- Notes
- Method Lookup Speedup
tr///CUandtr///UCRemovedis_utf8_string- Byte-Order Marks Return
pack("U")- Lexical variables and
eval() FILEGVperlhacktutperlutil.pod- Missing Methods
- Suppress prototype mismatch warnings
- Autoloaded Constants not Inlined
lib.pmuse English- Numeric opens in
IPC::Open3 - Regex Bug
Foo isa FooREADME.hpuxmy __PACKAGE__ $obj...- asdgasdfasd
- Various
Notes
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This week's report is a little late because I went to San Diego Usenix, and then I went to YAPC in Pittsburgh (probably the only person on the continent stupid enough to try to do both) and then I went back to Philadelphia and was driven to Washington DC for a party and came back on the train.
I was going to say it was a quiet week on the list. But it wasn't. It was merely a low-traffic week. It wasn't quiet at all; all sort of useful and interesting stuff was posted, and there was an unusually high signal-to-noise ratio.
This week has been named 'Doug MacEachern and Simon Cozens' week. Thank you Doug and Simon, and also everyone else who contributed to the unusually high signal-to-noise ratio this week.
Method Lookup Speedup
More discussion of Doug's patch of last week.
Last week, some people pointed out
that it would fail in the presence of code that modifies
@ISA at runtime; Sarathy suggested a pragma that would promise that this
would not happen. Nick suggested that
use base could do that.
Doug submitted an updated patch.
For your delectation, Simon Cozens wrote up an extensive explanation of the patch and how it works, including many details about the Perl internals. If you are interested in the Perl internals (and you should be) then this is strongly recommended reading.
I would like very much to run other articles of the same type in the future. This should be construed as a request for people to contribute them. They don't have to be as complete or detailed as Simon's.
Thank you very much, Simon.
tr///CU and tr///UC Removed
Simon, who has been working on the line discipline feature, got rid
of the nasty
tr///CU feature, which Larry had already decided was a bad idea and should be
eliminated.
is_utf8_string
Simon also added a function named
is_utf8_string that checks a string to make sure it is valid UTF8. The plan is that
if Perl is reading a putatively UTF8 file, it can check the input
before setting the UTF8 flag on the resulting scalar.
Byte-Order Marks Return
Simon submitted an improved patch for this. This one just has the lexer use
tell() to see if the putative byte-order mark is at the very beginning of
the file.
pack("U")
A few weeks ago there was discussion of what this should do.
Simon submitted a patch that implemented an idea of Larry's: That a
U at the beginning of the pack template indicates that the result of
pack will be a UTF8 string; anything else indicates a byte string. THis
means (for example) that you can put
U0 at the beginning of any pattern to force it to produce UTF8; if you
want to start with
U but have the result be bytes, add a do-nothing
C0 at the beginning instead.
Lexical variables and eval()
Yitzchak Scott-Thoennes reported on a number of puzzles related to the interaction of these features, including:
{ my $x; sub incx { eval '++$x' } }
Here
incx apparently increments the lexical variable; he expected it to
increment the global variable. (Rationale: The lexical variable
should be optimized away.)
Rick Delaney referred to a relevant article by Ilya in clp.misc.
Yitzchak says that code in a subroutine should not be able to alter
lexical variables in a more outer scope, unless it is a closure, which
incx here is not. Rick presents the following counterexample:
my $Pseudo_global = 2;
sub double {
my ($x) = @_;
eval '$x * $Pseudo_global';
}
Discussion seemed inconclusive. No patches were offered.
I said that I had done some research a while back about what Scheme and Common Lisp do in this sort of case, and that I would report back with a summary, but I have not done so.
FILEGV
There was some discussion about the
FILEGV macro. When Perl compiles the op tree, the line and file information
is stored in a GV. Or rather, it used to be so; now, if you compile
with ithreads, it just uses strings. There were some macros,
*FILEGV, to access this GV, but according to Sarathy, they was mostly used to
get at the filename, and there is a more straightforward macro family,
*FILE, which gets the filename directly. Doug MacEachern wanted to use the
original macro in
B::Graph, although I was not sure why; Sarathy said that probably
B::Graph needed to be fixed.
perlhacktut
Simon contributed the first half of a document titled
perlhacktut, a tutorial on hacking the Perl core. It talks about how to get
started and what to read, provides an overview of Perl's large
subsystems, and the begining of a discussions of Perl's basic data
types and op trees.
