接口组合与多态

type Reader interface {
    Read(p []byte) (n int, err error)
}

type Writer interface {
    Write(p []byte) (n int, err error)
}

type ReadWriter interface {
    Reader
    Writer
}

type Speaker interface {
    Speak() string
}

type Dog struct{}
func (d Dog) Speak() string { return "Woof!" }

type Cat struct{}
func (c Cat) Speak() string { return "Meow!" }

func SaySomething(s Speaker) {
    fmt.Println(s.Speak())
}

SaySomething(Dog{})  // 输出：Woof!
SaySomething(Cat{})  // 输出：Meow!