PERL5216DELTA(1) Perl Programmers Reference Guide PERL5216DELTA(1)NAMEperl5216delta - what is new for perl v5.21.6
DESCRIPTION
This document describes differences between the 5.21.5 release and the
5.21.6 release.
If you are upgrading from an earlier release such as 5.21.4, first read
perl5215delta, which describes differences between 5.21.4 and 5.21.5.
Core Enhancements
List form of pipe open implemented for Win32
The list form of pipe:
open my $fh, "-|", "program", @arguments;
is now implemented on Win32. It has the same limitations as "system
LIST" on Win32, since the Win32 API doesn't accept program arguments as
a list.
Assignment to list repetition
"(...) x ..." can now be used within a list that is assigned to, as
long as the left-hand side is a valid lvalue. This allows
"(undef,undef,$foo) = that_function()" to be written as "((undef)x2,
$foo) = that_function()".
"close" now sets $!
When an I/O error occurs, the fact that there has been an error is
recorded in the handle. "close" returns false for such a handle.
Previously, the value of $! would be untouched by "close", so the
common convention of writing "close $fh or die $!" did not work
reliably. Now the handle records the value of $!, too, and "close"
restores it.
Deprecations
Use of non-graphic characters in single-character variable names
The syntax for single-character variable names is more lenient than for
longer variable names, allowing the one-character name to be a
punctuation character or even invisible (a non-graphic). Perl v5.20
deprecated the ASCII-range controls as such a name. Now, all non-
graphic characters that formerly were allowed are deprecated. The
practical effect of this occurs only when not under "use utf8", and
affects just the C1 controls (code points 0x80 through 0xFF), NO-BREAK
SPACE, and SOFT HYPHEN.
Inlining of "sub () { $var }" with observable side-effects
In many cases Perl makes sub () { $var } into an inlinable constant
subroutine, capturing the value of $var at the time the "sub"
expression is evaluated. This can break the closure behaviour in those
cases where $var is subsequently modified. The subroutine won't return
the new value.
This usage is now deprecated in those cases where the variable could be
modified elsewhere. Perl detects those cases and emits a deprecation
warning. Such code will likely change in the future and stop producing
a constant.
If your variable is only modified in the place where it is declared,
then Perl will continue to make the sub inlinable with no warnings.
sub make_constant {
my $var = shift;
return sub () { $var }; # fine
}
sub make_constant_deprecated {
my $var;
$var = shift;
return sub () { $var }; # deprecated
}
sub make_constant_deprecated2 {
my $var = shift;
log_that_value($var); # could modify $var
return sub () { $var }; # deprecated
}
In the second example above, detecting that $var is assigned to only
once is too hard to detect. That it happens in a spot other than the
"my" declaration is enough for Perl to find it suspicious.
This deprecation warning happens only for a simple variable for the
body of the sub. (A "BEGIN" block or "use" statement inside the sub is
ignored, because it does not become part of the sub's body.) For more
complex cases, such as "sub () { do_something() if 0; $var }" the
behaviour has changed such that inlining does not happen if the
variable is modifiable elsewhere. Such cases should be rare.
Performance Enhancements
· "(...)x1", "("constant")x0" and "($scalar)x0" are now optimised in
list context. If the right-hand argument is a constant 1, the
repetition operator disappears. If the right-hand argument is a
constant 0, the whole expressions is optimised to the empty list,
so long as the left-hand argument is a simple scalar or constant.
"(foo())x0" is not optimised.
· "substr" assignment is now optimised into 4-argument "substr" at
the end of a subroutine (or as the argument to "return").
Previously, this optimisation only happened in void context.
· Assignment to lexical variables is often optimised away. For
instance, in "$lexical = chr $foo", the "chr" operator writes
directly to the lexical variable instead of returning a value that
gets copied. This optimisation has been extended to "split", "x"
and "vec" on the right-hand side. It has also been made to work
with state variable initialization.
· In "\L...", "\Q...", etc., the extra "stringify" op is now
optimised away, making these just as fast as "lcfirst",
"quotemeta", etc.
· Assignment to an empty list is now sometimes faster. In
particular, it never calls "FETCH" on tied arguments on the right-
hand side, whereas it used to sometimes.
Modules and Pragmata
Updated Modules and Pragmata
· B has been upgraded from version 1.52 to 1.53.
· B::Concise has been upgraded from version 0.994 to 0.995.
· B::Deparse has been upgraded from version 1.29 to 1.30.
