我嘗試使用 Golang 構建一個簡單的程序，這里是：package mainimport (        "net/http"        "net/http/httputil"        "log")func main(){        proxy := http.NewSingleHostReverseProxy( &http.URL{Scheme:"http",Host:"www.google.com",Path:"/"})        err := http.ListenAndServe(":8080", proxy)        if err != nil {                log.Fatal("ListenAndServe: ", err.String())        }}建造：go build myprogram.go輸出：command-line-arguments./myprogram.go:5: imported and not used: "net/http/httputil"./myprogram.go:11: undefined: http.NewSingleHostReverseProxy./myprogram.go:11: undefined: http.URL./myprogram.go:15: err.String undefined (type error has no field or method String)我注意到 http.NewSingleHostReverseProxy 在“net/http/httputil”包中，為什么我會看到這樣的錯誤？也許我需要一個特定的命令來正確構建它？編輯 后記，這是新的工作代碼：package mainimport (        "net/http"        "net/http/httputil"        "net/url"        "log")func main(){        proxy := httputil.NewSingleHostReverseProxy( &url.URL{Scheme:"http",Host:"www.google.com",Path:"/"})        err := http.ListenAndServe(":8080", proxy)        if err != nil {                log.Fatal("ListenAndServe: ", err)        }}