Golang策略模式动态选择算法实践

package main

import "fmt"

// OperationStrategy 定义策略接口，声明所有计算策略必须实现的方法
type OperationStrategy interface {
    Execute(a, b int) int
}

// AddStrategy 加法策略的实现
type AddStrategy struct{}

func (s *AddStrategy) Execute(a, b int) int {
    return a + b
}

// SubtractStrategy 减法策略的实现
type SubtractStrategy struct{}

func (s *SubtractStrategy) Execute(a, b int) int {
    return a - b
}

// MultiplyStrategy 乘法策略的实现
type MultiplyStrategy struct{}

func (s *MultiplyStrategy) Execute(a, b int) int {
    return a * b
}

// CalculatorContext 上下文，它持有并执行具体的策略
type CalculatorContext struct {
    strategy OperationStrategy
}

// SetStrategy 允许外部设置或更换当前的策略
func (c *CalculatorContext) SetStrategy(s OperationStrategy) {
    c.strategy = s
}

// PerformOperation 执行当前策略的计算方法
func (c *CalculatorContext) PerformOperation(a, b int) int {
    if c.strategy == nil {
        // 如果没有设置策略，可以提供一个默认行为或抛出错误
        fmt.Println("No strategy set, defaulting to addition.")
        return a + b
    }
    return c.strategy.Execute(a, b)
}

// 策略注册中心：用于动态选择算法的实践
// 我们通常会通过一个全局的map来注册和获取不同的策略实例
var strategyMap = make(map[string]OperationStrategy)

// init 函数在包被导入时自动执行，用于初始化策略注册中心
func init() {
    strategyMap["add"] = &AddStrategy{}
    strategyMap["subtract"] = &SubtractStrategy{}
    strategyMap["multiply"] = &MultiplyStrategy{}
}

// GetStrategy 根据名称从注册中心获取对应的策略实例
func GetStrategy(name string) OperationStrategy {
    return strategyMap[name]
}

func main() {
    calculator := &CalculatorContext{}

    // 模拟根据外部配置或请求参数动态选择策略
    selectedStrategyName := "multiply" // 假设这是从配置文件、命令行参数或HTTP请求中获取的
    if s := GetStrategy(selectedStrategyName); s != nil {
        calculator.SetStrategy(s)
        result := calculator.PerformOperation(10, 5)
        fmt.Printf("Using '%s' strategy: 10 op 5 = %d\n", selectedStrategyName, result)
    } else {
        fmt.Printf("Strategy '%s' not found.\n", selectedStrategyName)
    }

    selectedStrategyName = "add"
    if s := GetStrategy(selectedStrategyName); s != nil {
        calculator.SetStrategy(s)
        result := calculator.PerformOperation(20, 3)
        fmt.Printf("Using '%s' strategy: 20 op 3 = %d\n", selectedStrategyName, result)
    }

    // 尝试选择一个不存在的策略
    selectedStrategyName = "divide"
    if s := GetStrategy(selectedStrategyName); s != nil {
        calculator.SetStrategy(s)
        result := calculator.PerformOperation(10, 2)
        fmt.Printf("Using '%s' strategy: 10 op 2 = %d\n", selectedStrategyName, result)
    } else {
        fmt.Printf("Strategy '%s' not found, cannot perform operation.\n", selectedStrategyName)
        // 此时 calculator 仍持有之前的 "add" 策略，或者默认策略
        fmt.Printf("Current strategy still yields: 10 op 2 = %d\n", calculator.PerformOperation(10, 2))
    }
}

map

init

GetStrategy

main

if-else if-else

switch

if-else