Avoiding implicit def ambiguity in Scala

Question

I am trying to create an implicit conversion from any type (say, Int) to a String...

An implicit conversion to String means RichString methods (like reverse) are not available.

implicit def intToString(i: Int) = String.valueOf(i)
100.toCharArray  // => Array[Char] = Array(1, 0, 0)
100.reverse // => error: value reverse is not a member of Int
100.length // => 3

An implicit conversion to RichString means String methods (like toCharArray) are not available

implicit def intToRichString(i: Int) = new RichString(String.valueOf(i))
100.reverse // => "001"
100.toCharArray  // => error: value toCharArray is not a member of Int
100.length // => 3

Using both implicit conversions means duplicated methods (like length) are ambiguous.

implicit def intToString(i: Int) = String.valueOf(i)
implicit def intToRichString(i: Int) = new RichString(String.valueOf(i))
100.toCharArray  // => Array[Char] = Array(1, 0, 0)
100.reverse // => "001"
100.length // => both method intToString in object $iw of type 
   // (Int)java.lang.String and method intToRichString in object
   // $iw of type (Int)scala.runtime.RichString are possible 
   // conversion functions from Int to ?{val length: ?}

So, is it possible to implicitly convert to String and still support all String and RichString methods?

Answer 1

The only option I see is to create a new String Wrapper class MyString and let that call whatever method you want to be called in the ambiguous case. Then you could define implicit conversions to MyString and two implicit conversions from MyString to String and RichString, just in case you need to pass it to a library function.

Answer 2

I'm confused: can't you use .toString on any type anyway thus avoiding the need for implicit conversions?

Answer 3

Either make a huge proxy class, or suck it up and require the client to disambiguate it:

100.asInstanceOf[String].length

Answer 4

I don't have a solution, but will comment that the reason RichString methods are not available after your intToString implicit is that Scala does not chain implicit calls (see 21.2 "Rules for implicits" in Programming in Scala).

If you introduce an intermediate String, Scala will make the implict converstion to a RichString (that implicit is defined in Predef.scala).

E.g.,

$ scala
Welcome to Scala version 2.7.5.final [...].
Type in expressions to have them evaluated.
Type :help for more information.

scala> implicit def intToString(i: Int) = String.valueOf(i)
intToString: (Int)java.lang.String

scala> val i = 100
i: Int = 100

scala> val s: String = i
s: String = 100

scala> s.reverse
res1: scala.runtime.RichString = 001