in reply to eval: Why use the 'Zombie error' idiom?

Try::Tiny claims that up to 5.14, $@ was cleared at the beginning of the eval { block.

I think that also a destructor containing eval { can clear out $@, so the above idiom is necessary.

Using (for example) Try::Tiny helps avoiding that.

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Re^2: eval: Why use the 'Zombie error' idiom?
by DouglasDD (Beadle) on Oct 18, 2019 at 09:57 UTC
    ...So, would local-izing $@ be enough to work-around other code's evals messing with our own $@? 
    {   # scope the `local`
    local $@;
    eval {
        do_something_that_might_die();
        1;
    } or do {
        my $error = $@;  ## ?? No need for  || 'Zombie error' ??
        deal_w($error) || die;
    }
}

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[d/l]

      The docs for eval suggest this idiom:

           # alter $@ on nefarious repugnancy only
     {
        my $e;
        {
          local $@; # protect existing $@
          eval { test_repugnancy() };
          # $@ =~ /nefarious/ and die $@; # Perl 5.14 and higher only
          $@ =~ /nefarious/ and $e = $@;
        }
        die $e if defined $e
     }

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[d/l]

      I don't know - from the discussion in Try::Tiny, it sounds like that, but then, the code of Try::Tiny isn't really that large either. So maybe looking there (or in its test suite) helps find the nasty edge cases.

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Re^2: eval: Why use the 'Zombie error' idiom?
by DouglasDD (Beadle) on Oct 18, 2019 at 10:03 UTC
    Forgot to mention that our local coding standards discourage Try::Tiny apparently because it's edge cases have been tripped over in the past.
[reply]

      Interesting choice. I use Try::Tiny precisely to avoid having to work around the edge cases inherent in eval. YMMV, of course.

[reply]
        The reason I avoid Try::Tiny is that its catch block is actually a function in disguise, not just a block like with the original eval idiom. So a return from a Try::Tiny catch block returns just from that block, and not from the enclosing function, which is useless and misleading.
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