-TODO: perl591delta and further
+=encoding utf8
=head1 NAME
-perldelta - what is new for perl 5.10.0
+perl5100delta - what is new for perl 5.10.0
=head1 DESCRIPTION
releases; they are not duplicated here and are documented in the set of
man pages named perl58[1-8]?delta.
-=head1 Incompatible Changes
-
-=head2 Packing and UTF-8 strings
-
-=for XXX update this
-
-The semantics of pack() and unpack() regarding UTF-8-encoded data has been
-changed. Processing is now by default character per character instead of
-byte per byte on the underlying encoding. Notably, code that used things
-like C<pack("a*", $string)> to see through the encoding of string will now
-simply get back the original $string. Packed strings can also get upgraded
-during processing when you store upgraded characters. You can get the old
-behaviour by using C<use bytes>.
-
-To be consistent with pack(), the C<C0> in unpack() templates indicates
-that the data is to be processed in character mode, i.e. character by
-character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
-the packed string is processed in its UTF-8-encoded Unicode form on a byte
-by byte basis. This is reversed with regard to perl 5.8.X.
-
-Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
-respectively character and byte modes.
-
-C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
-specified encoding mode, honoring parens grouping. Previously, parens were
-ignored.
-
-Also, there is a new pack() character format, C<W>, which is intended to
-replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
-the strings internal representation. C<W> represents unsigned (logical)
-character values, which can be greater than 255. It is therefore more
-robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
-values outside the range 0..255, and not respect the string encoding).
-
-In practice, that means that pack formats are now encoding-neutral, except
-C<C>.
-
-For consistency, C<A> in unpack() format now trims all Unicode whitespace
-from the end of the string. Before perl 5.9.2, it used to strip only the
-classical ASCII space characters.
-
-=head2 Byte/character count feature in unpack()
-
-A new unpack() template character, C<".">, returns the number of bytes or
-characters (depending on the selected encoding mode, see above) read so far.
-
-=head2 The C<$*> and C<$#> variables have been removed
-
-C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
-modifiers, has been removed.
-
-The deprecated C<$#> variable (output format for numbers) has been
-removed.
-
-Two new warnings, C<$#/$* is no longer supported>, have been added.
-
-=head2 substr() lvalues are no longer fixed-length
-
-The lvalues returned by the three argument form of substr() used to be a
-"fixed length window" on the original string. In some cases this could
-cause surprising action at distance or other undefined behaviour. Now the
-length of the window adjusts itself to the length of the string assigned to
-it.
-
-=head2 Parsing of C<-f _>
-
-The identifier C<_> is now forced to be a bareword after a filetest
-operator. This solves a number of misparsing issues when a global C<_>
-subroutine is defined.
-
-=head2 C<:unique>
-
-The C<:unique> attribute has been made a no-op, since its current
-implementation was fundamentally flawed and not threadsafe.
-
-=head2 Scoping of the C<sort> pragma
-
-The C<sort> pragma is now lexically scoped. Its effect used to be global.
-
-=head2 Scoping of C<bignum>, C<bigint>, C<bigrat>
-
-The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
-lexically scoped. (Tels)
-
-=head2 Effect of pragmas in eval
-
-The compile-time value of the C<%^H> hint variable can now propagate into
-eval("")uated code. This makes it more useful to implement lexical
-pragmas.
-
-As a side-effect of this, the overloaded-ness of constants now propagates
-into eval("").
-
-=head2 chdir FOO
-
-A bareword argument to chdir() is now recognized as a file handle.
-Earlier releases interpreted the bareword as a directory name.
-(Gisle Aas)
-
-=head2 Handling of .pmc files
-
-An old feature of perl was that before C<require> or C<use> look for a
-file with a F<.pm> extension, they will first look for a similar filename
-with a F<.pmc> extension. If this file is found, it will be loaded in
-place of any potentially existing file ending in a F<.pm> extension.
-
-Previously, F<.pmc> files were loaded only if more recent than the
-matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
-they exist.
-
-=head2 @- and @+ in patterns
-
-The special arrays C<@-> and C<@+> are no longer interpolated in regular
-expressions. (Sadahiro Tomoyuki)
-
-=head2 $AUTOLOAD can now be tainted
-
-If you call a subroutine by a tainted name, and if it defers to an
-AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
-(Rick Delaney)
-
-=head2 Tainting and printf
-
-When perl is run under taint mode, C<printf()> and C<sprintf()> will now
-reject any tainted format argument. (Rafael Garcia-Suarez)
-
-=head2 undef and signal handlers
-
-Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
-equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
-
-=head2 strictures and array/hash dereferencing in defined()
-
-C<defined @$foo> and C<defined %$bar> are now subject to C<strict 'refs'>
-(that is, C<$foo> and C<$bar> shall be proper references there.)
-(Nicholas Clark)
-
-(However, C<defined(@foo)> and C<defined(%bar)> are discouraged constructs
-anyway.)
-
-=head2 C<(?p{})> has been removed
-
-The regular expression construct C<(?p{})>, which was deprecated in perl
-5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
-
-=head2 Pseudo-hashes have been removed
-
-Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
-pragma remains here, but uses an alternate implementation.)
-
-=head2 Removal of the bytecode compiler and of perlcc
-
-C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
-B::Bytecode, etc.) are no longer distributed with the perl sources. Those
-experimental tools have never worked reliably, and, due to the lack of
-volunteers to keep them in line with the perl interpreter developments, it
-was decided to remove them instead of shipping a broken version of those.
-The last version of those modules can be found with perl 5.9.4.
-
-However the B compiler framework stays supported in the perl core, as with
-the more useful modules it has permitted (among others, B::Deparse and
-B::Concise).
-
-=head2 Removal of the JPL
-
-The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
-
-=head2 Recursive inheritance detected earlier
-
-Perl will now immediately throw an exception if you modify any package's
-C<@ISA> in such a way that it would cause recursive inheritance.
-
-Previously, the exception would not occur until Perl attempted to make
-use of the recursive inheritance while resolving a method or doing a
-C<$foo-E<gt>isa($bar)> lookup.
-
=head1 Core Enhancements
=head2 The C<feature> pragma
Currently the following new features are available: C<switch> (adds a
switch statement), C<say> (adds a C<say> built-in function), and C<state>
-(adds an C<state> keyword for declaring "static" variables). Those
+(adds a C<state> keyword for declaring "static" variables). Those
features are described in their own sections of this document.
