I wrote a module that used attributes to make sorted hashes. But to get syntax like
in reply to RFC: Simulating Python's @decorators in Perl with Attributes
the 'Sorted' sub (that provides the sorting behaviour) had to be pushed into the UNIVERSAL package, so if someone else wanted to provide a 'Sorted' attribute there would be a name collision.
my %capital : Sorted;
The name collision could be avoided by using a non UNIVERSAL namespace, but then syntax like
would be too cumbersome.
my %capital : Hash::Sorted;