This Week on perl5-porters - 30 December 2007-5 January 2008
"That's now twice in this thread that I've been accused of favouring
languages that I actually dislike [...] . I think the Java model of
exception signatures is awful." Zefram (I hope you know this will go
down on your permanent record).
Topics of Interest
Exception roles, take 1
Ricardo Signes wrapped up the year with a first cut at doing exception
roles in Perl (the idea being that one would manage errors with some
formal mechanism, anything, than matching $! with regexps).
Zefram quoted lisp back at him for more background on handling error
conditions.
http://xrl.us/bd45y
The discussion continued in the new year, with people discussing how
to avoid creating elaborate Exception hierarchies that would wind up
looking like Java.
ewww
http://xrl.us/bd452
Lexicals used only once should warn (redux I)
This thread from last week, err month, um year continued in full swing
this week. There are two main points to come out of it. Firstly, given
the following statement:
my $opaque = xyzzy();
if $opaque appears nowhere else in the current scope, it is not
possible to determine at compile time whether or not its purpose is to
hold a reference to an acquired resource (and thus cannot be
considered "unused").
Secondly, and in light of the above, is it worth expending so much
effort to hunt down and carp about truly unused lexicals? From a
purist's point of view, the answer is yes, but from a pragmatist's
point of view, the better solution lies in a "lint"-like analysis.
http://xrl.us/bd454
Lexicals used only once should warn (redux II)
Another part of the thread from last week reminded Fergal Daly how
much he would like, in a loop like
for my $x (@list) { ... }
to obtain a trace that not only shows the call stack, but also shows
the value of $x. Even knowing that the loop was in the Nth iteration
would be better than nothing. chromatic suspected that if code were
written to handle that, it would come in handy for dealing with
tail-call optimisations.
That reminded Yves Orton about a "$^SUB" variable which would provide
a hinting mechanism to the compiler, thereby side-stepping the issue
of introducing unnecessary slowdowns in the general case, and putting
the onus on the programmer to get things right.
http://xrl.us/bd456
RAII: not an Italian TV station
http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization
"sub 2007{ ... goto &2008 }"
David Nicol broke out of the monster warnings thread and wondered
about tail recursion the light of RAII. The trouble is that an opaque
scalar in @_ holding a resource lock would get wiped out during the
tail recursion call. He was of the opinion that tail recursion could
not be done automatically by the compiler, but that it could be
possible to set it up yourself, if one was able to set up a new @_
explicitly, just before transfer.
finding the right syntax
http://xrl.us/bd458
In the new year, Aristotle Pagaltzis cautioned against diddling with
@_ since it is built for speed and thus behaves oddly in a number of
edge cases. Better to invent some sort of syntax that looks like a
regular function call, and deals with @_ itself away from prying eyes.
Jim Cromie pondered whether some sort of "pp_goto"/"pp_entersub"
mashup would do the trick.
http://xrl.us/bd46a
Optimising opcodes
Rafaël Garcia-Suarez, Nicholas Clark and Paul Johnson continued to
ponder ways to obtain line number information for warning messages if
all the nullops were thrown away.
pointer games
http://xrl.us/bd46c
Negated smart match
Ron Blaschke wanted to know why there was no "!~~" negated smart match
operator. There's one in Perl 6. In Perl 5.10, it gets parsed as the
slightly useless "!~ ~". In the meantime, one can get by with "!($thud
~~ @qux)".
one way to do it
http://xrl.us/bd46e
strictly by default
The debate continued over how and when strict would be enabled by
default in future versions of Perl. The key was to specify some sort
of "use 5.12" pragma or a feature, but there was disagreement over
whether they should behave the same, or differently.
http://xrl.us/bd46g
SV leak
Nicholas Clark looked at some code in "XS_PerlIO_get_layers" and
realised that it was probably leaking "SV"s. This made him wonder if
other XS code committed the same sin.
Marcus Holland-Moritz seemed to think so, and committed change #32816
it. And then committed #32817 when he realised that the routine's
"dTARGET" was now unused.
Vincent Pit had a look around and came up with a number of other
places where the same kind of misbehaviour was occurring. He whipped
up a patch, that Marcus applied.
http://xrl.us/bd46i
Handling of SET magic in "mX?PUSH" macros
After the above adventure, Marcus noted that there was no need to
handle the setting of magic in the "mPUSH" family of macros, since
they are creating new mortals that cannot have any magic on them
(yet). Which makes for less make-work code.
http://xrl.us/bd46k
MRO and "av_clear"
Torsten Schönfeld was having problems with perl 5.10 and XS code
diddling @ISA to change package hierarchies. As it happens, Torsten
was using the "av_clear" API call to clear out @ISA.
