Assignment, bar key is assigned the value 1
my %foo; $foo{bar} = 1;

Autovivification, a hashref springs into existence under key fa , bar key is assigned the value 1

my %foo; $foo{fa}{bar} = 1;

Autovivification, you use it as a reference to a hash, , it becomes a reference to a hash

 my $foo; $foo->{bar} = 1;

Autovivification, you use it as a reference to an array, it becomes a reference to an array

 my $foo; $foo->[0]= 1;

Initialization, you declare $foo and assign a reference, you can use it as a reference, but it doesn't become a reference, because it already is a reference

 my $foo = {}; $foo = \my %bar; $foo->{fa} = 1;

Error, can only autovivify if undef, Not an ARRAY reference

 my $foo = {}; $foo->[0] = 1;

Error, can only autovivify once, Not a HASH reference

 my $foo; $foo->[0] = 'autovivified'; $foo->{autovivified} = 'already';

In reply to Re^2: Unique value count in hash not working properly by Anonymous Monk
in thread Unique value count in hash not working properly by koolgirl

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