[cffi-devel] expressive types (was: cffi/allegro crash)

[James Bielman]

(Hi Joerg,)

On Tue, 2005-12-20 at 16:15 +0100, Hoehle, Joerg-Cyril wrote:
> Luis Oliveira
> >Let me see if I got this straight, your proposal is that the :pointer
> >type may or may not accept NIL (but it should documented as
> >non-portable),
> No. :pointer is documented to only accept valid CFFI pointers.
> These are documented as opaque.
> Code using NIL is in error, as well as code using 0.

I agree completely with this.  It's easy to define a translator
on :pointer to convert NIL to and from null pointers if this is desired.

> Another useful addition is a pointer type which does not accept a
> null-pointer, but signals an error instead, or just specifies that
> "passing (null-pointer) is an error".  This type can be used in
> function declarations.  The effect is two-fold:
> a) just from seeing the declaration, you know that NULL is not
> allowed.
> b) optionally, the transformers could check for this at run-time.

I'm not certain I see how you could do this at any other time besides
run-time, except for maybe some cases where the function argument is
CONSTANTP and evaluates to nil in some compiler-macro or so.

This is the sort of stuff that should be easy to define in "userland"
using the type translator mechanism, but I can see that this could be
usefully predefined by CFFI.

James