Re: Why does exists cause autovivication? (myth, mods)

exists has never had any special power over auto-vivification at all. See Re^10: searching a list (myth) for a full explanation of that.

See Data::Diver for an alternate solution. Well-considered suggestions for improvements welcome; I'm quite sure there is ample room for improvement.

Rather than "fix" exists to prevent auto-vivification, I'd prefer to have a pragma that makes auto-vivification a fatal error (or optionally a warning). There are times when I program very carefully and any case of autovivification is quite simply the indication of a bug. It is a rather like "use strict" or like the "Use of uninitialized value" warning. There are often times where the restrictions imposed by such things are inconvient (one-liners in the case of "use strict") but there are other times where enforcing "extra care" is a real boon.

I also think such a pragma would be easier to implement than changing exists. Also, once you have the pragma, it makes it easier to give that power to exists as well -- since the pragma requires a flag for "don't auto-vivify" that can be attached to op-nodes (that is how lexical pragmata work) and "fixing" exists would require the same flag.

- tye

Comment on Re: Why does exists cause autovivication? (myth, mods)

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Re^2: Why does exists cause autovivication? (myth, mods) by Dumu (Monk) on Jul 09, 2015 at 09:24 UTC
Fortunately, we now have the autovivification pragma on CPAN... tye, you couldn't have specified it better!	[reply]
Re^3: Why does exists cause autovivication? (XS--) by tye (Sage) on Jul 09, 2015 at 17:18 UTC
No, the autovivification pragma on CPAN tries to be what I described but it accomplishes it an unfortunately very complex way. It has to reimplement a bunch of Perl guts inside of the module. The level of hidden complexity is impressive, which makes the potential for subtle problems that are very hard to diagnose also high. As much as I'd like a "don't autovivify" pragma, I won't use its 1800 lines of XS code given how many subtle bugs I've spent way too much time on from much, much fewer and simpler lines of XS so many times. - tye	[reply]