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in reply to Re: Autovivification sucking the life out of me
in thread Autovivification sucking the life out of me

But I am not explicitly telling Perl to autovivify, rather I am (intending to) just reference the values, in this case using a slice.

Refer to my simpler example above. Using see_args( @foo{qw(BAR BAZ)} ); causes result: 

at start: BAR '<absent>'
at end: BAR '<undef>'

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But changing that to see_args( $foo{BAR}, $foo{BAZ} ); results in: 
at start: BAR '<absent>'
at end: BAR '<absent>'

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This is most perplexing to me.

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Re^3: Autovivification sucking the life out of me
by Skeeve (Parson) on Oct 14, 2005 at 08:17 UTC

    Tell you what: It's perplexing to me the other way around!

    Until 2 days ago I thought something like
    if ($foo{'BAR'}) ...
    would already vivify that hash entry.

    But then I learned in the Chatter Box that it doesn't in perl 5.8 (or maybe a bit earlier).

    And now I did a test. Compare the output 

    use Data::Dumper;
%foo=(BAZ=>1);
print Dumper \%foo if $foo{BAR} || 1;
print Dumper \%foo if @foo{BAR,BAZ} || 1;

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    Output:

    $VAR1 = {
              'BAZ' => 1
            };
    $VAR1 = {
              'BAZ' => 1
            }; 

    use Data::Dumper;
%foo=(BAZ=>1);
print Dumper \%foo if call($foo{BAR});
print Dumper \%foo if call(@foo{BAR,BAZ});
sub call { return 1 }

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    Output:

    $VAR1 = {
              'BAZ' => 1
            };
    $VAR1 = {
              'BAR' => undef,
              'BAZ' => 1
            };

    So it's really the fact that the slice is used in a subroutine call. When you replace call with print, autovivification does not happen

    So now I ask myself: Is there a bug and you are certified bugfinder!? ;-)

    s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
    +.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e
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