This Week on perl5-porters - 4-10 May 2008
Today, I was doing some mucking about with class data, generated
packages, and "Class::ISA", and I started to wail and gnash my teeth.
I cried, "Why can't I just replace the darn object system?"
-- Ricardo Signes, a man with a method.
Topics of Interest
fascinating paper: heapsort with n log(n) - 0.9n comparisons
Last week, Marc Lehmann had tossed out a link to an interesting paper
he had read on heapsorts, with a new implementation that purported to
require fewer comparisons.
This week John P. Lindeman wrote a very thoughtful reply that's worth
reading in its own right. In essence, one of the fundamental problems
facing heapsort these days is that it is very cache-unfriendly.
Quicksort and mergesort tend to process data sequentially, and that
plays nicely with how caches behave. Heapsort, on the other hand,
tends to skip around all over the place, and that leaves the cache
lines cold and unloved. And so John feels that heapsort will be
unlikely to beat the other algorithms consistently, especially when
large datasets are processed, which is where the correct use of cache
comes into play.
welcome to the real world
http://xrl.us/bkkda
Helping 5.8.9
Nicholas Clark asked for some volunteers to help with the mundane
pumpking tasks that need doing when a new release goes out the door.
Such things as checking author/email names, module versioning,
dual-life synchronisations and making suggestions for
perl589delta.pod.
Yitzchak Scott-Thoennes checked out most of the CPAN/core
discrepancies. Steffen Müller did the author names.
out-sourcing pumpkingship
http://xrl.us/bkkdc
add Porting/mk_gitignore.pl
Jim Cromie started to play around with git, and the more he looked at
it, the more he liked it. He proposed a script to deal with ignoring
files not under revision control, but Rafael thought that he had the
logic completely backwards.
git down
http://xrl.us/bkkde
Adding new keywords
Simon Wistow, in a flash of inspiration, realised that it would be fun
to dive into the guts and figure out how to add a new keyword to the
language, such as "method", which would start out being a simple alias
for "sub". He was quite surprised at how easy it was, and on which
side things that can be implemented both inside or outside the core
should be.
Jonathan Rockway muttered about "Devel::Declare" and
"Method::Signatures". Jesse Vincent revealed that Chia-liang Kao and
Yuval Kogman were working on "Perl6-Declare" that was much more robust
and flexible than "Method::Signatures".
Matt S. Trout thought that Jesse's recent work on MAD and Yuval's
start on "B::Simple" should be a big help in making the perl5 syntax
more malleable.
anyone for "with"
http://xrl.us/bkkdg
TODO Tests
Bram saw what he thought was a flaw in the infrastructure for dealing
with TODO tests. Imagine a function that should return 1. Except it
doesn't, because a bug that no-one understands makes it return 2.
So we write a TODO test to say "this should return 1". Now imagine
that the bug was tickled, and now the function returns 3. Currently
there's no way of detecting that the value, while still incorrect, has
changed. Some people were dubious about the value of detecting this.
different kinds of wrong
http://xrl.us/bkkdi
Documentation bug or brain bug? (or, what \k<name> and $+{name} refer to)
Sébastien Aperghis-Tramoni had a couple of questions about the new
5.10 regexp extensions (or rather, the documentation that explains
their behaviour). After a couple of porters worked the the problems in
the wording, Aristotle Pagaltzis wrote up a new description, that Yves
Orton thought was a good description.
http://xrl.us/bkkdk
Understanding refcounts
Simon Wistow was looking at "Devel::Gladiator", a module that examines
memory allocations in arenas (geddit?), and wondered why, given two
nearly identical snippets, one leaked massively while the other
didn't.
Naturally, Dave Mitchell gave a cogent explanation as to why, and
demonstrated a simpler case in a couple of lines of Perl, no modules
needed.
http://xrl.us/bkkdn
Thoughts about overloading method calls
Ricardo Signes want to do some exotic things with classes, objects and
overloading. Aristotle Pagaltzis admitted to having wanted to do as
much in the past. Ævar Arnfjörð Bjarmason had thought of doing even
more bizarre things, and I would say more, but alas this paragraph is
too small for it to fit.
