Is there a nice way to get length of slice elem in map regardless of its concrete type in golang?

For example, I have two maps, namely map[string][]structAand map[string][]int.

I want to iterate the map and print out length of every slice, can I implement this in a singler function?

I tried to define an interface and implement it in two kinds of slices, but the compiler just cannot do the type cast.

type Container interface{
    Len() int
}

type Slice1 []int
func (s Slice1) Len() int {
    return len(s)
}

type Slice2 []StructA
func (s Slice2) Len() int {
    return len(s)
}

func iterate(input map[string]Container) {
    for key, value := range input {
        log.Printf("key:%s, lenght:%d", key, value.Len())
    }
}

func main() {
    // cannot do the type cast
    iterate(map[string]Slice1{})
    iterate(map[string]Slice2{})
}