方便和函数的区别：
方法能给用户定义的类型添加新的行为。方法实际上也是函数，只是在声明时，在关键字func 和方法名之间增加了一个参数。
package main
import (
"fmt"
)
//define a use struct
type user struct {
name string
email string
}
//notyfy user recieve a method
func (u user) notify() {
fmt.Printf("Sending User Email to %s<%s>\n",
u.name,
u.email)
}
//changeEmail user make a method with pointer
func (u *user) changeEmail(email string) {
u.email = email
}
//main is the entry of the program
func main() {
bill := user{"Bill", "bill@email.com"}
bill.notify()
lisa := &user{"Lisa", "lisa@email.com"}
lisa.notify()
bill.changeEmail("bill@newdomain.com")
bill.notify()
lisa.changeEmail("lisa@newdomain.com")
lisa.notify()
}