The C<feature> pragma is also implicitly loaded when you require a minimal
=head2 Defined-or operator
A new operator C<//> (defined-or) has been implemented.
-The following statement:
+The following expression:
$a // $b
defined $a ? $a : $b
-and
+and the statement
$c //= $d;
< # match an opening angle bracket
(?: # match one of:
(?> # don't backtrack over the inside of this group
- [^<>]+ # one or more non angle brackets
+ [^<>]+ # one or more non angle brackets
) # end non backtracking group
| # ... or ...
(?1) # recurse to bracket 1 and try it again
$ # end of line
/x
-Note, users experienced with PCRE will find that the Perl implementation
-of this feature differs from the PCRE one in that it is possible to
-backtrack into a recursed pattern, whereas in PCRE the recursion is
-atomic or "possessive" in nature. (Yves Orton)
+PCRE users should note that Perl's recursive regex feature allows
+backtracking into a recursed pattern, whereas in PCRE the recursion is
+atomic or "possessive" in nature. As in the example above, you can
+add (?>) to control this selectively. (Yves Orton)
=item Named Capture Buffers
syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
access the contents of the capture buffers.
-Thus, to replace all doubled chars, one could write
+Thus, to replace all doubled chars with a single copy, one could write
s/(?<letter>.)\k<letter>/$+{letter}/g
=item C<\K> escape
The functionality of Jeff Pinyan's module Regexp::Keep has been added to
-the core. You can now use in regular expressions the special escape C<\K>
+the core. In regular expressions you can now use the special escape C<\K>
as a way to do something like floating length positive lookbehind. It is
also useful in substitutions like:
=item Vertical and horizontal whitespace, and linebreak
-Regular expressions now recognize the C<\v> and C<\h> escapes, that match
+Regular expressions now recognize the C<\v> and C<\h> escapes that match
vertical and horizontal whitespace, respectively. C<\V> and C<\H>
logically match their complements.
C<\R> matches a generic linebreak, that is, vertical whitespace, plus
the multi-character sequence C<"\x0D\x0A">.
+=item Optional pre-match and post-match captures with the /p flag
+
+There is a new flag C</p> for regular expressions. Using this
+makes the engine preserve a copy of the part of the matched string before
+the matching substring to the new special variable C<${^PREMATCH}>, the
+part after the matching substring to C<${^POSTMATCH}>, and the matched
+substring itself to C<${^MATCH}>.
+
+Perl is still able to store these substrings to the special variables
+C<$`>, C<$'>, C<$&>, but using these variables anywhere in the program
+adds a penalty to all regular expression matches, whereas if you use
+the C</p> flag and the new special variables instead, you pay only for
+the regular expressions where the flag is used.
+
+For more detail on the new variables, see L<perlvar>; for the use of
+the regular expression flag, see L<perlop> and L<perlre>.
+
=back
=head2 C<say()>
In a scope where C<$_> has been lexicalized, you can still have access to
the global version of C<$_> by using C<$::_>, or, more simply, by
-overriding the lexical declaration with C<our $_>.
+overriding the lexical declaration with C<our $_>. (Rafael Garcia-Suarez)
=head2 The C<_> prototype
-A new prototype character has been added. C<_> is equivalent to C<$> (it
-denotes a scalar), but defaults to C<$_> if the corresponding argument
-isn't supplied. Due to the optional nature of the argument, you can only
-use it at the end of a prototype, or before a semicolon.
+A new prototype character has been added. C<_> is equivalent to C<$> but
+defaults to C<$_> if the corresponding argument isn't supplied (both C<$>
+and C<_> denote a scalar). Due to the optional nature of the argument,
+you can only use it at the end of a prototype, or before a semicolon.
This has a small incompatible consequence: the prototype() function has
been adjusted to return C<_> for some built-ins in appropriate cases (for
A new pragma, C<mro> (for Method Resolution Order) has been added. It
permits to switch, on a per-class basis, the algorithm that perl uses to
-find inherited methods in case of a mutiple inheritance hierachy. The
+find inherited methods in case of a multiple inheritance hierarchy. The
default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
available: the C3 algorithm. See L<mro> for more information.
(Brandon Black)
-Note that, due to changes in the implentation of class hierarchy search,
+Note that, due to changes in the implementation of class hierarchy search,
code that used to undef the C<*ISA> glob will most probably break. Anyway,
undef'ing C<*ISA> had the side-effect of removing the magic on the @ISA
-array and should not have been done in the first place.
+array and should not have been done in the first place. Also, the
+cache C<*::ISA::CACHE::> no longer exists; to force reset the @ISA cache,
+you now need to use the C<mro> API, or more simply to assign to @ISA
+(e.g. with C<@ISA = @ISA>).
+
+=head2 readdir() may return a "short filename" on Windows
+
+The readdir() function may return a "short filename" when the long
+filename contains characters outside the ANSI codepage. Similarly
+Cwd::cwd() may return a short directory name, and glob() may return short
+names as well. On the NTFS file system these short names can always be
+represented in the ANSI codepage. This will not be true for all other file
+system drivers; e.g. the FAT filesystem stores short filenames in the OEM
+codepage, so some files on FAT volumes remain unaccessible through the
+ANSI APIs.
+
+Similarly, $^X, @INC, and $ENV{PATH} are preprocessed at startup to make
+sure all paths are valid in the ANSI codepage (if possible).
+
+The Win32::GetLongPathName() function now returns the UTF-8 encoded
+correct long file name instead of using replacement characters to force
+the name into the ANSI codepage. The new Win32::GetANSIPathName()
+function can be used to turn a long pathname into a short one only if the
+long one cannot be represented in the ANSI codepage.
+
+Many other functions in the C<Win32> module have been improved to accept
+UTF-8 encoded arguments. Please see L<Win32> for details.
=head2 readpipe() is now overridable
Moreover, it now defaults to C<$_> if no argument is provided. (Rafael
Garcia-Suarez)
-=head2 default argument for readline()
+=head2 Default argument for readline()
readline() now defaults to C<*ARGV> if no argument is provided. (Rafael
Garcia-Suarez)
To use state variables, one needs to enable them by using
- use feature "state";
+ use feature 'state';
or by using the C<-E> command-line switch in one-liners.
