http.Handle(Handler or HandlerFunc)

Question

以下函数是如何实现的？

func handle(pattern string, handler interface{}) {
    // ... what goes here? ...
    http.Handle(pattern, ?)
}
handle("/foo", func(w http.ResponseWriter, r http.Request) { io.WriteString(w, "foo") }
handle("/bar", BarHandler{})

handle（）被传递一个与http类型匹配的函数。HandlerFunc或实现http的类型。处理程序接口。

Answer 1

与其求助于反射，不如这样做：

func handle(pattern string, handler interface{}) {
    var h http.Handler
    switch handler := handler.(type) {
    case http.Handler:
        h = handler
    case func(http.ResponseWriter, *http.Request):
        h = http.HandlerFunc(handler)
    default:
        // error
    }
    http.Handle(pattern, h)
}

Answer 2

首先，我们需要在Java/C#的术语中引入术语"反射"，在C++的术语中介绍RTTI。其实很简单。编译器在运行时保存数据以查明实例var i SomeType的类型。Go支持反射，这就是它在运行时发现handler类型的方法。

handle函数使用反射。的粗略示例

package main
import ("reflect";"http")
type fakeHandler struct{}
func (frw *fakeHandler) ServeHTTP(http.ResponseWriter, *http.Request) {}
func handle(pattern string, handler interface{}) {
    handlerInterface := reflect.TypeOf(new(http.Handler)).Elem()
    handlerFunction  := reflect.TypeOf(new(http.HandlerFunc)).Elem()
    t := reflect.TypeOf(handler)
    if t.Implements(handlerInterface) {fmt.Println("http.Handler")}
    //http.HandlerFunc is a different type than
    // func(http.ResponseWriter, *http.Request), but we can do
    // var hf HandlerFunc = func(http.ResponseWriter, *http.Request){}
    if t.AssignableTo(handlerFunction) {fmt.Println("http.HandleFunc")}
}
func f(http.ResponseWriter, *http.Request) {}
func main() {
    handle("",&fakeHandler{})
    handle("",f)
}