state pattern

Author: fx-slayer

README.md

@@ -42,9 +42,9 @@ A curated collection of idiomatic design & application patterns for Go language.
 | [Memento](/behavioral/memento/main.go) | Generate an opaque token that can be used to go back to a previous state | ✔ |
 | [Observer](/behavioral/observer.md) | Provide a callback for notification of events/changes to data | ✔ |
 | [Registry](/behavioral/registry.md) | Keep track of all subclasses of a given class | ✘ |
-| [State](/behavioral/state.md) | Encapsulates varying behavior for the same object based on its internal state | ✘ |
+| [State](/behavioral/state.md) | Encapsulates varying behavior for the same object based on its internal state | ✔ |
 | [Strategy](/behavioral/strategy.md) | Enables an algorithm's behavior to be selected at runtime | ✔ |
-| [Template](/behavioral/template.md) | Defines a skeleton class which defers some methods to subclasses | ✘ |
+| [Template](/behavioral/template.md) | Defines a skeleton class which defers some methods to subclasses | ✔ |
 | [Visitor](/behavioral/visitor.md) | Separates an algorithm from an object on which it operates | ✘ |
 
 ## Synchronization Patterns

behavioral/command/main.go

@@ -69,13 +69,14 @@ func main(){
 	attk := CommandAttack{playerA}
 	escp := CommandEscape{playerA}
 
-	invoker.PushCommands(attk ,escp ,escp ,attk)
+	invoker.PushCommands(attk ,escp ,escp ,attk ,escp)
 	invoker.CallCommands()
 	// output:
 	/*
-		icg opened fire
-		icg escape
-		icg escape
-		icg opened fire
+	icg opened fire
+	icg escape
+	icg escape
+	icg opened fire
+	icg escape
 	*/
 }

behavioral/memento/main.go

@@ -8,10 +8,14 @@ import (
 	"log"
 )
 
+// originator
 type Player struct {
+	// 需要记录的数据可以考虑单独封装
+	// type Pos struct{X,Y int}
 	X,Y int
-	Name string
+
 	// other info
+	Name string
 }
 
 func (p *Player)MoveTo(x,y int){
@@ -31,10 +35,12 @@ func (p *Player)Restore(m PlayerMemento){
 	p.Y = m.Y
 }
 
+// memento
 type PlayerMemento struct {
 	X,Y int
 }
 
+// caretaker
 type PlayerCareTaker struct {
 	MementoList *list.List
 }
@@ -75,4 +81,12 @@ func main(){
 
 	icg.Restore(ct.RemoveLast())
 	log.Println(icg.X ,icg.Y)
+	/*
+	output:
+	2019/05/02 18:18:03 114 514
+	2019/05/02 18:18:03 810 19
+	2019/05/02 18:18:03 0 0
+	2019/05/02 18:18:03 810 19
+	2019/05/02 18:18:03 114 514
+	 */
 }

behavioral/state/main.go

@@ -0,0 +1,84 @@
+// 状态模式 state pattern.
+// 与策略模式在一些场景可以通用，但策略模式倾向于调用者根据情况手动改变内部策略以切换算法，
+// 状态模式倾向于由Context内部自行管理状态，只需要设定初始状态即可，不需要手动切换.
+//
+// 以下是以跷跷板seesaw为例，分为[左侧高LeftState|右侧高RightState]
+package main
+
+import (
+	"math/rand"
+	"time"
+)
+
+// state
+type SeesawState interface {
+	LiftLeftSide(S *Seesaw)
+	LiftRightSide(S *Seesaw)
+}
+
+type LeftState struct {}
+
+func (LeftState) LiftLeftSide(S *Seesaw) {
+	println("↑LEFT > left side wads already lifted")
+}
+
+func (l LeftState) LiftRightSide(S *Seesaw) {
+	println("RIGHT↑ > lift right side")
+	S.State = RightState{}
+}
+
+type RightState struct {}
+
+func (r RightState) LiftLeftSide(S *Seesaw) {
+	println("↑LEFT > lift left side")
+	S.State = LeftState{}
+}
+
+func (RightState) LiftRightSide(S *Seesaw) {
+	println("RIGHT↑ > right side wads already lifted")
+}
+
+// context
+type Seesaw struct {
+	State SeesawState
+}
+
+func (s *Seesaw)MakeLeftUp(){
+	s.State.LiftLeftSide(s)
+}
+
+func (s *Seesaw)MakeRightUp(){
+	s.State.LiftRightSide(s)
+}
+
+func main(){
+	// init left
+	seesaw := &Seesaw{
+		State:LeftState{},
+	}
+
+	rand.Seed(time.Now().UnixNano())
+	for i:=0 ;i<10 ;i++{
+		if rand.Intn(2) == 1{
+			// ▄▃▂
+			seesaw.MakeLeftUp()
+		}else{
+			// ▂▃▄
+			seesaw.MakeRightUp()
+		}
+	}
+	/*
+	output:
+	RIGHT↑ > lift right side
+	RIGHT↑ > right side wads already lifted
+	RIGHT↑ > right side wads already lifted
+	↑LEFT > lift left side
+	↑LEFT > left side wads already lifted
+	↑LEFT > left side wads already lifted
+	↑LEFT > left side wads already lifted
+	RIGHT↑ > lift right side
+	RIGHT↑ > right side wads already lifted
+	↑LEFT > lift left side
+	 */
+}
+

