my %testHash;                # initialize hash
   my $hashRef = \%testHash;    # get a reference to that

   # get a reference to an element 'a' inside the hash (that does not yet exist)
   my $destref = \${$hashRef->{'a'}}; # <- problematic line

   # assign a value to the hash element 'a'
   $destref = "value";

   # verify the result
   print $hashRef->{'a'} . "\n"; # outputs "SCALAR(0xaddress)"