You did this: my $vals = "a:1,b:2" then you would have an apparently atomic data item that it really not atomic, because you would have to do string-twiddling to extract relevant subparts.

I don't see why searching through an associative array stored as "a:1,b:2" makes the type not atomic when the example you used for an atomic type ({a=>1,b=>2}) is an associative array that requires searching through a list of buckets then through a linked list.