一、简介

代理模式（Proxy Design Pattern）在不改变原始类（或叫被代理类）代码的情况下，通过引入代理类来给原始类附加功能。

二、优点

• 关注点分离
• 访问控制
• 延迟实例化
• 远程访问
• 缓存
• 增加附加功能

三、应用场景

• 访问控制
• 缓存
• 保护代理
• 远程对象
• 智能引用
• 其他：日志记录、监控和审计等

四、UML类图

五、案例

银行提供存款和取款两种功能，不同权限的用户功能不同，只有管理权限的账号能存取款，普通用户只能存款。

package main

import "fmt"

type BankAccount interface {
	Deposit(amount float64)
	Withdraw(amount float64)
}

type RealBankAccount struct {
	Balance float64
}

func NewRealBankAccount(initialBalance float64) RealBankAccount {
	return RealBankAccount{Balance: initialBalance}
}

func (rba *RealBankAccount) Deposit(amount float64) {
	rba.Balance += amount
	fmt.Printf("Deposited: %v, new balance: %v\n", amount, rba.Balance)
}

func (rba *RealBankAccount) Withdraw(amount float64) {
	if rba.Balance >= amount {
		rba.Balance -= amount
		fmt.Printf("Withdrew: %v, new balance: %v\n", amount, rba.Balance)
	} else {
		fmt.Printf("Insufficient balance\n")
	}
}

type BankAccountProxy struct {
	UserRole        string
	RealBankAccount RealBankAccount
}

func NewBankAccountProxy(userRole string, initialBalance float64) BankAccountProxy {
	return BankAccountProxy{UserRole: userRole, RealBankAccount: NewRealBankAccount(initialBalance)}
}

func (proxy *BankAccountProxy) Deposit(amount float64) {
	if proxy.UserRole == "Admin" || proxy.UserRole == "User" {
		proxy.RealBankAccount.Deposit(amount)
	} else {
		fmt.Printf("Unauthorized access\n")
	}
}

func (proxy *BankAccountProxy) Withdraw(amount float64) {
	if proxy.UserRole == "Admin" {
		proxy.RealBankAccount.Withdraw(amount)
	} else {
		fmt.Printf("Unauthorized access\n")
	}
}

func main() {
	adminBankAccount := NewBankAccountProxy("Admin", 1000)
	adminBankAccount.Deposit(500)
	adminBankAccount.Withdraw(200)

	userBankAccount := NewBankAccountProxy("User", 1000)
	userBankAccount.Deposit(500)
	userBankAccount.Withdraw(200)
}