The two arguments to TRANSLATE-TO-FOREIGN are the Lisp object to be converted, and the name of the foreign type to convert to. First, declare a foreign typedef for :POINTER (since you will ultimately be returning a pointer from the type translator) that you use to hang your type translator on:
(defctype fnv-double :pointer)
Then you can specialize TRANSLATE-TO-FOREIGN on both the Lisp value and the foreign type (using an EQL specializer):
(defmethod translate-to-foreign ((value fnv-double) (name (eql 'fnv-double))) (fnv-foreign-pointer value))
It might be confusing to call both the Lisp and foreign types FNV-DOUBLE, but it is legal because foreign type names are a separate namespace from Lisp types (viva Lisp-N!). It is important to remember the distinction between the two though.
and then declaring something like
(defcfun ("foo" :%foo) :double (x fnv-double))
should just work!
(This is untested and I haven't really been doing any CFFI hacking lately, so I apologize if I missed something obvious here.)
James
I don't quite understand. fnv-double is NOT a pointer. It's a CL struct that holds two arguments, one of which is the foreign pointer. I see I was misusing translate-to-foreign, so maybe I don't need a defctype at all, just an appropriate translate-to-foreign?
rif