扔Throwable的fromTryCatch - 和調整方法的類型正確

Question

我有以下的現有方法：

def test: \/[Throwable, Person] = { 
    \/.fromTryCatch { 
    //existing logic has potential to throw exception (from calls like .toInt) etc 
    //now via following for comprehension want to combine Throwable with return type \/[Throwable,Person] 
    for { 
     p <- q.firstOption.\/>(new Throwable("can't find record for person with id = " + id)) 
    } yield p 
    } 
} 

將會產生以下錯誤：

type mismatch; found : scalaz.\/[Throwable,Person] (which expands to) scalaz.\/[Throwable,Person] required:Person 

我怎麼排列的返回值類型理解類型爲def test？

Answer 1

fromTryCatch預計值爲Person，可能會引發異常。

因此，您不需要在\/中包裝異常，只需在fromTryCatch塊中引發異常，它將自動捕獲幷包裝。

或者，您可以簡單地刪除fromTryCatch，因爲您已經在例如\/[Throwable, Person]（例如，

def test : \/[Throwable,Person] = 
    for { 
    p <- q.firstOption.\/>(new Throwable(s"can't find record for person with id = $id)) 
    } yield p 

---

如果您不是需要兩者混合使用，你可以這樣做

def test : \/[Throwable,Person] = \/.fromTryCatch { 
    mayThrow() 

    val res = for { 
    p <- q.firstOption.\/>(new Throwable("can't find record for person with id ="+id)) 
    } yield p 

    res match { 
    case \/-(p) => p 
    case -\/(e) => throw e 
    } 
} 

或更好的，你可以單獨的範圍和使用fromTryCatch只在必要時，像

def test : \/[Throwable,Person] = 
    for { 
    _ <- \/.fromTryCatch { mayThrow() } 
    p <- q.firstOption.\/>(new Throwable("can't find record for person with id ="+id)) 
    } yield p