2.4 Make a closure ¶

(ffi-make-closure CIF FUNCTION). Make a C pointer to the Lisp function. This pointer can then be passed to C functions that need a pointer-to-function argument, and FUNCTION will be called with whatever arguments are passed in.

CIF is a CIF as returned by ffi--prep-cif. It describes the function’s type (as needed by C).

This returns a C function pointer, wrapped in the usual way as a user-pointer object.

(defun callback (arg)
  (1+ arg))

(define-ffi-function test-call-callback "test_call_callback"
  :int [:pointer] test.so)

(let* ((cif (ffi--prep-cif :int [:int]))
       (pointer-to-callback (ffi-make-closure cif #'callback)))
  (test-call-callback pointer-to-callback))  ; => 23