From: Kero van Gelder <kero@...>
Date: 2003-08-15T06:30:57+09:00
Subject: Re: Exposing C "enums" through extensions

On Wed, 13 Aug 2003 13:03:14 +0900, Scott Thompson wrote:

> I'm allowing Ruby to access a C based library through an extension.  
> I'd like to expose some of the enums that are in the C interface, but 
> wasn't sure about the best way to do this.
> 
> My first thought was to define them as class variables within the 
> relevant class.  But then, as I discovered, there wasn't a good way I 
> could keep external code from modifying the values of those variables.  
> It would be really bad if someone set the value of the "miter line 
> join" constant to 7 when the only valid range of values is 0 - 3.

Can you prevent this in C?
you'll need to raise an ArgumentError somewhere, I'd say.

> On the "Extending Ruby"  web site at 
> <http://www.rubycentral.com/book/>, I found the 
> routine"rb_define_readonly_variable" which sounds pretty good.  But, so 
> far as I can tell, it defines a global variable and my preference would 
> be to scope the variables inside of a class (I don't know why... it 
> just seems "tidier").

rb_define_const() should do the trick. also works for #defines.

hth,
Kero.