# 創造世界

## 繞 S 形走完全世界

![](/files/-M5gL-kj96YLSFMmJoAR)

上面是一個空白的 12 x 12 的世界，下面的程式碼會放一個 [Actor](/ios/swift-playgrounds/learn-to-code-2/types/actor.md) 在原點，並讓他向東走、繞 S 形走完全世界。

{% tabs %}
{% tab title="main" %}

```swift
// GridWorld
let theWorld = world

// 新增角色放到(0,0)、面向東方
let actor = Actor(0,0)

// 判斷角色是否已經走到世界盡頭
var isOver = false

// 當角色還沒到世界盡頭，就繼續走
while !isOver {
    actor.navigate(onMove: { 
        // 往前一步要做的動作放這裡
    }) { 
        // onExit：
        // 到世界盡頭要做的動作放這裡
        isOver = true
        actor.danceLikeNoOneIsWatching()
    }
}
```

{% endtab %}

{% tab title="Actor" %}

```swift
extension Actor {
    
    // 新增角色放到 (x,y)、預設面向東方。
    convenience init(_ x: Int, _ y: Int, facing dir: Direction = .east){
        self.init()
        theWorld.place(self, facing: dir, at: Coordinate(column: x, row: y))
    }
    
    typealias Handler = () -> Void
    
    // 讓角色從原點向東「走 S 形的路線」到達終點。
    func navigate(onMove:Handler, onExit:Handler) {
        
        if !isBlocked {   // 如果前面沒擋住，就往前走
            moveForward()
            onMove()
        } else {          // 否則就轉彎
            
            // 先判斷要往哪邊轉、轉彎時要做什麼動作
            let turn = heading == .east ? turnLeft : turnRight   // 向東走時轉左邊，否則轉右邊
            let act  = heading == .east ? turnUp   : headScratch // 向東走時裝興奮，否則抓抓頭
            
            turn()  // 轉彎
            
            if !isBlocked { // 如果還沒到世界盡頭，就往前走再轉彎
                act()
                moveForward()
                onMove()
                turn()
            } else {        // 不然就是已經到了盡頭，就做到了盡頭該做的事。
                onExit()
            }
            
        }//end: if
        
    }//end: naviagate()
}
```

{% endtab %}
{% endtabs %}


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