2023 跟我一起学设计模式: 享元模式 (Cache)

// 享元类包含一个树的部分状态。这些成员变量保存的数值对于特定树而言是唯一
// 的。例如，你在这里找不到树的坐标。但这里有很多树木之间所共有的纹理和颜
// 色。由于这些数据的体积通常非常大，所以如果让每棵树都其进行保存的话将耗
// 费大量内存。因此，我们可将纹理、颜色和其他重复数据导出到一个单独的对象
// 中，然后让众多的单个树对象去引用它。
class TreeType is
    field name
    field color
    field texture
    constructor TreeType(name, color, texture) { …… }
    method draw(canvas, x, y) is
        // 1. 创建特定类型、颜色和纹理的位图。
        // 2. 在画布坐标 (X,Y) 处绘制位图。

// 享元工厂决定是否复用已有享元或者创建一个新的对象。
class TreeFactory is
    static field treeTypes: collection of tree types
    static method getTreeType(name, color, texture) is
        type = treeTypes.find(name, color, texture)
        if (type == null)
            type = new TreeType(name, color, texture)
            treeTypes.add(type)
        return type

// 情景对象包含树状态的外在部分。程序中可以创建数十亿个此类对象，因为它们
// 体积很小：仅有两个整型坐标和一个引用成员变量。
class Tree is
    field x,y
    field type: TreeType
    constructor Tree(x, y, type) { …… }
    method draw(canvas) is
        type.draw(canvas, this.x, this.y)

// 树（Tree）和森林（Forest）类是享元的客户端。如果不打算继续对树类进行开
// 发，你可以将它们合并。
class Forest is
    field trees: collection of Trees

    method plantTree(x, y, name, color, texture) is
        type = TreeFactory.getTreeType(name, color, texture)
        tree = new Tree(x, y, type)
        trees.add(tree)

    method draw(canvas) is
        foreach (tree in trees) do
            tree.draw(canvas)

type player struct {
  dress      dress
  playerType string // 可为 T 或 CT
  lat        int
  long       int
}

package main

import "fmt"

const (
  //TerroristDressType terrorist dress type
  TerroristDressType = "tDress"
  //CounterTerrroristDressType terrorist dress type
  CounterTerrroristDressType = "ctDress"
)

var (
  dressFactorySingleInstance = &DressFactory{
    dressMap: make(map[string]Dress),
  }
)

type DressFactory struct {
  dressMap map[string]Dress
}

func (d *DressFactory) getDressFactoryByType(dressType string) (Dress, error) {
  if d.dressMap[dressType] != nil {
    return d.dressMap[dressType], nil
  }
  if dressType == TerroristDressType {
    d.dressMap[dressType] = newTerrorisDress()
    return d.dressMap[dressType], nil
  }
  if dressType == CounterTerrroristDressType {
    d.dressMap[dressType] = newCounterTerrroristDress()
    return d.dressMap[dressType], nil
  }
  return nil, fmt.Errorf("Wrong dress type passed")
}

func getDressFactorySingleInstance() *DressFactory {
  return dressFactorySingleInstance
}

package main

// 享元接口
type Dress interface {
  getColor() string
}

package main

type TerroristDress struct {
  color string
}

func (t *TerroristDress) getColor() string {
  return t.color
}

func newTerrorisDress() *TerroristDress {
  return &TerroristDress{color: "red"}
}

package main

// 享元接口
type CounterTerrroristDress struct {
  color string
}

func (c *CounterTerrroristDress) getColor() string {
  return c.color
}

func newCounterTerrroristDress() *CounterTerrroristDress {
  return &CounterTerrroristDress{color: "green"}
}

package main

type Player struct {
  dress      Dress
  playerType string
  lat        int
  long       int
}

func newPlayer(playerType, dressType string) *Player {
  dress, _ := getDressFactorySingleInstance().getDressFactoryByType(dressType)
  return &Player{
    dress:      dress,
    playerType: playerType,
  }
}

func (p *Player) newLocation(lat, long int) {
  p.lat = lat
  p.long = long
}

package main

type game struct {
  terrorists        []*Player
  counterTerrorists []*Player
}

func newGame() *game {
  return &game{
    terrorists:        make([]*Player, 1),
    counterTerrorists: make([]*Player, 01),
  }
}

func (c *game) addTerrorist(dressType string) {
  player := newPlayer("T", dressType)
  c.terrorists = append(c.terrorists, player)
  return
}

func (c *game) addCounterTerrorist(dressType string) {
  player := newPlayer("CT", dressType)
  c.counterTerrorists = append(c.counterTerrorists, player)
  return
}

package main

import "fmt"

func main() {
  game := newGame()

  //Add Terrorist
  game.addTerrorist(TerroristDressType)
  game.addTerrorist(TerroristDressType)
  game.addTerrorist(TerroristDressType)
  game.addTerrorist(TerroristDressType)

  //Add CounterTerrorist
  game.addCounterTerrorist(CounterTerrroristDressType)
  game.addCounterTerrorist(CounterTerrroristDressType)
  game.addCounterTerrorist(CounterTerrroristDressType)

  dressFactoryInstance := getDressFactorySingleInstance()

  for dressType, dress := range dressFactoryInstance.dressMap {
    fmt.Printf("DressColorType: %s\nDressColor: %s\n", dressType, dress.getColor())
  }
}

DressColorType: tDress
DressColor: red
DressColorType: ctDress
DressColor: green