AW: ffi "parameter mode"

[Hoehle, Joerg-C. <Joe...@t-...>]

Sam asked:
>is this correct, i.e., should we just say that ":OUT requires 
>ALLOCATION :ALLOCA"?
Fine with me. Then perhaps add some clarification on pointers.
"Note that when the parameter type is either c-pointer or (c-pointer type), the programmer/user/developer is responsible for the correct allocation of the things being pointed to."
"The pointer itself is stack-allocated by CLISP (:alloca is the default) and using either :out or :in-out makes no sense with such a parameter type even though conceptually, that would be the proper mode" -- unclear, please rephrase

Or ":out or :in-out, although correctly describing a possible mode from a conceptual point of view, do not make sense to the FFI when the parameter type is [anything else than c-ptr and in particular] either c-pointer or (c-pointer <type>), because "... Hmm
perhaps "the FFI can only allocate the pointer ...
or "only that pointer is passed on the stack..."

The thing to keep in mind is, :out or :in-out require (c-ptr xyz), don't work with anything else -- unless one can propose another concept.
If somebody wants an API that would be
  :[in-]out, but with user-supplied pointer, possibly NULL (common in some places of the OS), then impnotes could mention that
what's to do is either use (c-pointer <type) or c-pointer with the default :in and do allocation oneself, or use two prototypes, one with :out (c-ptr ...) and one with NULL.
But that's possibly a different issue than explaining that user supplied foreign pointer parameters are/must be :in from the FFI POV, perhaps by analogy that C only knows about pointers and has no concept of such modes (but the rule still applies when interfacing to other languages)

Sorry that this is not clear,
	Jorg Hohle.