will cause perl to complain (if you have not declared (and thus created) $foo before), while writing

Oh will it now? 

$ perl -le " use warnings; use strict; my $foo; $foo++; print $foo "
1

[download]

So these two examples are not comparable. And I believe the second example actually is where we see autovivication at work.

Yes, they really are exactly comparable, and no, the second example is not autovivification any more than the first example is autovivification -- neither is autovivification

Growing an array is not autovivification. JavaScript doesn't support autovivification , try it if you have firefox ( Ctrl+Shift+K ) 

[03:41:08.755] var noauto = [ 0, 1 ]; noauto[ 6 ] = 66; noauto ;
[03:41:08.764] [0, 1, , , , , 66]
[03:43:06.834] noauto[2].failToAutoVivify = 12; noauto;
[03:43:06.843] TypeError: noauto[2] is undefined

[download]

JavaScript supports growing arrays but not autovivification, but perl does supports it, undef becomes a hashref if you treat it like a hashref 

$ perl -MData::Dump -le " my $auto = [ 0, 1 ]; $$auto[6]=66; dd $auto;
+ "
[0, 1, undef, undef, undef, undef, 66]


$ perl -MData::Dump -wle " my $auto = [ 0, 1 ]; $$auto[6]=66; $$auto[2
+]{VIVIFY}=12; dd $auto; "
[0, 1, { VIVIFY => 12 }, undef, undef, undef, 66]

[download]

In reply to Re^4: Occurence List by Anonymous Monk
in thread Occurence List by Hopfi

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