I'm trying to set a char at a particular index in a Ruby String in C 
using the rb_funcall method, but since there is no text signature for 
this method call (that I know of), I'm having a hard time with it. Right 
now I'm messing with something like:

    rb_funcall(textString, rb_intern("[]="), 2, index);

which throws an exception with the message: "`[]=': cannot convert false 
into String (TypeError)"

Any ideas?

I just need the C equivalent of "String"[n].

thanks,
Dave