[cffi-devel] A question about arrays and enums

[Luís Oliveira]

On Mon, Mar 7, 2011 at 4:55 PM, nitralime <nitralime at googlemail.com> wrote:
>>> (defcenum (:a 1) ... (:c #.(logior 1 2)) ...).
>
> My point regarding "enum" definition was actually if it is
> possible to write down a definition of enum in CFFI without
> breaking the "abstraction". In the body of enum as you see
> there is an interdependency between the fields of enum
> being defined: the value of c depends on a and b and
> the value of d depends on c.

Yeah. I'm afraid you'd need to do something along the lines of:

    (defconstant +a+ 1)
    (defcenunum (:a #.+a+) (:b #.(frob +a+)))


>>> but it has some limitations and it's
>>> undocumented (see src/types.lisp).
>
> With that CFFI array type "typedef char XXX[8]"
> can be translated now as "(defctype XXX (:array :char 8))"!
>
> What are those limitations?

One of the limitations is that it doesn't do proper memory management
on the array element type, which is not a problem for primitive types
such as :char.

Another limitation is that if you pass a Lisp array via the :array
type to a foreign function that modifies it you won't see any changes
reflected in the Lisp array, as the Lisp/foreign conversion is
currently one-way only.

Cheers,

-- 
Luís Oliveira
http://r42.eu/~luis/