The thread is well worth reading in its entirety, for a view on the
current thinking on allowing more flexible syntaxes.
http://xrl.us/bkkdp
Recursive inheritance detected while looking for method
Lyle ran into a problem with recursive inheritance and wondered why
things didn't work in a way that would make it possible.
Nicholas Clark explained that the code that looks after this was
heavily rewritten thanks to Brandon Black and his MRO work. He also
thought that it should be possible to plug in a custom MRO handler
that would do what Lyle wanted.
http://xrl.us/bkkdr
"File::Path::mkpath()" incompatibility in perl-5.10
Gisle Aas demonstrated a problem in the 2.x version of "File::Path"'s
mkpath creating unwanted directories. David Landgren offered a
work-around, and began to work a better solution.
the right path
http://xrl.us/bkkdt
Should potentially confusing labels emit a warning?
Following up on Andy Lester's blog about the grief caused by "BEGIN: {
}", which is a labelled lexical scope rather than a "BEGIN" block,
there was a tentative suggestion to make such things warn.
Most people weren't too comfortable with the idea, suggesting that if
it was really a problem then it would have wound up on the TODO list
at some point.
JFDDI
http://xrl.us/bkkdv
Special blocks below the top-level scope
In playing around with BEGIN blocks while researching things from the
above thread, Aristotle Pagaltzis came across some some strange
behaviour with a BEGIN block within a subroutine.
Nicholas explained how it was quite consistent given the rules
concerning compile-time and run-time effects, and Jan Dubois wrapped
out the remaining doubts.
http://xrl.us/bkkdx
On the almost impossibility to write correct XS modules
Marc Lehmann had raised the problem of "char *" as an interface to
character strings in XS last week. Yves Orton pointed out that this is
used internally by the core, and thus faces the same issues. Win32 is
particularly sensitive to the issue.
http://xrl.us/bkkdz
TODO of the week
chromatic proposed a patch for the TODO from last week. Yay!
the yada yada yada operator
http://xrl.us/bkkd3
and a revised patch to add the "...", "!!!", and "???" operators
the yada yada yada trinity
http://xrl.us/bkkd5
readpipe(LIST)
"system()" accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
running a shell. "readpipe()" (the function behind "qx//") could be
similarly extended.
Patches of Interest
Add Some Links to External (WWW) Resources to the Perldocs
David Landgren thought that the patch to add web page links to the
Perl documentation should be refused on the grounds of the likelihood
of them becoming obsolete and therefore contributing to the
maintenance burden.
looked at your 1996 bookmarks recently?
http://xrl.us/bkkd7
I must be *mad*
Jesse Vincent moved MAD's libraries under lib/ and placed them under
the "MAD::" namespace. Other than that he tidied up Gerrard Goossen's
work on the test suite and generally brought the bitrot level down
close to zero.
Gerrard wondered whether, because of the dependency on "XML::Parser",
if it wouldn't be better to spin the libraried out completely as CPAN
modules. Jesse felt that pulling MAD too far away from the core would
all but ensure its demise.
what, me worry?
http://xrl.us/bkkd9
Documentation typo fix for MRO
Florian Ragwitz suggested a documentation patch for MRO but it was
ignored.
the next self can
http://xrl.us/bkkeb
Call "SvMAGICAL_off" in "mg_free"
In the ongoing saga concerning "mg_free" and "mg_clear", Bram
identified only one other place in the core where "SV*MAGICAL_off()"
was called after "mg_free". So he cleaned things up, and Rafael
Garcia-Suarez applied his patch.
http://xrl.us/bkked
In the process of working with magic, Bram wanted to know how to
downgrade a "PVMG" to a "PV". John Peacock wondered why on earth
someone would want to do such a thing, to which Bram replied that it
would make testing easier. John suggested a different approach that,
while more work for Bram, better reflected what was going on under the
hood.
got magic?
http://xrl.us/bkkef
Add "SvMORTAL" to check if a SV is mortalized
Claes Jakobsson was grovelling deep in XS code, trying to figure out
whether SV were mortal or not, and was surprised to discover that
there was no simple check available. So he wrote a macro to allow SVs
to be tested as such.
