如何获取地图钥匙

Question

I have a function named Keys() to get all the keys of a map, here is the code:

func main() {
    m2 := map[int]interface{}{
        2:"string",
        3:"int",
    }
    fmt.Println(Keys(m2))
}
func Keys(m map[interface{}]interface{}) (keys []interface{}) {
    for k := range m {
        keys = append(keys, k)
    }
    return keys
}

But I got

cannot use m2 (type map[int]interface {}) as type map[interface {}]interface {} in argument to Keys

Does Go support generics and how should I fix my code?

Answer 1

1- Golang is strongly typed language, So the map[int]interface{} is not compatible with map[interface{}]interface{}.
int is different type than interface{}, and see: Go: What's the meaning of interface{}?

2- No, Golang doesn't support generics, and this is very good, because it makes language simple and fast.

---

You have some options:

If you don't want to change the type of map used:
1- You may edit the function to: func Keys(m map[int]interface{}) []int, like this working sample code:

package main

import "fmt"

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

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

output ( may not be in order):

[2 3]

---

2- Or you may edit the function to: func Keys(m map[int]interface{}) []interface{}, like this working sample code:

package main

import "fmt"

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

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

output ( may not be in order):

[2 3]

---

If you don't want to change the Keys function used:
3- You may edit the map to: map[interface{}]interface{}, like this working sample code:

package main

import "fmt"

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

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

---

4- Also you may use reflect package for some use cases, but with the performance (speed) penalty.
And See: The Laws of Reflection