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This Week on perl5-porters - 6-12 January 2008
"Um, I think you caused me negative work. I rather wanted
support and it seemed that because of you I didn't have to write
it." -- Nicholas Clark, on the joys of having other people do your
work for you.
In the continuing "strict by default in 5.12" thread, Glenn Linderman made a most pertinent remark: Perl 6 has staked the "strict be default" claim. Perl 5 may approach the same place, but will have to do so more slowly. Not that it shouldn't be done, we need not burden ourselves with bad practices forever, but deprecation cycles and dealing with dormant CPAN modules and code in the DarkPAN means it will take time.
The other contentious issue (should extra strictures be activated from a
feature pragma) was addressed by Abigail, who put forward the argument
feature should be considered no more than a message from the
programmer to the interpreter indicating that constraints regarding
backwards compatibility are hereby waived.
advancing, unmasked http://xrl.us/bec8z
the darkpan, defined http://xrl.us/bedds
brian d foy was puzzled upon learning that smart matching suffered
from action at a distance, and wondered if it was all documented.
David Landgren explained that it was a problem due to the
flag being set, which caused the smart matching code to use
numishness, rather than stringiness as a basis for matching.
Zefram rightly pointed out that this was exactly the sort of problem that prevented Perl from being able to be used in very large projects. Nicholas Clark asked himself what would happen if the IOK flag was not set during a numish comparison, were the number not truly numeric. And so now blead does just that.
no more action at a distance http://xrl.us/bec83
Andy Armstrong added dtrace support to perl to probe subroutine entry and exit points and was happy to announce that it incurs no measurable performance hit.
Nicholas Clark made a number of comments regarding the patch: things that need to be done and the ways to do it. He went ahead and cleared up the nits and applied it all.
the patch itself http://xrl.us/bec85
The main issue with the patch was dealing with
because not many people have strong
Configure-fu (and H.Merijn
Brand was busy using his fu to attend to some sorely needed work
Andy Dougherty helped out with a rough sketch of what needed to be done. Bryan Allen of pobox.com generously provided shell access to a Solaris box to get the kinks sorted out.
dtrace sees delight http://xrl.us/bec87
Once that was more or less under control, the next question to ask was what probes should we have? The following items were put forward:
Creation and destruction of SVs.
Interpreter set-up and tear down.
Module loading (
One of things that needs to be addressed is that in order to trace the stack (C's or Perl's, really), a so-called ustack helper is what's needed, but these are fiendishly difficult to write. For a start, much of dtrace runs in the kernel, not in userland.
Much of the more esoteric discussion was cross-posted from the dtrace-discuss mailing list, where talk of ustacks certainly appeared to give them The Fear.
In the process of producing
dtrace support, Andy ran into trouble
with getting the shellish idiom of if-not-condition-then correct.
H.Merijn Brand showed one way to do it, Zefram, another.
The discussion continued this week as to whether or not this would be a good idea. Michael Schwern started to jot down the history of why "map in void context" played such an important part in the history of Perl.
we have a wiki, man http://xrl.us/beddu
Abigail maintained that it would be insane to start warning about a construct that has not previously triggered a warning, even if the construct was not considered to be a best practice (in which case a Perl::Critic policy would be more suitable).
Zefram put forward a suggestion that was endorsed by Larry Wall.
should we, should we not http://xrl.us/bec9b
Rafaël Garcia-Suarez waved his hands vaguely at the new error that
comes out of
bleadperl -e 'use 5.10.1' and hoped something could
be done about it. Steffen Müller showed how difficult it would be
to solve the general case.
The only sane approach is for bleadperl to track feature sets in the current maintenance release. No new features could be added to 5.10.x after 5.12.0 comes out. Dave Mitchell thought add new features to a maintenance track was a bad idea anyway.
still waiting for patches http://xrl.us/bec9d
Adam Kennedy took his
YAML::Tiny module and made it even tinier by
throwing everything that is not required to parse a META.yml file.
