package main
import "fmt"
type PaymentStrategy interface {
    Pay(amount float64) error
}
type CreditCard struct {
    Number string
}
func (cc CreditCard) Pay(amount float64) error {
    fmt.Printf("Paid $%.2f with credit card %s\n", amount, cc.Number)
    return nil
}
type PayPal struct {
    Email string
}
func (pp PayPal) Pay(amount float64) error {
    fmt.Printf("Paid $%.2f via PayPal (%s)\n", amount, pp.Email)
    return nil
}
type Order struct {
    Amount   float64
    Strategy PaymentStrategy
}
func (o Order) Checkout() error {
    return o.Strategy.Pay(o.Amount)
}
func main() {
    order := Order{
        Amount:   99.99,
        Strategy: CreditCard{Number: "1234-5678"},
    }
    order.Checkout()  // Paid $99.99 with credit card 1234-5678
    order.Strategy = PayPal{Email: "user@example.com"}
    order.Checkout()  // Paid $99.99 via PayPal (user@example.com)
}

package main
import (
    "fmt"
    "os"
)
type Logger interface {
    Log(message string)
}
type ConsoleLogger struct{}
func (cl ConsoleLogger) Log(message string) {
    fmt.Println("[CONSOLE]", message)
}
type FileLogger struct {
    File *os.File
}
func (fl FileLogger) Log(message string) {
    fl.File.WriteString(message + "\n")
}
// 适配函数
type LogFunc func(string)
func (lf LogFunc) Log(message string) {
    lf(message)
}
func main() {
    // 使用函数作为适配器
    logger := LogFunc(func(msg string) {
       fmt.Println("[CUSTOM]", msg)
    })
    logger.Log("Hello")
    logger1 := ConsoleLogger{}
    logger1.Log("Hello")
}

// 1. 结构体 (Struct) - 替代类
type Person struct {
    Name string
    Age  int
}
// 方法绑定到结构体
func (p Person) SayHello() string {
    return fmt.Sprintf("Hello, my name is %s", p.Name)
}
// 2. 组合 - 替代继承
type Animal struct {
    Name string
}
func (a Animal) Speak() string {
    return "..."
}
type Dog struct {
    Animal  // 嵌入结构体,实现组合
    Breed   string
}
// Dog 自动拥有 Animal 的方法
dog := Dog{Animal: Animal{Name: "Buddy"}, Breed: "Labrador"}
fmt.Println(dog.Speak()) // 可以调用 Animal 的方法
# 3. 接口 (Interface) - 多态
type Speaker interface {
    Speak() string
}
type Cat struct {
    Name string
}
func (c Cat) Speak() string {
    return "Meow"
}
// 隐式实现接口,无需显式声明
func MakeSound(s Speaker) {
    fmt.Println(s.Speak())
}
MakeSound(Dog{})  // 输出: ...
MakeSound(Cat{})  // 输出: Meow
# 4. 封装 - 通过大小写控制可见性
type Account struct {
    balance float64  // 小写开头,私有字段
    Owner   string   // 大写开头,公有字段
}
// 公有方法访问私有字段
func (a *Account) Deposit(amount float64) {
    a.balance += amount
}
func (a *Account) GetBalance() float64 {
    return a.balance
}