While the read-only keys solutions (Tie::StrictHash and from Hash::Util) provide one method of preventing autovivification for hashes, they also prevent normal key creation.

What I've long wanted was a 'no autovivify;' pragma that would prevent autovivification in the scope where it is used (for both hashes and arrays) but that would not prevent normal hash key insertion.

I like to be able to assign new keys in the normal manner:

    $hash{key}= 'value';
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but I often prefer to not create new keys via autovivification, which is different:

    no autovivify;
    my %hash;
    # Examples of normal key insertion:
    $hash{key1}= 'value';       # succeeds
    $hash{key2}= {};            # succeeds
    $hash{key2}{key3}= 'value'; # succeeds
    # Examples of autovivification:
    $hash{key4}{key3}= 'value'; # should fail!
    $hash{key5}[0]= 1;          # should fail!
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Sometimes it is very nice to be very strict in how you code. It can often find lots of bugs for you. That is why we have use strict;. Perl could really use a similar tool for optionally turning off autovivification. I'd certainly make a lot of use of it (and I've found several bugs the hard way that would have been caught quite easily if I'd had such an option).

                - tye

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