One-Function Interface

在 goalng 中，函数可以直接实现只有一个方法的接口，标准库中 net/http 就用了该技巧：

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

正常情况下，需要定义一个结构体使用：

type MyService struct{}

// Implement the http.Handler interface method
func (h MyService) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "Hello World!")
}

http.Handle("/hello", MyService{})

而 golang 允许：

func myHandler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "Hello, World!")
}

http.Handle("/hello", http.HandlerFunc(myHandler))

因为：

// 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)
}

用强转将函数对象直接转为接口对象。^[1]