英文:
Get struct tag without pointer
问题
我正在为Go语言中的固定宽度文本创建一个简单的编组器，详细信息请参见这里。
编组器现在按照我的预期工作，尽管还缺少一些功能。我在编组函数中遇到的问题是：
相关的代码如下：
func Marshal(obj interface{}) (str string, err error) {
...
elemsType := reflect.TypeOf(obj).Elem()
正如你所看到的，我试图模仿json包的编组函数签名。问题在于，当我尝试将值传递给编组函数时，reflect.TypeOf返回的类型与我传递给它的类型不同。只有当我将指针传递给编组函数时，该函数才能执行。
这样可以工作：
user := User{"johnjohnjohn", "the", "doe", "smart", 26}
res, err := Marshal(&user)
这样不行：
user := User{"johnjohnjohn", "the", "doe", "smart", 26}
res, err := Marshal(user)
有没有办法只传递值，然后在编组函数内部获取结构体标签呢？
英文:
I was creating a simple marshaler for fixed with text into struct in Go, as detailed here.
The marshaler functions as I expected now, albeit still lacking some features. What I got stuck in is in the marshal function.
The relevant code is as follow
func Marshal(obj interface{}) (str string, err error) {
...
elemsType := reflect.TypeOf(obj).Elem()
As you can see, I tried to mimic the json package's marshal signature. Then only problem is when I tried to pass by value to the marshal function, the reflect.TypeOf returns a different type than the one I pass into it. The function can only executed if I'm passing pointer to the marshal function.
This works
user := User{"johnjohnjohn", "the", "doe", "smart", 26}
res, err := Marshal(&user)
This doesn't
user := User{"johnjohnjohn", "the", "doe", "smart", 26}
res, err := Marshal(user)
Is there any way to just pass by value, and then get the struct tag inside the marshal function?
答案1
得分: 6
如果你希望它适用于值，就不要在反射类型上调用Type.Elem()。为了处理指针和非指针类型，可以先检查是否为指针类型，然后再调用Type.Elem()：
elemsType := reflect.TypeOf(obj)
if elemsType.Kind() == reflect.Ptr {
elemsType = elemsType.Elem()
}
英文:
If you want it to work on values, don't call Type.Elem() on the reflect type. To handle both (pointers and non-pointers), check if it is of pointer type, and only then call Type.Elem():
elemsType := reflect.TypeOf(obj)
if elemsType.Kind() == reflect.Ptr {
elemsType = elemsType.Elem()
}
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