If you are interested in the Perl internals (and you should be) then this is strongly recommended reading. (Gosh, that sounds familiar.)
perlutil.pod
Simon also contributed a document describing the utility programs that cmoe
packaged with Perl, such as
perldoc,
pod2html,
roffitall, and
a2p.
Quite a busy week for Simon.
Missing Methods
Martyn Pierce pointed out that if you have code like this:
Foo->new('...');
it might fail for two reasons: because the
Foo class does not define that method, or because you forgot to put
use Foo in your program. In both cases the message is
Can't locate object method "new" via package "Foo" ...
Martyn suggested that in the second case, it could add a remark like
(perhaps you forgot to load module "Foo"?)
However, he did not provide a patch.
I also wonder why it says 'object method' when it is clearly a class method. I did not provide a patch either. This would be an excellent first patch for someone who wanted to get started patching. Write to me if you are interested in looking into it but do not know where to begin.
Suppress prototype mismatch warnings
Doug MacEachern discovered lots and lots of subroutine declarations in
Socket.pm that were there only to predeclare a bunch of autoloaded constants
like
AF_INET. The only purpose for the declarations was to prevent 'prototype
mismatch' warnings from occurring when the constants were actually
autoloaded at run time. He then put in a patch to suppress the
warning, if it appears that the subroutine will be autoloaded later,
and removed the 20K of constant sub declarations in
Socket.pm.
Autoloaded Constants not Inlined
Doug also discovered that these autoloaded constants' values are not
inlined, because the code that uses them is compiled before the
subroutine is loaded. Doug produced a patch to
Exporter.pm that lets you specify a name with a leading
+ sign in the
use line to indicate that the subroutine should be invoked once (and
hence autoloaded) immediately, when the module is loaded, so that
they can be inlined into the following code.
lib.pm
Doug MacEachern decided that it was a shame that
lib.pm has to pull in all of
Config.pm, so he recast
lib.pm as a script,
lib.pm.PL, which generates the real
lib.pm at install time, inserting the appropriate values of
$CONFIG variables inline.
(Many other utilities, such as
perlcc and
pod2html, are generated this way at present. Do
ls */*.PL in the source directory to see a list.)
use English
Barrie Slaymaker contributed a patch so that you can now say
use English '-no_match_english';
and it will import all the usual long names for the punctuation
variables,
except for
$`,
$&, and
$', which slow down your regexes. If you don't supply this flag, then
those variables are separately aliased via an
eval statement.
This has been a long time coming---I thought it had been done already.
There was a long sidetrack from having to do with some unimportant style issue, which should have been carried out in private email, or not at all.
Numeric opens in IPC::Open3
Frank Tobin submitted a patch that allows the user of
IPC::Open3 to request that any of the 'files' to be opened be an already open
file descriptor, analogous to the way
open FH, "<&=3" works with regular
open.
Regex Bug
Ian Flanigan found a very upsetting bug in the regex engine.
Foo isa Foo
Johan Vromans complained that
my $r = "Foo";
UNIVERSAL::isa($r, "Foo::");
returns true. Johan does not like that
$r (which is a string)
is reported to be a member of class
Foo. It was pointed out that the manual explicitly says that
UNIVERSAL::isa] may be called as a class method, to determine whether one class was a
subclass of another, in which case it could be invoked as
Foo->isa('Foo')
which is essentially the same as Johan's example, and which returns
true because the class
Foo is (trivially)
a subclass of itself.
Johan said 'Yuck.'
README.hpux
Jeff Okamoto updated it again.
my __PACKAGE__ $obj ...
Doug MacEachern submitted a patch to enable this. The patch came in just barely before the end-of-the week cutoff, and has already been a lot of discussion of it in the past two days, so I am going to defer talking about it any more until my next report.
Should you want to look at it before then, here it is.
asdgasdfasd
Some anonymous person running as root submitted a bug report (with
perlbug) that only said 'asdgasdfasd'. Martyn Pearce replied that it was not
a bug, but a feature.
Various
A large collection of bug reports, bug fixes, non-bug reports, questions, answers, and a very small amount and spam. No serious flamage however.
This is the end of the month, so I will summarize: I filed 97 messages
in the
junk folder, 311 in the
misc folder, and 329 messages in 45
various other folders pertaining to particular topics.
Until next week I remain, your humble and obedient servant,
Mark-Jason Dominus
