use strict;
use warnings;

my $hashRef;
# note how it is undefined at this moment!

$hashRef->{cogito} = "ergo sum";
print ref $hashRef, "\n"
# Output: HASH
# Hey... aint that cool?

# But we can go even further!
$hashRef->{"somewhere"}->{"deep down"}->{"this"}->{"data structure"} = "I think, so I exist.";