[racket] forward pointer declarations

From: Anthony Carrico (acarrico at memebeam.org)
Date: Mon Feb 2 09:41:46 EST 2015

Along these lines, I also am a little foggy on unions. This:

says, "Unions are always treated like structs." But I have no idea what
that phrase means. I don't get the impression that unions have tags like
structs can have. Or can they? Maybe any pointer can be tagged? For example:

(define _wl_argument
  (_union _int32
          (_cpointer/null 'wl_object)

Now suppose I need to pass an array of _wl_argument. Does it even make
sense to use a tag in the _cpointer?

(define _wl_argument-pointer (_cpointer 'wl_argument))

(define-wl-client wl_proxy_marshal_array_constructor
  (_fun #:save-errno 'posix
        -> _wl_proxy-pointer/null

So as I said, I'm just a little foggy on some of the concepts, but I do
think the FFI is very nice. Maybe I'm just trying to use stronger typing
than actually exists in the ffi. I've started reading
Eli Barzilay/Dmitry Orlovsky "Foreign Interface for PLT Scheme".

Anthony Carrico

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