-See L<perlsub/"Persistent variables via state()">.
+See L<perlsub/"Persistent Private Variables">.
=head2 Stacked filetest operators
See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
-=head2 C<CLONE_SKIP()>
-
-Perl has now support for the C<CLONE_SKIP> special subroutine. Like
-C<CLONE>, C<CLONE_SKIP> is called once per package; however, it is called
-just before cloning starts, and in the context of the parent thread. If it
-returns a true value, then no objects of that class will be cloned. See
-L<perlmod> for details. (Contributed by Dave Mitchell.)
-
=head2 Formats
Formats were improved in several ways. A new field, C<^*>, can be used for
The constant folding routine is now wrapped in an exception handler, and
if folding throws an exception (such as attempting to evaluate 0/0), perl
now retains the current optree, rather than aborting the whole program.
-(Nicholas Clark, Dave Mitchell)
+Without this change, programs would not compile if they had expressions that
+happened to generate exceptions, even though those expressions were in code
+that could never be reached at runtime. (Nicholas Clark, Dave Mitchell)
=head2 Source filters in @INC
This variable gives the native status returned by the last pipe close,
backtick command, successful call to wait() or waitpid(), or from the
-system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)
+system() operator. See L<perlvar> for details. (Contributed by Gisle Aas.)
+
+=item C<${^RE_TRIE_MAXBUF}>
+
+See L</"Trie optimisation of literal string alternations">.
+
+=item C<${^WIN32_SLOPPY_STAT}>
+
+See L</"Sloppy stat on Windows">.
=back
octal.
The B<-C> option can no longer be used on the C<#!> line. It wasn't
-working there anyway.
+working there anyway, since the standard streams are already set up
+at this point in the execution of the perl interpreter. You can use
+binmode() instead to get the desired behaviour.
=head2 UCD 5.0.0
The copy of the Unicode Character Database included in Perl 5 has
been updated to version 5.0.0.
-
=head2 MAD
-MAD, which stands for I<Misc Attribute Decoration>, is a
+MAD, which stands for I<Miscellaneous Attribute Decoration>, is a
still-in-development work leading to a Perl 5 to Perl 6 converter. To
enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
-obtained perl isn't binary compatible with a regular perl 5.9.4, and has
+obtained perl isn't binary compatible with a regular perl 5.10, and has
space and speed penalties; moreover not all regression tests still pass
with it. (Larry Wall, Nicholas Clark)
-=head1 Modules and Pragmata
+=head2 kill() on Windows
-=head1 Utility Changes
+On Windows platforms, C<kill(-9, $pid)> now kills a process tree.
+(On Unix, this delivers the signal to all processes in the same process
+group.)
-=over 4
+=head1 Incompatible Changes
-=item *
+=head2 Packing and UTF-8 strings
-The Perl debugger can now save all debugger commands for sourcing later;
-notably, it can now emulate stepping backwards, by restarting and
-rerunning all bar the last command from a saved command history.
+The semantics of pack() and unpack() regarding UTF-8-encoded data has been
+changed. Processing is now by default character per character instead of
+byte per byte on the underlying encoding. Notably, code that used things
+like C<pack("a*", $string)> to see through the encoding of string will now
+simply get back the original $string. Packed strings can also get upgraded
+during processing when you store upgraded characters. You can get the old
+behaviour by using C<use bytes>.
-It can also display the parent inheritance tree of a given class, with the
-C<i> command.
+To be consistent with pack(), the C<C0> in unpack() templates indicates
+that the data is to be processed in character mode, i.e. character by
+character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
+the packed string is processed in its UTF-8-encoded Unicode form on a byte
+by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
+between pack() and unpack().
-Perl has a new -dt command-line flag, which enables threads support in the
-debugger.
+Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
+respectively character and byte modes.
-=back
+C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
+specified encoding mode, honoring parens grouping. Previously, parens were
+ignored.
-=head1 New Documentation
+Also, there is a new pack() character format, C<W>, which is intended to
+replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
+the strings internal representation. C<W> represents unsigned (logical)
+character values, which can be greater than 255. It is therefore more
+robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
+values outside the range 0..255, and not respect the string encoding).
-The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
-is now documented.
+In practice, that means that pack formats are now encoding-neutral, except
+C<C>.
-=head1 Performance Enhancements
+For consistency, C<A> in unpack() format now trims all Unicode whitespace
+from the end of the string. Before perl 5.9.2, it used to strip only the
+classical ASCII space characters.
-Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
-making a temporary copy of the array.
+=head2 Byte/character count feature in unpack()
-Access to elements of lexical arrays via a numeric constant between 0 and
-255 is now faster. (This used to be only the case for global arrays.)
+A new unpack() template character, C<".">, returns the number of bytes or
+characters (depending on the selected encoding mode, see above) read so far.
-=head1 Installation and Configuration Improvements
+=head2 The C<$*> and C<$#> variables have been removed
-=head1 Selected Bug Fixes
+C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
+modifiers, has been removed.
-C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
+The deprecated C<$#> variable (output format for numbers) has been
+removed.
-=head1 New or Changed Diagnostics
+Two new severe warnings, C<$#/$* is no longer supported>, have been added.
-A new deprecation warning, I<Deprecated use of my() in false conditional>,
-has been added, to warn against the use of the dubious and deprecated
-construct
+=head2 substr() lvalues are no longer fixed-length
- my $x if 0;
+The lvalues returned by the three argument form of substr() used to be a
+"fixed length window" on the original string. In some cases this could
+cause surprising action at distance or other undefined behaviour. Now the
+length of the window adjusts itself to the length of the string assigned to
+it.
-See L<perldiag>. Use C<state> variables instead.
+=head2 Parsing of C<-f _>
-=head1 Changed Internals
+The identifier C<_> is now forced to be a bareword after a filetest
+operator. This solves a number of misparsing issues when a global C<_>
+subroutine is defined.
-=head2 Reordering of SVt_* constants
+=head2 C<:unique>
-The relative ordering of constants that define the various types of C<SV>
-have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
-C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
+The C<:unique> attribute has been made a no-op, since its current
+implementation was fundamentally flawed and not threadsafe.
+
+=head2 Effect of pragmas in eval
+
+The compile-time value of the C<%^H> hint variable can now propagate into
+eval("")uated code. This makes it more useful to implement lexical
+pragmas.
