FFI::Platypus::Type::PtrObject is a helper type for FFI::Platypus that handles
type checking for the common pattern where a Perl class is a simple wrapper
around an opaque pointer. The class should be implemented as a hash reference,
and the pointer itself is expected to be stored on the ptr key. If the caller of
the interface (Perl) is responsible for cleaning up the memory, then it normally
should be done in the DESTROY method (as above).

If you do not pass in the correct type, it will be detected before the C code is
called and an exception will be thrown. (otherwise you would probably get a
segment violation SEGV).