英文:
How I can write a single function to work with different types
问题
给定以下示例，是否有可能创建一个函数，可以完全复制（不仅仅是获取 reflect.Type）实际类型以进行进一步操作？我知道 Go 是静态类型的，虽然很酷的是我可以将任何结构体传递给定义了接口参数的函数，但是有没有可能反过来做更多的事情？
我已经查看了 reflect 包，但只找到了返回 reflect.Type 或 reflect.Value 的内容。我使用了 New() 方法，它返回一个新的 reflect.Value - 但在那里我无法设置任何字段。也许有经验的人可以告诉我，这是否肯定是可能的，或者是否有其他方法可以实现。
package main
import "fmt"
type User struct {
Name string
}
func main() {
user := User{Name:"FooBar"}
DoSomethingGenericWithStruct(user)
}
func DoSomethingGenericWithStruct(i interface{}) {
// 访问 i 的字段...
// 或者创建 i 类型的切片 ([]User)...
// 或者实例化 i 类型的新对象 (new User)...
// ...
}
英文:
Given the following example, is it anyhow possible to create a function that can literally reproduce (not only get the reflect.Type) the actual type for further manipulation? I know go is statically typed and although it's very cool that I can pass any struct to a function that defines an interface parameter, is there any chance I can do more the other way around?
I already looked into the reflect package but only found stuff that returned a reflect.Type or reflect.Value. I used the New() method which returned a new reflect.Value - and there I couldn't set any fields. Maybe someone experienced with the reflect package can tell me if this is definitely possible or not - or if there's another way to do it.
package main
import "fmt"
type User struct {
Name string
}
func main() {
user := User{Name:"FooBar"}
DoSomethingGenericWithStruct(user)
}
func DoSomethingGenericWithStruct(i interface{}) {
// access fields of i ...
// or create slice of type of i ([]User) ...
// or instantiate new object of type of i (new User) ...
// ...
}
答案1
得分: 1
你需要传递一个指向你的结构体的指针才能修改它。
同时要注意，使用反射会带来很高的运行时性能开销。
func DoSomethingGenericWithStruct(i interface{}) {
val := reflect.ValueOf(i)
if val.Kind() != reflect.Ptr {
panic("需要一个指针")
}
val = val.Elem() // 现在你可以修改它了
// 添加错误检查等，如果不是结构体或没有 "Name" 字段，这将会引发 panic
val.FieldByName("Name").SetString("stuff")
}
要创建一个新的元素并赋值：
val = val.Elem()
nval := reflect.New(val.Type()).Elem() // 创建一个相同类型的新结构体
nval.FieldByName("Name").SetString("stuff")
val.Set(nval)
要修改实际的结构体，而不是 reflect.Value，你需要将 interface{} 转换为你的类型，例如：
nval := reflect.New(val.Type()).Elem() // 创建一个相同类型的新结构体
user := nval.Interface().(User)
user.Name = "Stuff"
val.Set(reflect.ValueOf(user))
英文:
You would have to pass a pointer to your struct to be able to modify it.
Also keep in mind that using reflection has a high runtime performance cost.
func DoSomethingGenericWithStruct(i interface{}) {
val := reflect.ValueOf(i)
if val.Kind() != reflect.Ptr {
panic("need a pointer")
}
val = val.Elem() // now you can modify it
// add error checking and such, this will panic if it's not a struct or there's no "Name" field
val.FieldByName("Name").SetString("stuff")
}
<kbd>playground</kbd>
To create a new element and assign it:
val = val.Elem()
nval := reflect.New(val.Type()).Elem() // create a new struct of the same type
nval.FieldByName("Name").SetString("stuff")
val.Set(nval)
to modify the actual struct, not reflect.Value, you will have to get the interface{} to it then assert it to your type, for example:
nval := reflect.New(val.Type()).Elem() // create a new struct of the same type
user := nval.Interface().(User)
user.Name = "Stuff"
val.Set(reflect.ValueOf(user))
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