+
+As a side-effect of this, the overloaded-ness of constants now propagates
+into eval("").
+
+=head2 chdir FOO
+
+A bareword argument to chdir() is now recognized as a file handle.
+Earlier releases interpreted the bareword as a directory name.
+(Gisle Aas)
+
+=head2 Handling of .pmc files
+
+An old feature of perl was that before C<require> or C<use> look for a
+file with a F<.pm> extension, they will first look for a similar filename
+with a F<.pmc> extension. If this file is found, it will be loaded in
+place of any potentially existing file ending in a F<.pm> extension.
+
+Previously, F<.pmc> files were loaded only if more recent than the
+matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
+they exist.
+
+=head2 $^V is now a C<version> object instead of a v-string
+
+$^V can still be used with the C<%vd> format in printf, but any
+character-level operations will now access the string representation
+of the C<version> object and not the ordinals of a v-string.
+Expressions like C<< substr($^V, 0, 2) >> or C<< split //, $^V >>
+no longer work and must be rewritten.
+
+=head2 @- and @+ in patterns
+
+The special arrays C<@-> and C<@+> are no longer interpolated in regular
+expressions. (Sadahiro Tomoyuki)
+
+=head2 $AUTOLOAD can now be tainted
+
+If you call a subroutine by a tainted name, and if it defers to an
+AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
+(Rick Delaney)
+
+=head2 Tainting and printf
+
+When perl is run under taint mode, C<printf()> and C<sprintf()> will now
+reject any tainted format argument. (Rafael Garcia-Suarez)
+
+=head2 undef and signal handlers
+
+Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
+equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
+
+=head2 strictures and dereferencing in defined()
+
+C<use strict 'refs'> was ignoring taking a hard reference in an argument
+to defined(), as in :
+
+ use strict 'refs';
+ my $x = 'foo';
+ if (defined $$x) {...}
+
+This now correctly produces the run-time error C<Can't use string as a
+SCALAR ref while "strict refs" in use>.
+
+C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
+'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
+(C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
+(Nicholas Clark)
+
+=head2 C<(?p{})> has been removed
+
+The regular expression construct C<(?p{})>, which was deprecated in perl
+5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
+
+=head2 Pseudo-hashes have been removed
+
+Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
+pragma remains here, but uses an alternate implementation.)
+
+=head2 Removal of the bytecode compiler and of perlcc
+
+C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
+B::Bytecode, etc.) are no longer distributed with the perl sources. Those
+experimental tools have never worked reliably, and, due to the lack of
+volunteers to keep them in line with the perl interpreter developments, it
+was decided to remove them instead of shipping a broken version of those.
+The last version of those modules can be found with perl 5.9.4.
+
+However the B compiler framework stays supported in the perl core, as with
+the more useful modules it has permitted (among others, B::Deparse and
+B::Concise).
+
+=head2 Removal of the JPL
+
+The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.
+
+=head2 Recursive inheritance detected earlier
+
+Perl will now immediately throw an exception if you modify any package's
+C<@ISA> in such a way that it would cause recursive inheritance.
+
+Previously, the exception would not occur until Perl attempted to make
+use of the recursive inheritance while resolving a method or doing a
+C<$foo-E<gt>isa($bar)> lookup.
+
+=head2 warnings::enabled and warnings::warnif changed to favor users of modules
+
+The behaviour in 5.10.x favors the person using the module;
+The behaviour in 5.8.x favors the module writer;
+
+Assume the following code:
+
+ main calls Foo::Bar::baz()
+ Foo::Bar inherits from Foo::Base
+ Foo::Bar::baz() calls Foo::Base::_bazbaz()
+ Foo::Base::_bazbaz() calls: warnings::warnif('substr', 'some warning
+message');
+
+On 5.8.x, the code warns when Foo::Bar contains C<use warnings;>
+It does not matter if Foo::Base or main have warnings enabled
+to disable the warning one has to modify Foo::Bar.
+
+On 5.10.0 and newer, the code warns when main contains C<use warnings;>
+It does not matter if Foo::Base or Foo::Bar have warnings enabled
+to disable the warning one has to modify main.
+
+=head1 Modules and Pragmata
+
+=head2 Upgrading individual core modules
+
+Even more core modules are now also available separately through the
+CPAN. If you wish to update one of these modules, you don't need to
+wait for a new perl release. From within the cpan shell, running the
+'r' command will report on modules with upgrades available. See
+C<perldoc CPAN> for more information.
+
+=head2 Pragmata Changes
+
+=over 4
+
+=item C<feature>
+
+The new pragma C<feature> is used to enable new features that might break
+old code. See L</"The C<feature> pragma"> above.
+
+=item C<mro>
+
+This new pragma enables to change the algorithm used to resolve inherited
+methods. See L</"New Pragma, C<mro>"> above.
+
+=item Scoping of the C<sort> pragma
+
+The C<sort> pragma is now lexically scoped. Its effect used to be global.
+
+=item Scoping of C<bignum>, C<bigint>, C<bigrat>
+
+The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
+lexically scoped. (Tels)
+
+=item C<base>
+
+The C<base> pragma now warns if a class tries to inherit from itself.
+(Curtis "Ovid" Poe)
+
+=item C<strict> and C<warnings>
+
+C<strict> and C<warnings> will now complain loudly if they are loaded via
+incorrect casing (as in C<use Strict;>). (Johan Vromans)
+
+=item C<version>
+
+The C<version> module provides support for version objects.
+
+=item C<warnings>
+
+The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
+that used C<Carp> routines without having loaded it at compile time might
+need to be adjusted; typically, the following (faulty) code won't work
+anymore, and will require parentheses to be added after the function name:
+
+ use warnings;
+ require Carp;
+ Carp::confess 'argh';
+
+=item C<less>
+
+C<less> now does something useful (or at least it tries to). In fact, it
+has been turned into a lexical pragma. So, in your modules, you can now
+test whether your users have requested to use less CPU, or less memory,
+less magic, or maybe even less fat. See L<less> for more. (Joshua ben
+Jore)
+
+=back
+
+=head2 New modules
+
+=over 4
+
+=item *
+
+C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
+whenever an ASCII character string containing high-bit bytes is implicitly
+converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
+perls, its effect is global.
