In my previous journal entry I got talking about exception handling, following on doing a talk on it. The problem was I had a $SIG{__DIE__} handler that said "If the exception isn't of type 'MyException' then create a MyException class from the exception". Unfortunately when you try and plug two systems together and one $SIG{__DIE__} overrides another, you get a conflict - case in point TT2 and AxKit - both have exception objects, but both use different base classes, so the exception objects support different methods and are of different types.
After much umming and ahhing, I figured the best thing to do is leave exceptions well alone if they are references (you could say blessed() here, but ref() is normally good enough). If they aren't, you need to figure out what your $SIG{__DIE__} is there for - in my case it's to augment the exception with a stack trace for debugging. Then you simply augment it but just as a string - otherwise you break stuff...
So, in going through this, I think the best use of $SIG{__DIE__} looks like this:
$SIG{__DIE__} = sub {
my $err = shift;
return if ref($err);
die Carp::Heavy::longmess($err) if $DEBUGGING;
die $err;
};
if ($@) {
if ($@->isa('My::Exception')) {
warn("got a My::Exception\n");
}
else {
warn("Don't know this exception type: $@\n");
}
}