interface搞不懂。。

自己学习的，下面代码m转到p出错了，m2却可以。。这语言有点难 package main import "fmt" type People interface { say() } type Men struct { name string } func (men *Men) say() { fmt.Println("mem say hi:", men.name); } func main() { m := Men{"mike"} m.say() m2 := new(Men) m2.name = "new men" var p People p = m2 p = m //error cannot use m (type Men) as type People in assignment: p.say() }