How to Efficiently Retrieve Keys from Maps in Go?

How to Get Map Keys in Go

With Go's strong typing system, a function that takes a map with keys of type interface{} cannot be applied to a map with keys of type int. While Go does not currently support generics, we can implement a generic Keys function in several ways:

Option 1: Convert Map Type

If we wish to preserve the type of the map, we can modify the Keys function to take a map[int]interface{} argument and explicitly convert the keys to interface{}:

func Keys(m map[int]interface{}) []interface{} {
    keys := make([]interface{}, len(m))
    i := 0
    for k := range m {
        keys[i] = k
        i++
    }
    return keys
}

Option 2: Use Reflection

Alternatively, we can use Go's reflection package to access the map's keys and convert them to interface{}. However, this approach may have performance implications:

func Keys(m interface{}) []interface{} {
    t := reflect.TypeOf(m)
    if t.Kind() != reflect.Map {
        panic("argument must be a map")
    }
    keys := make([]interface{}, 0)
    for _, key := range reflect.ValueOf(m).MapKeys() {
        keys = append(keys, key.Interface())
    }
    return keys
}

Option 3: Define a Generic Helper Function

To avoid potential performance issues, we can define a generic helper function that converts a map[int]interface{} to a map[interface{}]interface{}:

func convertMap[K1 comparable, V1 any, K2 comparable, V2 any](m map[K1]V1) map[K2]V2 {
    ret := make(map[K2]V2, len(m))
    for k, v := range m {
        ret[k.(K2)] = v.(V2)
    }
    return ret
}

// Keys returns the keys of the provided map.
func Keys[K comparable, V any](m map[K]V) []K {
    keys := make([]K, len(m))
    i := 0
    for k := range m {
        keys[i] = k
        i++
    }
    return keys
}

With these helper functions, we can use the following code:

m2 := map[int]interface{}{
    2: "string",
    3: "int",
}
convertedMap := convertMap(m2)
result := Keys(convertedMap)
fmt.Println(result)

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