如何在未知接口上获得结构值{}

Question

If I have a struct and I want to get it's key, but it's currently of type interface{} how do I do that?

Currently I get the following compilation error:

invalid operation: d[label] (index of type interface {})

Play: http://play.golang.org/p/PLr91d55GX

package main

import "fmt"
import "reflect"

type Test struct {
    s string
}

func main() {
    test := Test{s: "blah"}
    fmt.Println(getProp(test, "s"))
}

func getProp(d interface{}, label string) (interface{}, bool) {
    switch reflect.TypeOf(d).Kind() {
    case reflect.Struct:
        _, ok := reflect.TypeOf(d).FieldByName(label)
        if ok {
                    // errors here because interface{} doesn't have index of type 
            return d[label], true
        } else {
            return nil, false
        }
    }
}

Do I really have to do the massive case statement on each different type and call the reflected reflect.ValueOf(x).String() etc? I'm hoping there is a more elegant way.

Answer 1

You could do this, however I think it'll only work if your struct member s was an exported field (i.e. use a capital S in your example)

func getProp(d interface{}, label string) (interface{}, bool) {
    switch reflect.TypeOf(d).Kind() {
    case reflect.Struct:
        v := reflect.ValueOf(d).FieldByName(label)
             return v.Interface(), true
    }
   return nil, false
}

(+ some more error handling)