From: why the lucky stiff <ruby-talk@...>
Date: 2006-06-06T05:40:12+09:00
Subject: Re: Call rb_instance_eval from C code

On Tue, Jun 06, 2006 at 04:43:10AM +0900, Mauricio Fernandez wrote:
> On Tue, Jun 06, 2006 at 04:12:14AM +0900, why the lucky stiff wrote:
> >   rb_funcall(obj, rb_intern("instance_eval"), 1, proc);
> 
> I don't think that will work: proc is not a String but a Proc (TypeError).
> 
> See [ruby-talk:180647] and [ruby-talk:188958].

Ohhhh.  I guess define_method can take a proc, though.  Back to ye olde cloaker.
Based on Guy's example:

  wagon$ cat a.c 
  #include <ruby.h>
  
  static VALUE
  rb_proc_bind(VALUE obj, VALUE a)
  {   
      VALUE meth, meta;
      VALUE cloaker = ID2SYM(rb_intern("__cloaker__"));
      meta = rb_singleton_class(obj);
      rb_funcall(meta, rb_intern("define_method"), 2, cloaker, a);
      meth = rb_funcall(meta, rb_intern("instance_method"), 1, cloaker);
      rb_funcall(meta, rb_intern("remove_method"), 1, cloaker);
      return rb_funcall(meth, rb_intern("bind"), 1, obj);
  }
  
  VALUE
  obj_eval_it(int argc, VALUE *argv, VALUE self)
  {   
      VALUE meth, proc;
      rb_scan_args(argc, argv, "0&", &proc);

      /* !^! here is your rb_instance_eval replacement, victor. !^! */
      meth = rb_proc_bind(self, proc);
      return rb_funcall(meth, rb_intern("call"), 0);
  }
  
  void Init_a()
  {   
      VALUE obj = rb_funcall(rb_cObject, rb_intern("new"), 0);
      rb_define_method(rb_cObject, "eval_it", obj_eval_it, -1);
      rb_const_set(rb_cObject, rb_intern("OBJ"), obj);
  }

  wagon$ ruby -ra -e 'p Object::OBJ; Object::OBJ.eval_it { @b = 12 }; p Object::OBJ'
  #<Object:0x80768dc>
  #<Object:0x80768dc @b=12>

But now I really don't understand specific_eval().

_why