in a separate interpreter and run the cloned subroutine
in a separate thread.  Since there is no shared data between the
interpreters, little or no locking will be needed (unless parts of
the symbol table are explicitly shared).  This is obviously intended
to be an easy-to-use replacement for the existing threads support.
.PP
Support for cloning interpreters and interpreter concurrency can be
enabled using the \-Dusethreads Configure option (see win32/Makefile for
how to enable it on Windows.)  The resulting perl executable will be
functionally identical to one that was built with \-Dmultiplicity, but
the \fIperl_clone()\fR \s-1API\s0 call will only be available in the former.
.PP
\&\-Dusethreads enables the cpp macro \s-1USE_ITHREADS\s0 by default, which in turn
enables Perl source code changes that provide a clear separation between
the op tree and the data it operates with.  The former is immutable, and
can therefore be shared between an interpreter and all of its clones,
while the latter is considered local to each interpreter, and is therefore
copied for each clone.
.PP
Note that building Perl with the \-Dusemultiplicity Configure option
is adequate if you wish to run multiple \fBindependent\fR interpreters
concurrently in different threads.  \-Dusethreads only provides the
additional functionality of the \fIperl_clone()\fR \s-1API\s0 call and other
support for running \fBcloned\fR interpreters concurrently.
.PP
.Vb 2
\&    NOTE: This is an experimental feature.  Implementation details are
\&    subject to change.
.Ve
.Sh "Lexically scoped warning categories"
.IX Subsection "Lexically scoped warning categories"
You can now control the granularity of warnings emitted by perl at a finer
level using the \f(CW\*(C`use warnings\*(C'\fR pragma.  warnings and perllexwarn
have copious documentation on this feature.
.Sh "Unicode and \s-1UTF\-8\s0 support"
.IX Subsection "Unicode and UTF-8 support"
Perl now uses \s-1UTF\-8\s0 as its internal representation for character
strings.  The \f(CW\*(C`utf8\*(C'\fR and \f(CW\*(C`bytes\*(C'\fR pragmas are used to control this support
in the current lexical scope.  See perlunicode, utf8 and bytes for
more information.
.PP
This feature is expected to evolve quickly to support some form of I/O
disciplines that can be used to specify the kind of input and output data
(bytes or characters).  Until that happens, additional modules from \s-1CPAN\s0
will be needed to complete the toolkit for dealing with Unicode.
.PP
.Vb 2
\&    NOTE: This should be considered an experimental feature.  Implementation
\&    details are subject to change.
.Ve
.Sh "Support for interpolating named characters"
.IX Subsection "Support for interpolating named characters"
The new \f(CW\*(C`\eN\*(C'\fR escape interpolates named characters within strings.
For example, \f(CW"Hi! \eN{WHITE SMILING FACE}"\fR evaluates to a string
with a unicode smiley face at the end.
.ie n .Sh """our"" declarations"
.el .Sh "``our'' declarations"
.IX Subsection "our declarations"
An \*(L"our\*(R" declaration introduces a value that can be best understood
as a lexically scoped symbolic alias to a global variable in the
package that was current where the variable was declared.  This is
mostly useful as an alternative to the \f(CW\*(C`vars\*(C'\fR pragma, but also provides
the opportunity to introduce typing and other attributes for such
variables.  See \*(L"our\*(R" in perlfunc.
.Sh "Support for strings represented as a vector of ordinals"
.IX Subsection "Support for strings represented as a vector of ordinals"
Literals of the form \f(CW\*(C`v1.2.3.4\*(C'\fR are now parsed as a string composed
of characters with the specified ordinals.  This is an alternative, more
readable way to construct (possibly unicode) strings instead of
interpolating characters, as in \f(CW"\ex{1}\ex{2}\ex{3}\ex{4}"\fR.  The leading
\&\f(CW\*(C`v\*(C'\fR may be omitted if there are more than two ordinals, so \f(CW1.2.3\fR is
parsed the same as \f(CW\*(C`v1.2.3\*(C'\fR.
.PP
Strings written in this form are also useful to represent version \*(L"numbers\*(R".
It is easy to compare such version \*(L"numbers\*(R" (which are really just plain
strings) using any of the usual string comparison operators \f(CW\*(C`eq\*(C'\fR, \f(CW\*(C`ne\*(C'\fR,
\&\f(CW\*(C`lt\*(C'\fR, \f(CW\*(C`gt\*(C'\fR, etc., or perform bitwise string operations on them using \f(CW\*(C`|\*(C'\fR,
\&\f(CW\*(C`&\*(C'\fR, etc.
.PP
In conjunction with the new \f(CW$^V\fR magic variable (which contains
the perl version as a string), such literals can be used as a readable way
to check if you're running a particular version of Perl:
.PP
.Vb 4
\&    # this will parse in older versions of Perl also
\&    if ($^V and $^V gt v5.6.0) {
\&        # new features supported
\&    }
.Ve
.PP
\&\f(CW\*(C`require\*(C'\fR and \f(CW\*(C`use\*(C'\fR also have some special magic to support such
literals, but this particular usage should be avoided because it leads to
misleading error messages under versions of Perl which don't support vector
strings.  Using a true version number will ensure correct behavior in all
versions of Perl:
.PP
.Vb 2
\&    require 5.006;    # run time check for v5.6
\&    use 5.006_001;    # compile time check for v5.6.1
.Ve
.PP
Also, \f(CW\*(C`sprintf\*(C'\fR and \f(CW\*(C`printf\*(C'\fR support the Perl-specific format flag \f(CW%v\fR
to print ordinals of characters in arbitrary strings:
.PP
.Vb 3
\&    printf "v%vd", $^V;         # prints current version, such as "v5.5.650"
\&    printf "%*vX", ":", $addr;  # formats IPv6 address
\&    printf "%*vb", " ", $bits;  # displays bitstring
.Ve
.PP
See \*(L"Scalar value constructors\*(R" in perldata for additional information.
.Sh "Improved Perl version numbering system"
.IX Subsection "Improved Perl version numbering system"
Beginning with Perl version 5.6.0, the version number convention has been
changed to a \*(L"dotted integer\*(R" scheme that is more commonly found in open
source projects.
.PP
Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc.
The next development series following v5.6.0 will be numbered v5.7.x,
beginning with v5.7.0, and the next major production release following
v5.6.0 will be v5.8.0.
.PP
The English module now sets \f(CW$PERL_VERSION\fR to $^V (a string value) rather
than \f(CW$]\fR (a numeric value).  (This is a potential incompatibility.
Send us a report via perlbug if you are affected by this.)
.PP
The v1.2.3 syntax is also now legal in Perl.
See \*(L"Support for strings represented as a vector of ordinals\*(R" for more on that.
.PP
To cope with the new versioning system's use of at least three significant
digits for each version component, the method used for incrementing the
subversion number has also changed slightly.  We assume that versions older