From: Scott Thompson <easco@...>
Date: 2003-08-13T13:03:14+09:00
Subject: Exposing C "enums" through extensions

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.

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").

Is there a common mechanism that is followed in other extensions?

Scott