RFC on changes to enum and bitfield semantics

[Attila Lendvai]

on my quest to implement an automatic generator for CFFI bindings
(using c2ffi), i've recorded some patches that change the semantics of
enums and bitfields.

automatically generated bindings (should) live in an empty lisp
package, and to avoid surprises it's also desirable to bring the CFFI
behavior (regarding e.g. C namespaces) as close to C as possible.

the code is available in this PR: https://github.com/cffi/cffi/pull/84

the following are controversial and i'd welcome some input on them
from CFFI gurus, especially regarding what should/could get into
master eventually:

 - enums don't demand member names to be CL:KEYWORDP anymore

 - DEFCENUM and DEFBITFIELD now expand a toplevel DEFCONSTANT for
   each member. the rationale is to bring it closer to the C enum
   semantics where they are in the main namespace.

 - BITFIELD now inherit from ENUM, and adds extra semantics for values
   that are the power of two. but should 0 be treated as a bitfield
   bitmask? IOW, should (FOREIGN-BITFIELD-SYMBOLS 'FOO 0) return NIL
   or '(ZERO-MEMBER-NAME)? the code currently does not treat 0 as a
   bitmask (which is an incompatible change).

 - the accessor names are rather inconsistent:
     FOREIGN-ENUM-VALUE           FOREIGN-BITFIELD-VALUE
     FOREIGN-ENUM-KEYWORD         FOREIGN-BITFIELD-SYMBOLS
     FOREIGN-ENUM-KEYWORD-LIST    FOREIGN-BITFIELD-SYMBOL-LIST
   i'd like to rename the last four of them to (not done yet):
     FOREIGN-ENUM-KEY            FOREIGN-BITFIELD-KEYS
     FOREIGN-ENUM-KEY-LIST       FOREIGN-BITFIELD-KEY-LIST
   and leave some aliases and deprecation warnings behind. but are the
   names ok? or any better ideas?

 - another minor issue is that 'bitfield' is a confusing name, because
   the C standard calls the 'int:3' kind of types as bitfields. i
   suggest to rename them to 'bitmask' in CFFI. maybe incompatibly? or
   only in a new major version?

it'd be nice if this could be merged before the next quicklisp
release, because there are some projects that depend on them that i'd
like to get into ql the sooner the better.

thanks, and happy hacking,

-- 
• attila lendvai
• PGP: 963F 5D5F 45C7 DFCD 0A39
--
“The cost of sanity in this society, is a certain level of alienation.”
	— Terence McKenna (1946–2000)