+
+=item *
+
+C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
+you what versions of core modules ship with any versions of Perl 5. It
+comes with a command-line frontend, C<corelist>.
+
+=item *
+
+C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
+C<Math::BigInt::Calc>.
+
+=item *
+
+C<Compress::Zlib> is an interface to the zlib compression library. It
+comes with a bundled version of zlib, so having a working zlib is not a
+prerequisite to install it. It's used by C<Archive::Tar> (see below).
+
+=item *
+
+C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
+
+=item *
+
+C<Archive::Tar> is a module to manipulate C<tar> archives.
+
+=item *
+
+C<Digest::SHA> is a module used to calculate many types of SHA digests,
+has been included for SHA support in the CPAN module.
+
+=item *
+
+C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
+
+=item *
+
+C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
+provides support for I<field hashes>: hashes that maintain an association
+of a reference with a value, in a thread-safe garbage-collected way.
+Such hashes are useful to implement inside-out objects.
+
+=item *
+
+C<Module::Build>, by Ken Williams, has been added. It's an alternative to
+C<ExtUtils::MakeMaker> to build and install perl modules.
+
+=item *
+
+C<Module::Load>, by Jos Boumans, has been added. It provides a single
+interface to load Perl modules and F<.pl> files.
+
+=item *
+
+C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
+modules as loaded or unloaded.
+
+=item *
+
+C<Package::Constants>, by Jos Boumans, has been added. It's a simple
+helper to list all constants declared in a given package.
+
+=item *
+
+C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
+This module provides low-level access to Win32 system API calls for
+files/dirs.
+
+=item *
+
+C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
+C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
+included in the perl core; the behaviour of C<Locale::Maketext::Simple>
+gracefully degrades when the later isn't present.
+
+=item *
+
+C<Params::Check> implements a generic input parsing/checking mechanism. It
+is used by CPANPLUS.
+
+=item *
+
+C<Term::UI> simplifies the task to ask questions at a terminal prompt.
+
+=item *
+
+C<Object::Accessor> provides an interface to create per-object accessors.
+
+=item *
+
+C<Module::Pluggable> is a simple framework to create modules that accept
+pluggable sub-modules.
+
+=item *
+
+C<Module::Load::Conditional> provides simple ways to query and possibly
+load installed modules.
+
+=item *
+
+C<Time::Piece> provides an object oriented interface to time functions,
+overriding the built-ins localtime() and gmtime().
+
+=item *
+
+C<IPC::Cmd> helps to find and run external commands, possibly
+interactively.
+
+=item *
+
+C<File::Fetch> provide a simple generic file fetching mechanism.
+
+=item *
+
+C<Log::Message> and C<Log::Message::Simple> are used by the log facility
+of C<CPANPLUS>.
+
+=item *
+
+C<Archive::Extract> is a generic archive extraction mechanism
+for F<.tar> (plain, gzipped or bzipped) or F<.zip> files.
+
+=item *
+
+C<CPANPLUS> provides an API and a command-line tool to access the CPAN
+mirrors.
+
+=item *
+
+C<Pod::Escapes> provides utilities that are useful in decoding Pod
+EE<lt>...E<gt> sequences.
+
+=item *
+
+C<Pod::Simple> is now the backend for several of the Pod-related modules
+included with Perl.
+
+=back
+
+=head2 Selected Changes to Core Modules
+
+=over 4
+
+=item C<Attribute::Handlers>
+
+C<Attribute::Handlers> can now report the caller's file and line number.
+(David Feldman)
+
+All interpreted attributes are now passed as array references. (Damian
+Conway)
+
+=item C<B::Lint>
+
+C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
+with plugins. (Joshua ben Jore)
+
+=item C<B>
+
+It's now possible to access the lexical pragma hints (C<%^H>) by using the
+method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
+can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
+ben Jore)
+
+=item C<Thread>
+
+As the old 5005thread threading model has been removed, in favor of the
+ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
+be used in old code only. It has been removed from the default list of
+dynamic extensions.
+
+=back
+
+=head1 Utility Changes
+
+=over 4
+
+=item perl -d
+
+The Perl debugger can now save all debugger commands for sourcing later;
+notably, it can now emulate stepping backwards, by restarting and
+rerunning all bar the last command from a saved command history.
+
+It can also display the parent inheritance tree of a given class, with the
+C<i> command.
+
+=item ptar
+
+C<ptar> is a pure perl implementation of C<tar> that comes with
+C<Archive::Tar>.
+
+=item ptardiff
+
+C<ptardiff> is a small utility used to generate a diff between the contents
+of a tar archive and a directory tree. Like C<ptar>, it comes with
+C<Archive::Tar>.
+
+=item shasum
+
+C<shasum> is a command-line utility, used to print or to check SHA
+digests. It comes with the new C<Digest::SHA> module.
+
+=item corelist
+
+The C<corelist> utility is now installed with perl (see L</"New modules">
+above).
+
+=item h2ph and h2xs
+
+C<h2ph> and C<h2xs> have been made more robust with regard to
+"modern" C code.
+
+C<h2xs> implements a new option C<--use-xsloader> to force use of
+C<XSLoader> even in backwards compatible modules.
+
+The handling of authors' names that had apostrophes has been fixed.
+
+Any enums with negative values are now skipped.
+
+=item perlivp
+
+C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
+option to run I<all> tests.
+
+=item find2perl
+
+C<find2perl> now assumes C<-print> as a default action. Previously, it
+needed to be specified explicitly.
+
+Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
+C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
+added.
+
+=item config_data
+
+C<config_data> is a new utility that comes with C<Module::Build>. It
+provides a command-line interface to the configuration of Perl modules
+that use Module::Build's framework of configurability (that is,
+C<*::ConfigData> modules that contain local configuration information for
+their parent modules.)
+
+=item cpanp
+
+C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, a
+helper for CPANPLUS operation, has been added too, but isn't intended for
+direct use).
+
+=item cpan2dist
+
+C<cpan2dist> is a new utility that comes with CPANPLUS. It's a tool to
+create distributions (or packages) from CPAN modules.
+
+=item pod2html
+
+The output of C<pod2html> has been enhanced to be more customizable via
+CSS. Some formatting problems were also corrected. (Jari Aalto)
+
+=back
+
+=head1 New Documentation
+
+The L<perlpragma> manpage documents how to write one's own lexical
+pragmas in pure Perl (something that is possible starting with 5.9.4).
