Please disregard this query. I see that I was clueless and apologize. I had forgotten my old C knowledge, and in particular, had forgotten that the desire to have multiple values, combined with call-by-value, means that one often must pass pointers to pointers as arguments, and then to get the pointer, one dereferences.... Never mind! Cheers, R Robert P. Goldman wrote:

I wonder if anyone who's familiar with SBCL aliens can give me some advice in my ongoing translation of the freetype code into CFFI. IIUC (I quite possibly don't), a difference between the two is that SBCL has much more "understanding" of the foreign data structures, and that it is able to work directly with foreign structures. CFFI works more with pointers, and requires more explicit reference to the foreign types when dereferencing.

I think I have mostly managed to translate the foreign data structures, and a good bit of the code. However, I am still having some trouble understanding a bit of the SBCL alien code, particularly the use of derefs when returning foreign values. For example, here's one of the original defuns:

(defun make-concrete-font (vague-font size &key (dpi *dpi*)) (with-slots (lib filename) vague-font (let* ((key (cons lib filename)) (val (gethash key *concrete-font-hash*))) (unless val (let ((facef (make-alien freetype:face))) (declare (type (alien (* freetype:face)) facef)) (if (zerop (freetype:new-face lib filename 0 facef)) (setf val (setf (gethash key *concrete-font-hash*) (deref facef))) (error "Freetype error in make-concrete-font")))) (let ((face val)) (declare (type (alien freetype:face) face)) (freetype:set-char-size face 0 (round (* size 64)) (round dpi) (round dpi)) face))))

I'm not at all sure, moving to CFFI, how to translate the DEREF calls. CFFI is essentially always working with pointers, IIUC, so I'm wondering if I should just eliminate deref calls like this (i.e., just set the hash table entry to facef)...

Any suggestions would be more than welcome.

Thanks, R