This Week on perl5-porters (17-23 October 2005)

This Week on perl5-porters - 17-23 October 2005

   Perl 5 was released this week, eleven years ago.

Defining "sub _ {...}" breaks "File::Find"

   Jeff "japhy" Pinyan mentioned the Issue That Will Not Die, that if you
   define "sub _ {...}", then "_" as a shorthand for *the file most
   recently statted* stops working. The problem at hand for japhy being
   that "File::Find" fails, and wondered what workarounds were possible.

   Mark Jason Dominus was against the idea of teaching "File::Find" to
   work around such damage, because it would probably not be the only
   module that breaks under this scenario. The best fix would be to
   adjust the parser to prefer string context for "_" where it makes
   sense (and thus not call "sub _"). And Rafael Garcia-Suarez did just
   that with a quick patch to put more DWIMery into the tokeniser in
   change #25799.

   It turns out that "_" is the usual idiom in the "gettext" world for
   dealing with internationalisation (i18n). Yitzchak Scott-Thoennes
   thought that a new warning should be generated for attempting to
   define "sub _". Abigail thought not. The thread then evolved into a
   discussion about how and when new warning can, or should, be added to
   the interpreter.

     Earlier thread, summarised here
     http://dev.perl.org/perl5/list-summaries/2005/20050909.html

     This time around
     http://xrl.us/h5ye

     Musing on warnings
     http://xrl.us/h5yf

Loading multiple versions of modules

   Nicholas Clark wants to know how much tweaking to the internals would
   be required in order to let perl load different versions of the same
   module. Something as mundane as package Alpha using version 1.0 of
   module Charlie, and package Bravo using version 2.0 of module Charlie
   would come in quite handy. Without getting into the brain-melting
   complexity of an @array containing heterogeneously versioned Charlie
   objects...

   The idea sounds quite exciting, sadly, after a few responses the
   thread flickered out.

     http://xrl.us/h5yg

Sub return values are inaccurately documented

   The monster thread of the week, with 44 replies. It starts with a
   sentence from "perlsub", noted by Xavier Noria: "The return value of a
   subroutine is the value of the last expression evaluated by that sub".
   Pop quiz: what does the following return?

     C<sub f { 1 for 1 }>

   Answer: ''. Adriano Ferreira supplied a number of variations on the
   theme, with "if" or "while" in the place of "for", and Abigail pointed
   out that "do {...}" has the same sorts of problems, so it's not only
   apparent in subroutines. The problem is that "for" is a control
   structure. And the value of a control structure is unspecified. In
   fact, it doesn't have one.

   Yves Orton noticed that "my @b=(0,1); print $b[0+do {1 for 1}]" dumps
   core. He also wanted to specify the last expression produced by a
   control structure. Xavier pointed out that control structure are not
   expressions. And Rafael concurred, saying that you can't say "my $x =
   while (...) { ... }". Yves countered with "my $x = do {while (...) {
   ... }}". Rafael put his foot down and said that loops are evaluated in
   void context. To change them now to be evaluated in scalar or list
   context (which is what Yves wanted) would break lots of code.

   But the core dump problem remained unresolved.

     The beginning
     http://xrl.us/h5yh

     Dave explains exactly what's going on
     http://xrl.us/h5yi

     Rafael explains from the other end
     http://xrl.us/h5yj

     Xavier summarises the current state of play
     http://xrl.us/h5yk

"do { EXPR for EXPR }"

   Robin Houston picked up the core dump noticed by Yves in the above
   thread and analysed it. And patched the source to fix it.

     http://xrl.us/h5ym

List slice subscripting

   Nicholas Clark said that he didn't want to see the new slicing syntax
   appearing in "maint", and related a horror story of battling with
   syntax variants in 5.004, when only 5.004_05 compiles easily on modern
   platforms due to compiler evolution (specifically, Configure-back-then
   gets confused by what compiler-right-here-right-now says in response
   to its probes).

