Converting Enumeration to Iterator
enumeration, generics, iterator, scala, type-inference
Solution
List.fromIterator expects a scala.Iterator but your implicit is returning a java.util.Iterator.
This works
import java.util.Enumeration
implicit def enum2Iterator[A](e : Enumeration[A]) = new Iterator[A] {
def next = e.nextElement
def hasNext = e.hasMoreElements
}
import java.util.zip.{ZipFile, ZipEntry}
val l = List.fromIterator(new ZipFile(null:java.io.File).entries)
Adding one import at the top prevents compilation
import java.util.Iterator
There's been some discussion about unifying Scala and Java in 2.8 by just using java.util.Iterator. On the downside, Java's Iterator has a remove method which makes no sense for Scala's immutable collections. UnsupportedOperationException? Blech! On the plus side that makes stuff like this error go away.
Edit: I've added a Trac issue that the error message would have been clearer had it said "required: scala.Iterator[?]" https://lampsvn.epfl.ch/trac/scala/ticket/2102
Problem
I have the following implicit conversion for `java.util.Enumerations` ``` implicit def enumerationIterator[A](e : Enumeration[A]) : Iterator[A] = { new Iterator[A] { def hasNext = e.hasMoreElements def next = e.nextElement def remove = throw new UnsupportedOperationException() } } ``` Unfortunately it does not work for `ZipFile.entries` because it returns an `Enumeration<? extends ZipEntry>` (see related question) and Scalac keeps telling me ``` type mismatch; found : java.util.Iterator[?0] where type ?0 <: java.util.zip.ZipEntry required: Iterator[?] ``` I can't figure out how to make the conversation work in sth. like ``` List.fromIterator(new ZipFile(z).entries)) ```