+
+The new L<perlglossary> manpage is a glossary of terms used in the Perl
+documentation, technical and otherwise, kindly provided by O'Reilly Media,
+Inc.
+
+The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
+Perl regular expression engine.
+
+The L<perlreapi> manpage describes the interface to the perl interpreter
+used to write pluggable regular expression engines (by Ævar Arnfjörð
+Bjarmason).
+
+The L<perlunitut> manpage is a tutorial for programming with Unicode and
+string encodings in Perl, courtesy of Juerd Waalboer.
+
+A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
+(Juerd Waalboer).
+
+The L<perlcommunity> manpage gives a description of the Perl community
+on the Internet and in real life. (Edgar "Trizor" Bering)
+
+The L<CORE> manual page documents the C<CORE::> namespace. (Tels)
+
+The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
+is now documented.
+
+=head1 Performance Enhancements
+
+=head2 In-place sorting
+
+Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
+making a temporary copy of the array.
+
+Likewise, C<reverse sort ...> is now optimized to sort in reverse,
+avoiding the generation of a temporary intermediate list.
+
+=head2 Lexical array access
+
+Access to elements of lexical arrays via a numeric constant between 0 and
+255 is now faster. (This used to be only the case for global arrays.)
+
+=head2 XS-assisted SWASHGET
+
+Some pure-perl code that perl was using to retrieve Unicode properties and
+transliteration mappings has been reimplemented in XS.
+
+=head2 Constant subroutines
+
+The interpreter internals now support a far more memory efficient form of
+inlineable constants. Storing a reference to a constant value in a symbol
+table is equivalent to a full typeglob referencing a constant subroutine,
+but using about 400 bytes less memory. This proxy constant subroutine is
+automatically upgraded to a real typeglob with subroutine if necessary.
+The approach taken is analogous to the existing space optimisation for
+subroutine stub declarations, which are stored as plain scalars in place
+of the full typeglob.
+
+Several of the core modules have been converted to use this feature for
+their system dependent constants - as a result C<use POSIX;> now takes about
+200K less memory.
+
+=head2 C<PERL_DONT_CREATE_GVSV>
+
+The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
+in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
+from creating an empty scalar with every new typeglob. See L<perl589delta>
+for details.
+
+=head2 Weak references are cheaper
+
+Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
+Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
+happens at program exit, it may be skipped completely.
+
+=head2 sort() enhancements
+
+Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
+and to speed up some cases.
+
+=head2 Memory optimisations
+
+Several internal data structures (typeglobs, GVs, CVs, formats) have been
+restructured to use less memory. (Nicholas Clark)
+
+=head2 UTF-8 cache optimisation
+
+The UTF-8 caching code is now more efficient, and used more often.
+(Nicholas Clark)
+
+=head2 Sloppy stat on Windows
+
+On Windows, perl's stat() function normally opens the file to determine
+the link count and update attributes that may have been changed through
+hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up
+stat() by not performing this operation. (Jan Dubois)
+
+=head2 Regular expressions optimisations
+
+=over 4
+
+=item Engine de-recursivised
+
+The regular expression engine is no longer recursive, meaning that
+patterns that used to overflow the stack will either die with useful
+explanations, or run to completion, which, since they were able to blow
+the stack before, will likely take a very long time to happen. If you were
+experiencing the occasional stack overflow (or segfault) and upgrade to
+discover that now perl apparently hangs instead, look for a degenerate
+regex. (Dave Mitchell)
+
+=item Single char char-classes treated as literals
+
+Classes of a single character are now treated the same as if the character
+had been used as a literal, meaning that code that uses char-classes as an
+escaping mechanism will see a speedup. (Yves Orton)
+
+=item Trie optimisation of literal string alternations
+
+Alternations, where possible, are optimised into more efficient matching
+structures. String literal alternations are merged into a trie and are
+matched simultaneously. This means that instead of O(N) time for matching
+N alternations at a given point, the new code performs in O(1) time.
+A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune
+this optimization. (Yves Orton)
+
+B<Note:> Much code exists that works around perl's historic poor
+performance on alternations. Often the tricks used to do so will disable
+the new optimisations. Hopefully the utility modules used for this purpose
+will be educated about these new optimisations.
+
+=item Aho-Corasick start-point optimisation
+
+When a pattern starts with a trie-able alternation and there aren't
+better optimisations available, the regex engine will use Aho-Corasick
+matching to find the start point. (Yves Orton)
+
+=back
+
+=head1 Installation and Configuration Improvements
+
+=head2 Configuration improvements
+
+=over 4
+
+=item C<-Dusesitecustomize>
+
+Run-time customization of @INC can be enabled by passing the
+C<-Dusesitecustomize> flag to Configure. When enabled, this will make perl
+run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
+then be set up to add additional entries to @INC.
+
+=item Relocatable installations
+
+There is now Configure support for creating a relocatable perl tree. If
+you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
+everything else in %Config) can be optionally located via the path of the
+perl executable.
+
+That means that, if the string C<".../"> is found at the start of any
+path, it's substituted with the directory of $^X. So, the relocation can
+be configured on a per-directory basis, although the default with
+C<-Duserelocatableinc> is that everything is relocated. The initial
+install is done to the original configured prefix.
+
+=item strlcat() and strlcpy()
+
+The configuration process now detects whether strlcat() and strlcpy() are
+available. When they are not available, perl's own version is used (from
+Russ Allbery's public domain implementation). Various places in the perl
+interpreter now use them. (Steve Peters)
+
+=item C<d_pseudofork> and C<d_printf_format_null>
+
+A new configuration variable, available as C<$Config{d_pseudofork}> in
+the L<Config> module, has been added, to distinguish real fork() support
+from fake pseudofork used on Windows platforms.
+
+A new configuration variable, C<d_printf_format_null>, has been added,
+to see if printf-like formats are allowed to be NULL.
+
+=item Configure help
+
+C<Configure -h> has been extended with the most commonly used options.
+
+=back
+
+=head2 Compilation improvements
+
+=over 4
+
+=item Parallel build
+
+Parallel makes should work properly now, although there may still be problems
+if C<make test> is instructed to run in parallel.
