享元模式

Flyweight Pattern

  在有大量对象时，有可能会造成内存溢出，我们把其中共同的部分抽象出来，如果有相同的业务请求，直接返回在内存中已有的对象，避免重新创建。

  它适合用于当大量物件只是重复因而导致无法令人接受的使用大量内存。通常物件中的部分状态是可以分享。常见做法是把它们放在外部数据结构，当需要使用时再将它们传递给享元。

实现

  我们举个例子:

• 游戏中的角色都有基础属性
• 游戏中的角色都会穿上装备
• 装备是不同的但基础属性都是一样的
  

  结合装饰者模式来开发一个角色穿上不同装备后，HP上限和MP上限增加的例子.

package flyweight

type IProperty interface{
	GetHPLimit()int
	GetMPLimit()int
}

type PeopleBase struct{
	MAX_HP int
	MAX_MP int
}

func NewPeopleBase()*PeopleBase{
	return &PeopleBase{100,100}
}

func (this *PeopleBase)GetHPLimit()int{
	return this.MAX_HP
}

func (this *PeopleBase)GetMPLimit()int{
	return this.MAX_MP
}

type Helmet struct{
	base IProperty
	HP_ADD int
	MP_ADD int
}

func (this *Helmet)GetHPLimit()int{
	return this.base.GetHPLimit()+this.HP_ADD
}

func (this *Helmet)GetMPLimit()int{
	return this.base.GetMPLimit()+this.MP_ADD
}

func NewHelmet(property IProperty,hp_add,mp_add int)*Helmet{
	return &Helmet{property,hp_add,mp_add}
}

  还需要一个享元工厂来存放享元

package flyweight

type Element struct {
	Value interface{}
}

func newElement(value interface{})*Element{
	return &Element{value}
}

type FlyweightFactory struct {
	pool map[string]*Element
}

func (this *FlyweightFactory) GetElement(key string) interface{} {
	return this.pool[key].Value
}



func (this *FlyweightFactory)SetElement(key string,value interface{}){
	ne := newElement(value)
	this.pool[key]=ne
}

func NewFlyweight()*FlyweightFactory{
	flyweight := FlyweightFactory{}
	flyweight.pool=make(map[string]*Element)
	return &flyweight
}

  最后模拟一个例子

package main

import (
	"projects/DesignPatternsByGo/structuralPatterns/flyweight"
	"fmt"
)

func main(){
    //	创建享元
	fly := flyweight.NewFlyweight()
	base := flyweight.NewPeopleBase()
	fly.SetElement("PeopleBase",base)

    //	生成两个人物, 从 interface{} 转到 IProperty
    //  people_1和people_2在内存中是同一份
	people_1 := fly.GetElement("PeopleBase").(flyweight.IProperty)
	people_2 := fly.GetElement("PeopleBase").(flyweight.IProperty)
  
    //	捡到装备了——装饰者
	people_1 = flyweight.NewHelmet(people_1,10,10)
	people_2 = flyweight.NewHelmet(people_2,100,100)

    //	获取它们血量上限和魔法上限
	hp_1 := people_1.GetHPLimit()
	mp_1 := people_1.GetMPLimit()

	hp_2 := people_2.GetHPLimit()
	mp_2 := people_2.GetMPLimit()

	fmt.Printf("People_1:\nHP:%d\nMP:%d\n",hp_1,mp_1)
	fmt.Printf("People_2:\nHP:%d\nMP:%d\n",hp_2,mp_2)
}