How to cast interface{} to a map in GO

Question

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

Please take the Tour of Go, especially tour.golang.org/methods/15. And do not use the empty interface. — Volker
– Volker, Commented Apr 5, 2020 at 5:58
the test method is like a replica of a predefined method. so cannot change that — user8606365
– user8606365, Commented Apr 5, 2020 at 6:01
Go does not have a cast feature like other languages. The feature that you are looking for is called a type assertion. Use m := v.(Map) to assert that v is aMap. — user5728991
– user5728991, Commented Apr 5, 2020 at 6:21
One this I noticed is fmt.Println("key : %v Value : %v", k, v) here you need to use fmt.Printf. — Arun
– Arun, Commented Apr 5, 2020 at 6:28
stackoverflow.com/questions/47496040/… have a look, may helpful — Arun
– Arun, Commented Apr 5, 2020 at 6:33

Akshay Bharambe · Accepted Answer · 2020-04-05 07:06:29Z

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

answered Apr 5, 2020 at 7:06

Akshay Bharambe

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