Rafael wondered whether it would be more interesting to wrap it up as
a module so that older perls could use it. In turn, Claes wondered if
the hassle of setting up the module and having the XS author bring it
in and use it was worth it.
Nicholas was hesitant to load up the core with yet another addition to
the API, and when Claes thought about writing regression tests for it,
he realised that the best place for it would be on CPAN.
mortal combat
http://xrl.us/bkkeh
New and old bugs from RT
Bug in "File::Find" on Windows when target dir is bare drive letter and
"no_chdir = 1" (#41555)
Last week, Bram fixed this bug, but wondered how one could write some
tests for it. This week, David Landgren sketched out an approach, but
no-one commented on its viability.
http://xrl.us/bkkej
Ambiguous Configure run/make error (#49946)
Stefan Schlotterbeck-Macht filed a bug back in January concerning a
cross-compilation failure, the exact problem being a "make" target
"<command-line>" not having a rule in the Makefile. Andy Dougherty
noticed it this week, and suggested that it was quite possible that
just deleting the target in the "Makefile" would be sufficient.
http://xrl.us/bkkem
"NDBM_File" fails to build (#50180)
Also back in January, Devogon filed a report with "NDBM_File" not
being built on 5.10.0 under Debian. Andy had a look at things, and saw
that they had changed both the name of the header file (now called
gdbm-ndbm.h) and the library file (gdbm-compat).
Andy wanted to patch Configure to do the right thing and so made a
request for comments. Currently there are three different header files
to search, as well as three different library names. The question was
whether there were any other possibilities lurking about on other
platforms.
speak up
http://xrl.us/bkkeo
Crash when localizing a symtab entry (#52740)
In April, Niko Tyni wrote a very detailed bug report concerning a
segfault in a mod_perl environment. This provided sufficient
information to Rafael Garcia-Suarez to make a small change to sv.c,
which was later officialised as change #33807.
one good turn deserves another
http://xrl.us/bkkeq
perl-5.10.0-33733 assertion with JSON::XS-2.2 (#53244)
This is the thread about the correct use of "SvCUR". Nicholas Clark
revived the thread when he explained that one of the reasons the code
broke was that because when gcc is instructed to add the "-g" compiler
switch for debugging purposes, Configure piggybacks this and enables a
raft of code assertions, and "JSON::XS" was tripping over one of them.
Many new assertions had been added to the code by Nicholas when he
worked on slimming down the SV bodies, and he needed to be sure that
nothing broke out in the wild (due to a cavalier approach to the
internals). Andreas König's long BBC smoke campaign showed that by and
large Nicolas's changes were completely transparent.
Marc Lehmann compared 5.8.8 and 5.10.0, running bare, or with POSIX
loaded, and noticed that while the bare binary was smaller, the size
when POSIX was loaded showed a larger increase on 5.10 compared to
5.8. This appeared to contradict the statement in perldelta, and this
left Marc feeling a bit confused.
http://xrl.us/bkkes
Bug in "if(open(my $fh,...)) { }" scoping (#53504)
Aristotle Pagaltzis showed how Perl 6 deals with the problem of
scoping lexicals to blocks, and that the rules there are much simpler.
http://xrl.us/bkkeu
bug with "index()" matching beyond end of string when \0 bytes are
involved (#53746)
Giuseppe Insana filed a fairly comprehensive report detailing his
surprise at some results with "index" when NUL bytes appear in the
string.
