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RE: my $@ - a proposal

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On Fri, 27 Jun 2008, David Nicol wrote:
> 
> On Fri, Jun 27, 2008 at 4:43 PM, Jan Dubois <jand@activestate.com> wrote:
> 
> > Why?  The whole point of putting the "require" inside an eval {}
> > was to *not* raise an exception.  How would you trap errors inside
> > a DESTROY method that you don't want to be propagated?
> 
> as documented:
> 
>      sub DESTROY { local $@; eval {require bar}}
> 
> The additional manouevers are to support not breaking premeditated
> non-suicidal setting of $@ within DESTROY, just in case such exists
> (it might not.)
Ok, true, but that works the same way to protect eval {} from overwriting
$@ with the empty string.  Why do you want to implement the semantics of
local($@) for only one of the 2 cases?
I find it rather bizarre that the $@ value should be assigned to $@ only when
the outer eval itself is dying:
    sub foo::DESTROY { eval {require foo} }
    eval { my $foo = bless [] => "foo"; 1 };
    print "\$\@ is $@\n" if $@;
This prints nothing. But if we call die() inside the outer eval, then
the failure in foo::DESTROY suddenly becomes significant enough to be
assigned to $@:
    sub foo::DESTROY { eval {require foo} }
    eval { my $foo = bless [] => "foo"; die "I'm dead\n" };
    print "\$\@ is $@\n" if $@;
    $@ is Can't locate foo.pm in @INC [...]
How does this make sense?  When would this ever be useful?  Errors
recorded in DESTROY methods that can only be detected when DESTROY
is being called as part of the stack-unwinding of a failed eval?
Cheers,
-Jan

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• RE: my $@ - a proposal by Jan Dubois
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