go 多态

demo1

// Sample program to show how polymorphic behavior with interfaces.
package main

import (
    "fmt"
)

// notifier is an interface that defines notification
// type behavior.
type notifier interface {
    notify()
}

// user defines a user in the program.
type user struct {
    name  string
    email string
}

// notify implements the notifier interface with a pointer receiver.
func (u *user) notify() {
    fmt.Printf("Sending user email to %s<%s>
",
        u.name,
        u.email)
}

// admin defines a admin in the program.
type admin struct {
    name  string
    email string
}

// notify implements the notifier interface with a pointer receiver.
func (a *admin) notify() {
    fmt.Printf("Sending admin email to %s<%s>
",
        a.name,
        a.email)
}

// main is the entry point for the application.
func main() {
    // Create a user value and pass it to sendNotification.
    bill := user{"Bill", "bill@email.com"}
    sendNotification(&bill)

    // Create an admin value and pass it to sendNotification.
    lisa := admin{"Lisa", "lisa@email.com"}
    sendNotification(&lisa)
}

// sendNotification accepts values that implement the notifier
// interface and sends notifications.
func sendNotification(n notifier) {
    n.notify()
}

输出

Sending user email to Bill<bill@email.com>
Sending admin email to Lisa<lisa@email.com>

demo2

// Sample program to show what happens when the outer and inner
// type implement the same interface.
package main

import (
    "fmt"
)

// notifier is an interface that defined notification
// type behavior.
type notifier interface {
    notify()
}

// user defines a user in the program.
type user struct {
    name  string
    email string
}

// notify implements a method that can be called via
// a value of type user.
func (u *user) notify() {
    fmt.Printf("Sending user email to %s<%s>
",
        u.name,
        u.email)
}

// admin represents an admin user with privileges.
type admin struct {
    user
    level string
}

// notify implements a method that can be called via
// a value of type Admin.
func (a *admin) notify() {
    fmt.Printf("Sending admin email to %s<%s>
",
        a.user.name,
        a.user.email)
}

// main is the entry point for the application.
func main() {
    // Create an admin user.
    ad := admin{
        user: user{
            name:  "john smith",
            email: "john@yahoo.com",
        },
        level: "super",
    }

    // Send the admin user a notification.
    // The embedded inner type's implementation of the
    // interface is NOT "promoted" to the outer type.
    sendNotification(&ad)

    // We can access the inner type's method directly.
    ad.user.notify()

    // The inner type's method is NOT promoted.
    ad.notify()
}

// sendNotification accepts values that implement the notifier
// interface and sends notifications.
func sendNotification(n notifier) {
    n.notify()
}

输出

Sending admin email to john smith<john@yahoo.com>
Sending user email to john smith<john@yahoo.com>
Sending admin email to john smith<john@yahoo.com>

demo3

// Sample program to show what happens when the outer and inner
// type implement the same interface.
package main

import (
    "fmt"
)

// notifier is an interface that defined notification
// type behavior.
type notifier interface {
    notify()
}

// user defines a user in the program.
type user struct {
    name  string
    email string
}

// notify implements a method that can be called via
// a value of type user.
func (u *user) notify() {
    fmt.Printf("Sending user email to %s<%s>
",
        u.name,
        u.email)
}

// admin represents an admin user with privileges.
type admin struct {
    user
    level string
}

// notify implements a method that can be called via
// a value of type Admin.
func (a *admin) notify() {
    fmt.Printf("Sending admin email to %s<%s>
",
        a.name,
        a.email)
}

// main is the entry point for the application.
func main() {
    // Create an admin user.
    ad := admin{
        user: user{
            name:  "john smith",
            email: "john@yahoo.com",
        },
        level: "super",
    }

    // Send the admin user a notification.
    // The embedded inner type's implementation of the
    // interface is NOT "promoted" to the outer type.
    sendNotification(&ad)

    // We can access the inner type's method directly.
    ad.user.notify()

    // The inner type's method is NOT promoted.
    ad.notify()
}

// sendNotification accepts values that implement the notifier
// interface and sends notifications.
func sendNotification(n notifier) {
    n.notify()
}

输出

Sending admin email to john smith<john@yahoo.com>
Sending user email to john smith<john@yahoo.com>
Sending admin email to john smith<john@yahoo.com>