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All the Perl that's Practical to Extract and Report

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  • Yes, this is a well-known problem with eval. You cannot, as the manual page suggests, do eval { ... } and then test $@ to see whether there was an error. The correct incantation is something like

    my $r = eval { ... };
    my $error = $@;
    $error //= 'unknown error' if not $r;
    if ($error) { ... }

    By well-known I mean known to a tiny minority of cognoscenti, while most perl programmers and the documentation are entirely ignorant of it. Which is the default situation for any trap or gotcha in the perl language. But
    -- Ed Avis
    • Yeah, I generally do that, and definitely suggest that anyone else do it, too. What I was wondering about, though, is prevention. People are going to *forget* to do that, and if my destructors localize $@, they won't clobber it. Where else is there clobbering potential?

      I'm not even sure the destructor in quesiton did call eval. I guess maybe somewhere down *its* calls. Blech!

      • For prevention, you just have to run perlcritic over your code. If you're calling other people's code that isn't perlcritic-clean, then 'local $@' in every DESTROY method might save you. I suppose there should be a perlcritic policy for that too.

        I don't like the way that the perl core has all sorts of traps for the unwary and can seemingly never be fixed for fear of breaking backwards compatibility, but perlcritic provides a useful sticking plaster.
        -- Ed Avis