using

static VALUE
mod_using(VALUE self, VALUE module)
{
    NODE *cref = rb_vm_cref();
    rb_control_frame_t *prev_cfp = previous_frame(GET_THREAD());

    if (prev_frame_func()) {
        rb_raise(rb_eRuntimeError,
                 "Module#using is not permitted in methods");
    }
    if (prev_cfp && prev_cfp->self != self) {
        rb_raise(rb_eRuntimeError, "Module#using is not called on self");
    }
    rb_using_module(cref, module);
    return self;
}