Implicit conversion from String to Int in scala 2.8

Question

Is there something I've got wrong with the following fragment:-

object Imp {
  implicit def string2Int(s: String): Int = s.toInt

  def f(i: Int) = i

  def main(args: Array[String]) {
    val n: Int = f("666")
  }
}

I get the following from the 2.8 compiler:-

Information:Compilation completed with 1 error and 0 warnings
Information:1 error
Information:0 warnings
...\scala-2.8-tests\src\Imp.scala
Error:Error:line (4)error: type mismatch;
found : String
required: ?{val toInt: ?}
Note that implicit conversions are not applicable because they are ambiguous:
both method string2Int in object Imp of type (s: String)Int
and method augmentString in object Predef of type (x:String)scala.collection.immutable.StringOps
are possible conversion functions from String to ?{val toInt: ?}
implicit def string2Int(s: String): Int = s.toInt

Answer 1

What is happening is that Java does not define a toInt method on String. In Scala, what defines that method is the class StringOps (Scala 2.8) or RichString (Scala 2.7).

On the other hand, there is a method toInt available on Int as well (through another implicit, perhaps?), so the compiler doesn't know if it is to convert the string to StringOps, through the defined implicit, or to Int, through your own implicit.

To solve it, call the implicit explicitly.

object Imp {
  implicit def string2Int(s: String): Int = augmentString(s).toInt

  def f(i: Int) = i

  def main(args: Array[String]) {
    val n: Int = f("666")
  }
}