来源问题。在finally block中尝试关闭时来自URL

以下代码段工作正常:

def using[A, B <: {def close(): Unit}] (closeable: B) (f: B => A): A =
  try { f(closeable) } finally { closeable.close() }

def loadDictionaryFromNet():List[String] =
  using(Source.fromURL("http://www.mieliestronk.com/corncob_caps.txt", "UTF-8"))(_.getLines().toList)

  val dictionary = loadDictionaryFromNet() filter(_.forall(_.isLetter))

但是当我尝试将类型更改为 Seq[String] 如下所示:

def using[A, B <: {def close(): Unit}] (closeable: B) (f: B => A): A =
  try { f(closeable) } finally { closeable.close() }

def loadDictionaryFromNet():Seq[String] =
  using(Source.fromURL("http://www.mieliestronk.com/corncob_caps.txt", "UTF-8"))(_.getLines().toSeq)

  val dictionary = loadDictionaryFromNet() filter(_.forall(_.isLetter))

然后抛出以下异常:

Exception in thread "main" java.io.IOException: stream is closed
    at sun.net.www.protocol.http.HttpURLConnection$HttpInputStream.ensureOpen(HttpURLConnection.java:3348)
    at sun.net.www.protocol.http.HttpURLConnection$HttpInputStream.read(HttpURLConnection.java:3373)
    at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
    at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
    at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
    at java.io.InputStreamReader.read(InputStreamReader.java:184)
    at java.io.BufferedReader.fill(BufferedReader.java:161)
    at java.io.BufferedReader.readLine(BufferedReader.java:324)
    at java.io.BufferedReader.readLine(BufferedReader.java:389)
    ... 

当我将类型更改为 IndexedSeq 它又起作用了。

“感觉”就像 toSeq 事实上,产生了一些部分延迟流,这些流没有立即完全消耗,但有一些延迟。

你能解释一下引擎盖下发生了什么吗?