[cffi-devel] Re: Enumerations cannot contain duplicate values

[Luis Oliveira]

On 2/set/2005, at 00:28, Rayiner Hashem wrote:
> Hello! I've encountered some behavior in C-FFI that I would like to 
> discuss.
>  When you try to define an enumeration containing duplicate values, 
> C-FFI gives the error:
>
>  "A foreign enum cannot contain duplicate values: 0."
>
>  However, C enumerations can contain duplicate values, and this 
> feature is used by real code.

My bad. When adding that check I wondered if duplicate values would 
make sense, IIRC I probably let the check in because I wondered about 
what to do in this case:

(defcenum foo
   (:a 0)
   (:b 0))

When for example some function with FOO as a return type returns 0, 
what keyword should 0 be translated to? :A or :B?

CLISP warns and uses the last value: [this is what James's tree does 
iirc, except it doesn't warn]

[1]> (ffi:def-c-enum foo (a 0) (b 0))
WARNING: FFI:DEF-C-ENUM (FOO): value 0 will be assigned to both A and B
FOO
[2]> (ffi:enum-from-value 'foo 0)
B


CMUCL and SBCL throw an error:

Error in function PARSE-ENUM:  Element value 0 used more than once.
    [Condition of type SIMPLE-ERROR]


Lispworks doesn't warn and uses the first:

CL-USER 1 > (fli:define-c-enum foo (a 0) (b 0))
(:ENUM FOO)

CL-USER 2 > (fli:enum-value-symbol 'foo 0)
A


Any suggestions?

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