+
+=item Borland's compilers support
+
+Building with Borland's compilers on Win32 should work more smoothly. In
+particular Steve Hay has worked to side step many warnings emitted by their
+compilers and at least one C compiler internal error.
+
+=item Static build on Windows
+
+Perl extensions on Windows now can be statically built into the Perl DLL.
+
+Also, it's now possible to build a C<perl-static.exe> that doesn't depend
+on the Perl DLL on Win32. See the Win32 makefiles for details.
+(Vadim Konovalov)
+
+=item ppport.h files
+
+All F<ppport.h> files in the XS modules bundled with perl are now
+autogenerated at build time. (Marcus Holland-Moritz)
+
+=item C++ compatibility
+
+Efforts have been made to make perl and the core XS modules compilable
+with various C++ compilers (although the situation is not perfect with
+some of the compilers on some of the platforms tested.)
+
+=item Support for Microsoft 64-bit compiler
+
+Support for building perl with Microsoft's 64-bit compiler has been
+improved. (ActiveState)
+
+=item Visual C++
+
+Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).
+
+=item Win32 builds
+
+All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
+
+=back
+
+=head2 Installation improvements
+
+=over 4
+
+=item Module auxiliary files
+
+README files and changelogs for CPAN modules bundled with perl are no
+longer installed.
+
+=back
+
+=head2 New Or Improved Platforms
+
+Perl has been reported to work on Symbian OS. See L<perlsymbian> for more
+information.
+
+Many improvements have been made towards making Perl work correctly on
+z/OS.
+
+Perl has been reported to work on DragonFlyBSD and MidnightBSD.
+
+Perl has also been reported to work on NexentaOS
+( http://www.gnusolaris.org/ ).
+
+The VMS port has been improved. See L<perlvms>.
+
+Support for Cray XT4 Catamount/Qk has been added. See
+F<hints/catamount.sh> in the source code distribution for more
+information.
+
+Vendor patches have been merged for RedHat and Gentoo.
+
+DynaLoader::dl_unload_file() now works on Windows.
+
+=head1 Selected Bug Fixes
+
+=over 4
+
+=item strictures in regexp-eval blocks
+
+C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
+
+=item Calling CORE::require()
+
+CORE::require() and CORE::do() were always parsed as require() and do()
+when they were overridden. This is now fixed.
+
+=item Subscripts of slices
+
+You can now use a non-arrowed form for chained subscripts after a list
+slice, like in:
+
+ ({foo => "bar"})[0]{foo}
+
+This used to be a syntax error; a C<< -> >> was required.
+
+=item C<no warnings 'category'> works correctly with -w
+
+Previously when running with warnings enabled globally via C<-w>, selective
+disabling of specific warning categories would actually turn off all warnings.
+This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
+C<io> class. Previously it would erroneously turn off all warnings.
+
+=item threads improvements
+
+Several memory leaks in ithreads were closed. Also, ithreads were made
+less memory-intensive.
+
+C<threads> is now a dual-life module, also available on CPAN. It has been
+expanded in many ways. A kill() method is available for thread signalling.
+One can get thread status, or the list of running or joinable threads.
+
+A new C<< threads->exit() >> method is used to exit from the application
+(this is the default for the main thread) or from the current thread only
+(this is the default for all other threads). On the other hand, the exit()
+built-in now always causes the whole application to terminate. (Jerry
+D. Hedden)
+
+=item chr() and negative values
+
+chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
+character, unless when the C<bytes> pragma is in effect, where the low
+eight bits of the value are used.
+
+=item PERL5SHELL and tainting
+
+On Windows, the PERL5SHELL environment variable is now checked for
+taintedness. (Rafael Garcia-Suarez)
+
+=item Using *FILE{IO}
+
+C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
+filehandles. (Steve Peters)
+
+=item Overloading and reblessing
+
+Overloading now works when references are reblessed into another class.
+Internally, this has been implemented by moving the flag for "overloading"
+from the reference to the referent, which logically is where it should
+always have been. (Nicholas Clark)
+
+=item Overloading and UTF-8
+
+A few bugs related to UTF-8 handling with objects that have
+stringification overloaded have been fixed. (Nicholas Clark)
+
+=item eval memory leaks fixed
+
+Traditionally, C<eval 'syntax error'> has leaked badly. Many (but not all)
+of these leaks have now been eliminated or reduced. (Dave Mitchell)
+
+=item Random device on Windows
+
+In previous versions, perl would read the file F</dev/urandom> if it
+existed when seeding its random number generator. That file is unlikely
+to exist on Windows, and if it did would probably not contain appropriate
+data, so perl no longer tries to read it on Windows. (Alex Davies)
+
+=item PERLIO_DEBUG
+
+The C<PERLIO_DEBUG> environment variable no longer has any effect for
+setuid scripts and for scripts run with B<-T>.
+
+Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
+an internal buffer overflow. This has been fixed.
+
+=item PerlIO::scalar and read-only scalars
+
+PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
+seek() is now supported with PerlIO::scalar-based filehandles, the
+underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
+
+=item study() and UTF-8
+
+study() never worked for UTF-8 strings, but could lead to false results.
+It's now a no-op on UTF-8 data. (Yves Orton)
+
+=item Critical signals
+
+The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
+"unsafe" manner (contrary to other signals, that are deferred until the
+perl interpreter reaches a reasonably stable state; see
+L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
+
+=item @INC-hook fix
+
+When a module or a file is loaded through an @INC-hook, and when this hook
+has set a filename entry in %INC, __FILE__ is now set for this module
+accordingly to the contents of that %INC entry. (Rafael)
+
+=item C<-t> switch fix
+
+The C<-w> and C<-t> switches can now be used together without messing
+up which categories of warnings are activated. (Rafael)
+
+=item Duping UTF-8 filehandles
+
+Duping a filehandle which has the C<:utf8> PerlIO layer set will now
+properly carry that layer on the duped filehandle. (Rafael)
+
+=item Localisation of hash elements
+
+Localizing a hash element whose key was given as a variable didn't work
+correctly if the variable was changed while the local() was in effect (as
+in C<local $h{$x}; ++$x>). (Bo Lindbergh)
+
+=back
+
+=head1 New or Changed Diagnostics
+
+=over 4
+
+=item Use of uninitialized value
+
+Perl will now try to tell you the name of the variable (if any) that was
+undefined.
