In Go, a type doesn't have to declare that it implements an interface; it automatically satisfies an interface if it implements the appropriate methods. Most interfaces in Go only contain one method.
If a type has a Close() method, then it is a Closer. The code that tries to cast it to a Closer will succeed. So to answer your question, it doesn't matter what the semantics of your Close() method are, it will succeed solely based on the fact that your type has a method with that name.
If a type has a Close() method, then it is a Closer. The code that tries to cast it to a Closer will succeed. So to answer your question, it doesn't matter what the semantics of your Close() method are, it will succeed solely based on the fact that your type has a method with that name.