It now deparses "+sub : attr { ... }" correctly at the start of a
statement. Without the initial "+", "sub" would be a statement
label.
"BEGIN" blocks are now emitted in the right place most of the time,
but the change unfortunately introduced a regression, in that
"BEGIN" blocks occurring just before the end of the enclosing block
may appear below it instead. So this change may need to be
reverted if it cannot be fixed before Perl 5.22. [perl #77452]
B::Deparse no longer puts erroneous "local" here and there, such as
for "LIST = tr/a//d". [perl #119815]
Adjacent "use" statements are no longer accidentally nested if one
contains a "do" block. [perl #115066]
· B::Op_private has been upgraded from version 5.021005 to 5.021006.
It now includes a hash named %ops_using, list all op types that use
a particular private flag.
· CPAN::Meta has been upgraded from version 2.142690 to 2.143240.
· CPAN::Meta::Requirements has been upgraded from version 2.128 to
2.130.
· Devel::Peek has been upgraded from version 1.18 to 1.19.
· Digest::SHA has been upgraded from version 5.92 to 5.93.
· DynaLoader has been upgraded from version 1.27 to 1.28.
· Encode has been upgraded from version 2.62 to 2.64.
· experimental has been upgraded from version 0.012 to 0.013.
· Exporter has been upgraded from version 5.71 to 5.72.
· ExtUtils::MakeMaker has been upgraded from version 6.98 to 7.02.
· ExtUtils::Manifest has been upgraded from version 1.68 to 1.69.
· ExtUtils::ParseXS has been upgraded from version 3.25 to 3.26.
· HTTP::Tiny has been upgraded from version 0.050 to 0.051.
· I18N::Langinfo has been upgraded from version 0.11 to 0.12.
· IO::Socket has been upgraded from version 1.37 to 1.38.
Document the limitations of the connected() method. [perl #123096]
· locale has been upgraded from version 1.04 to 1.05.
· Module::CoreList has been upgraded from version 5.20141020 to
5.20141120.
· overload has been upgraded from version 1.23 to 1.24.
· PerlIO::encoding has been upgraded from version 0.19 to 0.20.
· PerlIO::scalar has been upgraded from version 0.19 to 0.20.
· POSIX has been upgraded from version 1.45 to 1.46.
· re has been upgraded from version 0.27 to 0.28.
· Test::Harness has been upgraded from version 3.33 to 3.34.
· Test::Simple has been upgraded from version 1.001008 to
1.301001_075.
· Unicode::UCD has been upgraded from version 0.58 to 0.59.
· warnings has been upgraded from version 1.28 to 1.29.
· XSLoader has been upgraded from version 0.18 to 0.19.
Documentation
Changes to Existing Documentation
"Identifier parsing" in perldata
· The syntax of single-character variable names has been brought up-
to-date and more fully explained.
Diagnostics
The following additions or changes have been made to diagnostic output,
including warnings and fatal error messages. For the complete list of
diagnostic messages, see perldiag.
New Diagnostics
New Warnings
· Use of literal non-graphic characters in variable names is
deprecated
· A new "locale" warning category has been created, with the
following warning messages currently in it:
· Locale '%s' may not work well.%s
· Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".
· Warning: unable to close filehandle %s properly: %s
· The following two warnings for "tr///" used to be skipped if the
transliteration contained wide characters, but now they occur
regardless of whether there are wide characters or not:
Useless use of /d modifier in transliteration operator
Replacement list is longer than search list
Changes to Existing Diagnostics
· Quantifier unexpected on zero-length expression in regex m/%s/.
This message has had the "<-- HERE" marker removed, as it was
always placed at the end of the regular expression, regardless of
where the problem actually occurred. [perl #122680]
· Setting $/ to a reference to %s as a form of slurp is deprecated,
treating as undef
This warning is now a default warning, like other deprecation
warnings.
Configuration and Compilation
· Configure with "-Dmksymlinks" should now be faster. [perl #122002]
· As well as the gzip and bzip2 tarballs, this release has been made
available as an xz utils compressed tarball.
Platform Support
Platform-Specific Notes
Win32
· In the experimental ":win32" layer, a crash in "open" was fixed.
Also opening "/dev/null", which works the Win32 Perl's normal
":unix" layer, was implemented for ":win32". [perl #122224]
<https://rt.perl.org/Ticket/Display.html?id=122224>
· A new makefile option, "USE_LONG_DOUBLE", has been added to the
Windows dmake makefile for gcc builds only. Set this to "define"
if you want perl to use long doubles to give more accuracy and
range for floating point numbers.
