$a = zeroes 10,10; $$a{FOO} = "bar"
doesn't work. They are currently scalar references (to opaque C structures in finer terms) because of speed as well as syntactic issues. If you want to have a hash, use
$a->hdr()
which returns a reference to an anonymous hash. Also, subclassing works if you store a piddle in the hash member ``PDL''.
There are also many core enhancements to support Dataflow and Slicing tricks, but these do not introduce any incompatbilities.
=head1 SEE ALSO
The Changes file for exhaustive details on what changed.
The INSTALL file for how to build PDL.
The README file for general stuff.