   If you like this syntax, wait for 5.10. If you can't wait, try and
   help to make 5.10 get here faster.

     http://xrl.us/h5yn

     Initially summarised here
     http://dev.perl.org/perl5/list-summaries/2005/20050915.html

Recursive comparison routine can cause segfault in sort

   Robin Houston found that using a sort comparison routine that calls
   itself can cause perl to dump core. Dave Mitchell confirmed that the
   situation is deeply unsatisfactory. Even if the code base was patched
   to die gracefully when a recursive sort comparison was found, there
   are problems with threads that remain in any event. Hugo van der
   Sanden suggested an approach using attributes. Robin and Dave started
   to debate a way forward.

     The bug report
     http://xrl.us/h5yo

     The trouble with threads
     http://xrl.us/h5yp

     Hugo's suggestion
     http://xrl.us/h5yq

     Robin's way forward
     http://xrl.us/h5yr

What John E. Malmberg did this week

   John E. Malmberg got "open(FOO, "child.pl foo|")" working on VMS,
   applied by Craig Berry,

     http://xrl.us/h5ys

   and synced "exit"'s behaviour with the documentation

     http://xrl.us/h5yt

   and posted his VMS TODO list

     http://xrl.us/h5yu

   There's a lot there. And it probably may not be complete.

What Jarkko Hietaniemi did this week

   Jarkko Hietaniemi posted many patches to bring Perl on Symbian up to
   speed.

     http://xrl.us/h5yv
     http://xrl.us/h5yw
     http://xrl.us/h5yx
     http://xrl.us/h5yy
     http://xrl.us/h5yz

In brief

   I have the Perl5 bug summary in my spool, but for some reason I cannot
   find the message on "xray". There were 1507 open tickets as of
   2005-10-17.

   Nicholas Clark thinks he shook out a reference counting bug with a
   ponie build:

     http://xrl.us/h5y2

   Ilya Zakharevich cc'ed p5p about a bug in "if" and appended a patch.
   Some doubts were expressed about the error message (not everyone may
   catch the cultural context of "cryptocontext"). Others noted
   tangentially that testing for Windows platforms with "if ( $^O =~
   /Win/i )" will come to grief on "cygwin" and "Darwin".

     http://xrl.us/h5y3

   Andy Lester, continuing on his quest to conts, hoisted some repeated
   code out in av.c and thus shaved a few bytes of the resulting object
   code.

     http://xrl.us/h5y4

   Following on from the discussion of manipulating the environment last
   week, H.Merijn Brand added a configure probe for "clearenv".

     http://xrl.us/h5y5

   Sébastien Aperghis-Tramoni wrote patch #25802 for autodoc.pl so that
   it generates the index entries for perlapi.pod and perlintern.pod.

     http://xrl.us/h5y6

   Gisle Aas fixed up "pp_sselect"

     http://xrl.us/h5y7

   Nicholas upgraded "ExtUtils::MakeMaker" to 6.30 in "maint". And wanted
   to know what (is)? broke(n)?.

     http://xrl.us/h5y8

About this summary

   This summary was written by David Landgren, for once without Immediate
   Realtime Corrections (IRC), so any typos or wordos are truly my own.
   I'm offline as of tomorrow morning for a week. Yay!

   Information concerning bugs referenced in this summary (as #nnnnn) may
   be viewed at http://rt.perl.org/rt3/Ticket/Display.html?id=nnnnn

   Information concerning patches to maint or blead referenced in this
   summary (as #nnnnn) may be viewed at
   http://public.activestate.com/cgi-bin/perlbrowse?patch=nnnnn

   Weekly summaries are published on http://use.perl.org/ and posted on a
   mailing list, (subscription: [email protected]). The
   archive is at http://dev.perl.org/perl5/list-summaries/. Corrections
   and comments are welcome.

   If you found this summary useful or enjoyable, please consider
   contributing to the Perl Foundation to help support the development of
   Perl.