code: func (d *ResourceData) GetChange(key string) (interface{}, interface{}) {
  	o, n := d.getChange(key, getSourceState, getSourceDiff)
  	return o.Value, n.Value
  }
docs: // GetChange returns the old and new value for a given key.
  //
  // HasChange should be used to check if a change exists. It is possible
  // that both the old and new value are the same if the old value was not
  // set and the new value is. This is common, for example, for boolean
  // fields which have a zero value of false.