He named it
Parse::CPAN::Meta so that it doesn't say "YAML" on the
tin. The idea being is that it will permit richer semantics in dealing
with module requirements. This could come in handy for dual-lifed
modules and modules that depend on external libraries.
Ævar Arnfjörð Bjarmason found a minor YAML remnant in the test suite.
ain't what it used to be http://xrl.us/bec9f
Nicholas Clark was wondering what change caused a particular language construct to go boom! and asked Andreas König to fire up his magic binary search patch locator to find the offending change.
Andreas wasn't around, but Marcus Holland-Moritz was, and in about an hour had identified change #30755 as being the culprit. This enabled Nicholas to make the required correction.
homing in http://xrl.us/bec9h
Following that (if it's the same bug we're talking about) Dave Mitchell, Yves Orton and he kicked the problem around for a little while, and they appeared to arrive at the right solution by the end of the week.
stirring up trouble with re 'eval' http://xrl.us/bec9j
Michael G. Schwern had a chance encounter with a C-style
loop, and realising that the range operation (
..) used a lazy
implementation, noted that it was a Simple Matter Of Programming
for my $var (2..Inf) to Do The Right Thing. So he
coded a quick and dirty patch (with a test!) to prove that it
could be done. Much of the discussion that followed, apart from
mentioning Ruby and
bc involved what to do when adding 1 to an
integer value overflows.
from her to eternity http://xrl.us/bec9m
Jerry D. Hedden picked up the patch and ran with it, delivering a whole pile of code, documentation and tests to implement the whole show. Michael made a number of good comments, so Jerry returned to the lab and cooked up a fresh patch.
One sticking point was whether the range should stop or not, when
the value outgrew the maximum size of an integer. Yves thought that
if that was a problem, people should really be using
But even that approach is flawed, since after a few billion or
quintillion loops any integer-based counter will begin to lose
precision (after it is upgraded to a float following the overflow
an integer). And transparently switching over to
would be Really Hard.
I do it my way http://xrl.us/bec9o
A number of porters described the innovations they would like to see in perl 5.12, the next major release after 5.10. Nicholas Clark commented that a lot of the suggestions had high niftiness values, but noted that the difference between suggesting and implementing will impose its own natural selection of what gets done.
Firstly, a number of items were marked as deprecated in 5.10 and
thus may be removed from 5.12. All that could be recalled for the
moment was the
-P command-line switch and unnamed
declarations (which actually disappeared in 5.10).
all gone http://xrl.us/bec9q
Ricardo Signes wanted support from the language to let him know if the
routine had been called as a method. Currently, there is no mechanism
that lets you do this in the general case. One possible approach is to
do it by extending
caller already returns an impossible-to-remember list of values,
Mark Jason Dominus wondered whether the last element should be a hashref, or
whether an alternate hashified
caller hashref should be made available.
This suggestion attracted significant discussion, which evolved into calls
autobox brought into core. Nicholas Clark warned against
making that decision lightly.
just so long as the hashref is purple http://xrl.us/bec9s
Michael G. Schwern proposed a
method foo declaration, that would work like
sub foo, except that it fetches the
$self object from
@_ for free.
The open issues are, can you call it as a bare subroutine, what if you don't
like using the name
$self, what about class methods, and should
be removed from
@_ or should it remain?
and it's on the wiki http://xrl.us/beddw
Ricardo also suggested named lexical subroutines, to be used in situations
such as comparator routines for
sort, while avoiding namespace pollution.
Dave Mitchell pointed out the problems this would have in terms of closures. He sketched out two possible implementations and pointed out the flaws in both of them.
