在go中设置传递给函数的接口值

问题描述：

我想改变

Get(title string )(out interface{})

类似:

Get(title string,out interface{})

这样我就可以通过引用传递接口，并让该方法像这样为我填充它:

So that I can passing the interface by reference and let the method fill it for me like :

var i CustomInterface
Get("title" , CustomInterface)
i.SomeOperationWithoutTypeAssertion() //the i is nil here(my problem)

func Get(title string,typ interface{}){
     ...
     typ=new(ATypeWhichImplementsTheUnderlyingInterface)
}

，但i.SomeOperationWithoutTypeAssertion()不起作用，因为调用Get("title" , CustomInterface)

but the i.SomeOperationWithoutTypeAssertion() doesn't work because the i is nil after calling the Get("title" , CustomInterface)

答

Go没有像C ++这样的语言中存在的透明引用参数的概念，因此您无法提出以下要求:您的Get函数接收接口变量的副本，因此不会在调用范围内更新变量.

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.

如果您确实希望函数能够更新作为参数传递的内容，则必须将其作为指针传递(即称为Get("title", &i)).没有语法可以指定参数应该是指向任意类型的指针，但是所有指针都可以存储在interface{}中，以便可以将类型用作参数.然后，您可以使用类型声明/ reflect包确定您得到的是哪种类型.您需要依靠运行时错误或紧急情况来捕获参数的错误类型.

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.

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")
    }
}

在go中设置传递给函数的接口值

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