[cffi-devel] Changes to the type system, among others.

[Luis Oliveira]

On 26/ago/2005, at 23:06, Rayiner Hashem wrote:
> What are the ramifications of the anonymous type stuff? In particular, 
> does this mean that defctype behaves more like C's "typedef" (in that 
> the source type doesn't yet need to be defined)?

Hmm, I was going to say no. But actually that'll work for 
DEFINE-FOREIGN-TYPE.

CFFI> (define-foreign-type foo () 'bar)
FOO
CFFI> (defctype bar :boolean)
BAR
CFFI> (translate-from-c 0 (parse-type 'foo))
NIL
CFFI> (translate-from-c 666 (parse-type 'foo))
T

That won't work for types defined with DEFCTYPE because of some 
(premature?) optimizations though:

? (defctype foo unexistant-type)
 > Error in process listener(1): Unknown CFFI type: UNEXISTANT-TYPE.

This has nothing to do with anonymous types anyway.


> Could any of the new type system changes achieve that result? The 
> dependence of defctype on having its source type already defined makes 
> handling automatic declaration generation quite complicated in a lot 
> of idiomatic C code.

Use DEFINE-FOREIGN-TYPE instead of DEFCTYPE then, I'll remember to keep 
that feature when I refactor this stuff.


> Since the dependence graph of C type definitions might have cycles, it 
> becomes impossible to impose a total ordering on definitions. This 
> isn't a problem when typedefs are fully resolved to their target types 
> (as Verrazano does currently), but is a problem if you want the C-FFI 
> binding to more closely resemble the C header file with regards to 
> type naming.

Heh, I'm glad I helped then. My previous version of this type system 
didn't do that, but I noticed that it wouldn't always behave correctly 
because types defined with DEFINE-FOREIGN-TYPE can eventually resolve 
to different types depending on, say, its arguments.

(define-foreign-type type-picker (type-number)
   (case type-number
     (1 :int)
     (2 :float)))

(now this was a crappy example... Kenny I'll try to come up with better 
examples for the manual, heh. I'll probably search real life examples.)

-- 
Luís Oliveira
http://student.dei.uc.pt/~lmoliv/
Equipa Portuguesa do Translation Project
http://www2.iro.umontreal.ca/~pinard/po/registry.cgi?team=pt