Nicholas Clark recalled that Mark Jason Dominus was believed to be in the possession of a list of examples of the corner cases that would need to be addressed in any such proposal. Dave thought he could come up with one of his own at a pinch.
just a spoonful of sugar http://xrl.us/bec9w
Ricardo also mentioned a conversation with Matt Trout concerning the issue
of creating anonymous packages. Currently it can be hacked together using
Class::Mix. In any event, more thought needs to
go into what the syntax should be.
heh, inherit from *that* http://xrl.us/bec9y
Michael then kicked off a very large thread by p5p standards, proposing real honest-to-goodness named parameters. One point he stressed was that what ever solution is implemented, it doesn't have to be perfect. We could apply the 80/20 rule and strive for a simple solution that is satisfactory 80% of the time.
Then the difficulties began to surface: should the parameters that are named
be removed (or not) from
@_ (see also: the method declaration thread).
Should the parameters be aliases (fast, but dangerous) or copies (slow and
safe, and conforms to the Principle of Least Surprise). What happens if
not enough parameters are passed. Can we have defaults? How does this tie
in with prototype specifications?
One useful item to come out of the discussion was a post from Juerd Waalboer who stepped of with a review of subroutine signatures in Perl 6, and is worth stealing from it for Perl 5. Another point is that, one way or another, we'll need better support for aliases in the language. Solve that problem, and named parameters are a piece of cake.
also wikified http://xrl.us/beddy
Aristotle Pagaltzis put forward an elegant suggestion to deal with
length(undef). Rather than issuing a warning, it should quietly
undef. Rafaël Garcia-Suarez liked the idea so much
that he tried to implement, but was stumped by a number of strange
failures in the test suite.
Nicholas Clark picked up where he left off, and discovered that it is horrendously hard to get it to work correctly with tied variables. After a number of patches, the implementation was satisfactory, and in the process, Nicholas uncovered a bug involving (drum roll) UTF-8.
how long is a string http://xrl.us/bec94
Marcus Holland-Moritz's refactoring of PL_opargs generation in
opcode.pl from last week was applied. As was Jerry Hedden's
File::Temp cleanup and his
~~ is not a feature documentation
tweak. The perlcommunity.pod patch from brian d foy was also
applied, despite being in a yucky diff format.
\X is equivalent to an atomic group made it too.
see last week for URLs
Jari Aalto put forward the sensible suggestion of using
of backticks (`) since it's to confuse with an apostrophe, and some
non-English keyboards make it quite difficult to generate.
Tels fell of his chair since he didn't even know that
but made up for it by spotting an leftover ` in Jari's patch.
told you they were hard to see http://xrl.us/bec96
Rick Delaney picked up the gauntlet and delivered a patch to fix
the issue identified by Dave Mitchell, where the
wound up being set in error. The amazing part was that Rick
didn't even believe there was a performance problem, but fixed it
anyway. When the benchmarks were run, it was clear there was a net
Dave the M, right as usual http://xrl.us/bec98
Data::Dumper to handle blessed regexes in blead, but
cautioned that the code was probably still too raw for previous releases.
a blessing in disguise http://xrl.us/bedaa
That gave Jerry D. Hedden some grief, until he tracked down the reason for the failure.
that's not supposed to happen http://xrl.us/bedac
Jerry has been building perls for quite a while without including
the XS component of
re. Yves Orton thought a perl without
since it was a pragma.
Jerry revised the patch two more times to get it into shape.
running light http://xrl.us/bedae
During the discussion, Yves Orton noticed that
really belonged in universal.c.
So Jerry made the move, wrote the appropriate changes and their
attendant tests and this enabled other tests to be moved around and
simplified some additional housework in
Data::Dumper. All applied
moving to new digs http://xrl.us/bedag
Yitzchak Scott-Thoennes noticed that op/sprintf.t could produce meaningless messages on failure, and changed this to make it start making sense again. Applied by Nicholas Clark.
