如何在scala變更中創建變量？

Question

所以我有這個變量，currentPartNumber，它開始等於0.我想要發生的是在我的函數中，如果變量等於零，它將更改爲1，並將文本打印出來。我的第二個功能是一樣的 - 如果在我的第一個功能中變量變爲1，並且等於1，我希望變量變爲2，打印出文本。

問題是：如何讓我的變量隨每個函數調用而改變？

var currentPartNumber = 0 

def roomOne():Unit = { 
    if (currentPartNumber < 1) { 
     var currentPartNumber = 1 
     println("You now have parts 1 of 4.") 
    } else { 
     println("This part cannot be collected yet.") 
    { 
    } 


def roomTwo():Unit = { 
    if (currentPartNumber = 1) { 
     var currentPartNumber = 2 
     println("You now have parts 2 of 4.") 
    } else { 
     println("This part cannot be collected yet.") 
    { 
    } 

Answer 1

不要隱藏變量：從函數內部刪除var。

的var關鍵字聲明一個新構件/變量。在這種情況下，名稱是陰影相同的外部變量範圍。因此賦值（作爲聲明的一部分）對外部變量沒有影響。

// no var/val - assignment without declaration 
currentPartNumber = 2 

參見：

• Why does a scala try block allow variables from the enclosing scope to be redefined?
• Why does Scala support shadow variables?

Answer 2

的一類，其中roomOne()和roomTwo()可以訪問和修改其聲明currentPartNumber。

class Parts{ 
    var currentPartNumber = 0 

    def roomOne():Unit = { 
    if (currentPartNumber < 1) { 
     currentPartNumber = 1 
     println("You now have parts 1 of 4.") 
    } else { 
     println("This part cannot be collected yet.") 
    } 
    } 

    def roomTwo():Unit = { 
    if (currentPartNumber == 1) { 
     currentPartNumber = 2 
     println("You now have parts 2 of 4.") 
    } else { 
     println("This part cannot be collected yet.") 
    } 
    } 
} 



scala> :load Parts.scala 
Loading Parts.scala... 
defined class Parts 
scala> var parts = new Parts 
parts: Parts = Parts@5636a67c 
scala> parts.currentPartNumber 
res0: Int = 0 
scala> parts.roomOne 
You now have parts 1 of 4. 
scala> parts.roomTwo 
You now have parts 2 of 4.