This Week on p5p 2001/04/01

Apr 1, 2001 by Simon Cozens

Notes

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There were 446 messages this week.

Perl and HTML::Parser

Gisle complained that a recent snapshot of Perl broke HTML::Parser. Apparently, his code did something like

sv_catpvf(sv, “%c”, 128);

and Perl upgraded the SV to UTF8, which caused confusion when his C-level code then looked at the real value of the string. Jarkko asked why Gisle’s code cared about the representation of the string, but it seemed like Gisle expected it to be non-UTF8. (I could argue that this was Perl’s fault, and I could argue that it was Gisle’s.) Sarathy warned ominously: “We need to tread very carefully here, or 5.8.0 might break a lot of XS code out there.” Nick I-S pointed out the handy-looking SvPVbyte macro which returned a non-UTF8 version of the string’s contents, plus another way of doing things which was actually backwards compatible.

Autoloading Errno

Last week, we covered the fact that using %! should autoload the Errno module but at the time, it failed to. Robin Houston fixed that, with another quotable analysis:

I must admit that I’m slightly dubious as to the wisdom of doing this. It’s not needed for compatibility (it’s never worked), and any code which uses %! could simply put “ use Errno;” at the top.

The intention, presumably, is that code which doesn’t make use of %! shouldn’t have to incur the penalty of loading [Errno.pm].

Currently cleverness only takes place when a glob is created. So, if you use a hash called %^E then the magical scalar $^E is set up, even though you don’t use it.

In this case though, we want Errno.pm to be loaded only if %! is used. Loading the damned thing for every script which uses $! would be Bad.

The upshot of this all is that an extra test has to be inserted into the code which deals with creating new stash variables (not just the first variable of the particular glob). Even a marginal slowdown like this doesn’t seem worth the insignificant benefit of not having to load Errno yourself.

However, Sarathy commented that the intention was simplicity and transparency; the %! language feature should be implemented in a manner transparent to the end user, just like the loading of the Unicode swash tables. “Besides,” he concluded, “there is probably no precedent for forcing people to load a non-pragma to enable a language feature.”

Jarkko looked slightly guilty. “Ummm, well, in other news, I may have have just created one”, he said, referring to the new ability to export IO::Socket::atmark to sockatmark.

Robin also added some more reporting to B::Debug, and fixed up a parenthesis bug in B::Deparse.

Math::Big*

Tels and John Peacock have been working together to rewrite Math::BigInt and Math::BigFloat. Their version is on CPAN. Jarkko seems understandably a little hestitant about replacing the in-core version with this one; while we’re assured that it will be backwards compatible (minus bugfixes, naturally) but obviously a complete rewrite isn’t mature enough to be considered for core yet.

pack and unpack

Someone asked a (non-maintainance) question about pack and unpack which MJD dealt with; I took this as a cue to show my current work on a perlpacktut. A few people produced useful suggestions for that, which I’ll get finished when the next consignment of tuits arrives. There was a short diversion about what an asciz string was; (see the documentation for the “w” pack format) it’s actually a C-style null-terminated string.

Taint testing

For some reason, the usual way to detect taintedness in the test suite seems to be

    eval { $possibly_tainted, kill 0; 1 }
Nick Clark thinks this sucks, but it's a bit too late to change it now.

Of course, MacPerl doesn’t have kill so Chris found that his test suite was going horribly wrong. He had a number of violent suggestions to fix this up, including having kill be a no-op which died on tainted data. MJD suggested that kill should do what it does already but be a no-op if it’s passed a 0. The eventual solution was to have it return 0 but check for tainted data. He also hinted that this may be the precursor to Win32-like pseudoprocesses.

Various

Benjamin Sugars was at it again. He fixed a bug in socket which leaked file descriptors, wrote a test suite for Cwd, joined the bug admin team, patched up B::Terse and File::* to be warnings-happy, produced another version of his XS Cwd module. He didn’t document references in @INC, though, so he doesn’t get the gold star.

I zapped OPpRUNTIME, a flag that was set but never tested!

Stephen McCamant produced a couple of optimizations to peep(), the optimizer.

Thomas Wegner and Chris Nandor fixed up File::Glob for MacOS.

Jarkko floated the idea of a FETCHSLICE and STORESLICE for tied hashes and arrays to avoid multiple FETCH/ STORE operations; there was a little discussion about the syntax:

    STORESLICE($thing, $nkeys, $nvalues, @keys, @values)

would be more efficient but less user-friendly than

    STORESLICE($thing, \@keys, \@values)

but no implementation as yet.

Schwern asked if we were going to document the fact that ref qr/Foo/ returns “Regexp”. Everyone went very quiet.

Mark-Jason Dominus tried to introduce a new operator, epochtime, which return the time of the system epoch; for instance, one could use

    localtime(epochtime())

to portably find out the date of the system epoch, allowing you to write epoch-independent code. Jarkko rejected the patch on the grounds that it was not sufficiently portable.

Until next week, then, squawk,

Simon Cozens - Notes - Perl and HTML::Parser - Autoloading Errno - Math::Big* - pack and unpack - Taint testing - Various