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RE: my $@ - a proposal

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On Fri, 27 Jun 2008, Graham Barr wrote:
> On Jun 27, 2008, at 2:39 PM, Jan Dubois wrote:
>> That's not really good enough though. You need to restore ERRSV
>> whenever the initial substring of the saved ERRSV doesn't match the
>> current ERRSV (making sure that only cleanup errors have been
>> appended).
>
> You cannot do that. Where does it say that $@ is a string?
In that case you can restore it unconditionally and throw all the
(in cleanup) messages away.  Right now calling die() inside DESTROY
will reset $@ to "" if it is not SvPOK().  Otherwise it could not
append the "\t(in cleanup)" message.  So error objects right now
don't survive calls to die() inside DESTROY at all.
>> Otherwise you still end up with the wrong value in $@ when DESTROY
>> (or any code called from it) uses an eval that catches a die():
>>
>>    sub foo::DESTROY { eval {require bar} }
>>    eval { my $foo = bless [] => "foo"; die "I'm dead\n" };
>>    print "\$\@ is $@\n";
>>
>> With your patch you at least end up with a TRUE value in $@, but the
>> actual content is still not what you would expect.
>
> What do you expect ?
I expect the code to print
    $@ is I'm dead
regardless if DESTROY is any of these three:
1)  sub foo::DESTROY {  }
2)  sub foo::DESTROY { eval {} }
3)  sub foo::DESTROY { eval {require bar} }
Currently it does this only for 1), and the proposed patch only fixes 2)
but not 3) (assuming bar.pm cannot be loaded and %bar:: doesn't exist).
There is no reason for 3) to overwrite $@ because the exception has
already been caught and handled.
Cheers,
-Jan

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• my $@ - a proposal by Yuval Kogman
• RE: my $@ - a proposal by Jan Dubois
• Re: my $@ - a proposal by David Nicol
• Re: my $@ - a proposal by Graham Barr
• Re: my $@ - a proposal by David Nicol
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