From: Eric Hodel <drbrain@...7.net>
Date: 2006-12-08T09:39:20+09:00
Subject: Re: Ruby enums in C

On Dec 7, 2006, at 15:34 , Joe Van Dyk wrote:
> On 12/7/06, Jeremy Woertink <its_conebred_foo@hotmail.com> wrote:
>> Joe Van Dyk wrote:
>> > Each instance of Joe has a MOOD which can be HAPPY, SAD, or  
>> NEUTRAL.
>> >
>> > The Joe class is written in C.  In C, what's the appropriate way  
>> for
>> > setting MOOD to one of the appropriate values?
>> >
>> > Thanks,
>> > An instantiated Joe object
>>
>> http://www.google.com/search?hl=en&q=constants+in+C&btnG=Google 
>> +Search
>
> Is there much difference between using a C constant for that, and
> using a Ruby instance variable (like how Mr. Hodel did)?

A C constant takes more work to expose to Ruby.  You have to map that  
opaque integer into something sensible, and then you have uglier code.

#define JOE_SAD -1
#define JOE_NEUTRAL 0
#define JOE_HAPPY 1

/* ... */
rb_define_const(cJoe, "HAPPY", INT2FIX(JOE_HAPPY));

if Joe.state == Joe::HAPPY then ... end

A Symbol in an instance variable gives you zero extra work, allows  
for easier debugging on the Ruby side and gives you prettier code.

if Joe.state == :happy then ... end

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net

I LIT YOUR GEM ON FIRE!