[cffi-devel] trying to understand foreign types and translations

[rif]

I've been poking at this for over an hour, but I'm just not sure how to
get this to work.

I have a foreign object, points to a vector of (C) double-floats:

(defstruct (fnv-double (:constructor make-fnv-double-internal))
  (foreign-pointer nil :read-only t)
  (size 0 :type fixnum :read-only t))

I can create and manipulate it.  I need to know how to define (with
defcfun) an interface to a C function which expects a vector of
double-floats.  My attempts have been along the lines of:

(defmethod translate-to-foreign (val (f fnv-double)) (fnv-foreign-pointer f))

and then declaring something like

(defcfun ("foo" :%foo) :double
   (x fnv-double))

but neither this nor any of the variants I've tried seems to work at
all.  I think I need to either defctype or define-foreign-type first,
but I haven't gotten that to work either.  Can anyone suggest how to do
this?

Cheers,

rif