Notes
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I looked at 263 messages in total this week.
glob(), Cwd, etc.
Benjamin Stugars started running amok over anything related to
directories. Firstly, he looked at
POSIX::getcwd and made it call the
getcwdsystem call if available instead of doing
`pwd`, avoiding a fork.
Next, he implemented
Cwd in XS; however, this can't replace the current
Cwd module, because
miniperl needs to use it to install things. Instead, he had
Cwd::fastcwd bootstrap the XS module.
Then he turned to
glob, finding that, firstly, it gives a different sorting order (ASCII
rather than case-insensitive alphabetical) from the old implementation which
merely called out to
csh.
Gurusamy Sarathy fixed this up by adding an option for
csh compatibility. Ben put together a test suite for it.
He also found that
glob in a scalar context returns the last file found, rather than the number
of files found, but this was deemed to be a feature.
Ben also cleaned up the docs for
Cwd.pm, and made
Encode work under warnings and stricture. Wow. A good week's work there; thanks, Ben.
use Errno is broken
Tim Jenness and I discovered a bug in
h2xs. When you make an XS module, one of the things you might want to do is
make a set of constants available to Perl, so that Perl programmers can
call functions with the appropriate flags or whatever. The way
h2xs lets you do this is by defining an autoloaded subroutine that calls the
XS function
constant. If
constant returns a value, that's used. If it doesn't know anything about the
constant in question, it sets
errno to
EINVAL. The autoload sub then checks whether
$! is contains "Invalid" (not very I18N-friendly) or whether
$!{EINVAL} is set.
%! is a magical hash; it maps error constant numbers, like
ENOBRANE,
EBADF and so on, to true or false values, depending on the value of
errno. This lets you do error checking both portably and in a
local-independent manner.
It's supposed to be activated by
use Errno, but the stub modules provided by
h2xs didn't actually use the module; I sent in a patch to make it use
Errno.
However, Sarathy revealed that using
%! in a Perl program should cause
Errno to be used automagically - unfortunately, it didn't, so more hacking is
required.
Lexical Warnings
Mark-Jason Dominus found that lexical warnings in some cases aren't really lexical. Specifically, a module turning warnings on can trigger a "variable used once" warning in the main program. He correctly pointed out that:
The documentation in warnings.pm says:the pragma setting will not leak across files (via `use', `require' or `do').If it doesn't keep this promise, then there is little benefit to be had over using
$^W
Paul Marquess, the lexical warning pumpking, said that this was a design decision, but couldn't remember why. After some hints from Sarathy, he started working on a patch. The new rules are to be:
A variable will be checked for the "use once" warnings if:
- It is in the scope of a
use warnings 'once'- It isn't in the scope of the warnings pragma at all AND
$^Wis set.Otherwise it won't be checked at all.
Scalar repeat bug
Dominus found another interesting bug:
scalar and the repeat operator
x don't play nice together. For instance:
print scalar ((1,2,3)x4) # Prints "123333"
Robin Houston came to the rescue again with this typically brilliant analysis:
Really it's a perl bug, and another that goes back at least to the earliest perl I have available (5.00404).perl -e 'print -((1,2)x2)'will print
1-22. What happens is roughly:
- the values (1,2) are put onto the stack
pp_repeatsees that it's in a scalar context, so it changes the2on the top of the stack to22. The1remains beneath.pp_negatenegates the top of the stack, giving "-22".- so now the list
(1, -22)is on the stack, and is printed.The patch below makes pp_repeat drop the extraneous values, if its context is scalar but the OPpREPEAT_DOLIST flag is set.
open() trickery
Nick Ing-Simmons
came bearing gifts: specifically, funky new forms of
open. So far he has implemented the list form of pipes, so that:
$pid = open($fh, "-|", tac => $file);
will run
tac $file and pipe the output to the filehandle.
Next up came duplicating filehandles and file descriptors. His examples:
open(my $dup,"<&",$fh) # can now duplicate anonymous handles.
open(my $num,"<&",42) # Integers are considered file descriptors.
And also, something I know a lot of people have always wanted:
open(my $fh, "<", \$string)
which reads from the string as if it was a file on disk.
But no, he didn't stop there!
open(my $tempfile, "<+", undef);
is going to give you an anonymous temporary file on systems that support it. He also suggested opening different files on the read and write halves of a filehandle. That's to say, you could copy files like this:
open(my $fh, "<", $read_from, ">", $write_to);
while (<$fh>) {
print $fh $_;
}
By this time I was positively squealing with excitement.
Russ Allbery suggested a brilliantly devious way of doing IO layers at the Perl level: allow
open (my $fh, "<", \&coderef);
which would call a subroutine every time more data was needed.
Net::Ping
Colin McMillen had some suggestions (and, heavens above, an
implementation) for some changes he wanted to make to
Net::Ping. I'll quote his summary here, and you can read the details in
his mail .
- Removal of
alarm()function.- Incorrect returns of
falseremoved from TCP ping- Removal of unneeded warning in the module's POD
- Creation of a new "external" protocol
- Creation of a new "auto" protocol
- Documentation update
- Change in the default ping protocol
- Allowing for user-specified port in TCP ping
- UDP ping fixes?
There was some discussion of fine points; specifically, whether one
should necessarily return false when, for instance, a ping may be
blocked by a firewall. Abigail came up with a neat solution using an
overloaded value for the response; in the end, however, an
object-oriented approach was taken. Sarathy suggested that on Windows,
one can use
system 1, ... to spawn a child process.
Colin took away the discussion and came back with an excellent set of patches, which got applied.
New modules in core
Jarkko sneaked in a few more modules to the core:
Digest::MD5 and
MIME::Base64 are in there now. There were a couple of teething problems as the tests
for
MIME::QuotedPrint were marked as binary files by Perforce, and Nick spotted an ASCI-ism
in the code while working on yet another piece of PerlIO trickery. (He
wanted
use MIME::QuotedPrint; binmode(\*STDOUT,":Object(MIME::QuotedPrint)"); print "Just my 2? on the MIME stuff \n",scalar( '_' x 80),"\n";
to produce
Just my 2=A2 on the MIME stuff=20
___________________________________________________________________________=
_____
. Uhm, yum, I think.)
YAPC Registration
Rich Lafferty announced that the Third North American Yet Another Perl Conference registeration was open. YAPC::America::North will be held at McGill University, Monteral, Quebec from Wednesday June 13th to Friday June 15th.
Don't delay, register today!
Various
I called for
pack() recipes, since I'm trying to write a tutorial about the underused
functions
pack() and
unpack(). If you have any neat things you do with
pack(), please send them to me.
Peter Prymmer got 5.6.1 ready to go on OS/390, with updates to the documentation and test suites.
Chris Nandor got some more Mac portability patches in.
Radu Greab provided something I don't quite understand to work around socket brokenness in Linux.
Paul Johnson came up with some patches for mingw32; mainly to bring it closer towards Borland C-ness. (or, alternatively, further away from VC++) Nick I-S queried this, as he thought mingw32 was trying to be more VC++ compatible, but it seemed to be the right thing.
Jarkko documented how to use Third Degree and Pixie, two memory leak and
profiling tools, in
perlhack.pod.
Tim Jenness went through the typemap file and found some oddities in it; as well as fixing them up, he came up with an XS module to test them.
He also found that naughty, naughty Compaq shipped the Perl library
separately from the Perl binary with Digital U... uhm, I mean Tru64 v5.1.
Unfortunately,
perl -V needs
Config.pm, which is in the "optional subset" containing the rest of the Perl
library. Oops.
Until next week I remain, your humble and obedient servant,
Simon Cozens
