英文:
Set reference in Go
问题
如何通过引用传递接口，并让方法为我填充它？类似于这样：
var i CustomInterface
Get("title", &i)
i.SomeOperationWithoutTypeAssertion() // 这里 i 是 nil（我的问题）
func Get(title string, iRef interface{}) {
iRef = new(ATypeWhichImplementsTheUnderlyingInterface)
}
我希望在调用 Get 方法后，i 不是 nil。如何将 i 作为引用传递给 Get 方法？
英文:
How to pass an interface by reference and let the method fill it for me? Something like this:
var i CustomInterface
Get("title" , ref i)
i.SomeOperationWithoutTypeAssertion() //i is nil here(my problem)
func Get(title string, iRef ref interface{}){
iRef = new(ATypeWhichImplementsTheUnderlyingInterface)
}
I want i not to be nil after calling the Get method. How to pass i as reference to the Get method?
答案1
得分: 3
Go语言没有像C++等语言中的透明引用参数的概念，所以你所问的是不可能的：你的Get函数接收的是接口变量的副本，所以不会更新调用范围内的变量。
如果你确实希望函数能够更新传递的参数，那么必须将其作为指针传递（即调用为Get("title", &i)）。没有语法来指定参数应该是任意类型的指针，但是所有指针都可以存储在interface{}中，因此该类型可以用于参数。然后，你可以使用type assertion / switch或reflect包来确定你所获得的类型。你需要依赖运行时错误或恐慌来捕获参数的错误类型。
例如：
func Get(title string, out interface{}) {
...
switch p := out.(type) {
case *int:
*p = 42
case *string:
*p = "Hello world"
...
default:
panic("Unexpected type")
}
}
英文:
Go doesn't have the concept of transparent reference arguments as found in languages like C++, so what you are asking is not possible: Your Get function receives a copy of the interface variable, so won't be updating variable in the calling scope.
If you do want a function to be able to update something passed as an argument, then it must be passed as a pointer (i.e. called as Get("title", &i)). There is no syntax to specify that an argument should be a pointer to an arbitrary type, but all pointers can be stored in an interface{} so that type can be used for the argument. You can then use a type assertion / switch or the reflect package to determine what sort of type you've been given. You'll need to rely on a runtime error or panic to catch bad types for the argument.
For example:
func Get(title string, out interface{}) {
...
switch p := out.(type) {
case *int:
*p = 42
case *string:
*p = "Hello world"
...
default:
panic("Unexpected type")
}
}
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