package utf8 type InvalidUTF8Complainer interface { error InvalidUTF8Complainer() } type internalInvalidUTF8Complainer struct{} func (complainer internalInvalidUTF8Complainer) Error() string { return "Invalid UTF-8" } func (complainer internalInvalidUTF8Complainer) InvalidUTF8Complainer() { // Nothing here. }