From: Rob Biedenharn <Rob@...>
Date: 2007-01-12T00:41:11+09:00
Subject: Re: Sharing constants between C and Ruby code


On Jan 11, 2007, at 10:01 AM, gwtmp01@mac.com wrote:

>
> On Jan 11, 2007, at 9:04 AM, Rob Biedenharn wrote:
>>     rb_define_const(mMyConstants, "MY_CONSTANT",   INT2NUM 
>> (MY_CONSTANT));
>>     rb_define_const(mMyConstants, "YOUR_CONSTANT", INT2NUM 
>> (YOUR_CONSTANT));
>>     rb_define_const(mMyConstants, "HIS_CONSTANT",  INT2NUM 
>> (HIS_CONSTANT));
>
> Hah!  I wasn't too far off with my guess of:
>>   rb_constant_set( klass, 'MY_CONSTANT', MY_CONSTANT)
>
>
> Anyway, you are still stuck with having to keep the C .h file and  
> the Ruby
> .c extension in sync by hand.  I'd pick any other scheme that  
> allowed you
> to only worry about maintaining a single file with the constant  
> definitions.
>
> Gary Wright

It depends on whether the OP is adding new constants to the file  
(#define HER_CONSTANT 105) or just changing the values (#define  
MY_CONSTANT 42).

You could always generate the .c file from the .h if that were a  
problem -- and that's what others suggested doing from .h to .rb  
directly.  This solution however, lets the C preprocessor and/or  
compiler do the dirty work of parsing the value of the #define.  If  
they are non-trivial, this might be a big win.  If these constants  
are always numbers, hand-coding the rb_my_constants.c file may be the  
way to go (or you'd have to make parsing the .h file smarter (or give  
it hints?)).

Besides, if new constants are added, you'd have to know they existed  
to use them in the Ruby code anyway.

Perhaps Nathaniel can clear up the mystery for us by telling us what  
assumptions *he* is making and what solutions will work better for  
his situation.

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com