about golang interface loop

Question

I wanto print a complicate dataset like bellowing

package main
import (
    "fmt"
    // "reflect"
)

func main() {

    var initData []interface{}
    initData[0] = map[string]interface{}{
        "name": "k1",
        "type": "line",
        "data": []int{1, 2, 3, 4},
    }

    initData[1] = map[string]interface{}{
        "name": "k2",
        "type": "circle",
        "data": []int{11, 12, 13, 14},
    }

    for _, data := range initData {
        for k, v := range data {
            fmt.Println(k)
            for _, sv := range v {
                fmt.Println("  " + sv)
            }
        }

    }

}

but get an error

./maps-in-maps.go:56: cannot range over data (type interface {})

any help? to try to concert the interface typed dataset to interable like arry or slice

Answer 1

You must type assert each interface{} level first, in this case, use a type assertion at map[string]interface{} level since we know a definite type, and a type switch to check anticipated types for each nested value in the next level.

initData := []interface{}{
        map[string]interface{}{
            "name": "k1",
            "type": "line",
            "data": []int{1, 2, 3, 4},
        },

        map[string]interface{}{
            "name": "k2",
            "type": "circle",
            "data": []int{11, 12, 13, 14},
        },
    }

    for _, data := range initData {
        for _, v := range data.(map[string]interface{}) {
            switch t := v.(type) {
            case string, []int:
                fmt.Println(t)
            default:
                fmt.Println("wrong type")           
            }
        }
    }
}

Run playground here.