val lines: Dataset[String] = session.read.textFile("")
    val words: Dataset[String] = lines.flatMap(_.split(" "))
    
    linesdataSetflatMapdataSetIDEAflatMap:
    
    
      def flatMap[U : Encoder](func: T => TraversableOnce[U]): Dataset[U] =
    mapPartitions(_.flatMap(func))
    
    
   
    

question:
_ .split ("") is equivalent to a function. The input parameter is String, and the return type is split"s result type Array [String],

while the flatmap method is defined to receive func: T = > TraversableOnce [U], it is obvious that T here is of type String,
and Array [String] is not of type TraversableOnce [U], because Array does not implement the trait of TraversableOnce,

so my question is: why did I pass a function like _ .split ("") to flatMap,flatMap without reporting an error?

in a nutshell, the method type I passed in doesn"t seem to match the method type required by flatMap, does it?