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RE: my $@ - a proposal

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On Sun, 06 Jul 2008, Rafael Garcia-Suarez wrote:
> 2008/7/2 Mark Mielke <mark@mark.mielke.cc>:
>> But, to be nice, I'm happy with silencing them. The last code
>> submission that effectively does local($@, $?, $!) is good for me.
>
> I disagree here. As Graham said, I think $@ should be prevented to be
> cleared by a DESTROY; but if a DESTROY sets $@ to any true value, it
> should persist.
Can you explain _why_ you think it should work like this? I fail to
see how this would be useful. It also violates the current
documentation for eval():
|  If there was no error, $@ is guaranteed to be a null string.
This cannot be guaranteed if DESTROY can scribble over $@:
 1:   sub foo::DESTROY { eval {require foo} }
 2:   eval { my $foo = bless [] => "foo"; };
 3:   print "\$\@ is $@\n" if $@;
In this case the eval block in line 2 is successful, but $@ in line 3
still contains the error about the missing foo module.
Similarly, even if the eval in line 2 died, why should the DESTROY
methods be allowed to wipe out the error and replace it with something
else? Typically the first exception record is the one that contains
useful information; all following errors may just be caused by the
initial error condition.
You could still let an *uncaught* die() inside DESTROY append the "\t(in
cleanup) $msg" text to $@ if you want to, but I don't think any
exceptions completely handled inside DESTROY should modify the $@
outside the DESTROY.
Cheers,
-Jan

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