From: Chris Uzdavinis <chris@...>
Date: 2001-04-14T16:11:11+09:00
Subject: [ruby-talk:13656] create/init ruby object in C


Hi, Ruby is great, kudos to all who are involved.

I'm trying to embed ruby into an application, and I'm having a bit of
trouble.  I want to write a function (in C) that returns a ruby object
from a class that I defined.

For example, given this ruby class:

class X
  attr_reader :x, :y, :z
  attr_writer :x, :y, :z  
end


I want to write a C function that creates an instance of class X and
initializes it.  Here is how I'd do it in ruby, but how do I do it in C?

def example
  a = X.new
  a.x = 111
  a.y = 222
  a.z = 333
  return a
end


I've spent a while trying to come up with something, and most of that
time has been spent reading ruby source code, since I don't know which
API functions to call.  Here is pseudo-code that is pretty close to
what I want, except for all the errors in it.  :)


static VALUE
example(VALUE self)
{
  VALUE type, obj;
  ID id;

  // lookup type of X  (how?)
  type = ....

  //
  // instantiate object of that type 
  // (is this the Right Way to do it?)
  //
  obj = rb_obj_alloc(type);

  //
  // initialize members of obj x,y,z
  // (is this the Right Way to do it?)
  //
  id = rb_intern("X#x=");
  rb_funcall(obj, id, 1, INT2NUM(111));

  id = rb_intern("X#y=");
  rb_funcall(obj, id, 1, INT2NUM(222));

  id = rb_intern("X#z=");
  rb_funcall(obj, id, 1, INT2NUM(333));

  //
  // the following is the only line in this function where I have
  // confidence in what I wrote.  :) 
  //
  return obj; 
}


This isn't compiled or tested, but I think it shows what I'm trying to
do (and shows how new I am to the internals of ruby.)  I'm probably
doing this all wrong, but if someone could help me finish/fix the
above code such that it's equivalent to the ruby version, I'd be very
appreciative. 

Many thanks for any help!

-- 
Chris