+
+=item Deprecated use of my() in false conditional
+
+A new deprecation warning, I<Deprecated use of my() in false conditional>,
+has been added, to warn against the use of the dubious and deprecated
+construct
+
+ my $x if 0;
+
+See L<perldiag>. Use C<state> variables instead.
+
+=item !=~ should be !~
+
+A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
+of the non-matching operator.
+
+=item Newline in left-justified string
+
+The warning I<Newline in left-justified string> has been removed.
+
+=item Too late for "-T" option
+
+The error I<Too late for "-T" option> has been reformulated to be more
+descriptive.
+
+=item "%s" variable %s masks earlier declaration
+
+This warning is now emitted in more consistent cases; in short, when one
+of the declarations involved is a C<my> variable:
+
+ my $x; my $x; # warns
+ my $x; our $x; # warns
+ our $x; my $x; # warns
+
+On the other hand, the following:
+
+ our $x; our $x;
+
+now gives a C<"our" variable %s redeclared> warning.
+
+=item readdir()/closedir()/etc. attempted on invalid dirhandle
+
+These new warnings are now emitted when a dirhandle is used but is
+either closed or not really a dirhandle.
+
+=item Opening dirhandle/filehandle %s also as a file/directory
+
+Two deprecation warnings have been added: (Rafael)
+
+ Opening dirhandle %s also as a file
+ Opening filehandle %s also as a directory
+
+=item Use of -P is deprecated
+
+Perl's command-line switch C<-P> is now deprecated.
+
+=item v-string in use/require is non-portable
+
+Perl will warn you against potential backwards compatibility problems with
+the C<use VERSION> syntax.
+
+=item perl -V
+
+C<perl -V> has several improvements, making it more useable from shell
+scripts to get the value of configuration variables. See L<perlrun> for
+details.
+
+=back
+
+=head1 Changed Internals
+
+In general, the source code of perl has been refactored, tidied up,
+and optimized in many places. Also, memory management and allocation
+has been improved in several points.
+
+When compiling the perl core with gcc, as many gcc warning flags are
+turned on as is possible on the platform. (This quest for cleanliness
+doesn't extend to XS code because we cannot guarantee the tidiness of
+code we didn't write.) Similar strictness flags have been added or
+tightened for various other C compilers.
+
+=head2 Reordering of SVt_* constants
+
+The relative ordering of constants that define the various types of C<SV>
+have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
+C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
difference unless you have code that explicitly makes assumptions about that
ordering. (The inheritance hierarchy of C<B::*> objects has been changed
to reflect this.)
+=head2 Elimination of SVt_PVBM
+
+Related to this, the internal type C<SVt_PVBM> has been removed. This
+dedicated type of C<SV> was used by the C<index> operator and parts of the
+regexp engine to facilitate fast Boyer-Moore matches. Its use internally has
+been replaced by C<SV>s of type C<SVt_PVGV>.
+
+=head2 New type SVt_BIND
+
+A new type C<SVt_BIND> has been added, in readiness for the project to
+implement Perl 6 on 5. There deliberately is no implementation yet, and
+they cannot yet be created or destroyed.
+
=head2 Removal of CPP symbols
The C preprocessor symbols C<PERL_PM_APIVERSION> and
=head2 Less space is used by ops
The C<BASEOP> structure now uses less space. The C<op_seq> field has been
-removed and replaced by the one-bit fields C<op_opt>. C<op_type> is now 9
+removed and replaced by a single bit bit-field C<op_opt>. C<op_type> is now 9
bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
method anymore.)
perl's parser is now generated by bison (it used to be generated by
byacc.) As a result, it seems to be a bit more robust.
-=head1 New Tests
+Also, Dave Mitchell improved the lexer debugging output under C<-DT>.
+
+=head2 Use of C<const>
+
+Andy Lester supplied many improvements to determine which function
+parameters and local variables could actually be declared C<const> to the C
+compiler. Steve Peters provided new C<*_set> macros and reworked the core to
+use these rather than assigning to macros in LVALUE context.
+
+=head2 Mathoms
+
+A new file, F<mathoms.c>, has been added. It contains functions that are
+no longer used in the perl core, but that remain available for binary or
+source compatibility reasons. However, those functions will not be
+compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
+
+=head2 C<AvFLAGS> has been removed
+
+The C<AvFLAGS> macro has been removed.
+
+=head2 C<av_*> changes
+
+The C<av_*()> functions, used to manipulate arrays, no longer accept null
+C<AV*> parameters.
+
+=head2 $^H and %^H
+
+The implementation of the special variables $^H and %^H has changed, to
+allow implementing lexical pragmas in pure Perl.
+
+=head2 B:: modules inheritance changed
+
+The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
+inherits from C<B::SV> (it used to inherit from C<B::IV>).
+
+=head2 Anonymous hash and array constructors
+
+The anonymous hash and array constructors now take 1 op in the optree
+instead of 3, now that pp_anonhash and pp_anonlist return a reference to
+a hash/array when the op is flagged with OPf_SPECIAL. (Nicholas Clark)
=head1 Known Problems
C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
F<t/op/mydef.t>.)
+Stacked filetest operators won't work when the C<filetest> pragma is in
+effect, because they rely on the stat() buffer C<_> being populated, and
+filetest bypasses stat().
+
+=head2 UTF-8 problems
+
+The handling of Unicode still is unclean in several places, where it's
+dependent on whether a string is internally flagged as UTF-8. This will
+be made more consistent in perl 5.12, but that won't be possible without
+a certain amount of backwards incompatibility.
+
=head1 Platform Specific Problems
+When compiled with g++ and thread support on Linux, it's reported that the
+C<$!> stops working correctly. This is related to the fact that the glibc
+provides two strerror_r(3) implementation, and perl selects the wrong
+one.
+
=head1 Reporting Bugs
+If you find what you think is a bug, you might check the articles
+recently posted to the comp.lang.perl.misc newsgroup and the perl
+bug database at http://rt.perl.org/rt3/ . There may also be
+information at http://www.perl.org/ , the Perl Home Page.
+
+If you believe you have an unreported bug, please run the B<perlbug>
+program included with your release. Be 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.org to be
+analysed by the Perl porting team.
+
=head1 SEE ALSO
The F<Changes> file and the perl590delta to perl595delta man pages for
https://perl5.git.perl.org / perl5.git / blobdiff