1

I am new to Go & I am trying to learn how to cast interface{} to a Map. Here is an example of what I am trying to implement.

Playground link : https://play.golang.org/p/3jhKlGKO46Z

Thanks for the help. 

package main

import (
    "fmt"
)


func main() {

    Map := make(map[string]interface{})
    test(Map)

    for k,v := range Map {
        fmt.Println("key : %v Value : %v", k, v)
    }

}

func test(v interface{}) error{

    data := make(map[int]interface{})

    for i := 0; i < 10; i++ {
        data[i] = i * 5
    }

    for key,val := range data {
        //  fmt.Println("key : %v Value : %v", key, val)
        v[key] = val
    }

    return nil
user8606365
  • 59
  • 4
  • 1
    Please take the Tour of Go, especially https://tour.golang.org/methods/15. And _do_ _not_ use the empty interface. – Volker Apr 05 '20 at 05:58
  • the test method is like a replica of a predefined method. so cannot change that – user8606365 Apr 05 '20 at 06:01
  • Go does not have a cast feature like other languages. The feature that you are looking for is called a [type assertion](https://golang.org/ref/spec#Type_assertions). Use `m := v.(Map)` to assert that `v` is a`Map`. – Charlie Tumahai Apr 05 '20 at 06:21
  • One this I noticed is `fmt.Println("key : %v Value : %v", k, v)` here you need to use `fmt.Printf`. – Arun Apr 05 '20 at 06:28
  • https://stackoverflow.com/questions/47496040/type-interface-does-not-support-indexing-in-golang/47496108 have a look, may helpful – Arun Apr 05 '20 at 06:33

1 Answers1

4

Go supports type assertions for the interfaces. It provides the concrete value present in the interface.

You can achieve this with following code.

    m, ok := v.(map[int]interface{})
    if ok {
      // use m
      _ = m
    }

If the asserted value is not of given type, ok will be false

If you avoid second return value, the program will panic for wrong assertions.

I strongly recommend you to go through https://tour.golang.org

Akshay Bharambe
  • 76
  • 5