Bram simplified matters, which made it clear to see what the problem
was. Abigail wrote a series of TODO tests so that some budding
internals hacker who wanted to take a stab at fixing "pp_index" in
pp.c would know if their efforts were successful or not.
hint hint
http://xrl.us/bkkew
64-bit Integers -- inexact division gives odd result when is large (#53784)
Chris Hall ran into difficulties with the results of large integer
divisions being upgraded to floating point, with the loss of accuracy
that that implies. He and Dominic Dunlop kicked the problem around a
bit but were not able to come up with an explanation for what they
were seeing.
but -Mbigint ok
http://xrl.us/bkkey
No complain about bareword (#53806)
Ronald Fischer complained thusly when bitten by "print" merrily
accepting a bareword as its first argument and silently stringifying
it. Bram promised some TODO tests for this.
Something tells me this is not going to be simple to fix.
the magic of print
http://xrl.us/bkke4
perlpodspec typo "Encoding::Supported" (#53908)
Kevin Ryde found an instance of "Encoding::Supported" that he
suspected should read "Encode::Supported". And indeed it should.
Patched by H.Merijn Brand.
http://xrl.us/bkke6
"pod2man" loses "=head2" starting [with] ' or . (#53910)
Kevin also discovered that "Pod::Man" failed to properly escape POD
headings that begin with a quote or period, letting them be
interpreted by *roff and thus ignored. He proposed a simple patch that
should be enough to resolve the issue.
more POD love
http://xrl.us/bkke8
Perl5 Bug Summary
http://xrl.us/bkkfa
http://rt.perl.org/rt3/NoAuth/perl5/Overview.html
New Core Modules
Encode 2.25
Released by Dan "the Encode maintainer" Kogai.
http://xrl.us/bkkfc
IO::Compress::* 2.010
Paul Marquess synched blead with the current CPAN release, which
should make things play more nicely on 5.10
http://xrl.us/bkkfe
threads::shared 1.19
Jerry D. Hedden pushed the latest "threads::shared" out the door.
The main change is saner semantics for "ref()" on shared objects.
http://xrl.us/bkkfg
Thread::Queue 2.07
The above module in turn allowed Jerry to release a version of
"Thread::Queue" that allows one to enqueue structures with
circular references.
http://xrl.us/bkkfi
In Brief
Bhavna Yadav wondered how to port a Perl script on Vxworks. Dominic
Dunlop pointed out that Wind River ported Perl independently to their
Vxworks operating system... seven years ago, and as far as Dominic was
aware, no porter had any technical knowledge of the platform.
http://xrl.us/bkkfk
Thanks to Reini Urban, one can build a static perl on Cygwin.
no shared libraries
http://xrl.us/bkkfn
Alexandr Ciornii pinged the list with an 18 month old "Net::SMTP"
documentation patch that had never been applied.
http://xrl.us/bkkfp
In the Taint (PL_tainting, SvTAINTED_on, SvTAINTED_off, SvTAINT)
thread, Paul Fenwick explained that late-acting tainting left
"PERL5LIB" wide open.
this is a problem
http://xrl.us/bkkfr
Vadim Konovalov cross-posted a question regarding Perl
cross-compilation on arm-linux but no-one took him up on it.
http://xrl.us/bkkft
Abigail tweaked "File::Copy" to use the 3-arg open instead of a
slightly crufty and vaguely deprecated 2-arg form.
http://xrl.us/bkkfv
Abigail also wrote an initial cut to teach "File::Copy" to respect
permission bits. This caused problems on Cygwin, so, for want of a
better solution, Jerry D. Hedden changed some of the failing tests
into TODO tests for that platform.
http://xrl.us/bkkfx
Alexandr Ciornii supplied a "Data::Dumper" patch to make the latest
blead version compile on older perls.
http://xrl.us/bkkfz
Ricardo Signes fixed up a POD link for "perlunitut".
http://xrl.us/bkkf3
David Nicol wrote a wafer thin patch to underscore the semantic
importance of the empty pattern ("//").
http://xrl.us/bkkf5
Last week's summary
This Week on perl5-porters - 28 April-3 May 2008
http://xrl.us/bkkf7
About this summary
This summary was written by David Landgren.
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