Scala 数组上的多行匿名闭包映射

Question

I'm trying to map over an array using a multiline anonymous closure and I'm having trouble. Eg

val httpHosts = stringHosts.map(host => {
  val hostAndPort = host.split(":")
  return new HttpHost(hostAndPort(0), hostAndPort(1).toInt, "http")
})

I'm receiving the following warning:

enclosing method executePlan has result type Unit: return value of type org.apache.http.HttpHost discarded

Which implies that httpHosts is an Array[Unit] and not an Array[HttpHost] .

I understand that I can split this into two maps, but for the sake of understanding Scala better, what am I doing wrong here when doing this in a multiline closure?

Answer 1

As mentioned in the comments, the fact that you return within your map, cause you to not get your expected result. A quote from The Point of No Return that @LuisMiguelMejíaSuárez linked in the comments:

A return expression, when evaluated, abandons the current computation and returns to the caller of the method in which return appears.

Therefore you get this warning.

Similar to your code that works is:

case class HttpHost(host: String, port: Int, protocol: String)
val httpHosts = stringHosts.map(host => {
  val hostAndPort = host.split(":")
  HttpHost(hostAndPort(0), hostAndPort(1).toInt, "http")
})

Having said that, I'd write it the following:

val httpHosts1 = stringHosts.map(_.split(":")).collect {
  case Array(host, port) if port.toIntOption.isDefined =>
    HttpHost(host, port.toInt, "http")
}