使用默認參數類型處理scala函數，就好像它沒有默認參數

Question

聲明：我是新來的Scala。

我想通過使用默認參數的函數，就好像它的類型沒有默認參數

import scala.util.hashing.MurmurHash3 

type Record = Map[String, String] 
type Dataset = Seq[Record] 

def dropDuplicates(dataset: Dataset, keyF: Record => Any = recordHash) : Dataset = { 
    // keep only distinct records as defined by the key function 
    // removed method body for simplicity 
    return dataset 
} 

def recordHash(record: Record, attributes: Option[Seq[String]] = None) : Int = { 
    val values : Seq[String] = attributes 
    .getOrElse(record.keys.toSeq.sorted) 
    .map(attr => record(attr)) 
    return MurmurHash3.seqHash(values) 
} 

下面是我在編譯時得到的錯誤：

error: type mismatch; 
[ant:scalac] found : (Record, Option[Seq[String]]) => Int 
[ant:scalac] required: Record => Any 
[ant:scalac] def dropDuplicates(dataset: Dataset, keyF: Record => Any = recordHash) : Dataset = { 

直覺，我當沒有提供默認參數attributes時，將recordHash視爲Record => Int類型。有沒有辦法將作爲Record => Int類型？

Answer 1

我無法編譯您的代碼，因爲我錯過了一些類型，但我認爲這會起作用。

def dropDuplicates(dataset: Dataset, keyF: Record => Any = recordHash(_)) : Dataset = { 
    // keep only distinct records as defined by the key function 
} 

這工作，因爲recordHash(_)相當於x => recordHash(x)，這樣x（函數的輸入）爲Record這是你想要的類型。