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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