Steve Hay upgraded his smoking kit to the latest CPAN version, and discovered to his dismay that it could no longer mail the smoke results. He proffered a patch to get things going again.
still smoking http://xrl.us/bedap
Florian Ragwitz thought that the results of deparsing a switch statement were suboptimal and offered a patch to make things better. Rafaël applied the patch, and added a test too.
given a patch http://xrl.us/bedar
A thread in late November about slowness in
can for AutoLoader
was put on hold during the freeze for 5.10.0. Rafaël dug out
the final patches and applied them. Steffen Müller said he'd
push a new version out to CPAN.
picking up where we left off http://xrl.us/bedat
Andy Armstrong had been working on
IPC::SysV and noticed
that the droppings left over by revision control messed things
up and proposed a patch to fix things up again.
A debate followed as to how, when and where to solve the problem and at the end of the day, the appropriate repositories received the appropriate patches.
repository droppings http://xrl.us/bedav
Ævar Arnfjörð Bjarmason moved the stringification of regexps into sv.c following Nicholas Clark's work of raising regexps into first class objects. Ævar explained that this would not break the pluggable interface for the regexp engine.
Nicholas smoothed over some of the rough bits and applied it to blead.
just another SV http://xrl.us/bedax
Robin Barker noticed that the last patch to manicheck broke its
-m command line switches. So he fixed it. Applied by
switched on http://xrl.us/bedaz
Jarkko Hietaniemi desired bad code to die a quick death by way of a segmentation fault, Steve Peters complied.
0xfff58005fff58005: segmentation fault *and* NaN http://xrl.us/beda5
There was a problem with platforms that were able to fork, or merely pretend to, or cannot. This was corrected, and Steve Hay recommended that for dual-lifed modules that need to test forking, the best practices may be found in Test/Simple/t/fork.t and IO/t/io_pipe.t.
there is no fork http://xrl.us/beda7
A bug involving a child reading from a file and looping back to the beginning and reading again, and again was posted nearly eight years ago (hence the low bug id). The problem was kicked around for a while, but no-one was able to figure out what was going wrong.
And there the bug slumbered from many years, until Franz Fischer revived it a few days ago, having run into the same behaviour on HP-UX.
better luck this time http://xrl.us/bedbb
let's do the time warp http://rt.perl.org/rt3//Ticket/Display.html?id=3387
Abigail posted this bug four years ago, and noting that the problem was still present, created a TODO test for it.
Yves Orton wondered if the problem occurred outside of a
Abigail listed a number of variations on theme that produced an
interesting variety of segfaults, valgrind errors or memory exhaustion,
and some that worked just fine.
I told you map in void context was evil http://xrl.us/bedbd
Peter Dintelmann reported a bug that was actually due to a misunderstanding of the documentation, so Rafaël tried to improve that.
it's the way it is http://xrl.us/bedbh
Jason Hord filed a bug last month the behaviour of
-x when using
filetest pragma and attached a patch to fix it up. This week,
Rafaël applied the patch.
hooray for bug reports with patches http://xrl.us/bedbj
Rafaël committed a fix that he thought should fix the bug that David Leadbeater reported last week.
anon deparsing is go http://xrl.us/bedbm
Ben Okopnik pointed out that the documentation in this module refers to a book that never has, and probably never will be published.
a tad optimistic http://xrl.us/bedbo
"mz" reported a significant regression in the clarity of error messages between 5.8.8 and 5.10.0 when attributes are involved. No takers as yet.
Imacat from Taiwan, who runs a very tight testing ship, reported
Test::Harness::Straps shipped with 5.10.0 is quite
far behind the current CPAN version. Furthermore, upgrading the
module copies it to the site directory, hence shadowed by
the older core version. Michael G. Schwern fixed this.
Imacat also asked Michael to bundle a Makefile.PL, to enable
a vanilla 5.8.8 distribution (sans
install THS automatically in a CPAN shell.
Michael was a little more reluctant to take on this additional technical debt, but Andreas König thought he had little choice.
Abigail uncovered a curious omission in the implementation of
state variables, and wrote a TODO test to help with the
search for the solution.
here you see it, there you don't http://xrl.us/bedbu
Mark Overmeer wrote a small test case showing that
failed to honour encoding directives.
Goro Fuji noted that
overload::constant doesn't work if the
constant in question contains escaped characters. Michael G.
