Whenever I see code like: print $$hash_ref{$key}; I have to think hard as to whether that is equivalent to:

print ${ $hash_ref }{ $key };
[download]

Or:

print ${ $hash_ref{ $key } };
[download]

With the second form, I don't have that indecision.

In a similar vein, given this sub:

sub x{ print $$_[0][1] };;
[download]

What do you think these two calls print?:

x( [['a','b'],['c','d']] );;

x( ['a','b'],['c','d'] );;
[download]

Produces:

Is it clearer if the sub is defined this way?:

sub x{ print $_[0]->[1] };;

xx( [['a','b'],['c','d']] );;

xx( ['a','b'],['c','d'] );;
[download]

Produces: