code: func CopyExact(dest interface{}, src interface{}) {
  	dV := reflect.ValueOf(dest)
  	sV := reflect.ValueOf(src)
  	if dV.Kind() == reflect.Ptr {
  		dV = dV.Elem()
  	}
  	if dV.Kind() == reflect.Array && !dV.CanAddr() {
  		panic(fmt.Sprintf("dest not addressable: %T", dest))
  	}
  	if sV.Kind() == reflect.Ptr {
  		sV = sV.Elem()
  	}
  	if sV.Kind() == reflect.String {
  		sV = sV.Convert(reflect.SliceOf(dV.Type().Elem()))
  	}
  	if !sV.IsValid() {
  		panic("invalid source, probably nil")
  	}
  	if dV.Len() != sV.Len() {
  		panic(fmt.Sprintf("dest len (%d) != src len (%d)", dV.Len(), sV.Len()))
  	}
  	if dV.Len() != reflect.Copy(dV, sV) {
  		panic("dammit")
  	}
  }
docs: // Copy elements from src to dst. Panics if the length of src and dst are
  // different.