From: E S <eero.saynatkari@...>
Date: 2005-01-17T04:53:24+09:00
Subject: Re: rb_const_get documentation

> L�hett�j�: Brian Palmer <brian@pocketmartiansoftware.com>
> Aihe: rb_const_get documentation
> 
> What's the best place to find out more about the rb_const_get family of 
> functions for writing C extensions?  I'm writing my first C library for 
> Ruby, and struggling with how to get VALUEs for Classes and Modules 
> provided by Ruby and other extensions.  The Pickaxe 2.0 has a wonderful 
> section on C extensions, for the most part, but it seems to omit mention 
> of rb_const_get completely.  Took me an hour of searching the ml to even 
> discover its existence.
> 
> A few pressing questions:
> (1) What does the rb_cObject parameter that I'm always passing in do?  
> What other things might I pass in for this argument?
> (2) How do I get a handle to a Class that's inside a module?  I tried 
> calling (for example) rb_const_get(rc_cObject, rb_intern("GLIT::Vec")) 
> but I get an error.  However, calling GLIT::Vec.new from a ruby script 
> that's using the C extension works fine, so I must have the syntax wrong.

The signature is

VALUE  rb_const_get (VALUE klass, ID id) 

so the first parameter is the class in which to search for the 
constant (the second is a Symbol). For top-level, the class is Object 
(or rb_cObject). For a nested class, you should look in the enclosing 
class. So, you'd do 

VALUE cGlit    = rb_const_get(rb_cObject, rb_intern("GLIT"));
VALUE cGlitVec = rb_const_get(cGlit, rb_intern("Vec"));

I think :)
 
> Thanks a bundle for any help you all can provide.  I appreciate it.
> 
> -- Brian Palmer

E