如何实现golang语言的多态

例如：type People interface {
    // 只声明
    GetAge() int 
    GetName() string 
}

package main
import (
    "fmt"
)
type Biology interface {
    sayhi()
}
type Man struct {
    name string
    age  int
}
type Monster struct {
    name string
    age  int
}
func (this *Man) sayhi()  { // 实现抽象方法1
    fmt.Printf("Man[%s, %d] sayhi\n", this.name, this.age)
}
func (this *Monster) sayhi()  { // 实现抽象方法1
    fmt.Printf("Monster[%s, %d] sayhi\n", this.name, this.age)
}
func WhoSayHi(i Biology) {
    i.sayhi()
}
func main() {
    man := &Man{"我是人", 100}
    monster := &Monster{"妖怪", 1000}
    WhoSayHi(man)
    WhoSayHi(monster)
}