Internal Changes
· "screaminstr" has been removed. Although marked as public API, it
is undocumented and has no usage in modern perl versions on CPAN
Grep. Calling it has been fatal since 5.17.0.
· "newDEFSVOP", "block_start", "block_end" and "intro_my" have been
added to the API.
· The internal "convert" function in op.c has been renamed
"op_convert_list" and added to the API.
· "sv_magic" no longer forbids "ext" magic on read-only values.
After all, perl can't know whether the custom magic will modify the
SV or not. [perl #123103]
· Starting in 5.21.6, accessing "CvPADLIST" in perlapi in an XSUB is
forbidden. CvPADLIST has be reused for a different internal
purpose for XSUBs. Guard all CvPADLIST expressions with
"CvISXSUB()" if your code doesn't already block XSUB CV*s from
going through optree CV* expecting code.
Selected Bug Fixes
· fchmod() and futimes() now set $! when they fail due to being
passed a closed file handle. [perl #122703]
· Perl now comes with a corrected Unicode 7.0 for the erratum issued
on October 21, 2014 (see
<http://www.unicode.org/errata/#current_errata>), dealing with
glyph shaping in Arabic.
· op_free() no longer crashes due to a stack overflow when freeing a
deeply recursive op tree. [perl #108276]
· scalarvoid() would crash due to a stack overflow when processing a
deeply recursive op tree. [perl #108276]
· In Perl 5.20.0, $^N accidentally had the internal UTF8 flag turned
off if accessed from a code block within a regular expression,
effectively UTF8-encoding the value. This has been fixed. [perl
#123135]
· A failed "semctl" call no longer overwrites existing items on the
stack, causing "(semctl(-1,0,0,0))[0]" to give an "uninitialized"
warning.
· "else{foo()}" with no space before "foo" is now better at assigning
the right line number to that statement. [perl #122695]
· Sometimes the assignment in "@array = split" gets optimised and
"split" itself writes directly to the array. This caused a bug,
preventing this assignment from being used in lvalue context. So
"(@a=split//,"foo")=bar()" was an error. (This bug probably goes
back to Perl 3, when the optimisation was added.) This
optimisation, and the bug, started to happen in more cases in
5.21.5. It has now been fixed. [perl #123057]
· When argument lists that fail the checks installed by subroutine
signatures, the resulting error messages now give the file and line
number of the caller, not of the called subroutine. [perl #121374]
· Flip-flop operators (".." and "..." in scalar context) used to
maintain a separate state for each recursion level (the number of
times the enclosing sub was called recursively), contrary to the
documentation. Now each closure has one internal state for each
flip-flop. [perl #122829]
· "use", "no", statement labels, special blocks ("BEGIN") and pod are
now permitted as the first thing in a "map" or "grep" block, the
block after "print" or "say" (or other functions) returning a
handle, and within "${...}", "@{...}", etc. [perl #122782]
· The repetition operator "x" now propagates lvalue context to its
left-hand argument when used in contexts like "foreach". That
allows "for(($#that_array)x2) { ... }" to work as expected if the
loop modifies $_.
· "(...) x ..." in scalar context used to corrupt the stack if one
operand were an object with "x" overloading, causing erratic
behaviour. [perl #121827]
· Assignment to a lexical scalar is often optimised away (as
mentioned under "Performance Enhancements"). Various bugs related
to this optimisation have been fixed. Certain operators on the
right-hand side would sometimes fail to assign the value at all or
assign the wrong value, or would call STORE twice or not at all on
tied variables. The operators affected were "$foo++", "$foo--",
and "-$foo" under "use integer", "chomp", "chr" and "setpgrp".
· List assignments were sometimes buggy if the same scalar ended up
on both sides of the assignment due to used of "tied", "values" or
"each". The result would be the wrong value getting assigned.
· "setpgrp($nonzero)" (with one argument) was accidentally changed in
5.16 to mean setpgrp(0). This has been fixed.
· "__SUB__" could return the wrong value or even corrupt memory under
the debugger (the -d switch) and in subs containing "eval $string".
· When "sub () { $var }" becomes inlinable, it now returns a
different scalar each time, just as a non-inlinable sub would,
though Perl still optimises the copy away in cases where it would
make no observable difference.
· "my sub f () { $var }" and "sub () : attr { $var }" are no longer
eligible for inlining. The former would crash; the latter would
just throw the attributes away. An exception is made for the
little-known ":method" attribute, which does nothing much.