The problem is that @ISA has a certain amount of magic associated with
it. Rick Delaney had a look at what Torsten was trying to do, and once
he understood what was needed, was able to cook up a patch and toss in
a couple of regression tests to wrap things up.
introducing magic_clearisa()
http://xrl.us/bd46n
When will perl 5.10 be stable?
Alberto Simões asked why stable.tar.gz refers to 5.8.8 and not 5.10.0.
A long discussion ensued. Most people were happy to accept that it is
probably premature to label 5.10.0 to be stable, but it's going to
happen sooner or later. So when?
Michael G. Schwern suggested adopting Debian's
stable/testing/unstable/experimental labels. The main problem was that
people had difficulty trying to match Perl releases into the above
four categories. Dave Mitchell came up with an alternative eminently
pragmatic approach.
5.8 is the new 5.6
http://xrl.us/bd46p
"SvOOK()" now doesn't (ab)use "SvIVX"
Nicholas Clark, looking more closely at how macros expand, put forward
an alternative technique to deal with strings that get clipped from
the beginning. Instead of recopying the string, perl has always kept
the string as is, and moved a pointer forwards to point to the new
beginning.
Until now, the macro expanded to some bit-twiddling and possibly a
function call. By rearranging things, Nicholas was able to get rid of
the function call, but wondered if there was a way to trip things up
because of that.
After having played with it a bit more, Nicholas determined that it
was simpler to store an offset.
ook!
http://xrl.us/bd46r
Solving the "~~" changing behaviour after using "=="
Following on from the thread from last week where Gabor Szabo reported
that smart match could return a differing results from the same
inputs, Nicholas changed the behaviour in bleadperl so that "42x" (a
numeric value with trailing garbage) never gets the IOK or NOK flags
set. Thus solving the problem neatly.
It turns out that doing so didn't break the test suite, but the
question to ask is whether there were no tests for it. In which case,
careful analysis will be required to see whether it is safe to
backport to the 5.10 line.
http://xrl.us/bd46t
Patches of Interest
"mg_magical()" sometimes turns "SvRMAGICAL" on when it shouldn't
Vincent Pit detected problems in the chain of magic whereby different
ordering of magic would produce different results. Steve Peters wanted
to see some tests.
http://xrl.us/bd46v
refactor "PL_opargs" generation in opcode.pl and fix "helem"
Marcus Holland-Moritz was in the mood for adding a new op flag, and
suffered considerable pain when he gazed upon opcode.pl, as well as
some 8-year old code contributed by Ilya Zakharevich which he thought
was a "can't happen" scenario.
In tightening things up, he discovered a dormant bug that meant that
"helem" had an incorrect specification so he corrected it.
all applied
http://xrl.us/bd46x
Loading a "loadable object" with a non-standard file extension
One of things that was pushed for in 5.10 was to embed
platform-specific decisions into DynaLoader.pm when it was generated
during the build of Perl instead of deferring things until run-time.
The move proved to be a shade too aggressive and broke established
behaviour in 5.6 and 5.10.
Jan Dubois restored the old behaviour with a patch that was applied by
Rafaël.
http://xrl.us/bd46z
Clean up "File::Temp" test file
Jerry D. Hedden fixed up a leaking temporary file in
lib/File/Temp/t/fork.t. Applied by Rafaël.
http://xrl.us/bd463
Clean up lib/B
He also ensured that the "realclean" target removed lib/B. Not
applied.
http://xrl.us/bd465
"~~" is not a feature
Jerry also redelivered a Warnocked patch which, happily, was applied
the second time around.
if at first you do not succeed
http://xrl.us/bd467
"File::Temp::_gettemp" should ignore dir -w test on Cygwin
Jari Aalto could not install CPAN modules on Cygwin because of a
pointless check to see whether the directory was writable (which it
always is). Applied.
http://xrl.us/bd469
This is the BBC
"Params::Validate" and "Clone"
Andreas König, Rafaël Garcia-Suarez, Nicholas Clark and Steve Peters
had a closer look at this failure and tried to figure what could be
done to blead to reduce the breakage. To a certain extent, however,
some changes have been advertised for a long time, patches have been
sent to authors of problematic modules, but few distributions have
seen new releases.
not much we can do
http://xrl.us/bd47m
New and old bugs from RT
"say" behaves as just "print" on tied filehandle (#49264)
Ambrus Zsbán noticed that "say" on a tied filehandle lacks the "\n"
tacked on the end, and traced the problem as far as pp_hot.c but
didn't know how to fix it.
Schwern weighed in with a first cut at a patch. Graham Barr saw that
it leaked. Rafaël and Nicholas started debating internals, discussing
hitherto unknown macros (at least to the summariser). Something was
applied, in any event
say can you see
http://xrl.us/bd47o
"IO::Handle" method "say" should ignore $\ (#49266)
Ambrus, on a roll, found another edge case where "say" misbehaved.
