From: Vincent Fourmond <vincent.fourmond@9online.fr>
Date: 2007-02-14T07:38:34+09:00
Subject: Re: Converting class_for to a C extension

Daniel Berger wrote:
> Hi all,
> 
> I found this snippet posted to handle doing const_get for nested
> classes/modules:
> 
> def class_for(class_name)
>    names = class_name.split("::")
>    result = Object
>    names.each { |n|
>       result = result.const_get(n)
>    }
>    result
> rescue NameError
>    nil
> end
> 
> I'm trying to convert this to a C extension, but I'm having some
> trouble:
> 
> static VALUE class_for(VALUE klass_name){
>    VALUE v_names, v_result;
>    ID id_split = rb_intern("split");
>    int i;
> 
>    v_names  = rb_funcall(klass_name, id_split, 1, rb_str_new2("::"));
>    v_result = rb_cObject;
> 
>    for(i = 0; i < RARRAY(v_names)->len; i++)
>       v_result = rb_const_get(RBASIC(v_result)->klass, RARRAY(v_names)-
>> ptr[i]);
> 
>    return v_result;
> }
> 
> With this code I get "uninitialized constant Class::(null)
> (NameError)".
> 
> It appears to be a problem with the first argument to rb_const_get().
> I'm not sure what that value should be, but I also tried
> TYPE(v_result) - which caused a segfault - and just v_result - which
> resulted in a similar "uninitialized constant (null) (NameError)"
> error.
> 
> What am I doing wrong here?
> 
> Thanks,
> 
> Dan
> 
> PS - Yes, I realize I'm not doing error handling in the C extension -
> I'm not worried about that for now.

  You should ;-) the (null) stuff is a sign that you're using a NULL
pointer somewhere, though I can't get where. The segfault is another
indication. So one thing here is returning false or NULL...

  The problem, in my opinion, is here:

RBASIC(v_result)->klass

  Why do you need to use ->klass ?? All objects you're getting *are*
classes or modules already. You end up looking for constants in the
Class class, and that is not where they are defined.

  Cheers,

	Vince
-- 
Vincent Fourmond, PhD student (not for long anymore)
http://vincent.fourmond.neuf.fr/