· Inlining of subs with an empty prototype is now more consistent
than before. Previously, a sub with multiple statements, all but
the last optimised away, would be inlinable only if it were an
anonymous sub containing a string "eval" or "state" declaration or
closing over an outer lexical variable (or any anonymous sub under
the debugger). Now any sub that gets folded to a single constant
after statements have been optimised away is eligible for inlining.
This applies to things like "sub () { jabber() if DEBUG; 42 }".
Some subroutines with an explicit "return" were being made
inlinable, contrary to the documentation, Now "return" always
prevents inlining.
· On some systems, such as VMS, "crypt" can return a non-ASCII
string. If a scalar assigned to had contained a UTF8 string
previously, then "crypt" would not turn off the UTF8 flag, thus
corrupting the return value. This would happen with "$lexical =
crypt ...".
· "crypt" no longer calls "FETCH" twice on a tied first argument.
· An unterminated here-doc on the last line of a quote-like operator
("qq[${ <<END }]", "/(?{ <<END })/") no longer causes a double
free. It started doing so in 5.18.
· Fixed two assertion failures introduced into "-DPERL_OP_PARENT"
builds. [perl #108276]
Known Problems
· Builds on FreeBSD 10.x currently fail when compiling POSIX. A
workaround is to specify "-Ui_fenv" when running "Configure".
Errata From Previous Releases
· Due to a mistake in the string-copying logic, copying the value of
a state variable could instead steal the value and undefine the
variable. This bug, introduced in 5.20, would happen mostly for
long strings (1250 chars or more), but could happen for any strings
under builds with copy-on-write disabled. [perl #123029]
This bug was actually fixed in 5.21.5, but it was not until after
that release that this bug, and the fact that it had been fixed,
were discovered.
· If a named sub tries to access a scalar declared in an outer
anonymous sub, the variable is not available, so the named sub gets
its own undefined scalar. In 5.10, attempts to take a reference to
the variable ("\$that_variable") began returning a reference to a
copy of it instead. This was accidentally fixed in 5.21.4, but the
bug and its fix were not noticed till now.
Acknowledgements
Perl 5.21.6 represents approximately 4 weeks of development since Perl
5.21.5 and contains approximately 60,000 lines of changes across 920
files from 25 authors.
Excluding auto-generated files, documentation and release tools, there
were approximately 48,000 lines of changes to 630 .pm, .t, .c and .h
files.
Perl continues to flourish into its third decade thanks to a vibrant
community of users and developers. The following people are known to
have contributed the improvements that became Perl 5.21.6:
Aaron Crane, Abigail, Andrew Fresh, Andy Dougherty, Brian Fraser, Chad
Granum, Chris 'BinGOs' Williams, Craig A. Berry, Daniel Dragan, David
Mitchell, Doug Bell, Father Chrysostomos, Glenn D. Golden, James E
Keenan, Jarkko Hietaniemi, Jim Cromie, Karen Etheridge, Karl
Williamson, Lukas Mai, Ricardo Signes, Shlomi Fish, Slaven Rezic, Steve
Hay, Tony Cook, Yaroslav Kuzmin.
The list above is almost certainly incomplete as it is automatically
generated from version control history. In particular, it does not
include the names of the (very much appreciated) contributors who
reported issues to the Perl bug tracker.
Many of the changes included in this version originated in the CPAN
modules included in Perl's core. We're grateful to the entire CPAN
community for helping Perl to flourish.
For a more complete list of all of Perl's historical contributors,
please see the AUTHORS file in the Perl source distribution.
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 https://rt.perl.org/ . 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 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 "perl -V", will be sent off to perlbug@perl.org to be analysed by
the Perl porting team.
If the bug you are reporting has security implications, which make it
inappropriate to send to a publicly archived mailing list, then please
send it to perl5-security-report@perl.org. This points to a closed
subscription unarchived mailing list, which includes all the core
committers, who will be able to help assess the impact of issues,
figure out a resolution, and help co-ordinate the release of patches to
mitigate or fix the problem across all platforms on which Perl is
supported. Please only use this address for security issues in the
Perl core, not for modules independently distributed on CPAN.
SEE ALSO
The Changes file for an explanation of how to view exhaustive details
on what changed.
The INSTALL file for how to build Perl.
The README file for general stuff.
The Artistic and Copying files for copyright information.
perl v5.22.0 2015-05-13 PERL5216DELTA(1)
