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Postings from November 2009
Nicholas Clark wrote:
> On Sat, Nov 28, 2009 at 06:37:15PM -0700, karl williamson wrote:
>> I'm not sure what to do here. When Carp is called by mktables from an
>> object that has overloading (stringify, I suspect), Carp tries to call
>> Scalar::Util::refaddr, and fails because we are running under miniperl.
>> It gives the message:
>> Attempt to reload Scalar/Util.pm aborted.
>> Compilation failed in require at lib/overload.pm line 95.
>>
>> I think it actually does the stringify correctly, but fails in the
>> backtrace.
>>
>> Any suggestions? I suppose I could just not use carp.
>
> My test case:
>
> ./miniperl -Ilib -MCarp -e '{ package A; use overload q{""} => sub {local $^D="t"; Carp::carp("Oops")};} print bless {}, "A"'
>
> fails slightly differently:
>
> ...
> Can't load module B, dynamic loading not available in this perl.
> (You may need to build a new perl executable which either supports
> dynamic loading or has the B module statically linked into it.)
> at lib/Scalar/Util/PP.pm line 15
> Compilation failed in require at lib/Scalar/Util/PP.pm line 15.
> BEGIN failed--compilation aborted at lib/Scalar/Util/PP.pm line 15.
> Compilation failed in require at lib/Scalar/Util.pm line 21.
> Compilation failed in require at lib/overload.pm line 95.
>
>
> suggesting that it's this bit of Carp:
>
> # Transform an argument to a function into a string.
> sub format_arg {
> my $arg = shift;
> if (ref($arg)) {
> $arg = defined($overload::VERSION) ? overload::StrVal($arg) : "$arg";
> }
>
> calling overload:
>
> sub AddrRef {
> my $package = ref $_[0];
> return "$_[0]" unless $package;
>
> local $@;
> local $!;
> require Scalar::Util;
> my $class = Scalar::Util::blessed($_[0]);
> my $class_prefix = defined($class) ? "$class=" : "";
> my $type = Scalar::Util::reftype($_[0]);
> my $addr = Scalar::Util::refaddr($_[0]);
> return sprintf("$class_prefix$type(0x%x)", $addr);
> }
>
>
> and that's failing.
>
>
> The work-around hack would seem to be to add
>
> undef $overload::VERSION;
>
> to mktables :-)
Well that seems to work. Thank you.
>
> Given that we removed Carp::Heavy, with the reasoning that it's wrong for an
> error reporting module to require more resources at error reporting time, as
> it might fail and hence eat the error message, we seem to be in the same
> trap here. The test on $overload::VERSION seems logical though - if overload
> is not loaded, there's (in theory*) no need to check for overloading. But I
> can't see a clean way to plug this loophole, short of a tight coupling
> between Carp and overload such that if either spots that the other is already
> loaded, then it requires Scalar::Util, to make sure that it's there for error
> reporting.
Yet another way to plug the loophole is to put Scalar::Util::refaddr in
the core. My recollection, which I think is correct, is that consensus
had been reached; it's just a matter of finding someone to do it.
Perhaps it could be put on the Todo list, as some sort of encouragement.
>
> Nicholas Clark
>
> * In theory, sure. In practice, XS code can create overloaded objects:
>
> $ ./perl -Ilib -MCarp -e 'sub a {carp("Hello world")} a($^V)'
> Hello world at -e line 1
> main::a('v5.11.2') called at -e line 1
> $ ./perl -Ilib -MCarp -e 'use overload; sub a {carp("Hello world")} a($^V)'
> Hello world at -e line 1
> main::a('version=HASH(0x10081e720)') called at -e line 1
>
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