Passes a foreign object of a specified type by reference, and automatically dereferences the object.
The type of the object to pass by reference.
If non- nil , if the input argument is nil a null pointer is passed instead of a reference to an object containing nil .
If non- nil , allow conversion from Lisp to the foreign language. The default value is t .
If non- nil , allow conversion from the foreign language to Lisp. The default value is t
The FLI :reference type is essentially the same as a :pointer type, except that :reference is automatically dereferenced when it is processed.
The :reference type is useful as a foreign function argument. When a function is called with an argument of the type (:reference type ) , an object of type is dynamically allocated across the scope of the foreign function, and is automatically de-allocated once the foreign function terminates. The value of the argument is not copied into the temporary instance of the object if lisp-to-foreign is nil , and similarly, the return value is not copied back into a Lisp object if foreign-to-lisp is nil .
In the following example an :int is allocated, and a pointer to the integer is bound to the Lisp variable number . Then a pointer to number , called point1 , is defined. The pointer point1 is set to point to number , itself a pointer, but to an :int .
(setq number (fli:allocate-foreign-object :type :int)) (setf (fli:dereference number) 42)(setq point1 (fli:allocate-foreign-object
:type '(:pointer :pointer)))
(setf (fli:dereference point1) number) If point1 is dereferenced, it returns a pointer to an :int . To get at the value stored in the integer, we need to dereference twice:
(fli:dereference (fli:dereference point1)) However, if we dereference point1 as a :reference , we only have to dereference it once to get the value:
(fli:dereference point1 :type '(:reference :int))