英文:
function used as value error while trying to wrap functions
问题
我正在自学使用net/http包，使用《The Way to Go》这本书。他提到了一种将处理函数包装在闭包中的方法，以处理panics，如下所示：
func Index(w http.ResponseWriter, req *http.Request) {
w.Header().Set("Content-Type", "text/html")
fmt.Fprint(w, "<h2>Index</h2>")
}
func logPanics(function HandleFunc) HandleFunc {
return func(w http.ResponseWriter, req *http.Request) {
defer func() {
if err := recover(); err != nil {
log.Printf("[%v] caught panic: %v", req.RemoteAddr, err)
}
}()
function(w, req)
}
}
然后可以像这样调用http.HandleFunc：
http.HandleFunc("/", logPanics(Index))
我想做的是“堆叠”多个函数以包含更多功能。我想添加一个通过.Header().Set(...)添加mime类型的闭包，并且可以像这样调用它：
func addHeader(function HandleFunc) HandleFunc {
return func(w http.ResponseWriter, req *http.Request) {
w.Header().Set("Content-Type", "text/html")
function(w, req)
}
}
(然后在main()中)
http.HandleFunc("/", logPanics(addHeader(Index)))
但我认为通过使用一个包装函数来缩短代码会更好，同时保持这些函数的分离：
func HandleWrapper(function HandleFunc) HandleFunc {
return func(w http.ResponseWriter, req *http.Request) {
logPanics(addHeader(function(w, req)))
}
}
但是我得到了一个function(w, req) used as value的错误。我之前没有太多使用闭包的经验，感觉肯定漏掉了什么。
谢谢帮助！
英文:
I'm teaching myself to use the net/http package using The Way to Go book. He mentions a way to wrap handling functions in a closure that takes care of panics like so:
func Index(w http.ResponseWriter, req *http.Request) {
w.Header().Set("Content-Type", "text/html")
fmt.Fprint(w, "<h2>Index</h2>")
}
func logPanics(function HandleFunc) HandleFunc {
return func(w http.ResponseWriter, req *http.Request) {
defer func() {
if err := recover(); err != nil {
log.Printf("[%v] caught panic: %v", req.RemoteAddr, err)
}
}()
function(w, req)
}
}
And then call http.HandleFunc using the above like so:
http.HandleFunc("/", logPanics(Index))
What I want to do is to "stack" more than one function to include more functionality. I wanted to add a closure that adds a mime type via .Header().Set(...) and I can call it like this:
func addHeader(function HandleFunc) HandleFunc {
return func(w http.ResponseWriter, req *http.Request) {
w.Header().Set("Content-Type", "text/html")
function(w, req)
}
}
(then in main())
http.HandleFunc("/", logPanics(addHeader(Index)))
But I thought it would be nice to shorten that whilst still keeping these functions separate using a wrapper function:
func HandleWrapper(function HandleFunc) HandleFunc {
return func(w http.ResponseWriter, req *http.Request) {
logPanics(addHeader(function(w, req)))
}
}
But I get a function(w, req) used as value error. I haven't
worked much with closures before and I feel like I'm definitely missing something here.
Thanks for the help!
答案1
得分: 2
function(w, req)是一个没有返回值的函数调用，而addHeader期望一个函数作为其参数。
如果你想要将这两个包装函数结合起来，你可能想要像这样做：
func HandleWrapper(function HandleFunc) HandleFunc {
return logPanics(addHeader(function))
}
英文:
function(w, req) is a function call without a return value, while addHeader expects a function as its argument.
If you want to combine the two wrapper functions, you probably want something like this:
func HandleWrapper(function HandleFunc) HandleFunc {
return logPanics(addHeader(function))
}
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