Schwern hypothesised that the presence of a backslashed character
caused the code to run down the wrong path.
the high road be shorter, but the low road prettier http://xrl.us/bedb2
Mashrab Kuvatov filed a bug regarding problems with locales, UTF-8 and Cyrillic. Rafaël trimmed down the test case, saw the problem, but wanted to obtain some reference material on how to read encoding definitions.
Marc Lehmann ran into a bug with
File::Copy but couldn't reproduce
it (although unfortunately the effect was to remove the file being copied).
310 new + 1470 open = 1780 (8 created, 4 closed). Robin Barker wondered where his #49302 bug went.
- Math-Complex 1.43
Black smoke emerged from 1.42, reasons why
ok($a == $b)may be needed instead of
cmp_ok($a, '==', $b)were given, long doubles were overlooked and so Jarkko Hietaniemi pushed out a new version.
Andreas König identified the source of H.Merijn Brand's double free error in 5.10.0
it says "rgs@stencil" on the tin http://xrl.us/bedcc
And Moritz Lenz's bugs in extended regexp features were Warnocked.
perlbug it http://xrl.us/bedce
H.Merijn continued to plough through his
Configure and metaunits work and
was happy to report that he was down to a mere 193 warning messages.
a mere SMOP http://xrl.us/bedcg
Jari Aalto wanted an URL for Perl documentation. Two were given.
a vast program http://xrl.us/bedci
Nicholas Clark was Warnocked over a parallel make bug in
because no-one uses it? http://xrl.us/bedck
Craig Berry noticed that the latest REGEXP patches produced black smoke on VMS. Robin Barker and Nicholas Clark vied to produce the best patch to resolve the problem and at the end of the day VMS and Craig were happy again.
Yves Orton complained that development version numbers, warnings, XS and MakeMaker don't mix. The concensus is that using underscore in a version number to signify the beta release of a module to PAUSE blows chunks, and a much better idea would be to have something in META.yml.
a call for metadata http://xrl.us/bedcp
Nicholas welcomed Marcus Holland-Moritz's correction of an 8 year old bug, and wondered how much perl 4 code still remained in the code base, as this could lead to the possibility of correcting an 18 year old bug.
Andy Dougherty thought that much of doio.c dated back to Perl 4 and significant parts of sv.c could be traced all the way back to Perl 1.
layer upon layer upon layer http://xrl.us/bedcr
Coverity was a great help to the development of perl 5.10, helping pin down a number of questionable C practices. Andy Lester asked for volunteers to say good things about the product.
scratch my back http://xrl.us/bedct
Max "Corion" Maischein made perl build again on Win32 when the path contains whitespace.
under program files http://xrl.us/bedcv
Patrick Rutkowski ran into a problem with
typedef definitions in XS code
written in C++. Jan Dubois had already dealt with the problem in the past
and show Patrick what to do.
Ask Bjørn Hansen encountered some weird behaviour when
./ (that is, with a trailing slash). Andy Armstrong noted that the perl in
question was from a Red Hat distribution, and wondered if one of their own
patches was interfering with normal
The latest version of the smoking harness for the perl core fell apart, and some fixes were made. Further improvements may be necessary.
sync early, sync often http://xrl.us/bedc3
Gerard Goossen released kurila 1.7, an experimental fork of the perl codebase, the aim of which is wto see what would happen if one were to free one's self completely of any notions of backwards compatibility.
where does a kurila sit? http://xrl.us/bedc5
Rick Delaney's patch from last week to allow the clearing of
@ISA from XS
assign with impunity http://xrl.us/bedc7
Robin Barker had some more consting goodness applied to POSIX.xs
strtoul() and helper http://xrl.us/bedc9
as well as
a short time back.
Nicholas Clark's change to assert that these are the regexps you were looking for came to grief on Jerry D. Hedden's machine. A revised patch appears to have fixed the problem.
This summary was written by David Landgren.
last week's http://xrl.us/beddf
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