Is there a way to compare with any pointer objects in golang?

Question

I am trying to make a comparator, that takes either two string pointers, or two integer pointers and returns the result. any of pointer can be nil and i want true only when they have value and value is equal.

I tried with interface like

type T *interface{}
func compare(a T,b T) bool

because i had to check nil when cast *string to T, it is useless.

I am expecting to call function like

var a *string
var b *string
if compare(a, b){
  // do something
}

or

var a *string
var b *string
if a.equal(b){ 
  // do sth 
}

Answer 1

Given that you are only working with two types, use type assertions to get the concrete pointer types and compare:

func compare(a interface{}, b interface{}) bool {
    switch a := a.(type) {
    case *string:
        b, _ := b.(*string)
        return a != nil && b != nil && *a == *b
    case *int:
        b, _ := b.(*int)
        return a != nil && b != nil && *a == *b
    default:
        return false
    }
}

Here are some examples of calling the function:

a := "hello"
b := "world"
c := "hello"
fmt.Println(compare(&a, nil))
fmt.Println(compare(nil, &a))
fmt.Println(compare(&a, &b))
fmt.Println(compare(&a, &a))
fmt.Println(compare(&a, &c))

Run it in the Playground

Use the reflect API to compare all comparable types:

func compare(a interface{}, b interface{}) bool {
    if a == nil && b == nil {
        return true
    }
    if a == nil || b == nil {
        return false
    }
    va := reflect.ValueOf(a)
    vb := reflect.ValueOf(b)
    if va.Type() != vb.Type() {
        return false
    }
    if va.Kind() == reflect.Ptr {
        if va.IsNil() || vb.IsNil() {
            return false
        }
        va = va.Elem()
        vb = vb.Elem()
    }
    if !va.Type().Comparable() {
        return false
    }
    return va.Interface() == vb.Interface()
}