code: func (d *ResourceDiff) SetNew(key string, value interface{}) error {
  	if err := d.checkKey(key, "SetNew", false); err != nil {
  		return err
  	}
  
  	return d.setDiff(key, value, false)
  }
docs: // SetNew is used to set a new diff value for the mentioned key. The value must
  // be correct for the attribute's schema (mostly relevant for maps, lists, and
  // sets). The original value from the state is used as the old value.
  //
  // This function is only allowed on computed attributes.