Expecting Array[String] but type is Array[Byte]

Question

Experimenting with map, flatMap and flatten and the following output is unexpected :

  case class T(data: String)
  val s = Set(T("1") , T("2"))
  val a: Array[Byte] = s.map(transaction => transaction.data).flatten.toArray

Should a not be of type Array[String]? , as data is of type String. Why is a of type Array[Byte]?

gregghz · Accepted Answer · 2021-03-22 22:41:55Z

3

The call to flatten is happening on a Set[String]. The String is treated something like an Iterable[Byte] (since that's more or less what a string is). So the flatten call is effecitively taking a Set[Iterable[Byte]] and flattening it into a Set[Byte] (which you then convert to an Array[Byte]).

Drop the flatten call and you'll get what you're after.

https://scastie.scala-lang.org/GqQiOHiWSZ6GKwdoM41yAg

answered Mar 22, 2021 at 22:41

gregghz

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