From: Joel VanderWerf <vjoel@...>
Date: 2004-04-26T16:48:10+09:00
Subject: instance_eval from C ext


I'm stumped... how do I call instance_eval from a C extension?

I have an object and a proc:

   VALUE obj, pr;

and I want to eval pr with obj as self.

Currently, I do something like this, which works, but it's inefficient:

   rb_funcall(obj, rb_intern("insteval_proc"), 1, pr);

and I have the following defined in ruby:

class Object
   def insteval_proc pr
     instance_eval &pr
   end
end

I'd rather avoid the extra method call.

It doesn't seem like I can use rb_obj_instance_eval(), because that 
takes string arguments, not block arguments. Of course, if you have a 
block accompanying the method call, it will instance_eval that, but I 
don't know how to set that up in C. That's why I do "instance_eval &pr" 
in my little hack.

And I can't see how to use rb_iterate(). This is what I tried:


static VALUE my_instance_eval(VALUE obj)
{
     return rb_obj_instance_eval(0, 0, obj);
}

static VALUE call_block(VALUE arg1, VALUE block)
{
     return rb_funcall(block, ID_call, 0);
}

//...
     rb_iterate(my_instance_eval, obj, call_block, pr);


but I get "block not supplied (ArgumentError)", so I guess it's  not 
being propagted into the rb_funcall.

Is there a simple way to emulate "&block" in C?

Even better, is there a way to rebind the proc's self to my object, so I 
only have to do it once, and can just call the block instead of using 
instance eval?