This was either ignored, or solved by the same patch that fixed bug
#49264.
say it ain't so
http://xrl.us/bd47q
"B::Deparse" fails to deparse a reference to an anonymous hash (#49298)
David Leadbeater noticed that "B::Deparse" was incapable of dealing
with coderef that returns a reference to an anonymous array or hash.
Rafaël muttered something about someone having to teach something
about something, and then did just exactly that.
special ops
http://xrl.us/bd47s
"[[:print:]]" *versus* "\p{Print}" (#49302)
According to the documentation, any "[[:...:]]" and "\p{Is....}" pair
should match the same thing. Robin Barker showed that this was not
always the case.
http://xrl.us/bd47u
segfault in 5.10 (and earlier) (#49322)
A bug report from Will Coleda showed that
@r=eval [EMAIL PROTECTED](@n=(1,2) && ($n[1],$n[0]))};
@r=eval [EMAIL PROTECTED](@n=(1,2) && ($n[1],$n[0]))};
will crash on any number of different versions of Perl.
so that's pretty sick code
http://xrl.us/bd47w
Steve Peters noted that in 5.10... it still dumps core, but with a new
error message!
progress at last
http://xrl.us/bd47y
Segfault with with "tie" and "STDOUT" (#49366)
Steve Peters noted that if you are not careful when creating "tie"d
objects that print, and the thing tied is "STDOUT", perl goes into a
loop of infinite recursion and dumps core (after exhausting its C
stack). Ways to have interpreter deal with the situation more
gracefully foundered on the problem of determining the maximum stack
size in C.
and portably, while you're at it
http://xrl.us/bd472
Perl5 Bug Summary
Ticket Counts: 310 new + 1470 open = 1780 (8 created, 4 closed this
week)
http://rt.perl.org/rt3/NoAuth/perl5/Overview.html
New Core Modules
Math-Complex 1.38
documentation and test tweaks, courtesy Jarkko Hietaniemi (applied)
http://xrl.us/bd474
Sys-Syslog 0.24
tests that skip, courtesy Sébastien Aperghis-Tramoni (applied)
http://xrl.us/bd476
constant 1.15
tests that behave on 5.8.[0-3], also Sébastien, also applied
http://xrl.us/bd478
ExtUtils-MakeMaker 6.43_01
lots of bug fixes, courtesy Michael G. Schwern
http://xrl.us/bd48a
In Brief
Nicholas Clark thought that having "gcc -pedantic" on by default would
be useful more for debugging builds than production builds.
http://xrl.us/bd48c
Jan Dubois traced a perl 5.10 failure on Linux 2.4 to a bug report and
its corresponding patch. Even so, he couldn't see why it caused the
failure, but an environment variable tweak to the system provided a
reasonable work-around.
more fun with glibc
http://xrl.us/bd48e
Nicholas responded to Larry's remarks about the fact that the Perl 5
smart match was not quite the same as the Perl 6 smart match. The
problem is that there is insufficient cross-pollination between the
two development camps. Certainly, there have been no patches from Perl
6 developers to adjust the Perl 5 implementations of Perl 6 ideas to
keep them in line with the functionality du jour.
obscured by crowds
http://xrl.us/bd48g
Vincent Pit thought that "DEBUG_S" should meet the thin end of a
chainsaw.
remnants of 5.005 threads
http://xrl.us/bd48i
After having manually expanded macros once too often, Nicholas finally
got fed up enough to write a short Perl program to automate the task.
good laziness
http://xrl.us/bd48k
Rafaël killed the v-string portability warning in 5.10, declaring that
it would no longer be present in 5.10.1.
no-one shed a tear
500 Can't connect to metamark.net:80 (connect: Operation not permitted)
Robin Barker's consting goodness to "Compress::Raw::Zlib" and
"Filter::Util::Call" were applied.
http://xrl.us/bd48n
Sébastien Aperghis-Tramoni delivered some small documentation tweaks,
applied.
http://xrl.us/bd48p
Marcus Holland-Moritz eliminated some magic numbers in "NewOp()"
calls. Code that invents new ops is likely to break.
but code that invents new ops is unlikely
http://xrl.us/bd48r
Michael G. Schwern tweaked t/test.pl to make it resistant to changes
to $\, $" and $,.
no more havoc
http://xrl.us/bd48t
The "strict by default for 5.12" discussion got bogged down in details
of whether it should be a feature and how should it really be enabled
but sometimes we don't unless we do although maybe we might if we
should.
or words to that effect
http://xrl.us/bd48v
About this summary
get last week's here
http://xrl.us/bd48x
This summary was written by David Landgren. It does not exactly cover
the entire week, as I want to move from Monday through Sunday to
Sunday through Saturday. So some threads will be dealt next week.
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, please consider contributing to the
Perl Foundation to help support the development of Perl.
