通过switch语句分配类型/创建结构

Question

I'm having a bit of trouble figuring out how to either create a struct in a switch statement or assign a type to it in a switch statement. Here's some non-working code illustrating what I'm trying to do:

var result

switch structPickingString {
case "struct1":
    result = new(struct1)
case "struct2":
    result = new(struct2)
}

//unmarshall some json into the appropriate struct type
if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
    log.Println(err)
}
//print out that json with a function specific to that type of struct
result.Print()

I think something involving an empty interface{} might be related to solving this issue but unfortunately I'm still a bit ignorant with golang and I'm not seeing how to make it work.

Here's a link to a slightly modified version of the code for more context: https://play.golang.org/p/Rb1oaMuvmU2

The issue is not defining the print function, it's assigning a specific type of struct to the result variable based on using the individual Print function that the struct implements.

Let me know if there's any more info I could provide.

Answer 1

Since you are calling .Print, you need to use an interface which has that method. I think you are looking for something like

type Printer interface {
    Print()
}

func (s *struct1) Print() {
  // ...
}

func (s *struct2) Print() {
  // ...
}
var result Printer
switch structPickingString {
case "struct1":
    result = new(struct1)
case "struct2":
    result = new(struct2)
}

https://play.golang.org/p/W9r6UfeQSCz