Go之接口型函数用法

type Handler interface {
    ServeHTTP(ResponseWriter, *Request)
}

// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as HTTP handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler that calls f.
type HandlerFunc func(ResponseWriter, *Request)

// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
    f(w, r)
}

func Handle(pattern string, handler Handler)

func home(w http.ResponseWriter, r *http.Request) {
    w.WriteHeader(http.StatusOK)
    _, _ = w.Write([]byte("hello, index page"))
}

func main() {
    http.Handle("/home", http.HandlerFunc(home))
    // http.HandlerFunc(home)->HandlerFunc->默认的多路复用器会调用它的ServeHTTP()方法
    _ = http.ListenAndServe("localhost:8000", nil)
}

func HandleFunc(pattern string, handler func(ResponseWriter, *Request))

func main() {
    http.HandleFunc("/home", home)
    _ = http.ListenAndServe("localhost:8000", nil)
}

func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
    if handler == nil {
        panic("http: nil handler")
    }
    mux.Handle(pattern, HandlerFunc(handler))
}

// A Getter loads data for a key.
type Getter interface {
    Get(key string) ([]byte, error)
}

// A GetterFunc implements Getter with a function.
type GetterFunc func(key string) ([]byte, error)

// Get implements Getter interface function
func (f GetterFunc) Get(key string) ([]byte, error) {
    return f(key)
}

func GetData(getter Getter, key string) []byte {
    buf, err := getter.Get(key)
    if err == nil {
        return buf
    }
    return nil
}

GetData(GetterFunc(func(key string) ([]byte, error) {
    return []byte(key), nil
}), "hello")

func test(key string) ([]byte, error) {
    return []byte(key), nil
}

func main() {
    GetData(GetterFunc(test), "hello")
}

type DB struct{ url string}

func (db *DB) Query(sql string, args ...string) string {
    // ...
    return "hello"
}

func (db *DB) Get(key string) ([]byte, error) {
    // ...
    v := db.Query("SELECT NAME FROM TABLE WHEN NAME= ?", key)
    return []byte(v), nil
}

func main() {
    GetData(new(DB), "hello")
}