behavioral/state/problem.go

@@ -0,0 +1,118 @@
+// 存疑部分.
+//
+// 这里是以玩家的健康状态为基准，影响生命回复和受到伤害的例子，有三个状态[健康HealthyState|受伤WoundedState|死亡DeadState].
+// 和main.go中的跷跷板例子由行为驱动状态变化不同.以下例子的行为是受到数据影响的,结果就是达不到完全消除if-else的效果
+//
+// 疑问：
+// 1. 很多地方说状态模式可以消除if-else，事实上要做到自行的状态切换很多时候还是会用到if-else，这里的消除应当是指
+// 将巨大的条件语句拆分开(?)
+// 2. 还是说这种由数据决定状态的事务逻辑下不适合使用状态模式
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+// state
+type PlayerState interface {
+	Heal(p *Player) error
+	Hurt(p *Player ,dmg int)
+}
+
+type HealthyState struct {}
+
+func (h HealthyState)Heal(p *Player) error{
+	return nil
+}
+
+func (h HealthyState)Hurt(p *Player ,dmg int){
+	if dmg > 0 && dmg < p.MaxHealth{
+		p.Health = p.Health - dmg
+		p.State = WoundedState{}
+	}else if dmg > p.MaxHealth{
+		p.Health = 0
+		p.State = DeadState{}
+	}
+}
+
+type WoundedState struct {}
+
+func (WoundedState)Heal(p *Player) error{
+	if p.Health >= p.MaxHealth - 5{
+		fmt.Printf("healing from %d to %d\n" ,p.Health ,p.MaxHealth)
+		p.State = HealthyState{}
+		p.Health = p.MaxHealth
+	}else{
+		fmt.Printf("healing from %d to %d\n" ,p.Health ,p.Health+5)
+		p.Health = p.Health + 5
+	}
+	return nil
+}
+
+func (h WoundedState)Hurt(p *Player ,dmg int){
+	if p.Health > dmg{
+		p.Health = p.Health - dmg
+	}else {
+		p.State = DeadState{}
+		p.Health = 0
+	}
+}
+
+type DeadState struct {}
+
+func (DeadState)Heal(P *Player) error{
+	return errors.New("you are dead")
+}
+
+func (DeadState)Hurt(P *Player ,dmg int){}
+
+// context
+type Player struct {
+	Health int
+	MaxHealth int
+	State PlayerState
+}
+
+func (p *Player)HealPlayer()error{
+	return p.State.Heal(p)
+}
+
+func (p *Player)HurtPlayer(damage int){
+	fmt.Printf("damage %d\n" ,damage)
+	p.State.Hurt(p ,damage)
+}
+
+//func main(){
+//	player := &Player{
+//		Health:100,
+//		MaxHealth:100,
+//		State:HealthyState{},
+//	}
+//
+//	rand.Seed(time.Now().UnixNano())
+//	for i:=0 ;i<10 ;i++{
+//		if err := player.HealPlayer();err != nil{
+//			fmt.Println(err)
+//			break
+//		}
+//		player.HurtPlayer(rand.Intn(30))
+//	}
+//	/*
+//	output:
+//	damage 28
+//	healing from 72 to 77
+//	damage 29
+//	healing from 48 to 53
+//	damage 15
+//	healing from 38 to 43
+//	damage 1
+//	healing from 42 to 47
+//	damage 19
+//	healing from 28 to 33
+//	damage 27
+//	healing from 6 to 11
+//	damage 16
+//	you are dead
+//	 */
+//}