如何將以下var Scala代碼轉換爲vals？

Question

var exit: String = expensiveOperation 
if (exit.contains(...)) exit = somethingElse 

最關鍵的是我只希望調用

expensiveOperation

一次，因爲它消耗的時鐘週期數

Answer 1

如果你不想暴露其他val，做內聯：

val exit = { 
    val result = expensiveOperation 
    if (result.contains(...)) somethingElse 
    else result 
} 

，或者，如果你喜歡

val exit = expensiveOperation match { 
    case res if res.contains(...) => somethingElse 
    case res if res.contains(...) => somethingBetter 
    // ... 
    case res => res 
} 

Answer 2

一個愚蠢的解決方案：只引入另一VAL。

val expected = expensiveOperation 
    val exit = if(expected.contains(...)) expected else something else 

Answer 3

一個可能的解決方案：提取一種方法。

def exitValue(...): String = { 
    val exit: String = expensiveOperation 
    if (exit.contains(...)) somethingElse else exit 
} 

val exit = exitValue(...)