[cffi-devel] Mutable Pointers

[Stuart Sierra]

Luís Oliveira wrote:
> On 2006-jul-14, at 02:38, Stuart Sierra wrote:
>> But POINTER-ADDRESS is not setf-able, is it?
> 
> Right. AFAICT, some of the Lisps supported by CFFI don't have mutable 
> pointers.

I suspected as much.  I couldn't find it in SBCL's FFI, at least.

> (setf *stack-pointer* (inc-pointer *stack-pointer* 1)) should work. 
 > You can abstract that with a simple macro:
> 
>   (defmacro incf-pointer (place &optional (offset 1))
>     `(setf ,place (inc-pointer ,place ,offset)))

But won't that set the value that *STACK-POINTER* points to?  In my 
example, *STACK-POINTER* is not a Lisp object but a foreign global 
variable accessed by name with DEFCVAR.  As I understand CFFI's :POINTER 
type, the above macro will modify the memory location that PLACE points 
to but will not modify PLACE itself.

-Stuart