指针与值。

Question

我有点想知道为什么下面的代码确实有效：

var serverStartedTime time.Time // Holds the time since the server is started.

type ServerInformation struct {

    Uptime ServerUptimeInformation `json:"uptime"`

}

type ServerUptimeInformation struct {

    Hours       int64 `json:"hours"`

    Minutes     int64 `json:"minutes"`

    Seconds     int64 `json:"seconds"`

    NanoSeconds int64 `json:"nanoSeconds"`

}

func main() {

    serverStartedTime = time.Now()

    http.HandleFunc("/api/v1/health", getHealthHandler)

    log.Fatal(http.ListenAndServe(":8000", nil))

}

func handler(writer http.ResponseWriter, request *http.Request) {

    fmt.Fprintf(writer, "URL.Path = %q\n", request.URL.Path)

}

func getHealthHandler(writer http.ResponseWriter, request *http.Request) {

    serverUptime := time.Now().Sub(serverStartedTime)

    hours := int64(serverUptime.Hours())

    minutes := int64(serverUptime.Minutes()) - (hours * 60)

    seconds := int64(serverUptime.Seconds()) - (hours * 60) - (minutes * 60)

    nanoSeconds := int64(serverUptime.Nanoseconds()) - (hours * 60) - (minutes * 60) - (seconds * 1000000000)

    serverInformation := ServerInformation{

        ServerUptimeInformation{

            hours, minutes, seconds, nanoSeconds,

        },

    }

    returnJSON(writer, serverInformation)

}

func returnJSON(writer http.ResponseWriter, data ...interface{}) {

    dataJSON, marshalError := json.Marshal(data)

    if marshalError != nil {

        writer.WriteHeader(http.StatusInternalServerError)

    } else {

        writer.WriteHeader(http.StatusOK)

        writer.Header().Set("Content-Type", "application/json")

        writer.Write(dataJSON)

    }

}

默认情况下，Go 复制提供给方法的参数。因此，“/api/v1/health”的 HTTP 处理程序确实需要一个编写器，我们将其传递给该returnJSON方法。

因此，此方法确实收到了它写入的副本。

我怎么会在我的浏览器中看到响应？没想到作者被抄袭了。

Answer 1

你认为ResponseWriter是一个结构体，但它是一个接口。每次您发送writer http.ResponseWriter到您的方法时，您都会发送指向实现该接口的结构的指针。执行此行以查看实际类型：fmt.Printf("%T\n", writer)