Go设计模式之策略模式讲解和代码示例

package main
// 策略接口
type EvictionAlgo interface {
	evict(c *Cache)
}

package main
import "fmt"
type Fifo struct{}
func (l *Fifo) evict(c *Cache) {
	fmt.Println("Evicting by fifo strtegy")
}

package main
import "fmt"
type Lru struct{}
func (l *Lru) evict(c *Cache) {
	fmt.Println("Evicting by lru strtegy")
}

package main
import "fmt"
type Lfu struct{}
func (l *Lfu) evict(c *Cache) {
	fmt.Println("Evicting by lfu strtegy")
}

package main
type Cache struct {
	storage      map[string]string
	evictionAlgo EvictionAlgo
	capacity     int
	macCapacity  int
}
// 初始化的时候将策略注入到 cache 中
func initCache(e EvictionAlgo) *Cache {
	storage := make(map[string]string)
	return &Cache{
		storage:      storage,
		evictionAlgo: e,
		capacity:     0,
		macCapacity:  2,
	}
}
// 动态修改策略
func (c *Cache) setEvictionAlgo(e EvictionAlgo) {
	c.evictionAlgo = e
}
func (c *Cache) add(key, value string) {
	// 如果缓存中的容量等于了最大容量，则需要执行策略来移除 s
	if c.capacity == c.macCapacity {
		c.evict()
	}
	c.capacity++
	c.storage[key] = value
}
func (c *Cache) evict() {
	c.evictionAlgo.evict(c)
	c.capacity--
}
func (c *Cache) get(key string) {
	delete(c.storage, key)
}

package main
func main() {
	lfu := &Lfu{}
	cache := initCache(lfu)
	cache.add("a", "1")
	cache.add("b", "2")
	cache.add("c", "3")
	lru := &Lru{}
	cache.setEvictionAlgo(lru)
	cache.add("d", "4")
	fifo := &Fifo{}
	cache.setEvictionAlgo(fifo)
	cache.add("e", "5")
}