How to Index into an interface{} Map in Go?

How to Index an Interface Map in Go: Resolving "type interface {} does not support indexing"

In Go, attempting to index an interface{} map with a specific key can lead to the error "type interface {} does not support indexing." This arises when trying to access elements from a map where values are stored as interfaces, and the specific types of these values are unknown.

One way to overcome this error is to explicitly type-cast the value returned from the map using the slice type that you expect the value to be. For instance, consider the following code snippet where a map called TopologyMap contains mappings from strings to arrays of objects:

Map := make(map[string]interface{})
Map["Users"] = Users_Array
Map["Hosts"] = Hosts_Array

To retrieve elements from this map, you can use the following syntax, but it will result in the "type interface {} does not support indexing" error:

Map["Users"][0]

To resolve this, explicitly convert the interface value to its desired type using a type assertion. Here's an example that demonstrates how to do this for a map of strings and slices of hosts:

import (
    "fmt"
)

type Host struct {
    Name string
}

func main() {
    Map := make(map[string]interface{})
    Map["hosts"] = []Host{Host{"test.com"}, Host{"test2.com"}}

    hm := Map["hosts"].([]Host)
    fmt.Println(hm[0])
}

In this example, we explicitly type-convert the value stored under the "hosts" key to a slice of Host objects, making it possible to access individual host elements.

By using this approach, you can effectively index an interface{} map and retrieve the specific values you need, even if their types are not known at compile time.

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