in reply to Re^2: Possible useless use of map
in thread Possible useless use of map

Well the first version also auotovivifies.... i'm not sure what you mean about tied hashes.

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Re^4: Possible useless use of map
by almut (Canon) on Mar 18, 2010 at 10:39 UTC

    No, $hr->{stuff} alone doesn't autovivify the element. It's the dereferencing operation 

         $hr->{stuff}->{foo}
                 ^^

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    that autovivifies, not merely accessing the hash element.

    As for side effects with tied hashes, I mean that arbitrary code could be associated with the tied read operation.

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      :D You're not paying attention 
      $ perl -MDDS -w -le " my $hr; $hr->{stuff}; Dump($hr)"
$HASH1 = {};

$ perl -MDDS -Mwarnings -le " my $hr; $hr->{stuff}; Dump($hr)"
Useless use of hash element in void context at -e line 1.
$HASH1 = {};

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      $hr used to be undef, after $hr->{stuff} it is a hashref.

      Curiously, my little test reveals Data::Dump::Streamer breaks the -w switch .

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        I see what you mean.  So, one could conclude that getting no warning in the OP's case (with map) is in fact the appropriate behavior (as the $hr->{$_} is not useless), while getting the warning with for seems more questionable  (in which case I wouldn't consider it a bug to silence a useless "Useless use of..." warning :)

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