策略模式：使用上下文来传递参数

package main

import "fmt"


// Strategy Interface
type PaymentStrategy interface {
  Pay(ctx *PaymentContext) string
}


// Concrete Strategy
type PayPalStrategy struct{}


func (p *PayPalStrategy) Pay(ctx *PaymentContext) string {
  return fmt.Sprintf("Paid %d using PayPal. PayPal user: %s", ctx.Amount, ctx.PayPalUser)
}


// Concrete Strategy
type CreditCardStrategy struct{}


func (c *CreditCardStrategy) Pay(ctx *PaymentContext) string {
  return fmt.Sprintf("Paid %d using Credit Card. Card Number: %s", ctx.Amount, ctx.CreditCardNumber)
}


// Context
type ShoppingCart struct {
  ctx *PaymentContext
}


func (s *ShoppingCart) checkout() string {
  return s.ctx.Strategy.Pay(s.ctx)
}


// PaymentContext serves as the context for payment strategies
type PaymentContext struct {
  Strategy         PaymentStrategy
  Amount           int
  PayPalUser       string
  CreditCardNumber string
}


func main() {
  ctx := &PaymentContext{Strategy: &PayPalStrategy{}, Amount: 200, PayPalUser: "user@example.com"}
  cart := &ShoppingCart{ctx: ctx}
  fmt.Println(cart.checkout()) // Paid 200 using PayPal. PayPal user: user@example.com


  ctx = &PaymentContext{Strategy: &CreditCardStrategy{}, Amount: 300, CreditCardNumber: "1234-5678-9012-3456"}
  cart = &ShoppingCart{ctx: ctx}
  fmt.Println(cart.checkout()) // Paid 300 using Credit Card. Card Number: 1234-5678-9012-3456
}